DESIGN OF A MTBE REMEDIATION TECHNOLOGY EVALUATION

EPA Science Inventory

This study examines the intrinsic variability of dissolved MTBE concentrations in ground water during the course of a pilot-scale bioremedial technology trial in Port Hueneme, California. A pre-trial natural gradient tracer experiment using bromide was conducted in an anaerobic t...

Edge wrinkling of a soft ridge with gradient thickness

NASA Astrophysics Data System (ADS)

Zhao, Yan; Shao, Zhi-Chun; Li, Guo-Yang; Zheng, Yang; Zhang, Wan-Yu; Li, Bo; Cao, Yanping; Feng, Xi-Qiao

2017-06-01

We investigate the edge wrinkling of a soft ridge with gradient thickness under axial compression. Our experiments show that the wrinkling wavelength undergoes a considerable increase with increasing load. Simple scaling laws are derived based on an upper-bound analysis to predict the critical buckling conditions and the evolution of wrinkling wavelength during the post-buckling stage, and the results show good accordance with our finite element simulations and experiments. We also report a pattern transformation triggered by the edge wrinkling of soft ridge arrays. The results and method not only help understand the correlation between the growth and form observed in some natural systems but also inspire a strategy to fabricate advanced functional surfaces.

Emergence of life from multicomponent mixtures of chemicals: the case for experiments with cycling physicochemical gradients.

PubMed

Spitzer, Jan

2013-04-01

The emergence of life from planetary multicomponent mixtures of chemicals is arguably the most complicated and least understood natural phenomenon. The fact that living cells are non-equilibrium systems suggests that life can emerge only from non-equilibrium chemical systems. From an astrobiological standpoint, non-equilibrium chemical systems arise naturally when solar irradiation strikes rotating surfaces of habitable planets: the resulting cycling physicochemical gradients persistently drive planetary chemistries toward "embryonic" living systems and an eventual emergence of life. To better understand the factors that lead to the emergence of life, I argue for cycling non-equilibrium experiments with multicomponent chemical systems designed to represent the evolving chemistry of Hadean Earth ("prebiotic soups"). Specifically, I suggest experimentation with chemical engineering simulators of Hadean Earth to observe and analyze (i) the appearances and phase separations of surface active and polymeric materials as precursors of the first "cell envelopes" (membranes) and (ii) the accumulations, commingling, and co-reactivity of chemicals from atmospheric, oceanic, and terrestrial locations.

Diffusive-convective physical vapor transport of PbTe from a Te-rich solid source

NASA Technical Reports Server (NTRS)

Zoutendyk, J.; Akutagawa, W.

1982-01-01

Crystal growth of PbTe by physical vapor transport (sublimation) in a closed ampoule is governed by the vapor species in thermal equilibrium with the solid compound. Deviations from stoichiometry in the source material cause diffusion limitation of the transport rate, which can be modified by natural (gravity-driven) convection. Mass-transport experiments have been performed using Te-rich material wherein sublimation rates have been measured in order to study the effects of natural convection in diffusion-limited vapor transport. Linear velocities for both crystal growth and evaporation (back sublimation) have been measured for transport in the direction of gravity, horizontally, and opposite to gravity. The experimental results are discussed in terms of both the one-dimensional diffusive-advective model and current, more sophisticated theory which includes natural convection. There is some evidence that convection effects from radial temperature gradients and solutal density gradients have been observed.

Advancing from Rules of Thumb: Quantifying the Effects of Small Density Changes in Mass Transport to Electrodes. Understanding Natural Convection.

PubMed

Ngamchuea, Kamonwad; Eloul, Shaltiel; Tschulik, Kristina; Compton, Richard G

2015-07-21

Understanding mass transport is prerequisite to all quantitative analysis of electrochemical experiments. While the contribution of diffusion is well understood, the influence of density gradient-driven natural convection on the mass transport in electrochemical systems is not. To date, it has been assumed to be relevant only for high concentrations of redox-active species and at long experimental time scales. If unjustified, this assumption risks misinterpretation of analytical data obtained from scanning electrochemical microscopy (SECM) and generator-collector experiments, as well as analytical sensors utilizing macroelectrodes/microelectrode arrays. It also affects the results expected from electrodeposition. On the basis of numerical simulation, herein it is demonstrated that even at less than 10 mM concentrations and short experimental times of tens of seconds, density gradient-driven natural convection significantly affects mass transport. This is evident from in-depth numerical simulation for the oxidation of hexacyanoferrate (II) at various electrode sizes and electrode orientations. In each case, the induced convection and its influence on the diffusion layer established near the electrode are illustrated by maps of the velocity fields and concentration distributions evolving with time. The effects of natural convection on mass transport and chronoamperometric currents are thus quantified and discussed for the different cases studied.

Switch between competition and facilitation within a seasonal scale at colony level in bryophytes.

PubMed

Spitale, Daniel

2009-06-01

The relative importance of positive and negative interaction in species assemblages is thought to be dependent on the harshness of the physical environment. I studied the consistency of this prediction in a field experiment using growth of the target species Warnstorfia exannulata as influenced by the presence or absence of two adjacent species, Sphagnum warnstorfii and Scapania undulata. In particular, I focused on the mechanism by which colony-colony interactions occur, elucidating how the balance of positive and negative interactions changes along a water gradient. Because the natural fluctuations of the environment modify the water gradient, it was expected that the competitive hierarchies of the species would not remain consistent over time. Results indicated that the different hydrological properties of the colonies, thought to be the necessary condition for the appearance of species interactions, were not sufficient to explain the outcome of the species interactions. The switch from competition to facilitation under more stressful conditions was not confirmed along a water stress gradient. In addition, natural climatic fluctuations, by affecting the length of the water gradient, changed the competitive hierarchies of the species on a seasonal scale.

Exploiting the Temperature Dependence of Magnetic Susceptibility to Control Convective in Fundamental Studies of Solidification Phenomena

NASA Technical Reports Server (NTRS)

Seybert, C.; Evans, J. W.; Leslie, F.; Jones, W. K., Jr.

2001-01-01

It is well known that convection is a dominant mass transport mechanism when materials are solidified on Earth's surface. This convection is caused by gradients in density (and therefore gravitational force) that are brought about by gradients in temperature, composition or both. Diffusion of solute is therefore dwarfed by convection and the study of fundamental parameters, such as dendrite tip shape and growth velocity in the absence of convection is nearly impossible. Significant experimental work has therefore been carried out in orbiting laboratories with the intent of minimizing convection by minimizing gravity. One of the best known experiments of this kind is the Isothermal Dendritic Growth Experiment (IDGE), supported by NASA. Naturally such experiments are costly and one objective of the present investigation is to develop an experimental method whereby convection can be halted, in solidification and other experiments, on the Earth's surface. A second objective is to use the method to minimize convection resulting from the residual accelerations suffered by experiments in microgravity.

Final Technical Report: The effects of climate, forest age, and disturbance history on carbon and water processes at AmeriFlux sites across gradients in Pacific Northwest forests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Law, Beverly E.

Investigate the effects of disturbance and climate variables on processes controlling carbon and water processes at AmeriFlux cluster sites in semi-arid and mesic forests in Oregon. The observations were made at three existing and productive AmeriFlux research sites that represent climate and disturbance gradients as a natural experiment of the influence of climatic and hydrologic variability on carbon sequestration and resulting atmospheric CO 2 feedback that includes anomalies during the warm/ dry phase of the Pacific Decadal Oscillation.

Practical and efficient magnetic heat pump

NASA Technical Reports Server (NTRS)

Brown, G. V.

1978-01-01

Method for pumping heat magnetically at room temperature is more economical than existing refrigeration systems. Method uses natural magneto-thermal effect of gadolinium metal to establish temperature gradient across length of tube. Regenerative cyclic process in which gadolinium sample is magnetized and gives off heat at one end of tube, and then is demagnetized at other end to absorb heat has established temperature gradients of 144 degrees F in experiments near room temperature. Other materials with large magnetothermal effects can be used below room temperature. Possible commercial applications include freeze-drying and food processing, cold storage, and heating and cooling of buildings, plants, and ships.

Large-scale natural gradient tracer test in sand and gravel, Cape Cod, Massachusetts: 1. Experimental design and observed tracer movement

USGS Publications Warehouse

LeBlanc, Denis R.; Garabedian, Stephen P.; Hess, Kathryn M.; Gelhar, Lynn W.; Quadri, Richard D.; Stollenwerk, Kenneth G.; Wood, Warren W.

1991-01-01

A large-scale natural gradient tracer experiment was conducted on Cape Cod, Massachusetts, to examine the transport and dispersion of solutes in a sand and gravel aquifer. The nonreactive tracer, bromide, and the reactive tracers, lithium and molybdate, were injected as a pulse in July 1985 and monitored in three dimensions as they moved as far as 280 m down-gradient through an array of multilevel samplers. The bromide cloud moved horizontally at a rate of 0.42 m per day. It also moved downward about 4 m because of density-induced sinking early in the test and accretion of areal recharge from precipitation. After 200 m of transport, the bromide cloud had spread more than 80 m in the direction of flow, but was only 14 m wide and 4–6 m thick. The lithium and molybdate clouds followed the same path as the bromide cloud, but their rates of movement were retarded about 50% relative to bromide movement because of sorption onto the sediments.

The natural statistics of blur

PubMed Central

Sprague, William W.; Cooper, Emily A.; Reissier, Sylvain; Yellapragada, Baladitya; Banks, Martin S.

2016-01-01

Blur from defocus can be both useful and detrimental for visual perception: It can be useful as a source of depth information and detrimental because it degrades image quality. We examined these aspects of blur by measuring the natural statistics of defocus blur across the visual field. Participants wore an eye-and-scene tracker that measured gaze direction, pupil diameter, and scene distances as they performed everyday tasks. We found that blur magnitude increases with increasing eccentricity. There is a vertical gradient in the distances that generate defocus blur: Blur below the fovea is generally due to scene points nearer than fixation; blur above the fovea is mostly due to points farther than fixation. There is no systematic horizontal gradient. Large blurs are generally caused by points farther rather than nearer than fixation. Consistent with the statistics, participants in a perceptual experiment perceived vertical blur gradients as slanted top-back whereas horizontal gradients were perceived equally as left-back and right-back. The tendency for people to see sharp as near and blurred as far is also consistent with the observed statistics. We calculated how many observations will be perceived as unsharp and found that perceptible blur is rare. Finally, we found that eye shape in ground-dwelling animals conforms to that required to put likely distances in best focus. PMID:27580043

In situ measurement of methane oxidation in groundwater by using natural-gradient tracer tests

USGS Publications Warehouse

Smith, R.L.; Howes, B.L.; Garabedian, S.P.

1991-01-01

Methane oxidation was measured in an unconfined sand and gravel aquifer (Cape Cod, Mass.) by using in situ natural-gradient tracer tests at both a pristine, oxygenated site and an anoxic, sewage-contaminated site. The tracer sites were equipped with multilevel sampling devices to create target grids of sampling points; the injectate was prepared with groundwater from the tracer site to maintain the same geochemical conditions. Methane oxidation was calculated from breakthrough curves of methane relative to halide and inert gas (hexafluoroethane) tracers and was confirmed by the appearance of 13C-enriched carbon dioxide in experiments in which 13C-enriched methane was used as the tracer. A V(max) for methane oxidation could be calculated when the methane concentration was sufficiently high to result in zero-order kinetics throughout the entire transport interval. Methane breakthrough curves could be simulated by modifying a one-dimensional advection-dispersion transport model to include a Michaelis-Menten-based consumption term for methane oxidation. The K(m) values for methane oxidation that gave the best match for the breakthrough curve peaks were 6.0 and 9.0 ??M for the uncontaminated and contaminated sites, respectively. Natural-gradient tracer tests are a promising approach for assessing microbial processes and for testing in situ bioremediation potential in groundwater systems.

In situ measurement of methane oxidation in groundwater by using natural-gradient tracer tests.

PubMed Central

Smith, R L; Howes, B L; Garabedian, S P

1991-01-01

Methane oxidation was measured in an unconfined sand and gravel aquifer (Cape Cod, Mass.) by using in situ natural-gradient tracer tests at both a pristine, oxygenated site and an anoxic, sewage-contaminated site. The tracer sites were equipped with multilevel sampling devices to create target grids of sampling points; the injectate was prepared with groundwater from the tracer site to maintain the same geochemical conditions. Methane oxidation was calculated from breakthrough curves of methane relative to halide and inert gas (hexafluroethane) tracers and was confirmed by the appearance of 13C-enriched carbon dioxide in experiments in which 13C-enriched methane was used as the tracer. A Vmax for methane oxidation could be calculated when the methane concentration was sufficiently high to result in zero-order kinetics throughout the entire transport interval. Methane breakthrough curves could be simulated by modifying a one-dimensional adevection-dispersion transport model to include a Michaelis-Menten-based consumption term for methane oxidation. The Km values for methane oxidation that gave the best match for the breakthrough curve peaks were 6.0 and 9.0 microM for the uncontaminated and contaminated sites, respectively. Natural-gradient tracer tests are a promising approach for assessing microbial processes and for testing in situ bioremediation potential in groundwater systems. PMID:1892389

Three-dimensional Gravity Inversion with a New Gradient Scheme on Unstructured Grids

NASA Astrophysics Data System (ADS)

Sun, S.; Yin, C.; Gao, X.; Liu, Y.; Zhang, B.

2017-12-01

Stabilized gradient-based methods have been proved to be efficient for inverse problems. Based on these methods, setting gradient close to zero can effectively minimize the objective function. Thus the gradient of objective function determines the inversion results. By analyzing the cause of poor resolution on depth in gradient-based gravity inversion methods, we find that imposing depth weighting functional in conventional gradient can improve the depth resolution to some extent. However, the improvement is affected by the regularization parameter and the effect of the regularization term becomes smaller with increasing depth (shown as Figure 1 (a)). In this paper, we propose a new gradient scheme for gravity inversion by introducing a weighted model vector. The new gradient can improve the depth resolution more efficiently, which is independent of the regularization parameter, and the effect of regularization term will not be weakened when depth increases. Besides, fuzzy c-means clustering method and smooth operator are both used as regularization terms to yield an internal consecutive inverse model with sharp boundaries (Sun and Li, 2015). We have tested our new gradient scheme with unstructured grids on synthetic data to illustrate the effectiveness of the algorithm. Gravity forward modeling with unstructured grids is based on the algorithm proposed by Okbe (1979). We use a linear conjugate gradient inversion scheme to solve the inversion problem. The numerical experiments show a great improvement in depth resolution compared with regular gradient scheme, and the inverse model is compact at all depths (shown as Figure 1 (b)). AcknowledgeThis research is supported by Key Program of National Natural Science Foundation of China (41530320), China Natural Science Foundation for Young Scientists (41404093), and Key National Research Project of China (2016YFC0303100, 2017YFC0601900). ReferencesSun J, Li Y. 2015. Multidomain petrophysically constrained inversion and geology differentiation using guided fuzzy c-means clustering. Geophysics, 80(4): ID1-ID18. Okabe M. 1979. Analytical expressions for gravity anomalies due to homogeneous polyhedral bodies and translations into magnetic anomalies. Geophysics, 44(4), 730-741.

ASSOCIATIONS AMONG WATERSHED- AND SITE-SCALE DISTURBANCES INDICATORS AND FISH ASSEMBLAGES AT LEAST- AND MOST-DISTURBED STREAM AND RIVER SITES IN WESTERN USA

EPA Science Inventory

At broad scales, the kinds and intensity of human disturbance to streams vary with natural gradients (e.g., elevation). While fish assemblages vary with both human and natural gradients, ecological condition assessments need to partition out the natural gradients to evaluate hum...

Natural convection in the Hale-Shaw cell of horizontal Bridgman solidification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Y.; Liu, J.; Zhou, Y.

1995-08-01

The numerical simulation of natural convection in the Hale-Shaw cell during horizontal Bridgman solidification reveals that the convection is present even for the very thin cell. The effects of the horizontal temperature gradient, G, thickness of the cell, H, temperature difference between the top and bottom of the cell, and other parameters have been studied. These findings have been confirmed by experiments through direct observation and measurement of convection in the cell containing succinonitrile transparent model alloy.

Advanced technique for long term culture of epithelia in a continuous luminal-basal medium gradient.

PubMed

Schumacher, Karl; Strehl, Raimund; de, Vries Uwe; Minuth, Will W

2002-02-01

The majority of epithelia in our organism perform barrier functions on being exposed to different fluids at the luminal and basal sides. To simulate this natural situation under in vitro conditions for biomaterial testing and tissue engineering the epithelia have to withstand mechanical and fluid stress over a prolonged period of time. Leakage, edge damage and pressure differences in the culture system have to be avoided so that the epithelial barrier function is maintained. Besides, the environmental influences on important cell biological features such as, sealing or transport functions, have to remain upregulated and a loss of characteristics by dedifferentiation is prevented. Our aim is to expose embryonic renal collecting duct (CD) epithelia as model tissue for 14 days to fluid gradients and to monitor the development of tissue-specific features. For these experiments, cultured embryonic epithelia are placed in tissue carriers and in gradient containers, where different media are superfused at the luminal and basal sides. Epithelia growing on the tissue carriers act as a physiological barrier during the whole culture period. To avoid mechanical damage of the tissue and to suppress fluid pressure differences between the luminal and basal compartments improved transport of the medium and an elimination of unilaterally accumulated gas bubbles in the gradient container compartments by newly developed gas expander modules is introduced. By the application of these tools the yield of embryonic renal collecting duct epithelia with intact barrier function on a fragile natural support material could be increased significantly as compared to earlier experiments. Epithelia treated with a luminal NaCl load ranging from 3 to 24 mmol l were analyzed by immunohistochemical methods to determine the degree of differentiation. The tissue showed an upregulation of individual CD cell features as compared to embryonic epithelia in the neonatal kidney.

Egg discrimination along a gradient of natural variation in eggshell coloration.

PubMed

Hanley, Daniel; Grim, Tomáš; Igic, Branislav; Samaš, Peter; López, Analía V; Shawkey, Matthew D; Hauber, Mark E

2017-02-08

Accurate recognition of salient cues is critical for adaptive responses, but the underlying sensory and cognitive processes are often poorly understood. For example, hosts of avian brood parasites have long been assumed to reject foreign eggs from their nests based on the total degree of dissimilarity in colour to their own eggs, regardless of the foreign eggs' colours. We tested hosts' responses to gradients of natural (blue-green to brown) and artificial (green to purple) egg colours, and demonstrate that hosts base rejection decisions on both the direction and degree of colour dissimilarity along the natural, but not artificial, gradient of egg colours. Hosts rejected brown eggs and accepted blue-green eggs along the natural egg colour gradient, irrespective of the total perceived dissimilarity from their own egg's colour. By contrast, their responses did not vary along the artificial colour gradient. Our results demonstrate that egg recognition is specifically tuned to the natural gradient of avian eggshell colour and suggest a novel decision rule. These results highlight the importance of considering sensory reception and decision rules when studying perception, and illustrate that our understanding of recognition processes benefits from examining natural variation in phenotypes. © 2017 The Authors.

Egg discrimination along a gradient of natural variation in eggshell coloration

PubMed Central

Grim, Tomáš; Igic, Branislav; Samaš, Peter; López, Analía V.; Shawkey, Matthew D.; Hauber, Mark E.

2017-01-01

Accurate recognition of salient cues is critical for adaptive responses, but the underlying sensory and cognitive processes are often poorly understood. For example, hosts of avian brood parasites have long been assumed to reject foreign eggs from their nests based on the total degree of dissimilarity in colour to their own eggs, regardless of the foreign eggs' colours. We tested hosts' responses to gradients of natural (blue-green to brown) and artificial (green to purple) egg colours, and demonstrate that hosts base rejection decisions on both the direction and degree of colour dissimilarity along the natural, but not artificial, gradient of egg colours. Hosts rejected brown eggs and accepted blue-green eggs along the natural egg colour gradient, irrespective of the total perceived dissimilarity from their own egg's colour. By contrast, their responses did not vary along the artificial colour gradient. Our results demonstrate that egg recognition is specifically tuned to the natural gradient of avian eggshell colour and suggest a novel decision rule. These results highlight the importance of considering sensory reception and decision rules when studying perception, and illustrate that our understanding of recognition processes benefits from examining natural variation in phenotypes. PMID:28179521

Moisture drives surface decomposition in thawing tundra

NASA Astrophysics Data System (ADS)

Hicks Pries, Caitlin E.; Schuur, E. A. G.; Vogel, Jason G.; Natali, Susan M.

2013-07-01

Permafrost thaw can affect decomposition rates by changing environmental conditions and litter quality. As permafrost thaws, soils warm and thermokarst (ground subsidence) features form, causing some areas to become wetter while other areas become drier. We used a common substrate to measure how permafrost thaw affects decomposition rates in the surface soil in a natural permafrost thaw gradient and a warming experiment in Healy, Alaska. Permafrost thaw also changes plant community composition. We decomposed 12 plant litters in a common garden to test how changing plant litter inputs would affect decomposition. We combined species' tissue-specific decomposition rates with species and tissue-level estimates of aboveground net primary productivity to calculate community-weighted decomposition constants at both the thaw gradient and warming experiment. Moisture, specifically growing season precipitation and water table depth, was the most significant driver of decomposition. At the gradient, an increase in growing season precipitation from 200 to 300 mm increased mass loss of the common substrate by 100%. At the warming experiment, a decrease in the depth to the water table from 30 to 15 cm increased mass loss by 100%. At the gradient, community-weighted decomposition was 21% faster in extensive than in minimal thaw, but was similar when moss production was included. Overall, the effect of climate change and permafrost thaw on surface soil decomposition are driven more by precipitation and soil environment than by changes to plant communities. Increasing soil moisture is thereby another mechanism by which permafrost thaw can become a positive feedback to climate change.

A test of size-scaling and relative-size hypotheses for the moon illusion.

PubMed

Redding, Gordon M

2002-11-01

In two experiments participants reproduced the size of the moon in pictorial scenes under two conditions: when the scene element was normally oriented, producing a depth gradient like a floor, or when the scene element was inverted, producing a depth gradient like a ceiling. Target moons were located near to or far from the scene element. Consistent with size constancy scaling, the illusion reversed when the "floor" of a pictorial scene was inverted to represent a "ceiling." Relative size contrast predicted a reduction or increase in the illusion with no change in direction. The relation between pictorial and natural moon illusions is discussed.

Interaction strength between different grazers and macroalgae mediated by ocean acidification over warming gradients.

PubMed

Sampaio, E; Rodil, I F; Vaz-Pinto, F; Fernández, A; Arenas, F

2017-04-01

Since the past century, rising CO 2 levels have led to global changes (ocean warming and acidification) with subsequent effects on marine ecosystems and organisms. Macroalgae-herbivore interactions have a main role in the regulation of marine community structure (top-down control). Gradients of warming prompt complex non-linear effects on organism metabolism, cascading into altered trophic interactions and community dynamics. However, not much is known on how will acidification and grazer assemblage composition shape these effects. Within this context, we aimed to assess the combined effects of warming gradients and acidification on macroalgae-herbivore interactions, using three cosmopolitan species, abundant in the Iberian Peninsula and closely associated in nature: the amphipod Melita palmata, the gastropod Gibbula umbilicalis, and the green macroalga Ulva rigida. Under two CO 2 treatments (ΔCO 2 ≃ 450 μatm) across a temperature gradient (13.5, 16.6, 19.9 and 22.1 °C), two mesocosm experiments were performed to assess grazer consumption rates and macroalgae-herbivore interaction, respectively. Warming (Experiment I and II) and acidification (Experiment II) prompted negative effects in grazer's survival and species-specific differences in consumption rates. M. palmata was shown to be the stronger grazer per biomass (but not per capita), and also the most affected by climate stressors. Macroalgae-herbivore interaction strength was markedly shaped by the temperature gradient, while simultaneous acidification lowered thermal optimal threshold. In the near future, warming and acidification are likely to strengthen top-down control, but further increases in disturbances may lead to bottom-up regulated communities. Finally, our results suggest that grazer assemblage composition may modulate future macroalgae-herbivore interactions. Copyright © 2017 Elsevier Ltd. All rights reserved.

Ant predation on herbivores through a multitrophic lens: how effects of ants on plant herbivore defense and natural enemies vary along temperature gradients.

PubMed

Rodríguez-Castañeda, G; Brehm, G; Fiedler, K; Dyer, L A

2016-04-01

Ants are keystone predators in terrestrial trophic cascades. Addressing ants' roles in multitrophic interactions across regional gradients is important for understanding mechanisms behind range limits of species. We present four hypotheses of trophic dynamics occurring when ants are rare: first, there is a shift in predator communities; second, plants decrease investments in ant attraction and increase production of secondary metabolites; third, lower herbivory at high elevations allows plants to tolerate herbivory; and fourth, distribution of ant-plants can be limited based on ant abundance. Conducting experiments on multitrophic effects of ants across elevational gradients, and incorporating these results to ecological niche modeling (ENM) will improve our knowledge of the impacts of global change on ants, trophic interactions, and biodiversity. Copyright © 2016 Elsevier Inc. All rights reserved.

MULTISPECIES REACTIVE TRACER TEST IN A SAND AND GRAVEL AQUIFER, CAPE COD, MASSACHUSETTS: PART 2: TRANSPORT OF CHROMIUM (VI) AND LEAD-, COPPER-, AND ZINC-EDTA TRACERS

EPA Science Inventory

This report discusses the transport of a group of reactive tracers over the course of a large-scale, natural gradient tracer test conducted at the USGS Cape Cod Toxic Substances Hydrology Research site, near Falmouth, Massachusetts. The overall objectives of the experiment were ...

Changes in coral reef communities across a natural gradient in seawater pH.

PubMed

Barkley, Hannah C; Cohen, Anne L; Golbuu, Yimnang; Starczak, Victoria R; DeCarlo, Thomas M; Shamberger, Kathryn E F

2015-06-01

Ocean acidification threatens the survival of coral reef ecosystems worldwide. The negative effects of ocean acidification observed in many laboratory experiments have been seen in studies of naturally low-pH reefs, with little evidence to date for adaptation. Recently, we reported initial data suggesting that low-pH coral communities of the Palau Rock Islands appear healthy despite the extreme conditions in which they live. Here, we build on that observation with a comprehensive statistical analysis of benthic communities across Palau's natural acidification gradient. Our analysis revealed a shift in coral community composition but no impact of acidification on coral richness, coralline algae abundance, macroalgae cover, coral calcification, or skeletal density. However, coral bioerosion increased 11-fold as pH decreased from the barrier reefs to the Rock Island bays. Indeed, a comparison of the naturally low-pH coral reef systems studied so far revealed increased bioerosion to be the only consistent feature among them, as responses varied across other indices of ecosystem health. Our results imply that whereas community responses may vary, escalation of coral reef bioerosion and acceleration of a shift from net accreting to net eroding reef structures will likely be a global signature of ocean acidification.

Deltas as Ecomorphodynamic Systems: Effects of Vegetation Gradients on Sediment Trapping and Channel Dynamics

NASA Astrophysics Data System (ADS)

Piliouras, A.; Kim, W.; Goggin, H.

2014-12-01

Understanding the feedbacks between water, sediment, and vegetation in deltas is an important part of understanding deltas as ecomorphodynamic systems. We conducted a set of laboratory experiments using alfalfa (Medicago sativa) as a proxy for delta vegetation to determine (1) the effects of plants on delta growth and channel dynamics and (2) the influence of fine material on delta evolution. Vegetated experiments were compared to a control run without plants to isolate the effects of vegetation, and experiments with fine sediment were compared to a set of similar experiments with only sand. We found that alfalfa increased sediment trapping on the delta topset, and that the plants were especially effective at retaining fine material. Compared to the control run, the vegetated experiments showed an increased retention of fine sediment on the floodplain that resulted in increased delta relief and stronger pulses of shoreline progradation when channel avulsion and migration occurred. In other words, a higher amount of sediment storage with the addition of vegetation corresponded to a higher amount of sediment excavation during channelization events. In natural systems, dense bank vegetation is typically expected to help confine flow. We seeded our delta uniformly, which eliminated typical vegetation density gradients from riverbank to island center and therefore diminished the gradient in overbank sedimentation that best confines channels by creating levees. Dense clusters of alfalfa throughout the interior of the floodplain and delta islands were therefore able to induce flow splitting, where channels diverged around a stand of plants. This created several smaller channels that were then able to more widely distribute sediment at the delta front compared to unvegetated experiments. We conclude that plants are efficient sediment trappers that change the rate and amount of sediment storage in the delta topset, and that gradients in vegetation density are an important factor in determining how channel behavior may change.

The response of forest plant regeneration to temperature variation along a latitudinal gradient

PubMed Central

De Frenne, Pieter; Graae, Bente J.; Brunet, Jörg; Shevtsova, Anna; De Schrijver, An; Chabrerie, Olivier; Cousins, Sara A. O.; Decocq, Guillaume; Diekmann, Martin; Hermy, Martin; Heinken, Thilo; Kolb, Annette; Nilsson, Christer; Stanton, Sharon; Verheyen, Kris

2012-01-01

Background and Aims The response of forest herb regeneration from seed to temperature variations across latitudes was experimentally assessed in order to forecast the likely response of understorey community dynamics to climate warming. Methods Seeds of two characteristic forest plants (Anemone nemorosa and Milium effusum) were collected in natural populations along a latitudinal gradient from northern France to northern Sweden and exposed to three temperature regimes in growth chambers (first experiment). To test the importance of local adaptation, reciprocal transplants were also made of adult individuals that originated from the same populations in three common gardens located in southern, central and northern sites along the same gradient, and the resulting seeds were germinated (second experiment). Seedling establishment was quantified by measuring the timing and percentage of seedling emergence, and seedling biomass in both experiments. Key Results Spring warming increased emergence rates and seedling growth in the early-flowering forb A. nemorosa. Seedlings of the summer-flowering grass M. effusum originating from northern populations responded more strongly in terms of biomass growth to temperature than southern populations. The above-ground biomass of the seedlings of both species decreased with increasing latitude of origin, irrespective of whether seeds were collected from natural populations or from the common gardens. The emergence percentage decreased with increasing home-away distance in seeds from the transplant experiment, suggesting that the maternal plants were locally adapted. Conclusions Decreasing seedling emergence and growth were found from the centre to the northern edge of the distribution range for both species. Stronger responses to temperature variation in seedling growth of the grass M. effusum in the north may offer a way to cope with environmental change. The results further suggest that climate warming might differentially affect seedling establishment of understorey plants across their distribution range and thus alter future understorey plant dynamics. PMID:22345113

Glass fining experiments in zero gravity

NASA Technical Reports Server (NTRS)

Smith, H. D.

1977-01-01

Ground based experiments were conducted to demonstrate that thermal migration actually operated in glass melts. Thermal migration consistent with the theory was found in one experiment on a borax melt, i.e., there was an approximately linear relation between the bubble diameter and bubble velocity for a given temperature and temperature gradient. It also appeared that nearby bubbles were attracted to one another, which could greatly aid fining. Interpretation of these results was not possible because of complications arising from gravity, i.e., floating of the bubbles, circulation currents due to buoyancy-driven natural connection, and flow of the melt out from the cell.

Sedimentary organic matter distributions, burrowing activity, and biogeochemical cycling: Natural patterns and experimental artifacts

NASA Astrophysics Data System (ADS)

Michaud, Emma; Aller, Robert, C.; Stora, Georges

2010-11-01

The coupling between biogenic reworking activity and reactive organic matter patterns within deposits is poorly understood and often ignored. In this study, we examined how common experimental treatments of sediment affect the burrowing behavior of the polychaete Nephtys incisa and how these effects may interact with reactive organic matter distributions to alter diagenetic transport - reaction balances. Sediment and animals were recovered from a subtidal site in central Long Island Sound, USA. The upper 15 cm of the sediment was sectioned into sub-intervals, and each interval separately sieved and homogenized. Three initial distributions of sediment and organic substrate reactivity were setup in a series of microcosms: (1) a reconstituted natural pattern with surface-derived sediment overlying sediment obtained from progressively deeper material to a depth of 15 cm (Natural); (2) a 15 cm thick sediment layer composed only of surface-derived sediment (Rich); and (3) a 15 cm thick layer composed of uniformally mixed sediment from the original 15 cm sediment profile (Averaged). The two last treatments are comparable to that used in microcosms in many previous studies of bioturbation and interspecific functional interaction experiments. Sediment grain size distributions were 97.5% silt-clay and showed no depth dependent patterns. Sediment porosity gradients were slightly altered by the treatments. Nepthys were reintroduced and aquariums were X-rayed regularly over 5 months to visualize and quantify spatial and temporal dynamics of burrows. The burrowing behaviour of adult populations having similar total biovolume, biomass, abundance, and individual sizes differed substantially as a function of treatment. Burrows in sediment with natural property gradients were much shallower and less dense than those in microcosms with altered gradients. The burrow volume/biovolume ratio was also lower in the substrate with natural organic reactivity gradients. Variation in food resources or in sediment mechanical properties associated with treatments, the latter in part coupled to remineralization processes such as exopolymer production, may explain the burrowing responses. In addition to demonstrating how species may respond to physical sedimentation events (substrate homogenization) and patterns of reactive organic matter redistribution, these experiments suggest that infaunal species interactions in microcosms, including the absolute and relative fluxes of remineralized solutes, may be subject to artifacts depending on exactly how sediments are introduced experimentally. Nonlocal transport and cylinder microenvironment transport - reaction models readily demonstrate how the multiple interactions between burrowing patterns and remineralization rate distributions can alter relative flux balances, decomposition pathways, and time to steady state.

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.

Statistics of Experiments on Cluster Formation and Transport in a Gravitational Field

NASA Technical Reports Server (NTRS)

Izmailov, Alexander F.; Myerson, Allan S.

1993-01-01

Metastable state relaxation in a gravitational field is investigated in the case of non-critical binary solutions. A relaxation description is presented in terms of the time-dependent Ginzburg-Landau formalism for a non-conserved order parameter. A new ansatz for solution of the corresponding partial nonlinear stochastic differential equation is discussed. It is proved that, for the supersaturated solution under consideration, the metastable state relaxation in a gravitational field leads to formation of solute concentration gradients due to the sedimentation of subcritical solute clusters. The pure discussion of the possible methods to compare theoretical results and experimental data related to solute sedimentation in a gravitational field is presented. It is shown that in order to describe these experiments it is necessary to deal both with the value of the solute concentration gradient and with its formation rate. The stochastic nature of the sedimentation process is shown.

Turbulent-Spot Growth Characteristics: Wind-Tunnel and Flight Measurements of Natural Transition at High Reynolds and Mach Numbers

NASA Technical Reports Server (NTRS)

Clark, J. P.; Jones, T. V.; LaGraff, J. E.

2007-01-01

A series of experiments are described which examine the growth of turbulent spots on a flat plate at Reynolds and Mach numbers typical of gas-turbine blading. A short-duration piston tunnel is employed and rapid-response miniature surface-heat-transfer gauges are used to asses the state of the boundary layer. The leading- and trailing-edge velocities of spots are reported for different external pressure gradients and Mach numbers. Also, the lateral spreading angle is determined from the heat-transfer signals which demonstrate dramatically the reduction in spot growth associated with favorable pressure gradients. An associated experiment on the development of turbulent wedges is also reported where liquid-crystal heat-transfer techniques are employed in low-speed wind tunnel to visualize and measure the wedge characteristics. Finally, both liquid crystal techniques and hot-film measurements from flight tests at Mach number of 0.6 are presented.

AQUATIC VERTEBRATE ASSEMBLAGES AT LEAST- AND MOST-IMPACTED STREAM AND RIVER SITES IN THE WESTERN FORESTED MOUNTAINS AGGREGATE ECOREGIONS

EPA Science Inventory

In the West, development of indicators of aquatic vertebrate assemblages condition in streams and rivers is challenged by low species richness (often < 3 species), by strong natural gradients (e.g., elevation), by human impact gradients that often co-vary with natural gradients, ...

Protein gradient films of fibroin and gelatine.

PubMed

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

2013-10-01

Gradients are a natural design principle in biological systems that are used to diminish stress concentration where materials of differing mechanical properties connect. An interesting example of a natural gradient material is byssus, which anchors mussels to rocks and other hard substrata. Building upon previous work with synthetic polymers and inspired by byssal threads, protein gradient films are cast using glycerine-plasticized gelatine and fibroin exhibiting a highly reproducible and smooth mechanical gradient, which encompasses a large range of modulus from 160 to 550 MPa. The reproducible production of biocompatible gradient films represents a first step towards medical applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Geophysical constraints on contaminant transport modeling in a heterogeneous fluvial aquifer.

PubMed

Bowling, Jerry C; Zheng, Chunmiao; Rodriguez, Antonio B; Harry, Dennis L

2006-05-05

Approximately 3000 measurements of hydraulic conductivity in over 50 flowmeter boreholes were available at the Macro-Dispersion Experiment (MADE) site in Columbus, Mississippi, USA to quantify the heterogeneity in hydraulic conductivity at the site scale. This high-density measurement approach is perhaps infeasible for time and expense in typical groundwater remediation sites. A natural-gradient tracer experiment from the MADE site was simulated by a groundwater flow and solute transport model incorporating direct-current (DC) resistivity data collected over the observed plume location. Hydraulic conductivity from one borehole collected during the original site characterization was used to calibrate the electrical resistivity data to hydraulic conductivity using a previously derived log-log relationship. Application of this relationship, using site-specific empirical constants determined from the data, transforms the 3D electrical resistivity data into a 3D description of hydraulic conductivity that can be used in groundwater models. The validity of this approach was tested by using the geophysically derived hydraulic conductivity representation in numerical simulations of the natural-gradient tracer experiment. The agreement between the simulated and observed tracer plumes was quantified to gauge the effectiveness of geophysically derived and flowmeter based representations of the hydraulic conductivity field. This study demonstrates that a highly heterogeneous aquifer can be modeled with minimal hydrological data supplemented with geophysical data at least as well as previous models of the site using purely hydrologic data.

Isotopic Expression of Soil Denitrification across Gradients in Nitrogen and Carbon Availability

NASA Astrophysics Data System (ADS)

Walker, R.; Houlton, B. Z.; Perakis, S. S.

2016-12-01

Denitrification removes biologically available nitrogen (N) from ecosystems, making it an important control over the biosphere's N balance, with implications for air quality, human health and climate change. Despite its importance, estimates of the global soil denitrification flux remain highly uncertain. Major challenges lie in directly measuring the gaseous by-products of denitrification and scaling this complex microbial processes in both space and time. Process-based models constrained by empirical isotopic evidence have emerged as a method to help overcome these challenges. These models use the terrestrial 15N budget, along with soil moisture and N input data, to quantify denitrification fluxes and its gaseous forms, including NO, N2O and N2. However, the robustness of this method is limited by incomplete understanding of isotopic expression of denitrification and how it varies across known controls, such as carbon (C) and nitrate (NO3) availability. Here, we present a quantitative assessment of the isotope effect expression of in situ soil denitrification across gradients in N and C concentrations. This experiment tests the hypothesis that isotopic expression of soil denitrification (a kinetic process) increases with NO3 availability (reaction substrate) and decreases with increasing availability of organic C (electron donor). To test the impact of NO3 availability on the isotope effect of denitrification, field incubations experiments were conducted across a natural soil N gradient, ranging from 0.11 to 0.69% N. Similarly, the impact of electron donor availability was tested by conducting field incubations across a natural soil C gradient ranging from 1.94 to 11.60%. Data show that in lower N sites, the percent of NO3 consumed during the incubation was higher, while C availability neither affected the fraction of NO3 consumed nor the rate of consumption. These findings suggest that greater NO3 concentrations allow for greater isotope expression of denitrification in soil, supporting the working hypothesis. These results will be complemented by laboratory experiments in which NO3 concentration, C availability, and temperature are systematically varied. Future goals include the incorporation of these data into existing models to improve estimates of global N fluxes.

Controlling three-dimensional vortices using multiple and moving external fields

NASA Astrophysics Data System (ADS)

Das, Nirmali Prabha; Dutta, Sumana

2017-08-01

Spirals or scroll wave activities in cardiac tissues are the cause of lethal arrhythmias. The external control of these waves is thus of prime interest to scientists and physicians. In this article, we demonstrate the spatial control of scroll waves by using external electric fields and thermal gradients in experiments with the Belousov-Zhabotinsky reaction. We show that a scroll ring can be made to trace cyclic trajectories under a rotating electric field. Application of a thermal gradient in addition to the electric field deflects the motion and changes the nature of the trajectory. Our experimental results are analyzed and corroborated by numerical simulations based on an excitable reaction diffusion model.

QMR: A Quasi-Minimal Residual method for non-Hermitian linear systems

NASA Technical Reports Server (NTRS)

Freund, Roland W.; Nachtigal, Noel M.

1990-01-01

The biconjugate gradient (BCG) method is the natural generalization of the classical conjugate gradient algorithm for Hermitian positive definite matrices to general non-Hermitian linear systems. Unfortunately, the original BCG algorithm is susceptible to possible breakdowns and numerical instabilities. A novel BCG like approach is presented called the quasi-minimal residual (QMR) method, which overcomes the problems of BCG. An implementation of QMR based on a look-ahead version of the nonsymmetric Lanczos algorithm is proposed. It is shown how BCG iterates can be recovered stably from the QMR process. Some further properties of the QMR approach are given and an error bound is presented. Finally, numerical experiments are reported.

Changes in microbial communities associated with the sea anemone Anemonia viridis in a natural pH gradient.

PubMed

Meron, Dalit; Buia, Maria-Cristina; Fine, Maoz; Banin, Ehud

2013-02-01

Ocean acidification, resulting from rising atmospheric carbon dioxide concentrations, is a pervasive stressor that can affect many marine organisms and their symbionts. Studies which examine the host physiology and microbial communities have shown a variety of responses to the ocean acidification process. Recently, several studies were conducted based on field experiments, which take place in natural CO(2) vents, exposing the host to natural environmental conditions of varying pH. This study examines the sea anemone Anemonia viridis which is found naturally along the pH gradient in Ischia, Italy, with an aim to characterize whether exposure to pH impacts the holobiont. The physiological parameters of A. viridis (Symbiodinium density, protein, and chlorophyll a+c concentration) and its microbial community were monitored. Although reduction in pH was seen to have had an impact on composition and diversity of associated microbial communities, no significant changes were observed in A. viridis physiology, and no microbial stress indicators (i.e., pathogens, antibacterial activity, etc.) were detected. In light of these results, it appears that elevated CO(2) does not have a negative influence on A. viridis that live naturally in the site. This suggests that natural long-term exposure and dynamic diverse microbial communities may contribute to the acclimation process of the host in a changing pH environment.

Influence of natural temperature gradients on measurements of xylem sap flow with thermal dissipation probes. 1. Field observations and possible remedies.

PubMed

Do, F; Rocheteau, A

2002-06-01

The thermal dissipation method is simple and widely used for measuring sap flow in large stems. As with several other thermal methods, natural temperature gradients are assumed to be negligible in the sapwood being measured. We studied the magnitude and variability of natural temperature gradients in sapwood of Acacia trees growing in the Sahelian zone of Senegal, analyzed their effects on sap flow measurements, and investigated possible solutions. A new measurement approach employing cyclic heating (45 minutes of heating and 15 minutes of cooling; 45/15) was also tested. Three-day measurement sequences that included 1 day without heating, a second day with continuous heating and a third day with cyclic heating were recorded during a 6.5-month period using probes installed at three azimuths in a tree trunk. Natural temperature gradients between the two probes of the sensor unit, spaced 8 to 10 cm vertically, were rarely negligible (i.e., < 0.2 degrees C): they were positive during the night and negative during the day, with an amplitude ranging from 0.3 to 3.5 degrees C depending on trunk azimuth, day and season. These temperature gradients had a direct influence on the signal from the continuously heated sensors, inducing fluctuations in the nighttime reference signal. The resulting errors in sap flow estimates can be greater than 100%. Correction protocols have been proposed in previous studies, but they were unsuitable because of the high spatial and temporal variability of the natural temperature gradients. We found that a measurement signal derived from a noncontinuous heating system could be an attractive solution because it appears to be independent of natural temperature gradients. The magnitude and variability of temperature gradients that we observed were likely exacerbated by the combination of open stand, high solar radiation and low sap flow rate. However, for all applications of the thermal dissipation method, it is wise to check regularly for natural temperature gradients by switching off the heater.

Methods to test the interactive effects of drought and plant invasion on ecosystem structure and function using complementary common garden and field experiments.

PubMed

Alba, Christina; NeSmith, Julienne E; Fahey, Catherine; Angelini, Christine; Flory, Stephen Luke

2017-03-01

Abiotic global change drivers affect ecosystem structure and function, but how they interact with biotic factors such as invasive plants is understudied. Such interactions may be additive, synergistic, or offsetting, and difficult to predict. We present methods to test the individual and interactive effects of drought and plant invasion on native ecosystems. We coupled a factorial common garden experiment containing resident communities exposed to drought (imposed with rainout shelters) and invasion with a field experiment where the invader was removed from sites spanning a natural soil moisture gradient. We detail treatments and their effects on abiotic conditions, including soil moisture, light, temperature, and humidity, which shape community and ecosystem responses. Ambient precipitation during the garden experiment exceeded historic norms despite severe drought in prior years. Soil moisture was 48% lower in drought than ambient plots, but the invader largely offset drought effects. Additionally, temperature and light were lower and humidity higher in invaded plots. Field sites spanned up to a 10-fold range in soil moisture and up to a 2.5-fold range in light availability. Invaded and resident vegetation did not differentially mediate soil moisture, unlike in the garden experiment. Herbicide effectively removed invaded and resident vegetation, with removal having site-specific effects on soil moisture and light availability. However, light was generally higher in invader-removal than control plots, whereas resident removal had less effect on light, similar to the garden experiment. Invasion mitigated a constellation of abiotic conditions associated with drought stress in the garden experiment. In the field, where other factors co-varied, these patterns did not emerge. Still, neither experiment suggested that drought and invasion will have synergistic negative effects on ecosystems, although invasion can limit light availability. Coupling factorial garden experiments with field experiments across environmental gradients will be effective for predicting how multiple stressors interact in natural systems.

Mobilization of natural colloids from an iron oxide-coated sand aquifer--Effect of pH and ionic strength

USGS Publications Warehouse

Bunn, Rebecca A.; Magelky, Robin D.; Ryan, Joseph N.; Elimelech, Menachem

2002-01-01

Field and laboratory column experiments were performed to assess the effect of elevated pH and reduced ionic strength on the mobilization of natural colloids in a ferric oxyhydroxide-coated aquifer sediment. The field experiments were conducted as natural gradient injections of groundwater amended by sodium hydroxide additions. The laboratory experiments were conducted in columns of undisturbed, oriented sediments and disturbed, disoriented sediments. In the field, the breakthrough of released colloids coincided with the pH pulse breakthrough and lagged the bromide tracer breakthrough. The breakthrough behavior suggested that the progress of the elevated pH front controlled the transport of the mobilized colloids. In the laboratory, about twice as much colloid release occurred in the disturbed sediments as in the undisturbed sediments. The field and laboratory experiments both showed that the total mass of colloid release increased with increasing pH until the concurrent increase in ionic strength limited release. A decrease in ionic strength did not mobilize significant amounts of colloids in the field. The amount of colloids released normalized to the mass of the sediments was similar for the field and the undisturbed laboratory experiments.

Sediment-peridotite interactions in a thermal gradient: mineralogic and geochemical effects and the "sedimentary signature" of arc magmas

NASA Astrophysics Data System (ADS)

Woodland, Alan; Girnis, Andrei; Bulatov, Vadim; Brey, Gerhard; Höfer, Heidi; Gerdes, Axel

2017-04-01

Strong thermal and chemical gradients are characteristic of the slab-mantle interface in subduction zones where relatively cold sediments become juxtaposed with hotter peridotite of the mantle wedge. The formation of arc magmas is directly related to mass transfer processes under these conditions. We have undertaken a series of experiments to simulate interactions and mass transfer at the slab-mantle interface. In addition to having juxtaposed sediment and peridotite layers, the experiments were performed under different thermal gradients. The sediment had a composition similar to GLOSS (1) and also served as the source of H2O, CO2 and a large selection of trace elements. The peridotite was a depleted garnet harzburgite formed from a mixture of natural hand-picked olivine, opx and garnet. Graphite was added to this mixture to establish a redox gradient between the two layers. Experiments were performed at 7.5-10 GPa to simulate the processes during deep subduction. The thermal gradient was achieved by displacing the sample capsule (Re-lined Pt) from the center of the pressure cell. The gradient was monitored with separate thermocouples at each end of the capsule and by subsequent opx-garnet thermometry across the sample. Maximum temperatures varied from 1400˚ -900˚ C and gradients ranged from 200˚ -800˚ C. Thus, in some experiments melting occurred in the sediment layer and in others this layer remained subsolidus, only devolatilizing. Major and trace elements were transported both in the direction of melt percolation to the hot zone, as well as down temperature. This leads to the development of zones with discrete phase assemblages. Olivine in the peridotite layer becomes converted to orthopyroxene, which is due to Si addition, but also migration of Mg and Fe towards the sediment. In the coldest part of a sample, the sediment is converted into an eclogitic cpx + garnet assemblage. A thin zone depleted in almost all trace elements is formed in peridotite directly above the sediment/peridotite boundary and defines the region of maximum metasomatic alteration. With a low Tmin, fluid-mobile Ba, Rb, Sr and Li are more strongly transported into the melt zone compared to HFSE and REE. At Tmin > 700˚ C, all incompatible elements are extracted from the solid into the melt. However, the mineral assemblage controls which elements are held back in the solid residue (i.e. MREE, HREE, Y, Sc, and to a lesser extent Ti, Zr and Hf in garnet). Peridotite-sediment interaction can produce humite-group minerals, particularly in the presence of F. Negative Nb-Ta anomalies are caused by rutile and/or humite phases. Transport of melt or fluid from the sediment to the overlying mantle wedge produces metasomatized magma sources from which basaltic melts with sedimentary geochemical signatures can be derived. Adding even 1% of melt or fluid to depleted mantle peridotite is sufficient to produce basaltic melts with incompatible element contents similar to those observed in natural subduction-related magmas. Such signatures are retained at 6.5 and even 10 GPa when Tmin < 700˚ C. Plank, T., Langmuir C., 1998. Chem. Geol. 145, 325-394.

The NTF Inlet Guide Vanes Thermal Gradient Problem and Its Mitigation

NASA Technical Reports Server (NTRS)

Venkat, Venki S.; Paryz, Roman W.; Bissett, Owen W.; Kilgore, W.

2013-01-01

The National Transonic Facility (NTF) utilizes Inlet Guide Vanes (IGV) to provide precise, quick response Mach number control for the tunnel. During cryogenic operations, the massive IGV structure can experience large thermal gradients, measured as "Delta T or (Delta)T", between the IGV ring and its support structure called the transfer case. If these temperature gradients are too large, the IGV structure can be stressed beyond its safety limit and cease operation. In recent years, (Delta)T readings exceeding the prescribed safety limits were observed frequently during cryogenic operations, particularly during model access. The tactical operation methods of the tunnel to minimize (Delta)T did not always succeed. One obvious option to remedy this condition is to warm up the IGV structure by disabling the main drive operation, but this "natural" warm up method can takes days in some cases, resulting in productivity loss. This paper documents the thermal gradient problem associated with the IGV structure during cryogenic operation and how the facility has recently achieved an acceptable mitigation which has resulted in improved efficiency of operations.

Power-law versus log-law in wall-bounded turbulence: A large-eddy simulation perspective

NASA Astrophysics Data System (ADS)

Cheng, W.; Samtaney, R.

2014-01-01

The debate whether the mean streamwise velocity in wall-bounded turbulent flows obeys a log-law or a power-law scaling originated over two decades ago, and continues to ferment in recent years. As experiments and direct numerical simulation can not provide sufficient clues, in this study we present an insight into this debate from a large-eddy simulation (LES) viewpoint. The LES organically combines state-of-the-art models (the stretched-vortex model and inflow rescaling method) with a virtual-wall model derived under different scaling law assumptions (the log-law or the power-law by George and Castillo ["Zero-pressure-gradient turbulent boundary layer," Appl. Mech. Rev. 50, 689 (1997)]). Comparison of LES results for Reθ ranging from 105 to 1011 for zero-pressure-gradient turbulent boundary layer flows are carried out for the mean streamwise velocity, its gradient and its scaled gradient. Our results provide strong evidence that for both sets of modeling assumption (log law or power law), the turbulence gravitates naturally towards the log-law scaling at extremely large Reynolds numbers.

Changes in coral reef communities across a natural gradient in seawater pH

PubMed Central

Barkley, Hannah C.; Cohen, Anne L.; Golbuu, Yimnang; Starczak, Victoria R.; DeCarlo, Thomas M.; Shamberger, Kathryn E. F.

2015-01-01

Ocean acidification threatens the survival of coral reef ecosystems worldwide. The negative effects of ocean acidification observed in many laboratory experiments have been seen in studies of naturally low-pH reefs, with little evidence to date for adaptation. Recently, we reported initial data suggesting that low-pH coral communities of the Palau Rock Islands appear healthy despite the extreme conditions in which they live. Here, we build on that observation with a comprehensive statistical analysis of benthic communities across Palau’s natural acidification gradient. Our analysis revealed a shift in coral community composition but no impact of acidification on coral richness, coralline algae abundance, macroalgae cover, coral calcification, or skeletal density. However, coral bioerosion increased 11-fold as pH decreased from the barrier reefs to the Rock Island bays. Indeed, a comparison of the naturally low-pH coral reef systems studied so far revealed increased bioerosion to be the only consistent feature among them, as responses varied across other indices of ecosystem health. Our results imply that whereas community responses may vary, escalation of coral reef bioerosion and acceleration of a shift from net accreting to net eroding reef structures will likely be a global signature of ocean acidification. PMID:26601203

Directional solidification of C8-BTBT films induced by temperature gradients and its application for transistors

NASA Astrophysics Data System (ADS)

Fujieda, Ichiro; Iizuka, Naoki; Onishi, Yosuke

2015-03-01

Because charge transport in a single crystal is anisotropic in nature, directional growth of single crystals would enhance device performance and reduce its variation among devices. For an organic thin film, a method based on a temperature gradient would offer advantages in throughput and cleanliness. In experiments, a temperature gradient was established in a spin-coated film of 2,7-dioctyl [1]benzothieno[3,2-b]benzothiophene (C8-BTBT) by two methods. First, a sample was placed on a metal plate bridging two heat stages. When one of the heat stages was cooled, the material started to solidify from the colder region. The melt-solid interface proceeded along the temperature gradient. Cracks were formed perpendicular to the solidification direction. Second, a line-shaped region on the film was continuously exposed to the light from a halogen lamp. After the heat stage was cooled, cracks similar to the first experiment were observed, indicating that the melt-solid interface moved laterally. We fabricated top-contact, bottom-gate transistors with these films. Despite the cracks, field-effect mobility of the transistors fabricated with these films was close to 6 cm2 /Vs and 4 cm2 /Vs in the first and second experiment, respectively. Elimination of cracks would improve charge transport and reduce performance variation among devices. It should be noted that the intense light from the halogen lamp did not damage the C8-BTBT films. The vast knowledge on laser annealing is now available for directional growth of this type of materials. The associated cost would be much smaller because an organic thin film melts at a low temperature.

Coarse graining Escherichia coli chemotaxis: from multi-flagella propulsion to logarithmic sensing.

PubMed

Curk, Tine; Matthäus, Franziska; Brill-Karniely, Yifat; Dobnikar, Jure

2012-01-01

Various sensing mechanisms in nature can be described by the Weber-Fechner law stating that the response to varying stimuli is proportional to their relative rather than absolute changes. The chemotaxis of bacteria Escherichia coli is an example where such logarithmic sensing enables sensitivity over large range of concentrations. It has recently been experimentally demonstrated that under certain conditions E. coli indeed respond to relative gradients of ligands. We use numerical simulations of bacteria in food gradients to investigate the limits of validity of the logarithmic behavior. We model the chemotactic signaling pathway reactions, couple them to a multi-flagella model for propelling and take the effects of rotational diffusion into account to accurately reproduce the experimental observations of single cell swimming. Using this simulation scheme we analyze the type of response of bacteria subject to exponential ligand profiles and identify the regimes of absolute gradient sensing, relative gradient sensing, and a rotational diffusion dominated regime. We explore dependance of the swimming speed, average run time and the clockwise (CW) bias on ligand variation and derive a small set of relations that define a coarse grained model for bacterial chemotaxis. Simulations based on this coarse grained model compare well with microfluidic experiments on E. coli diffusion in linear and exponential gradients of aspartate.

Coral Calcification Across a Natural Gradient in Ocean Acidification

NASA Astrophysics Data System (ADS)

Cohen, A. L.; Brainard, R. E.; Young, C.; Shamberger, K. E.; McCorkle, D. C.; Feely, R. A.; Mcleod, E.; Cantin, N.; Rose, K.; Lohmann, G. P.

2011-12-01

Much of our understanding of the impact of ocean acidification on coral calcification comes from laboratory manipulation experiments in which corals are reared under a range of seawater pH and aragonite saturation states (μar) equivalent to those projected for the next hundred years. In general, experiments show a consistently negative impact of acidification on coral calcification, leading to predictions of mass coral reef extinctions by dissolution as natural rates of carbonate erosion exceed the rates at which corals and other reef calcifiers can replace it. The tropical oceans provide a natural laboratory within which to test hypotheses about the longer term impact and adaptive potential of corals to acidification of the reef environment. Here we report results of a study in which 3-D CT scan and imaging techniques were used to quantify annual rates of calcification by conspecifics at 12 reefs sites spanning a natural gradient in ocean acidification. In situ μar calculated from alkalinity and DIC measurements of reef seawater ranged from less than 2.7 on an eastern Pacific Reef to greater than 4.0 in the central Red Sea. No correlation between μar and calcification was observed across this range. Corals living on low μar reefs appear to be calcifying as fast, sometimes faster than conspecifics living on high μar reefs. We used total lipid and tissue thickness to index the energetic status of colonies collected at each of our study sites. Our results support the hypothesis that energetics plays a key role in the coral calcification response to ocean acidification. Indeed, the true impact of acidification on coral reefs will likely be felt as temperatures rise and the ocean becomes more stratified, depleting coral energetic reserves through bleaching and reduced nutrient delivery to oceanic reefs.

Tropical forest soil microbes and climate warming: An Andean-Amazon gradient and `SWELTR'

NASA Astrophysics Data System (ADS)

Nottingham, A.; Turner, B. L.; Fierer, N.; Whitaker, J.; Ostle, N. J.; McNamara, N. P.; Bardgett, R.; Silman, M.; Bååth, E.; Salinas, N.; Meir, P.

2017-12-01

Climate warming predicted for the tropics in the coming century will result in average temperatures under which no closed canopy forest exists today. There is, therefore, great uncertainty associated with the direction and magnitude of feedbacks between tropical forests and our future climate - especially relating to the response of soil microbes and the third of global soil carbon contained in tropical forests. While warming experiments are yet to be performed in tropical forests, natural temperature gradients are powerful tools to investigate temperature effects on soil microbes. Here we draw on studies from a 3.5 km elevation gradient - and 20oC mean annual temperature gradient - in Peruvian tropical forest, to investigate how temperature affects the structure of microbial communities, microbial metabolism, enzymatic activity and soil organic matter cycling. With decreased elevation, soil microbial diversity increased and community composition shifted, from taxa associated with oligotrophic towards copiotrophic traits. A key role for temperature in shaping these patterns was demonstrated by a soil translocation experiment, where temperature-manipulation altered the relative abundance of specific taxa. Functional implications of these community composition shifts were indicated by changes in enzyme activities, the temperature sensitivity of bacterial and fungal growth rates, and the presence of temperature-adapted iso-enzymes at different elevations. Studies from a Peruvian elevation transect indicated that soil microbial communities are adapted to long-term (differences with elevation) and short-term (translocation responses) temperature changes. These findings indicate the potential for adaptation of soil microbes in tropical soils to future climate warming. However, in order to evaluate the sensitivity of these processes to climate warming in lowland forests, in situ experimentation is required. Finally, we describe SWELTR (Soil Warming Experiment in Lowland Tropical Rainforest), a new soil warming experiment being undertaken on Barro Colorado Island, Panama, designed to improve our understanding of biogeochemical feedbacks to climate warming in lowland tropical forests.

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

Transient heterogeneity in an aquifer undergoing bioremediation of hydrocarbons.

PubMed

Schillig, P C; Devlin, J F; Roberts, J A; Tsoflias, G P; McGlashan, M A

2011-01-01

Localized, transient heterogeneity was studied in a sand aquifer undergoing benzene, toluene, ethylbenzene, and xylene bioremediation using a novel array of multilevel, in situ point velocity probes (PVPs). The experiment was conducted within a sheet-pile alleyway to maintain a constant average flow direction through time. The PVPs measured changes in groundwater velocity direction and magnitude at the centimeter scale, making them ideal to monitor small-scale changes in hydraulic conductivity (K). Velocities were shown to vary nonuniformly by up to a factor of 3 when a source of oxygen was established down-gradient of the petroleum spill. In spite of these local variations, the average groundwater velocity within the 7 m × 20 m sheet-piled test area only varied within ± 25%. The nonuniform nature of the velocity variations across the gate indicated that the changes were not due solely to seasonal hydraulic gradient fluctuations. At the conclusion of the experiment, microbial biomass levels in the aquifer sediments was approximately 1 order of magnitude higher in the oxygen-amended portion of the aquifer than at the edge of the plume or in locations up-gradient of the source. These data suggest that the transient velocities resulted, at least in part, from enhanced biological activity that caused transient heterogeneities in the porous medium.

Locating Pleistocene Refugia: Comparing Phylogeographic and Ecological Niche Model Predictions

DTIC Science & Technology

2007-07-01

the nature of the paleoclimatic layers currently available. Mountain ranges or large ice sheets are reflected in climate layers, as they present major...environmental gradients running both north-south (latitu- dinal) and east to west (North American mountain ranges). To assure that the test could be...Conceived and designed the experiments: RG EW. Analyzed the data: RG EW. Other: Contributed to project planning: SP AN. Provided data layers: AP RH

Does Hunger Contribute to Socioeconomic Gradients in Behavior?

PubMed Central

Nettle, Daniel

2017-01-01

Recent research has uncovered many examples of socioeconomic gradients in behavior and psychological states. As yet there is no theoretical consensus on the nature of the causal processes that produce these gradients. Here, I present the hunger hypothesis, namely the claim that part of the reason that people of lower socioeconomic position behave and feel as they do is that they are relatively often hungry. The hunger hypothesis applies in particular to impulsivity-hyperactivity, irritability-aggression, anxiety, and persistent narcotic use, all of which have been found to show socioeconomic gradients. I review multiple lines of evidence showing that hunger produces strong increases in these outcomes. I also review the literatures on food insufficiency and food insecurity to show that, within affluent societies, the poor experience a substantial burden of hunger, despite obtaining sufficient or excess calories on average. This leads to the distinctive prediction that hunger is an important mediator of the relationships between socioeconomic variables and the behavioral/psychological outcomes. This approach has a number of far-reaching implications, not least that some behavioral and psychological differences between social groups, though persistent under current economic arrangements, are potentially highly reversible with changes to the distribution of financial resources and food. PMID:28344567

Natural convection in low-g environments

NASA Technical Reports Server (NTRS)

Grodzka, P. G.; Bannister, T. C.

1974-01-01

The present state of knowledge in the area of low-g natural convection is reviewed, taking into account a number of experiments conducted during the Apollo 14, 16, and 17 space flights. Convections due to steady low-g accelerations are considered. Steady g-levels result from spacecraft rotation, gravity gradients, solar wind, and solar pressure. Varying g-levels are produced by engine burns, attitude control maneuvers, and onboard vibrations from machinery or astronaut movement. Thermoacoustic convection in a low-g environment is discussed together with g-jitter convection, surface tension-driven convection, electrohydrodynamics under low-g conditions, phase change convection, and approaches for the control and the utilization of convection in space.

Field-scale prediction of enhanced DNAPL dissolution based on partitioning tracers.

PubMed

Wang, Fang; Annable, Michael D; Jawitz, James W

2013-09-01

The equilibrium streamtube model (EST) has demonstrated the ability to accurately predict dense nonaqueous phase liquid (DNAPL) dissolution in laboratory experiments and numerical simulations. Here the model is applied to predict DNAPL dissolution at a tetrachloroethylene (PCE)-contaminated dry cleaner site, located in Jacksonville, Florida. The EST model is an analytical solution with field-measurable input parameters. Measured data from a field-scale partitioning tracer test were used to parameterize the EST model and the predicted PCE dissolution was compared to measured data from an in-situ ethanol flood. In addition, a simulated partitioning tracer test from a calibrated, three-dimensional, spatially explicit multiphase flow model (UTCHEM) was also used to parameterize the EST analytical solution. The EST ethanol prediction based on both the field partitioning tracer test and the simulation closely matched the total recovery well field ethanol data with Nash-Sutcliffe efficiency E=0.96 and 0.90, respectively. The EST PCE predictions showed a peak shift to earlier arrival times for models based on either field-measured or simulated partitioning tracer tests, resulting in poorer matches to the field PCE data in both cases. The peak shifts were concluded to be caused by well screen interval differences between the field tracer test and ethanol flood. Both the EST model and UTCHEM were also used to predict PCE aqueous dissolution under natural gradient conditions, which has a much less complex flow pattern than the forced-gradient double five spot used for the ethanol flood. The natural gradient EST predictions based on parameters determined from tracer tests conducted with a complex flow pattern underestimated the UTCHEM-simulated natural gradient total mass removal by 12% after 170 pore volumes of water flushing indicating that some mass was not detected by the tracers likely due to stagnation zones in the flow field. These findings highlight the important influence of well configuration and the associated flow patterns on dissolution. © 2013.

Field-scale prediction of enhanced DNAPL dissolution based on partitioning tracers

NASA Astrophysics Data System (ADS)

Wang, Fang; Annable, Michael D.; Jawitz, James W.

2013-09-01

The equilibrium streamtube model (EST) has demonstrated the ability to accurately predict dense nonaqueous phase liquid (DNAPL) dissolution in laboratory experiments and numerical simulations. Here the model is applied to predict DNAPL dissolution at a tetrachloroethylene (PCE)-contaminated dry cleaner site, located in Jacksonville, Florida. The EST model is an analytical solution with field-measurable input parameters. Measured data from a field-scale partitioning tracer test were used to parameterize the EST model and the predicted PCE dissolution was compared to measured data from an in-situ ethanol flood. In addition, a simulated partitioning tracer test from a calibrated, three-dimensional, spatially explicit multiphase flow model (UTCHEM) was also used to parameterize the EST analytical solution. The EST ethanol prediction based on both the field partitioning tracer test and the simulation closely matched the total recovery well field ethanol data with Nash-Sutcliffe efficiency E = 0.96 and 0.90, respectively. The EST PCE predictions showed a peak shift to earlier arrival times for models based on either field-measured or simulated partitioning tracer tests, resulting in poorer matches to the field PCE data in both cases. The peak shifts were concluded to be caused by well screen interval differences between the field tracer test and ethanol flood. Both the EST model and UTCHEM were also used to predict PCE aqueous dissolution under natural gradient conditions, which has a much less complex flow pattern than the forced-gradient double five spot used for the ethanol flood. The natural gradient EST predictions based on parameters determined from tracer tests conducted with a complex flow pattern underestimated the UTCHEM-simulated natural gradient total mass removal by 12% after 170 pore volumes of water flushing indicating that some mass was not detected by the tracers likely due to stagnation zones in the flow field. These findings highlight the important influence of well configuration and the associated flow patterns on dissolution.

Paramecium swimming in capillary tube

NASA Astrophysics Data System (ADS)

Jana, Saikat; Um, Soong Ho; Jung, Sunghwan

2012-04-01

Swimming organisms in their natural habitat need to navigate through a wide range of geometries and chemical environments. Interaction with boundaries in such situations is ubiquitous and can significantly modify the swimming characteristics of the organism when compared to ideal laboratory conditions. We study the different patterns of ciliary locomotion in glass capillaries of varying diameter and characterize the effect of the solid boundaries on the velocities of the organism. Experimental observations show that Paramecium executes helical trajectories that slowly transition to straight lines as the diameter of the capillary tubes decreases. We predict the swimming velocity in capillaries by modeling the system as a confined cylinder propagating longitudinal metachronal waves that create a finite pressure gradient. Comparing with experiments, we find that such pressure gradient considerations are necessary for modeling finite sized ciliary organisms in restrictive geometries.

Impact of Ozone Gradient on Grapevine Leaves

NASA Astrophysics Data System (ADS)

Alebic-Juretic, Ana; Bokan-Vucelic, Itana; Mifka, Boris; Zatezalo, Marija; Zubak, Velimir

2017-04-01

Due to complex orography and air mass circulation, the Rijeka Bay area is characterized by O3 gradient, with concentrations risen with the altitude (1). Therefore AOT40 values were often exceeded and should result in harmful effects on vegetation. Based on previous controlled experiments (2), we examined the possible effect of atmospheric ozone on grape leaves under natural O3 gradient. Grapevine leaves (2-5) were collected from May to September 2016 at two sampling points in the proximity of two AQM stations: Site 1 in the city centre (20m asl) and Site 2 (186m asl) in the suburban settlement. Subsequent to weighing and determination of surface area, the leaves (0,5 g) were extracted in 95% ethanol and analysed on chlorophyl a (Chla), chlorophyl b (Chlb) and carotene (Car) content by UV-VIS spectrometry on 3 wavelengths (664, 649, 470 nm) (3) In summer 2016 O3 gradient was not that pronounced as usual (1), but stil the concentrations differed by approx. 20%, exceeding national AOT40 value at both sites (22.360 and 28.061 μg m-3 h, respectively, at Sites 1 and 2). The concentrations of other pollutants were bellow limit values (LV). The Cha and Chb in a sample leaves collected at the end of May at Site 2 are equal to that with filtered O3 in control experiment (2), i.e. without damage caused by ozone, while the Car content is lower approx. 50% and is kept at the same level. The con-centrations of pigments obtained in July prooved the possible damage by O3, while in subsequent months could speed up natural ageing. This is the first evidence of O3 damage on plants in the Rijeka Bay area, in spite of weaker O3 gradient and lacking visible signs of damage. Preliminary results indicate the need for more frequent sampling, particularly in the period included in AOT40 (May-July). References: 1. Alebić-Juretić A (2012) Int J Remote Sensing, 33(2): 335-345 2. Britvec M, Reichenauer T, Soja G., Ljubešić N, Pećina M (2001) Biologia (Bratislava),56/4: 417-424 3. Sumanata N, Haque CI, Nishika J, Suprakash R (2014) Res J Chem Sci, 4(9):63-69

Growth reaction norms of domesticated, wild and hybrid Atlantic salmon families in response to differing social and physical environments

PubMed Central

2013-01-01

Background Directional selection for growth has resulted in the 9-10th generation of domesticated Atlantic salmon Salmo salar L. outgrowing wild salmon by a ratio of approximately 3:1 when reared under standard hatchery conditions. In the wild however, growth of domesticated and wild salmon is more similar, and seems to differ at the most by a ratio of 1.25:1. Comparative studies of quantitative traits in farmed and wild salmon are often performed by the use of common-garden experiments where salmon of all origins are reared together to avoid origin-specific environmental differences. As social interaction may influence growth, the large observed difference in growth between wild and domesticated salmon in the hatchery may not be entirely genetically based, but inflated by inter-strain competition. This study had two primary aims: (i) investigate the effect of social interaction and inter-strain competition in common-garden experiments, by comparing the relative growth of farmed, hybrid and wild salmon when reared together and separately; (ii) investigate the competitive balance between wild and farmed salmon by comparing their norm of reaction for survival and growth along an environmental gradient ranging from standard hatchery conditions to a semi-natural environment with restricted feed. Results The main results of this study, which are based upon the analysis of more than 6000 juvenile salmon, can be summarised as; (i) there was no difference in relative growth between wild and farmed salmon when reared together and separately; (ii) the relative difference in body weight at termination between wild and farmed salmon decreased as mortality increased along the environmental gradient approaching natural conditions. Conclusions This study demonstrates that potential social interactions between wild and farmed salmon when reared communally are not likely to cause an overestimation of the genetic growth differences between them. Therefore, common-garden experiments represent a valid methodological approach to investigate genetic differences between wild and farmed salmon. As growth of surviving salmon of all origins became more similar as mortality increased along the environmental gradient approaching natural conditions, a hypothesis is presented suggesting that size-selective mortality is a possible factor reducing growth differences between these groups in the wild. PMID:24165438

Intraguild predation may reinforce a species-environment gradient

NASA Astrophysics Data System (ADS)

MacNeil, Calum; Dick, Jaimie T. A.

2012-05-01

Species-environment gradients are ubiquitous in nature, with studies often partially explaining the replacement of species along such gradients by autecological factors such as differential physiological tolerances. However, lacking direct evidence, the majority of studies only infer some form of inter-specific interaction, often competition, as reinforcing these gradients. There is usually the further implication that environmental factors mediate asymmetries in the interaction. Recognising the lack of explicit experimental considerations of how key inter-specific interactions are modified by the environment, we chose a study system where we were able to bring the species in question into the laboratory and conduct experiments to test hypotheses about gradient-induced asymmetries in an inter-specific interaction. To this end, we tested the hypothesis that a species-salinity gradient may be reinforced by changes in the asymmetry of intraguild predation between two species of amphipod crustaceans with wide salinity tolerances. River and estuary surveys showed that Gammarus duebeni and Gammarus zaddachi have overlapping distributions, with both surviving and reproducing in salinities ranging from freshwater to fully marine. However, the former species is relatively more abundant in low salinities and the latter in higher salinities. In the laboratory, survival of both species was high in all salinities and cannibalism occurred at low frequencies. However, intraguild predation by males on moulted females was asymmetric in favour of G. duebeni at low salinities, this asymmetry completely reversing to favour G. zaddachi at higher salinities. Thus, we provide evidence that this species-environment gradient occurs due to overlapping physiological tolerances and salinity-driven shifts in the asymmetry of a key inter-specific interaction, intraguild predation.

Design of a High Thermal Gradient Bridgman Furnace

NASA Technical Reports Server (NTRS)

LeCroy, J. E.; Popok, D. P.

1994-01-01

The Advanced Automated Directional Solidification Furnace (AADSF) is a Bridgman-Stockbarger microgravity processing facility, designed and manifested to first fly aboard the second United States Microgravity Payload (USMP-2) Space Shuttle mission. The AADSF was principally designed to produce high axial thermal gradients, and is particularly suitable for metals solidification experiments, including non-dilute alloys. To accommodate a wider range of experimental conditions, the AADSF is equipped with a reconfigurable gradient zone. The overall design of the AADSF and the relationship between gradient zone design and furnace performance are described. Parametric thermal analysis was performed and used to select gradient zone design features that fulfill the high thermal gradient requirements of the USMP-2 experiment. The thermal model and analytical procedure, and parametric results leading to the first flight gradient zone configuration, are presented. Performance for the USMP-2 flight experiment is also predicted, and analysis results are compared to test data.

An Experiment Using Sucrose Density Gradients in the Undergraduate Biochemistry Laboratory.

ERIC Educational Resources Information Center

Turchi, Sandra L.; Weiss, Monica

1988-01-01

Describes an experiment to be performed in an undergraduate biochemistry laboratory that is based on a gradient centrifugation system employing a simple bench top centrifuge, a freezer, and frozen surcose gradient solution to separate macromolecules and subcellular components. (CW)

Thermal Gradient Fining of Glass

NASA Technical Reports Server (NTRS)

Wilcox, W.

1983-01-01

Molten glass fined (cleared of bubbles) by heating with suitable temperature gradient, according to preliminary experiments. Temperature gradient produces force on gas bubbles trapped in molten glass pushing bubbles to higher temperature region where they are collected. Concept demonstrated in experiments on Earth and on rocket.

DETERMINING LEAST- AND MOST-IMPACTED STREAM CONDITIONS USING SURVEY DATA ACROSS THE RANGE OF NATURAL GRADIENTS

EPA Science Inventory

One of the challenges to developing indicators of ecological condition is to determine what reference conditions are for a given ecosystem. Because human activity often co-varies with natural gradients (e.g., elevation) one cannot simply extrapolate from, for example, small strea...

Exploiting the Temperature Dependence of Magnetic Susceptibility to Control Convection in Fundamental Studies of Solidification Phenomena

NASA Technical Reports Server (NTRS)

Seybert, C. D.; Evans, J. W.; Leslie, Fred; Jones, W. K., Jr.

2000-01-01

It is well known that convection is a dominant mass transport mechanism when materials are solidified on Earth's surface. This convection is caused by gradients in density (and therefore gravitational force) that are brought about by gradients in temperature, composition or both. Diffusion of solute is therefore dwarfed by convection and the study of fundamental parameters, such as dendrite tip shape and growth velocity in the absence of convection is nearly impossible. Significant experimental work has therefore been carried out in orbiting laboratories with the intent of minimizing convection by minimizing gravity. One of the best known experiments of this kind is the Isothermal Dendritic Growth Experiment (IDGE), supported by NASA. Naturally such experiments are costly and one objective of the present investigation is to develop an experimental method whereby convection can be- halted, in solidification and other experiments, on the surface. A second objective is to use the method to minimize convection resulting from the residual accelerations suffered by experiments in microgravity. The method to be used to minimize convection relies on the dependence of the magnetic susceptibility of a fluid on temperature or composition (whichever is driving convection). All materials experience a force when placed in a magnetic field gradient. The direction and magnitude of that force depend on the magnetic susceptibility of the material. Consequently the force will vary if the susceptibility varies with temperature or composition. With a magnetic field gradient in the right direction (typically upward) and of the right magnitude, this variation in the magnetic force can be made to exactly cancel the variation in the gravitational force. Expressed another way, normal buoyancy is exactly countered by a "magnetic buoyancy". To demonstrate the principle, a solution of MnC12 in water has been used. First the variation of the susceptibility of this paramagnetic solution with temperature and concentration was measured. Then a "cell", containing this solution and 50mm long by 15mm high by 155mm wide, was placed in a superconducting magnet at Marshall Space Flight Center. The magnetic field was measured at various positions within the bore of the magnet using a Hall effect probe. In this way, a position was found where the magnetic field gradient was predominantly upward; the magnitude of the gradient could then be adjusted by adjusting the current of the magnet. The ends of the cell consisted of machined copper blocks maintained at controlled temperatures by circulating water from constant temperature baths. The walls of the cell were of rectangular section glass tubing so that the cell contents could be seen. Velocities arising from thermal gradients within the cell were measured by particle image velocimetry (PIV). Particles used for this purpose were silver-coated hollow glass spheres of micrometers diameter and nearly the same density as the solution. A central vertical plane of the cell was illuminated by a laser beam passing through a cylindrical lens. Digital images of the particles were captured on a CCD camera and fed to a computer so that frame-to-frame movements of particles traveling with the fluid were captured. These images were employed to compute velocity maps using commercial PIV software. In a typical experiment the cold end of the cell was maintained at 10C and the warm end at 30 C. With no current in the magnet, i.e.- with natural -convection allowed to occur, the fluid was observed to circulate with an average speed of approximately 0.3 millimeters per second. It was visually apparent that this circulation was diminished as the current was increased. At currents of approximately 20A the flow was halted, to within the precision of the PIV measurements. At yet higher currents the convection was reversed with the hotter solution sinking and the cooler solution rising. At 40A this reversed convection had speeds averaging 0.43 millimeters per second. The measurements of susceptibility and density allow an estimate of the field gradient necessary to halt convection in the experiment. That estimate was 7.8T (squared) per meter and the convection was observed to halt in the magnet at a current giving 7.21T (squared) per meter from the magnetic field measurements. Calculations of the flow have been carried out using the computational fluid dynamics software FLUENT and show good agreement with the measurements.

Ancient Living Organisms Escaping from, or Imprisoned in, the Vents?

PubMed Central

Jackson, J. Baz

2017-01-01

We have recently criticised the natural pH gradient hypothesis which purports to explain how the difference in pH between fluid issuing from ancient alkali vents and the more acidic Hadean ocean could have driven molecular machines that catalyse reactions that are useful in prebiotic and autotrophic chemistry. In this article, we temporarily suspend our earlier criticism while we consider difficulties for primitive organisms to have managed their energy supply and to have left the vents and become free-living. We point out that it may have been impossible for organisms to have acquired membrane-located proton (or sodium ion) pumps to replace the natural pH gradient, and independently to have driven essential molecular machines such as the ATP synthase. The volumes of the ocean and of the vent fluids were too large for a membrane-located pump to have generated a significant ion concentration gradient. Our arguments apply to three of the four concurrent models employed by the proponents of the natural pH gradient hypothesis. A fourth model is exempt from these arguments but has other intrinsic difficulties that we briefly consider. We conclude that ancient organisms utilising a natural pH gradient would have been imprisoned in the vents, unable to escape and become free-living. PMID:28914790

An experimental test of fitness variation across a hydrologic gradient predicts willow and poplar species distributions.

PubMed

Wei, Xiaojing; Savage, Jessica A; Riggs, Charlotte E; Cavender-Bares, Jeannine

2017-05-01

Environmental filtering is an important community assembly process influencing species distributions. Contrasting species abundance patterns along environmental gradients are commonly used to provide evidence for environmental filtering. However, the same abundance patterns may result from alternative or concurrent assembly processes. Experimental tests are an important means to decipher whether species fitness varies with environment, in the absence of dispersal constraints and biotic interactions, and to draw conclusions about the importance of environmental filtering in community assembly. We performed an experimental test of environmental filtering in 14 closely related willow and poplar species (family Salicaceae) by transplanting cuttings of each species into 40 common gardens established along a natural hydrologic gradient in the field, where competition was minimized and herbivory was controlled. We analyzed species fitness responses to the hydrologic environment based on cumulative growth and survival over two years using aster fitness models. We also examined variation in nine drought and flooding tolerance traits expected to contribute to performance based on a priori understanding of plant function in relation to water availability and stress. We found substantial evidence that environmental filtering along the hydrologic gradient played a critical role in determining species distributions. Fitness variation of each species in the field experiment was used to model their water table depth optima. These optima predicted 68% of the variation in species realized hydrologic niches based on peak abundance in naturally assembled communities in the surrounding region. Multiple traits associated with water transport efficiency and water stress tolerance were correlated with species hydrologic niches, but they did not necessarily covary with each other. As a consequence, species occupying similar hydrologic niches had different combinations of trait values. Moreover, individual traits were less phylogenetically conserved than species hydrologic niches and integrated water stress tolerance as determined by multiple traits. We conclude that differential fitness among species along the hydrologic gradient was the consequence of multiple traits associated with water transport and water stress tolerance, expressed in different combinations by different species. Varying environmental tolerance, in turn, played a critical role in driving niche segregation among close relatives along the hydrologic gradient. © 2017 by the Ecological Society of America.

Spatial gradient tuning in metamaterials

NASA Astrophysics Data System (ADS)

Driscoll, Tom; Goldflam, Michael; Jokerst, Nan; Basov, Dimitri; Smith, David

2011-03-01

Gradient Index (GRIN) metamaterials have been used to create devices inspired by, but often surpassing the potential of, conventional GRIN optics. The unit-cell nature of metamaterials presents the opportunity to exert much greater control over spatial gradients than is possible in natural materials. This is true not only during the design phase but also offers the potential for real-time reconfiguration of the metamaterial gradient. This ability fits nicely into the picture of transformation-optics, in which spatial gradients can enable an impressive suite of innovative devices. We discuss methods to exert control over metamaterial response, focusing on our recent demonstrations using Vanadium Dioxide. We give special attention to role of memristance and mem-capacitance observed in Vanadium Dioxide, which simplify the demands of stimuli and addressing, as well as intersecting metamaterials with the field of memory-materials.

The effects of CO2 on phytoplankton community structure in the Amazon River Plume

NASA Astrophysics Data System (ADS)

Chen, T. L.; Goes, J. I.; Gomes, H. R.; McKee, K. T.

2013-12-01

The Amazon River Plume results from an enormous discharge of freshwater and organic matter into the Atlantic Ocean. It is a unique environment with a natural pCO2 gradient in the surface waters of the plume that range from 130-950 μatm. The response of coastal marine phytoplankton to increased anthropogenic CO2 emission is still unknown, hence the Amazon River Plume gradient can serve as a natural laboratory to examine the potential influence of atmospheric CO2 increases and ocean acidification on phytoplankton community composition. A two pronged study was undertaken: the first in which shipboard samples from a 2010 cruise to the Amazon River Plume were analyzed to examine the distribution of 3 major phytoplankton groups (diatoms, diatom-diazotroph associations [DDAs], and the diazotroph Trichodesmium spp.) with respect to the natural pCO2 gradient; the second in which the growth response of Thalassiosira weisflogii, a representative diatom species, was examined under experimentally manipulated CO2 conditions. Cruise data analysis showed that diatoms were found with higher cell counts around 150 μatm; DDAs seemed to dominate waters within the narrow range of 350-400 μatm CO2; and the diazotroph Trichodesmium spp. grew in a wide range of pCO2 conditions, but with higher cell counts at upwards of 500 μatm. Phytoplankton group distributions along the CO2 gradient may be due to differences in their carbon-concentrating mechanism (CCMs) efficiencies. The CO2 manipulation apparatus was assembled such that the cells were grown under three different CO2 environments. Differential growth of T. weisflogii was observed at 150, 400, and 800 ppm CO2 treatment. T. weisflogii grew at all three CO2 concentrations, reflecting diatoms' physiological flexibility and efficient CCMs. Absorption spectra analysis of pigments and Fast Repetition Rate Fluorometer analysis indicate potential changes in photosynthetic machinery with different CO2 treatments. Future CO2 manipulation experiments on representative DDA and diazotroph species will be undertaken to compare the growth responses of the 3 major phytoplankton groups to changes in CO2. Additionally, analysis on fatty acid compositions with different CO2 treatments will be done to assess potential changes in nutritive value for higher trophic levels. Underway pCO2 measurements with overlaid cell counts from the 2010 cruise data CO2 manipulation experiment data- growth curve (in vivo chlorophyll a fluorescence) for the 3 CO2 treatments

Integrated electrokinetics-adsorption remediation of saline-sodic soils: effects of voltage gradient and contaminant concentration on soil electrical conductivity.

PubMed

Essa, Mohammed Hussain; Mu'azu, Nuhu Dalhat; Lukman, Salihu; Bukhari, Alaadin

2013-01-01

In this study, an integrated in situ remediation technique which couples electrokinetics with adsorption, using locally produced granular activated carbon from date palm pits in the treatment zones that are installed directly to bracket the contaminated soils at bench-scale, is investigated. Natural saline-sodic clay soil, spiked with contaminant mixture (kerosene, phenol, Cr, Cd, Cu, Zn, Pb, and Hg), was used in this study to investigate the effects of voltage gradient, initial contaminant concentration, and polarity reversal rate on the soil electrical conductivity. Box-Behnken Design (BBD) was used for the experimental design and response surface methodology (RSM) was employed to model, optimize, and interpret the results obtained using Design-Expert version 8 platform. The total number of experiments conducted was 15 with voltage gradient, polarity reversal rate, and initial contaminant concentration as variables. The main target response discussed in this paper is the soil electrical conductivity due to its importance in electrokinetic remediation process. Responses obtained were fitted to quadratic models whose R (2) ranges from 84.66% to 99.19% with insignificant lack of fit in each case. Among the investigated factors, voltage gradient and initial contaminant concentration were found to be the most significant influential factors.

Effects of eddy currents on selective spectral editing experiments at 3T.

PubMed

Oeltzschner, Georg; Snoussi, Karim; Puts, Nicolaas A; Mikkelsen, Mark; Harris, Ashley D; Pradhan, Subechhya; Tsapkini, Kyrana; Schär, Michael; Barker, Peter B; Edden, Richard A E

2018-03-01

To investigate frequency-offset effects in edited magnetic resonance spectroscopy (MRS) experiments arising from B 0 eddy currents. Macromolecule-suppressed (MM-suppressed) γ-aminobutyric acid (GABA)-edited experiments were performed at 3T. Saturation-offset series of MEGA-PRESS experiments were performed in phantoms, in order to investigate different aspects of the relationship between the effective editing frequencies and eddy currents associated with gradient pulses in the sequence. Difference integrals were quantified for each series, and the offset dependence of the integrals was analyzed to quantify the difference in frequency (Δf) between the actual vs. nominal expected saturation frequency. Saturation-offset N-acetyl-aspartate-phantom experiments show that Δf varied with voxel orientation, ranging from 10.4 Hz (unrotated) to 6.4 Hz (45° rotation about the caudal-cranial axis) and 0.4 Hz (45° rotation about left-right axis), indicating that gradient-related B 0 eddy currents vary with crusher-gradient orientation. Fixing the crusher-gradient coordinate-frame substantially reduced the orientation dependence of Δf (to ∼2 Hz). Water-suppression crusher gradients also introduced a frequency offset, with Δf = 0.6 Hz ("excitation" water suppression), compared to 10.2 Hz (no water suppression). In vivo spectra showed a negative edited "GABA" signal, suggesting Δf on the order of 10 Hz; with fixed crusher-gradient coordinate-frame, the expected positive edited "GABA" signal was observed. Eddy currents associated with pulsed field gradients may have a considerable impact on highly frequency-selective spectral-editing experiments, such as MM-suppressed GABA editing at 3T. Careful selection of crusher gradient orientation may ameliorate these effects. 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:673-681. © 2017 International Society for Magnetic Resonance in Medicine.

Anthropogenic and natural disturbances to marine benthic communities in Antarctica

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lenihan, H.; Oliver, J.S.

1995-05-01

Sampling and field experiments were conducted from 1975 to 1990 to test how the structure of marine benthic communities around McMurdo Station, Antarctica varied with levels of anthropogenic contaminants in marine sediments. The structure of communities (e.g., infauna density, species composition, and life history characteristics) in contaminated and uncontaminated areas were compared with the structure of communities influenced by two large-scale natural disturbances, anchor ice formation and uplift or iceberg scour. Benthic communities changed radically along a steep spatial gradient of anthropogenic hydrocarbon, metal, and PCB contamination around McMurdo Station. The heavily contaminated end of the gradient, Winter Quarters Bay,more » was low in infaunal and epifaunal abundance and was dominated by a few opportunistic species of polychaete worms. The edge of the heavily contaminated bay, the transition area, contained several motile polychaete species with less opportunistic life histories. Uncontaminated sedimentary habitats harbored dense tube mats of infaunal animals numerically dominated by populations of polychaete worms, crustaceans, and a large suspension feeding bivalve. These species are generally large and relatively sessile, except for several crustacean species living among the tubes. Although the community patterns around anthropogenic and natural disturbances were similar, particularly motile and opportunistic species at heavily disturbed and marginal areas, the natural disturbances cover much greater areas of the sea floor about the entire Antarctic continent. On the other hand, recovery from chemical contamination is likely to take many more decades than recovery from natural disturbances as contaminant degradation is a slow process. 77 refs., 6 figs., 5 tabs.« less

Composition, structure, and intra-stand spatial patterns along a disturbance severity gradient in a Quercus stand

Treesearch

Lauren E. Cox; Justin L. Hart; Daniel C. Dey; Callie J. Schweitzer

2016-01-01

Natural forest disturbances, which drive succession and development, differ in extent, severity, and return interval and range from frequent, gap-scale disturbances, to infrequent stand-replacing events. Most studies have focused on natural disturbances near the ends of the disturbance severity gradient and relatively little quantitative information is available on...

ASSOCIATIONS AMONG CATCHMENT- AND SITE-SCALE DISTURBANCE INDICATORS AND BIOLOGICAL ASSEMBLAGES AT LEAST- AND MOST-DISTURBED STREAM AND RIVER SITES IN THE WESTERN UNITED STATES

EPA Science Inventory

At broad scales, the types and intensities of human disturbances to ecosystems vary along natural gradients. Biological assemblages also vary with natural and human disturbance gradients. We defined least-disturbed conditions for a set of water chemistry, catchment, and site-sc...

Characterizing the production and retention of dissolved iron as Fe(II) across a natural gradient in chlorophyll concentrations in the Southern Drake Passage - Final Technical Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katherine Barbeau

2007-04-10

Recent mesoscale iron fertilization studies in the Southern Ocean (e.g. SOIREE, EisenEx, SOFeX) have demonstrated the importance of iron as a limiting factor for phytoplankton growth in these high nutrient, low-chlorophyll (HNLC) waters. Results of these experiments have demonstrated that factors which influence the biological availability of the iron supplied to phytoplankton are crucial in bloom development, longevity, and generation of carbon export flux. These findings have important implications for the future development of iron fertilization protocols to enhance carbon sequestration in high-latitude oceans. In particular, processes which lead to the mobilization and retention of iron in dissolved form inmore » the upper ocean are important in promoting continued biological availability of iron. Such processes can include photochemical redox cycling, which leads to the formation of soluble reduced iron, Fe(II), within iron-enriched waters. Creation of effective fertilization schemes will thus require more information about Fe(II) photoproduction in Southern Ocean waters as a means to retain new iron within the euphotic zone. To contribute to our knowledge base in this area, this project was funded by DOE with a goal of characterizing the production and retention of dissolved Fe as Fe(II) in an area of the southern Drake Passage near the Shackleton Transverse Ridge, a region with a strong recurrent chlorophyll gradient which is believed to be a site of natural iron enrichment in the Southern Ocean. This area was the focus of a multidisciplinary NSF/OPP-funded investigation in February 2004 (OPP02-30443, lead PI Greg Mitchell, SIO/UCSD) to determine the influence of mesoscale circulation and iron transport with regard to the observed patterns in sea surface chlorophyll in the region near the Shackleton Transverse Ridge. A number of parameters were assessed across this gradient in order to reveal interactions between plankton community structure and iron distributions. As a co-PI in the NSF/OPP-funded project, I was responsible for iron addition incubation and radiotracer experiments, and analysis of iron chemistry, including iron-organic speciation. This final technical report describes the results of my DOE funded project to analyse reduced iron species using an FeLume flow injection analysis chemiluminescence system as an extension of my work on the NSF/OPP project. On the cruise in 2004, spatial and temporal gradients in Fe(II) were determined, and on-board incubations were conducted to study Fe(II) lifetime and production. Following the cruise a further series of experiments was conducted in my laboratory to study Fe(II) lifetimes and photoproduction under conditions typical of high latitude waters. The findings of this study suggest that, in contrast to results observed during mesoscale iron addition experiments, steady-state levels of Fe(II) are likely to remain low (below detection) even within a significant gradient in dissolved Fe concentrations produced as a result of natural iron enrichment processes. Fe(II) is likely to be produced, however, as a reactive intermediate associated with photochemical reactions in surface waters. While Fe(II) lifetimes measured in the field in this study were commensurate with those determined in previously published Southern Ocean work, Fe(II) lifetimes reflective of realistic Southern Ocean environmental conditions have proven difficult to determine in a laboratory setting, due to contamination by trace levels of H2O2. Laboratory experiments demonstrated that direct ligand-to-metal charge transfer reactions of strong Fe(III)-organic complexes do appear to be a viable source of available Fe(II) in Antarctic waters, and further studies are needed to characterize the temperature dependence of this phenomenon.« less

Microgravity Particle Dynamics

NASA Technical Reports Server (NTRS)

Clark, Ivan O.; Johnson, Edward J.

1996-01-01

This research seeks to identify the experiment design parameters for future flight experiments to better resolve the effects of thermal and velocity gradients on gas-solid flows. By exploiting the reduced body forces and minimized thermal convection current of reduced gravity experiments, features of gas-solid flow normally masked by gravitationally induced effects can be studied using flow regimes unattainable under unigravity. This paper assesses the physical scales of velocity, length, time, thermal gradient magnitude, and velocity gradient magnitude likely to be involved in laminar gas-solid multiphase flight experiments for 1-100 micro-m particles.

An "Inefficient Fin" Non-Dimensional Parameter to Measure Gas Temperatures Efficiently

NASA Technical Reports Server (NTRS)

Lemieux, Patrick; Murray, William; Cooke, Terry; Gerhardt, James

2012-01-01

A gas containment vessel that is not in thermal equilibrium with the bulk gas can affect its temperature measurement. The physical nature of many gas dynamics experiments often makes the accurate measurement of temperature a challenge. The environment itself typically requires that the thermocouple be sheathed, both to protect the wires and hot junction of the instrument from their environment, and to provide a smooth, rigid surface for pressure sealing of the enclosure. However, that enclosure may also be much colder than the gas to be sensed, or vice-versa. Either way, the effect of such gradients is to potentially skew the temperature measurements themselves, since heat may then be conducted by the instrument. Thermocouple designers traditionally address this problem by insulating the sheath from the thermocouple leads and hot junction as much as possible. The thermocouple leads are typically packed in a ceramic powder inside the sheath, protecting them somewhat from temperature gradients along the sheath, but there is no effective mechanism to shield the sheath from the enclosure body itself. Standard practice dictates that thermocouples be used in installations that do not present large thermal gradients along the probe. If this conduction dominates heat transfer near the tip of the probe, then temperature measurements may be expected to be skewed. While the same problem may be experienced in the measurement of temperature at various points within a solid in a gradient, it tends to be aggravated in the measurements of gas temperature, since heat transfer dependent on convection is often less efficient than conduction along the thermocouple. The proposed solution is an inefficient fin thermocouple probe. Conventional wisdom suggests that in many experiments where gas flows through an enclosure (e.g., flow in pipe, manifold, nozzle, etc.), the thermocouple be introduced flush to the surface, so as not to interfere with the flow. In practice, however, many such experiments take place where the flow is already turbulent, so that a protruding thermocouple probe has a negligible effect on the flow characteristics. The key question then becomes just how far into the flow should a thermocouple protrude in order to properly sense the gas temperature at that point. Modeling the thermocouple as an "inefficient fin" directly addresses this question. The appropriate assumptions in this case are: one-dimensional conduction along the fin; steady-state, constant, and homogeneous thermal conductivity; negligible radiation; and a uniform, constant heat transfer coefficient over the probe surface. It is noted that the nature of the ceramic-filled probe makes the key assumption of homogeneous thermal conductivity that much more conservative.

The effects of oil spills on marine fish: Implications of spatial variation in natural mortality.

PubMed

Langangen, Ø; Olsen, E; Stige, L C; Ohlberger, J; Yaragina, N A; Vikebø, F B; Bogstad, B; Stenseth, N C; Hjermann, D Ø

2017-06-15

The effects of oil spills on marine biological systems are of great concern, especially in regions with high biological production of harvested resources such as in the Northeastern Atlantic. The scientific studies of the impact of oil spills on fish stocks tend to ignore that spatial patterns of natural mortality may influence the magnitude of the impact over time. Here, we first illustrate how spatial variation in natural mortality may affect the population impact by considering a thought experiment. Second, we consider an empirically based example of Northeast Arctic cod to extend the concept to a realistic setting. Finally, we present a scenario-based investigation of how the degree of spatial variation in natural mortality affects the impact over a gradient of oil spill sizes. Including the effects of spatial variations in natural mortality tends to widen the impact distribution, hence increasing the probability of both high and low impact events. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

The Galapagos archipelago: A natural laboratory to examine sharp hydroclimatic, geologic and anthropogenic gradients

USGS Publications Warehouse

Percy, Madelyn; Schmitt, Sarah; Riveros-Iregui, Diego; Mirus, Benjamin B.

2016-01-01

Poor understanding of the water cycle in tropical ecosystems has the potential to exacerbate water shortages and water crises in the region. We suggest that the Galápagos Islands provide an excellent proxy to regions across the tropics as a result of sharp hydroclimatic, anthropogenic, and pedohydrologic gradients across the archipelago. Hydroclimatic and pedohydrologic gradients are found across different elevations on single islands, as well as across the archipelago, whereas anthropogenic gradients reflect land use and land cover change across islands as population and growth in tourism have affected individual islands differently. This article highlights specific opportunities to further examine our understanding of the interactions between water and critical zone processes in tropical ecosystems, making connections between the Galápagos archipelago and much of the understudied tropics. The Galápagos archipelago offers a natural laboratory through which we can examine current threats to freshwater security as well as the dynamics of coupled natural and human systems.

Hyporheic hot moments: Dissolved oxygen dynamics in the hyporheic zone in response to surface flow perturbations

NASA Astrophysics Data System (ADS)

Kaufman, Matthew H.; Cardenas, M. Bayani; Buttles, Jim; Kessler, Adam J.; Cook, Perran L. M.

2017-08-01

Dissolved oxygen (DO) is a key environmental variable that drives and feeds back with numerous processes. In the aquatic sediment that makes up the hyporheic zone, DO may exhibit pronounced spatial gradients and complex patterns which control the distribution of a series of redox processes. Yet, little is known regarding the dynamics of hyporheic zone DO, especially under transitional flow regimes. Considering the natural tendency of rivers to be highly responsive to external forcing, these temporal dynamics are potentially just as important and pronounced as the spatial gradients. Here we use laboratory flume experiments and multiphysics flow and reactive transport modeling to investigate surface flow controls on the depth of oxygen penetration in the bed as well as the area of oxygenated sediment. We show that the hyporheic zone DO conditions respond over time scales of hours-to-days when subjected to practically instantaneous surface flow perturbations. Additionally, the flume experiments demonstrate that hyporheic zone DO conditions respond faster to surface flow acceleration than to deceleration. Finally, we found that the morphology of the dissolved oxygen plume front depends on surface flow acceleration or deceleration. This study thus shows that the highly dynamic nature of typical streams and rivers drives equally dynamic redox conditions in the hyporheic zone. Because the redox conditions and their distribution within the hyporheic zone are important from biological, ecological, and contaminant perspectives, this hyporheic redox dynamism has the potential to impact system scale aquatic chemical cycles.

Complex Diffusion Mechanisms for Li in Feldspar: Re-thinking Li-in-Plag Geospeedometry

NASA Astrophysics Data System (ADS)

Holycross, M.; Watson, E. B.

2017-12-01

In recent years, the lithium isotope system has been applied to model processes in a wide variety of terrestrial environments. In igneous settings, Li diffusion gradients have been frequently used to time heating episodes. Lithium partitioning behavior during decompression or cooling events drives Li transfer between phases, but the extent of Li exchange may be limited by its diffusion rate in geologic materials. Lithium is an exceptionally fast diffuser in silicate media, making it uniquely suited to record short-lived volcanic phenomena. The Li-in-plagioclase geospeedometer is often used to time explosive eruptions by applying laboratory-calibrated Li diffusion coefficients to model concentration profiles in magmatic feldspar samples. To quantify Li transport in natural scenarios, experimental measurements are needed that account for changing temperature and oxygen fugacity as well as different feldspar compositions and crystallographic orientation. Ambient pressure experiments were run at RPI to diffuse Li from a powdered spodumene source into polished sanidine, albite, oligoclase or anorthite crystals over the temperature range 500-950 ºC. The resulting 7Li concentration gradients developed in the mineral specimens were evaluated using laser ablation ICP-MS. The new data show that Li diffusion in all feldspar compositions simultaneously operates by both a "fast" and "slow" diffusion mechanism. Fast path diffusivities are similar to those found by Giletti and Shanahan [1997] for Li diffusion in plagioclase and are typically 10 to 20 times greater than slow path diffusivities. Lithium concentration gradients in the feldspar experiments plot in the shape of two superimposed error function curves with the slow diffusion regime in the near-surface of the crystal. Lithium diffusion is most sluggish in sanidine and is significantly faster in the plagioclase feldspars. It is still unclear what diffusion mechanism operates in nature, but the new measurements may impact how Li-in-plagioclase geospeedometry is used to time igneous processes. Giletti, B.J., and T.M. Shanahan (1997) Alkali diffusion in plagioclase feldspar, Chem. Geol., 139, 3-20

Silica-coated titania and zirconia colloids for subsurface transport field experiments

USGS Publications Warehouse

Ryan, Joseph N.; Elimelech, Menachem; Baeseman, Jenny L.; Magelky, Robin D.

2000-01-01

Silica-coated titania (TiO2) and zirconia (ZrO2) colloids were synthesized in two sizes to provide easily traced mineral colloids for subsurface transport experiments. Electrophoretic mobility measurements showed that coating with silica imparted surface properties similar to pure silica to the titania and zirconia colloids. Measurements of steady electrophoretic mobility and size (by dynamic light scattering) over a 90-day period showed that the silica-coated colloids were stable to aggregation and loss of coating. A natural gradient field experiment conducted in an iron oxide-coated sand and gravel aquifer also showed that the surface properties of the silica-coated colloids were similar. Colloid transport was traced at μg L-1 concentrations by inductively coupled plasma-atomic emission spectroscopy measurement of Ti and Zr in acidified samples.

Nonnative invasive plants: Maintaining biotic and soceioeconomic integrity along the urban-rural-natural gradient

Treesearch

Cynthia D. Huebner; David J. Nowak; Richard V. Pouyat; Allison R. Bodine

2012-01-01

In this chapter, we evaluate nonnative invasive plant species of the urban-rural-natural area gradient in order to reduce negative impacts of invasive plants on native species and ecosystems. This evaluation includes addressing (i) the concept of urban areas as the primary source of invasive plant species and characteristics of urban nonnative plants, including their...

Simulating Electrochemistry of Hydrothermal Vents on Enceladus and Other Ocean Worlds

NASA Astrophysics Data System (ADS)

Barge, L. M.; Krause, F. C.; Jones, J. P.; Billings, K.; Sobron, P.

2017-12-01

Gradients generated in hydrothermal systems provide a significant source of free energy for chemosynthetic life, and may play a role in present-day habitability on ocean worlds such as Enceladus that are thought to host hydrothermal activity. Hydrothermal vents are similar in some ways to typical fuel cell devices: redox/pH gradients between seawater and hydrothermal fluid are analogous to the oxidant and fuel reservoirs; conductive natural mineral deposits are analogous to electrodes; and, in hydrothermal chimneys, the porous chimney wall can function as a separator or ion-exchange membrane. Electrochemistry, founded on quantitative study of redox and other chemical disequilibria as well as the chemistry of interfaces, is uniquely suited to studying these systems. We have performed electrochemical studies to better understand the catalytic potential of seafloor minerals and vent chimneys, using samples from a black smoker vent chimney as an initial demonstration. Fuel cell experiments with electrodes made from black smoker chimney material accurately simulated the redox reactions that occur in a geological setting with this particular catalyst. Similar methods with other geo-catalysts (natural or synthetic) could be utilized to test which redox reactions or metabolisms could be driven in other hydrothermal systems, including putative vent systems on other worlds.

A microfluidics assay to study invasion of human placental trophoblast cells.

PubMed

Abbas, Yassen; Oefner, Carolin Melati; Polacheck, William J; Gardner, Lucy; Farrell, Lydia; Sharkey, Andrew; Kamm, Roger; Moffett, Ashley; Oyen, Michelle L

2017-05-01

Pre-eclampsia, fetal growth restriction and stillbirth are major pregnancy disorders throughout the world. The underlying pathogenesis of these diseases is defective placentation characterized by inadequate invasion of extravillous placental trophoblast cells into the uterine arteries. How trophoblast invasion is controlled remains an unanswered question but is influenced by maternal uterine immune cells called decidual natural killer cells. Here, we describe an in vitro microfluidic invasion assay to study the migration of primary human trophoblast cells. Each experiment can be performed with a small number of cells making it possible to conduct research on human samples despite the challenges of isolating primary trophoblast cells. Cells are exposed to a chemical gradient and tracked in a three-dimensional microenvironment using real-time high-resolution imaging, so that dynamic readouts on cell migration such as directionality, motility and velocity are obtained. The microfluidic system was validated using isolated trophoblast and a gradient of granulocyte-macrophage colony-stimulating factor, a cytokine produced by activated decidual natural killer cells. This microfluidic model provides detailed analysis of the dynamics of trophoblast migration compared to previous assays and can be modified in future to study in vitro how human trophoblast behaves during placentation. © 2017 The Authors.

The Impact of Gulf Stream-Induced Diabatic Forcing on Coastal Mid-Atlantic Surface Cyclogenesis

NASA Astrophysics Data System (ADS)

Cione, Joseph Jerome

In this dissertation, numerical experiments were conducted using a mesoscale atmospheric model developed at North Carolina State University. Three sets of numerical experiments were conducted and were designed to: quantify the impact Gulf Stream frontal distance, initial surface air temperature and cold air outbreak timing each have on the subsequent development of the marine atmospheric boundary layer during periods of offshore cold advection; investigate critical processes associated with Gulf Stream -induced mesocyclogenesis and; elucidate the role SST gradients and surface fluxes of heat and moisture have on the intensification and track of propagating mesocyclonic systems within the highly baroclinic Gulf Stream region. A major finding from the offshore cold advection simulations is that the initial air-sea contrast is the dominant forcing mechanism linked to the offshore circulation development and marine boundary layer modification. Results from the mesocyclogenesis experiments indicate that surface cyclogenesis was simulated to occur along a Gulf Stream meander in a region where the gradients in sea surface temperature (SST) were maximized. Results from sensitivity experiments illustrate that changes in the Gulf Stream SST gradient pattern can act to alter the timing and degree of cyclonic development simulated, while the inclusion of surface fluxes and moist convective processes during the development phase act to strongly enhance the intensity and/or occurrence of simulated mesocyclogenesis. Both observational and numerical results from studies investigating the impact strong Gulf Stream SST gradients have on the development of pre-existing, propagating cyclonic systems show that the baroclinic nature of the low level environment near the circulation center (as well as the degree of simulated/observed surface cyclonic intensification) appear to be highly dependent upon the mesoscale storm track within the Gulf Stream frontal zone. Furthermore, the numerical storm track experiments conducted in this research illustrate that surfaces fluxes can act to significantly alter the storm track of the surface mesocyclone (in addition to impacting the overall intensification of the simulated cyclonic system). This work also presents the technique development and operational utilization of the recently devised Atlantic Surface Cyclone Intensification Index (ASCII). The index continues to be implemented by the National Weather Service at the Raleigh-Durham and surrounding coastal forecast offices, and to date, has been successfully utilized for 11 coastal winter storm events over the February 1994-January 1996 period.

Ultrafast NMR diffusion measurements exploiting chirp spin echoes.

PubMed

Ahola, Susanna; Mankinen, Otto; Telkki, Ville-Veikko

2017-04-01

Standard diffusion NMR measurements require the repetition of the experiment multiple times with varying gradient strength or diffusion delay. This makes the experiment time-consuming and restricts the use of hyperpolarized substances to boost sensitivity. We propose a novel single-scan diffusion experiment, which is based on spatial encoding of two-dimensional data, employing the spin-echoes created by two successive adiabatic frequency-swept chirp π pulses. The experiment is called ultrafast pulsed-field-gradient spin-echo (UF-PGSE). We present a rigorous derivation of the echo amplitude in the UF-PGSE experiment, justifying the theoretical basis of the method. The theory reveals also that the standard analysis of experimental data leads to a diffusion coefficient value overestimated by a few per cent. Although the overestimation is of the order of experimental error and thus insignificant in many practical applications, we propose that it can be compensated by a bipolar gradient version of the experiment, UF-BP-PGSE, or by corresponding stimulated-echo experiment, UF-BP-pulsed-field-gradient stimulated-echo. The latter also removes the effect of uniform background gradients. The experiments offer significant prospects for monitoring fast processes in real time as well as for increasing the sensitivity of experiments by several orders of magnitude by nuclear spin hyperpolarization. Furthermore, they can be applied as basic blocks in various ultrafast multidimensional Laplace NMR experiments. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Experimental feasibility of investigating acoustic waves in Couette flow with entropy and pressure gradients

NASA Technical Reports Server (NTRS)

Parrott, Tony L.; Zorumski, William E.; Rawls, John W., Jr.

1990-01-01

The feasibility is discussed for an experimental program for studying the behavior of acoustic wave propagation in the presence of strong gradients of pressure, temperature, and flow. Theory suggests that gradients effects can be experimentally observed as resonant frequency shifts and mode shape changes in a waveguide. A convenient experimental geometry for such experiments is the annular region between two co-rotating cylinders. Radial temperature gradients in a spinning annulus can be generated by differentially heating the two cylinders via electromagnetic induction. Radial pressure gradients can be controlled by varying the cylinder spin rates. Present technology appears adequate to construct an apparatus to allow independent control of temperature and pressure gradients. A complicating feature of a more advanced experiment, involving flow gradients, is the requirement for independently controlled cylinder spin rates. Also, the boundary condition at annulus terminations must be such that flow gradients are minimally disturbed. The design and construction of an advanced apparatus to include flow gradients will require additional technology development.

Test and On-Orbit Experiences of FalconSAT-3

NASA Astrophysics Data System (ADS)

Saylor, W. W.; France, M. E. B.

2008-08-01

The fundamental objectives of the capstone design project in the Department of Astronautics at the United States Air Force Academy (USAFA) are for cadets to learn important engineering lessons by executing a real space mission on a Department of Defense-funded satellite project. FalconSAT-3 is a 50 kg, gravity gradient-stabilized designed and built by cadets and launched March 2007 on the first ESPA (Enhanced extended launch vehicle Satellite Payload Adapter) mission. FalconSAT-3 was one of six satellites integrated onto the launch vehicle and the nature of the mission made it that the satellite was subject to the full formality of testing requirements. Two successive gravity gradient booms failed either design requirements or environmental testing; design requirements grew dramatically during the design phase; ambiguous thermal vacuum test results led to uncertainty at launch; and after launch it was not possible to contact the satellite for several weeks.

3D braid scaffolds for regeneration of articular cartilage.

PubMed

Ahn, Hyunchul; Kim, Kyoung Ju; Park, Sook Young; Huh, Jeong Eun; Kim, Hyun Jeong; Yu, Woong-Ryeol

2014-06-01

Regenerating articular cartilage in vivo from cultured chondrocytes requires that the cells be cultured and implanted within a biocompatible, biodegradable scaffold. Such scaffolds must be mechanically stable; otherwise chondrocytes would not be supported and patients would experience severe pain. Here we report a new 3D braid scaffold that matches the anisotropic (gradient) mechanical properties of natural articular cartilage and is permissive to cell cultivation. To design an optimal structure, the scaffold unit cell was mathematically modeled and imported into finite element analysis. Based on this analysis, a 3D braid structure with gradient axial yarn distribution was designed and manufactured using a custom-built braiding machine. The mechanical properties of the 3D braid scaffold were evaluated and compared with simulated results, demonstrating that a multi-scale approach consisting of unit cell modeling and continuum analysis facilitates design of scaffolds that meet the requirements for mechanical compatibility with tissues. Copyright © 2014 Elsevier Ltd. All rights reserved.

Experiments on the Motion of Drops on a Horizontal Solid Surface due to a Wettability Gradient

NASA Technical Reports Server (NTRS)

Moumen, Nadjoua; Subramanian, R, Shankar; MLaughlin, john B.

2006-01-01

Results from experiments performed on the motion of drops of tetraethylene glycol in a wettability gradient present on a silicon surface are reported and compared with predictions from a recently developed theoretical model. The gradient in wettability was formed by exposing strips cut from a silicon wafer to decyltrichlorosiland vapors. Video images of the drops captured during the experiments were subsequently analyzed for drop size and velocity as functions of position along the gradient. In separate experiments on the same strips, the static contact angle formed by small drops was measured and used to obtain the local wettability gradient to which a drop is subjected. The velocity of the drops was found to be a strong function of position along the gradient. A quasi-steady theoretical model that balances the local hydrodynamic resistance with the local driving force generally describes the observations; possible reasons for the remaining discrepancies are discussed. It is shown that a model in which the driving force is reduced to accomodate the hysteresis effect inferred from the data is able to remove most of the discrepancy between the observed and predicted velocities.

High angular resolution diffusion imaging with stimulated echoes: compensation and correction in experiment design and analysis.

PubMed

Lundell, Henrik; Alexander, Daniel C; Dyrby, Tim B

2014-08-01

Stimulated echo acquisition mode (STEAM) diffusion MRI can be advantageous over pulsed-gradient spin-echo (PGSE) for diffusion times that are long compared with T2 . It therefore has potential for biomedical diffusion imaging applications at 7T and above where T2 is short. However, gradient pulses other than the diffusion gradients in the STEAM sequence contribute much greater diffusion weighting than in PGSE and lead to a disrupted experimental design. Here, we introduce a simple compensation to the STEAM acquisition that avoids the orientational bias and disrupted experiment design that these gradient pulses can otherwise produce. The compensation is simple to implement by adjusting the gradient vectors in the diffusion pulses of the STEAM sequence, so that the net effective gradient vector including contributions from diffusion and other gradient pulses is as the experiment intends. High angular resolution diffusion imaging (HARDI) data were acquired with and without the proposed compensation. The data were processed to derive standard diffusion tensor imaging (DTI) maps, which highlight the need for the compensation. Ignoring the other gradient pulses, a bias in DTI parameters from STEAM acquisition is found, due both to confounds in the analysis and the experiment design. Retrospectively correcting the analysis with a calculation of the full B matrix can partly correct for these confounds, but an acquisition that is compensated as proposed is needed to remove the effect entirely. © 2014 The Authors. NMR in Biomedicine published by John Wiley & Sons, Ltd.

Fourier domain preconditioned conjugate gradient algorithm for atmospheric tomography.

PubMed

Yang, Qiang; Vogel, Curtis R; Ellerbroek, Brent L

2006-07-20

By 'atmospheric tomography' we mean the estimation of a layered atmospheric turbulence profile from measurements of the pupil-plane phase (or phase gradients) corresponding to several different guide star directions. We introduce what we believe to be a new Fourier domain preconditioned conjugate gradient (FD-PCG) algorithm for atmospheric tomography, and we compare its performance against an existing multigrid preconditioned conjugate gradient (MG-PCG) approach. Numerical results indicate that on conventional serial computers, FD-PCG is as accurate and robust as MG-PCG, but it is from one to two orders of magnitude faster for atmospheric tomography on 30 m class telescopes. Simulations are carried out for both natural guide stars and for a combination of finite-altitude laser guide stars and natural guide stars to resolve tip-tilt uncertainty.

Modeling of natural organic matter transport processes in groundwater.

PubMed Central

Yeh, T C; Mas-Pla, J; McCarthy, J F; Williams, T M

1995-01-01

A forced-gradient tracer test was conducted at the Georgetown site to study the transport of natural organic matter (NOM) in groundwater. In particular, the goal of this experiment was to investigate the interactions between NOM and the aquifer matrix. A detailed three-dimensional characterization of the hydrologic conductivity heterogeneity of the site was obtained using slug tests. The transport of a conservative tracer (chloride) was successfully reproduced using these conductivity data. Despite the good simulation of the flow field, NOM breakthrough curves could not be reproduced using a two-site sorption model with spatially constant parameters. Preliminary results suggest that different mechanisms for the adsorption/desorption processes, as well as their spatial variability, may significantly affect the transport and fate of NOM. PMID:7621798

Evaluation of multiple tracer methods to estimate low groundwater flow velocities.

PubMed

Reimus, Paul W; Arnold, Bill W

2017-04-01

Four different tracer methods were used to estimate groundwater flow velocity at a multiple-well site in the saturated alluvium south of Yucca Mountain, Nevada: (1) two single-well tracer tests with different rest or "shut-in" periods, (2) a cross-hole tracer test with an extended flow interruption, (3) a comparison of two tracer decay curves in an injection borehole with and without pumping of a downgradient well, and (4) a natural-gradient tracer test. Such tracer methods are potentially very useful for estimating groundwater velocities when hydraulic gradients are flat (and hence uncertain) and also when water level and hydraulic conductivity data are sparse, both of which were the case at this test location. The purpose of the study was to evaluate the first three methods for their ability to provide reasonable estimates of relatively low groundwater flow velocities in such low-hydraulic-gradient environments. The natural-gradient method is generally considered to be the most robust and direct method, so it was used to provide a "ground truth" velocity estimate. However, this method usually requires several wells, so it is often not practical in systems with large depths to groundwater and correspondingly high well installation costs. The fact that a successful natural gradient test was conducted at the test location offered a unique opportunity to compare the flow velocity estimates obtained by the more easily deployed and lower risk methods with the ground-truth natural-gradient method. The groundwater flow velocity estimates from the four methods agreed very well with each other, suggesting that the first three methods all provided reasonably good estimates of groundwater flow velocity at the site. The advantages and disadvantages of the different methods, as well as some of the uncertainties associated with them are discussed. Published by Elsevier B.V.

Living on the edge: adaptive and plastic responses of the tree Nothofagus pumilio to a long-term transplant experiment predict rear-edge upward expansion.

PubMed

Mathiasen, Paula; Premoli, Andrea C

2016-06-01

Current climate change affects the competitive ability and reproductive success of many species, leading to local extinctions, adjustment to novel local conditions by phenotypic plasticity or rapid adaptation, or tracking their optima through range shifts. However, many species have limited ability to expand to suitable areas. Altitudinal gradients, with abrupt changes in abiotic conditions over short distances, represent "natural experiments" for the evaluation of ecological and evolutionary responses under scenarios of climate change. Nothofagus pumilio is the tree species which dominates as pure stands the montane forests of Patagonia. We evaluated the adaptive value of variation in quantitative traits of N. pumilio under contrasting conditions of the altitudinal gradient with a long-term reciprocal transplant experimental design. While high-elevation plants show little response in plant, leaf, and phenological traits to the experimental trials, low-elevation ones show greater plasticity in their responses to changing environments, particularly at high elevation. Our results suggest a relatively reduced potential for evolutionary adaptation of high-elevation genotypes, and a greater evolutionary potential of low-elevation ones. Under global warming scenarios of forest upslope migration, high-elevation variants may be outperformed by low-elevation ones during this process, leading to the local extinction and/or replacement of these genotypes. These results challenge previous models and predictions expected under global warming for altitudinal gradients, on which the leading edge is considered to be the upper treeline forests.

Modeling SST gradient changes, the hydrological cycle response, and deep water formation in the North Pacific

NASA Astrophysics Data System (ADS)

Burls, N.; Ford, H. L.; Fedorov, A. V.; Jahn, A.; Jacobs, P.

2017-12-01

The absence of deep-water formation and a deep meridional overturning cell in the modern North Pacific has been attributed to the relatively fresh surface conditions in the subarctic. These conditions are, in turn, best explained by the local excess of precipitation over evaporation in the northern Pacific due to net moisture transport from the Atlantic to the Pacific and/or moisture transport associated with the Asian monsoon. Some studies link the lack of deep-water formation in the Pacific directly to its occurrence in the Atlantic via the Atlantic-Pacific seesaw effect and idealized experiments indicate that the smaller width of the Atlantic predisposes it to higher salinity and deep-water formation. We have conducted a series of coupled model experiments across which global mean temperatures and large-scale meridional SST gradients are varied. We perturb either atmospheric CO2 concentrations or the meridional gradient in cloud radiative forcing and run each experiment out to 3000 years so that the deep ocean has equilibrated. As the strength of the meridional temperature gradient decreases across our experiments, a Pacific Meridional Overturning Circulation develops. The strength of this Pacific Meridional Overturning Circulation generally increases as the gradient weakens. In one of these experiments where the meridional SST gradient most closely resembles Pliocene reconstructions, a PMOC exists of comparable in strength to the modern AMOC. We will describe how the hydrological cycle response to reduced meridional SST gradients acts to increase the strength of the PMOC across our sensitivity experiments. Additionally, we will discuss our effort to include carbon isotopes in our Pliocene-like simulation for data-model comparisons. Calcium carbonate accumulation data from Subarctic North Pacific Site 882 and new and previously published carbon isotope records from the Pacific appear to support our modelling results suggesting that weaker meridonal SST gradients during the Pliocene could have supported deep water formation in the subarctic Pacific and a strong PMOC.

Competitive ability, stress tolerance and plant interactions along stress gradients.

PubMed

Qi, Man; Sun, Tao; Xue, SuFeng; Yang, Wei; Shao, DongDong; Martínez-López, Javier

2018-04-01

Exceptions to the generality of the stress-gradient hypothesis (SGH) may be reconciled by considering species-specific traits and stress tolerance strategies. Studies have tested stress tolerance and competitive ability in mediating interaction outcomes, but few have incorporated this to predict how species interactions shift between competition and facilitation along stress gradients. We used field surveys, salt tolerance and competition experiments to develop a predictive model interspecific interaction shifts across salinity stress gradients. Field survey and greenhouse tolerance tests revealed tradeoffs between stress tolerance and competitive ability. Modeling showed that along salinity gradients, (1) plant interactions shifted from competition to facilitation at high salinities within the physiological limits of salt-intolerant plants, (2) facilitation collapsed when salinity stress exceeded the physiological tolerance of salt-intolerant plants, and (3) neighbor removal experiments overestimate interspecific facilitation by including intraspecific effects. A community-level field experiment, suggested that (1) species interactions are competitive in benign and, facilitative in harsh condition, but fuzzy under medium environmental stress due to niche differences of species and weak stress amelioration, and (2) the SGH works on strong but not weak stress gradients, so SGH confusion arises when it is applied across questionable stress gradients. Our study clarifies how species interactions vary along stress gradients. Moving forward, focusing on SGH applications rather than exceptions on weak or nonexistent gradients would be most productive. © 2018 by the Ecological Society of America.

A Motor-Gradient and Clustering Model of the Centripetal Motility of MTOCs in Meiosis I of Mouse Oocytes

PubMed Central

2016-01-01

Asters nucleated by Microtubule (MT) organizing centers (MTOCs) converge on chromosomes during spindle assembly in mouse oocytes undergoing meiosis I. Time-lapse imaging suggests that this centripetal motion is driven by a biased ‘search-and-capture’ mechanism. Here, we develop a model of a random walk in a drift field to test the nature of the bias and the spatio-temporal dynamics of the search process. The model is used to optimize the spatial field of drift in simulations, by comparison to experimental motility statistics. In a second step, this optimized gradient is used to determine the location of immobilized dynein motors and MT polymerization parameters, since these are hypothesized to generate the gradient of forces needed to move MTOCs. We compare these scenarios to self-organized mechanisms by which asters have been hypothesized to find the cell-center- MT pushing at the cell-boundary and clustering motor complexes. By minimizing the error between simulation outputs and experiments, we find a model of “pulling” by a gradient of dynein motors alone can drive the centripetal motility. Interestingly, models of passive MT based “pushing” at the cortex, clustering by cross-linking motors and MT-dynamic instability gradients alone, by themselves do not result in the observed motility. The model predicts the sensitivity of the results to motor density and stall force, but not MTs per aster. A hybrid model combining a chromatin-centered immobilized dynein gradient, diffusible minus-end directed clustering motors and pushing at the cell cortex, is required to comprehensively explain the available data. The model makes experimentally testable predictions of a spatial bias and self-organized mechanisms by which MT asters can find the center of a large cell. PMID:27706163

Intestinal transport: studies with isolated epithelial cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kimmich, G.A.

1979-12-01

Isolated intestinal epithelial cells have been extremely useful for characterizing the nature of intestinal absorption processes and for providing insight into the energetics of Na/sup +/-dependent transport systems. This report describes a number of experimental approaches which have been used for investigating the specific epithelial transport systems involved in sugar absorption, but provides information which ultimately should prove useful for characterizing a number of different intestinal transport events. Similar experiments should also prove useful for exploring the effect of environmental agents on the function of intestinal tissue. In the case of sugars, net absorption is accomplished via a mucosal, Na/supmore » +/-dependent concentrative transport system acting in sequence with a passive serosal system which does not require Na/sup +/. The serosal system limits the full gradient-forming capability of the muscosal system. Agents such as phloretin or cytochalasin B which inhibit serosal transport allow the cells to establish sugar gradients as high as 70 fold in contrast to 10 to 15 fold gradients observed for control cells. Sevety-fold sugar gradients cannot be explained in terms of the energy available in the electrochemical potential for Na/sup +/ if the Na/sub 2/: sugar coupling stoichiometry is 1:1 as commonly assumed. New information indicates that the true Na/sup +/:sugar stoichiometry is in fact 2:1. Flow of two Na/sup +/ ions per sugar molecule down the transmembrane electrochemical potential for Na/sup +/ provides more than sufficient energy to account for observed 70 fold sugar gradients. If flow of sugar by other routes could be completely inhibited, theoretical sugar gradients as high as 400 could be achieved assuming that the cells maintain a membrane potential of -36 mV as measured for intact tissue.« less

A Motor-Gradient and Clustering Model of the Centripetal Motility of MTOCs in Meiosis I of Mouse Oocytes.

PubMed

Khetan, Neha; Athale, Chaitanya A

2016-10-01

Asters nucleated by Microtubule (MT) organizing centers (MTOCs) converge on chromosomes during spindle assembly in mouse oocytes undergoing meiosis I. Time-lapse imaging suggests that this centripetal motion is driven by a biased 'search-and-capture' mechanism. Here, we develop a model of a random walk in a drift field to test the nature of the bias and the spatio-temporal dynamics of the search process. The model is used to optimize the spatial field of drift in simulations, by comparison to experimental motility statistics. In a second step, this optimized gradient is used to determine the location of immobilized dynein motors and MT polymerization parameters, since these are hypothesized to generate the gradient of forces needed to move MTOCs. We compare these scenarios to self-organized mechanisms by which asters have been hypothesized to find the cell-center- MT pushing at the cell-boundary and clustering motor complexes. By minimizing the error between simulation outputs and experiments, we find a model of "pulling" by a gradient of dynein motors alone can drive the centripetal motility. Interestingly, models of passive MT based "pushing" at the cortex, clustering by cross-linking motors and MT-dynamic instability gradients alone, by themselves do not result in the observed motility. The model predicts the sensitivity of the results to motor density and stall force, but not MTs per aster. A hybrid model combining a chromatin-centered immobilized dynein gradient, diffusible minus-end directed clustering motors and pushing at the cell cortex, is required to comprehensively explain the available data. The model makes experimentally testable predictions of a spatial bias and self-organized mechanisms by which MT asters can find the center of a large cell.

Comparison of genetic algorithms with conjugate gradient methods

NASA Technical Reports Server (NTRS)

Bosworth, J. L.; Foo, N. Y.; Zeigler, B. P.

1972-01-01

Genetic algorithms for mathematical function optimization are modeled on search strategies employed in natural adaptation. Comparisons of genetic algorithms with conjugate gradient methods, which were made on an IBM 1800 digital computer, show that genetic algorithms display superior performance over gradient methods for functions which are poorly behaved mathematically, for multimodal functions, and for functions obscured by additive random noise. Genetic methods offer performance comparable to gradient methods for many of the standard functions.

Effect of centrifugal fractionation protocols on quality and recovery rate of equine sperm.

PubMed

Edmond, A J; Brinsko, S P; Love, C C; Blanchard, T L; Teague, S R; Varner, D D

2012-03-15

Centrifugal fractionation of semen is commonly done to improve quality of human semen in assisted-reproduction laboratories, allowing sperm separation based on their isopycnic points. Sperm with morphologic abnormalities are often more buoyant, promoting their retention above defined density media, with structurally normal sperm passing through the media following centrifugation. Three experiments were conducted to evaluate the effects of density-medium type, centrifuge-tube size, sperm number, and density-medium volume (column height) on stallion sperm quality and recovery rate in sperm pellets following centrifugation. In all three experiments, equine semen was initially centrifuged to increase sperm concentration. In Experiment 1, semen was layered over continuous or discontinuous gradients. For Experiment 2, semen was layered over three column heights of continuous gradients in 15- or 50-ml conical-bottom tubes. For Experiment 3, increasing sperm numbers were layered over continuous gradient in 15- or 50-ml conical-bottom tubes. Following centrifugation, sperm pellets were evaluated for sperm morphologic quality, motility, DNA integrity, and recovery rate. Centrifugal fractionation improved (P < 0.05) sperm morphology, motility, and DNA integrity, as compared to controls. The continuous gradient increased (P < 0.05) sperm recovery rate relative to the discontinuous gradient, whereas sperm processed in 15-ml tubes yielded higher velocity and higher recovery rates (P < 0.05 for each) than that processed in 50-ml tubes. Sperm recovery rate was not affected (P > 0.05) by column height of gradient. Increasing sperm number subjected to gradient centrifugation decreased (P < 0.05) sperm recovery rate when 15-ml tubes were used. Copyright © 2012 Elsevier Inc. All rights reserved.

Bioturbation transports secondary microplastics to deeper layers in soft marine sediments of the northern Baltic Sea.

PubMed

Näkki, Pinja; Setälä, Outi; Lehtiniemi, Maiju

2017-06-15

Microplastics (MPs) are observed to be present on the seafloor ranging from coastal areas to deep seas. Because bioturbation alters the distribution of natural particles on inhabited soft bottoms, a mesocosm experiment with common benthic invertebrates was conducted to study their effect on the distribution of secondary MPs (different-sized pieces of fishing line<1mm). During the study period of three weeks, the benthic community increased MP concentration in the depth of 1.7-5.1cm in the sediment. The experiment revealed a clear vertical gradient in MP distribution with their abundance being highest in the uppermost parts of the sediment and decreasing with depth. The Baltic clam Macoma balthica was the only study animal that ingested MPs. This study highlights the need to further examine the vertical distribution of MPs in natural sediments to reliably assess their abundance on the seafloor as well as their potential impacts on benthic communities. Copyright © 2017 Elsevier Ltd. All rights reserved.

Responses of East Asian Summer Monsoon to Natural and Anthropogenic Forcings in the 17 Latest CMIP5 Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Fengfei; Zhou, Tianjun; Qian, Yun

2014-01-31

In this study, we examined the responses of East Asian Summer Monsoon (EASM) to natural (solar variability and volcanic aerosols) and anthropogenic (greenhouse gasses and aerosols) forcings simulated in the 17 latest Coupled Model Intercomparison Program phase 5 (CMIP5) models with 105 realizations. The observed weakening trend of low-level EASM circulation during 1958-2001 is partly reproduced under all-forcing runs. A comparison of separate forcing experiments reveals that the aerosol-forcing plays a primary role in driving the weakened low-level monsoon circulation. The preferential cooling over continental East Asia caused by aerosol affects the monsoon circulation through reducing the land-sea thermal contrastmore » and results in higher sea level pressure over northern China. In the upper-level, both natural-forcing and aerosol-forcing contribute to the observed southward shift of East Asian subtropical jet through changing the meridional temperature gradient.« less

Calibration of a rotating accelerometer gravity gradiometer using centrifugal gradients

NASA Astrophysics Data System (ADS)

Yu, Mingbiao; Cai, Tijing

2018-05-01

The purpose of this study is to calibrate scale factors and equivalent zero biases of a rotating accelerometer gravity gradiometer (RAGG). We calibrate scale factors by determining the relationship between the centrifugal gradient excitation and RAGG response. Compared with calibration by changing the gravitational gradient excitation, this method does not need test masses and is easier to implement. The equivalent zero biases are superpositions of self-gradients and the intrinsic zero biases of the RAGG. A self-gradient is the gravitational gradient produced by surrounding masses, and it correlates well with the RAGG attitude angle. We propose a self-gradient model that includes self-gradients and the intrinsic zero biases of the RAGG. The self-gradient model is a function of the RAGG attitude, and it includes parameters related to surrounding masses. The calibration of equivalent zero biases determines the parameters of the self-gradient model. We provide detailed procedures and mathematical formulations for calibrating scale factors and parameters in the self-gradient model. A RAGG physical simulation system substitutes for the actual RAGG in the calibration and validation experiments. Four point masses simulate four types of surrounding masses producing self-gradients. Validation experiments show that the self-gradients predicted by the self-gradient model are consistent with those from the outputs of the RAGG physical simulation system, suggesting that the presented calibration method is valid.

The layered evolution of fabric and microstructure of snow at Point Barnola, Central East Antarctica

NASA Astrophysics Data System (ADS)

Calonne, Neige; Montagnat, Maurine; Matzl, Margret; Schneebeli, Martin

2017-02-01

Snow fabric, defined as the distribution of the c-axis orientations of the ice crystals in snow, is poorly known. So far, only one study exits that measured snow fabric based on a statistically representative technique. This recent study has revealed the impact of temperature gradient metamorphism on the evolution of fabric in natural snow, based on cold laboratory experiments. On polar ice sheets, snow properties are currently investigated regarding their strong variability in time and space, notably because of their potential influence on firn processes and consequently on ice core analysis. Here, we present measurements of fabric and microstructure of snow from Point Barnola, East Antarctica (close to Dome C). We analyzed a snow profile from 0 to 3 m depth, where temperature gradients occur. The main contributions of the paper are (1) a detailed characterization of snow in the upper meters of the ice sheet, especially by providing data on snow fabric, and (2) the study of a fundamental snow process, never observed up to now in a natural snowpack, namely the role of temperature gradient metamorphism on the evolution of the snow fabric. Snow samples were scanned by micro-tomography to measure continuous profiles of microstructural properties (density, specific surface area and pore thickness). Fabric analysis was performed using an automatic ice texture analyzer on 77 representative thin sections cut out from the samples. Different types of snow fabric could be identified and persist at depth. Snow fabric is significantly correlated with snow microstructure, pointing to the simultaneous influence of temperature gradient metamorphism on both properties. We propose a mechanism based on preferential grain growth to explain the fabric evolution under temperature gradients. Our work opens the question of how such a layered profile of fabric and microstructure evolves at depth and further influences the physical and mechanical properties of snow and firn. More generally, it opens the way to further studies on the influence of the snow fabric in snow processes related to anisotropic properties of ice such as grain growth, mechanical response, electromagnetic behavior.

Micropower Mixed-signal VLSI Independent Component Analysis for Gradient Flow Acoustic Source Separation.

PubMed

Stanaćević, Milutin; Li, Shuo; Cauwenberghs, Gert

2016-07-01

A parallel micro-power mixed-signal VLSI implementation of independent component analysis (ICA) with reconfigurable outer-product learning rules is presented. With the gradient sensing of the acoustic field over a miniature microphone array as a pre-processing method, the proposed ICA implementation can separate and localize up to 3 sources in mild reverberant environment. The ICA processor is implemented in 0.5 µm CMOS technology and occupies 3 mm × 3 mm area. At 16 kHz sampling rate, ASIC consumes 195 µW power from a 3 V supply. The outer-product implementation of natural gradient and Herault-Jutten ICA update rules demonstrates comparable performance to benchmark FastICA algorithm in ideal conditions and more robust performance in noisy and reverberant environment. Experiments demonstrate perceptually clear separation and precise localization over wide range of separation angles of two speech sources presented through speakers positioned at 1.5 m from the array on a conference room table. The presented ASIC leads to a extreme small form factor and low power consumption microsystem for source separation and localization required in applications like intelligent hearing aids and wireless distributed acoustic sensor arrays.

Slope-velocity equilibrium and evolution of surface roughness on a stony hillslope

NASA Astrophysics Data System (ADS)

Nearing, Mark A.; Polyakov, Viktor O.; Nichols, Mary H.; Hernandez, Mariano; Li, Li; Zhao, Ying; Armendariz, Gerardo

2017-06-01

Slope-velocity equilibrium is hypothesized as a state that evolves naturally over time due to the interaction between overland flow and surface morphology, wherein steeper areas develop a relative increase in physical and hydraulic roughness such that flow velocity is a unique function of overland flow rate independent of slope gradient. This study tests this hypothesis under controlled conditions. Artificial rainfall was applied to 2 m by 6 m plots at 5, 12, and 20 % slope gradients. A series of simulations were made with two replications for each treatment with measurements of runoff rate, velocity, rock cover, and surface roughness. Velocities measured at the end of each experiment were a unique function of discharge rates, independent of slope gradient or rainfall intensity. Physical surface roughness was greater at steeper slopes. The data clearly showed that there was no unique hydraulic coefficient for a given slope, surface condition, or rainfall rate, with hydraulic roughness greater at steeper slopes and lower intensities. This study supports the hypothesis of slope-velocity equilibrium, implying that use of hydraulic equations, such as Chezy and Manning, in hillslope-scale runoff models is problematic because the coefficients vary with both slope and rainfall intensity.

Urbanization drives the evolution of parallel clines in plant populations

PubMed Central

Renaudin, Marie; Johnson, Marc T. J.

2016-01-01

Urban ecosystems are an increasingly dominant feature of terrestrial landscapes. While evidence that species can adapt to urban environments is accumulating, the mechanisms through which urbanization imposes natural selection on populations are poorly understood. The identification of adaptive phenotypic changes (i.e. clines) along urbanization gradients would facilitate our understanding of the selective factors driving adaptation in cities. Here, we test for phenotypic clines in urban ecosystems by sampling the frequency of a Mendelian-inherited trait—cyanogenesis—in white clover (Trifolium repens L.) populations along urbanization gradients in four cities. Cyanogenesis protects plants from herbivores, but reduces tolerance to freezing temperatures. We found that the frequency of cyanogenic plants within populations decreased towards the urban centre in three of four cities. A field experiment indicated that spatial variation in herbivory is unlikely to explain these clines. Rather, colder minimum winter ground temperatures in urban areas compared with non-urban areas, caused by reduced snow cover in cities, may select against cyanogenesis. In the city with no cline, high snow cover might protect plants from freezing damage in the city centre. Our study suggests that populations are adapting to urbanization gradients, but regional climatic patterns may ultimately determine whether adaptation occurs. PMID:28003451

Urbanization drives the evolution of parallel clines in plant populations.

PubMed

Thompson, Ken A; Renaudin, Marie; Johnson, Marc T J

2016-12-28

Urban ecosystems are an increasingly dominant feature of terrestrial landscapes. While evidence that species can adapt to urban environments is accumulating, the mechanisms through which urbanization imposes natural selection on populations are poorly understood. The identification of adaptive phenotypic changes (i.e. clines) along urbanization gradients would facilitate our understanding of the selective factors driving adaptation in cities. Here, we test for phenotypic clines in urban ecosystems by sampling the frequency of a Mendelian-inherited trait-cyanogenesis-in white clover (Trifolium repens L.) populations along urbanization gradients in four cities. Cyanogenesis protects plants from herbivores, but reduces tolerance to freezing temperatures. We found that the frequency of cyanogenic plants within populations decreased towards the urban centre in three of four cities. A field experiment indicated that spatial variation in herbivory is unlikely to explain these clines. Rather, colder minimum winter ground temperatures in urban areas compared with non-urban areas, caused by reduced snow cover in cities, may select against cyanogenesis. In the city with no cline, high snow cover might protect plants from freezing damage in the city centre. Our study suggests that populations are adapting to urbanization gradients, but regional climatic patterns may ultimately determine whether adaptation occurs. © 2016 The Author(s).

Biological Experiments in Microgravity Conditions Using Magnetic Micro- and Nano-Particles

NASA Astrophysics Data System (ADS)

Nechitailo, Galina S.; Kuznetsov, Anatoli; Kuznetsov, Oleg

2016-07-01

Gravity affects all living organisms on Earth, and plays a role in multiple processes in them. In microgravity conditions (e.g., on board of a spacecraft) many of these processes are disturbed, e.g., spatial orientation is lost, mass and heat exchange is distorted, many adaptive mechanisms no longer function, etc. Negation of these adverse effects by creation of pseudo-gravity to by centrifugation is complicated, expensive and unpractical. We propose to use naturally occurring magnetic heterogeneity of all living cells and high gradient magnetic fields as an alternative approach to negating the adverse effects of microgravity on living systems. In non-uniform magnetic field, magnetically heterogeneous objects experience a system of ponderomotive forces. For a weak magnetic particle, the net ponderomotive magnetic force: Fm = Δχ•V•grad(H2/2), where Δχ is the difference of susceptibilities of the particle and the surrounding media, V is the volume of the particle, grad(H2/2) is the dynamic factor of the magnetic field. We studied magnetic heterogeneity of plant gravity receptor cells, prepared and conducted experiments on board of the space station "Mir" on providing a gravity-like stimulus for flax seedlings using high gradient magnetic field ("Magnetogravistat" experiment). Later, a more sophisticated version of this experiment was flown on STS-107. These experiments provided new data on the mechanisms of plant gravity reception and created a method for substituting gravity for a living organism by a force of a different physical nature, to negate the adverse effects of microgravity. Since the ponderomotive force is proportional to the dynamic factor of the field grad(H2/2), the stronger the field, and the faster it changes over distance, the higher is the dynamic factor and the stronger the ponderomotive force. Therefore, in the small vicinity of a small ferromagnetic particle (preferably metallic micro or nano-particles), the forces are very significant even for weak magnetic objects, and can have significant effects on multiple processes in living cells/organisms. It was reported, that such high gradient magnetic fields can affect cell differentiation and cell proliferation processes in ground-based experiments. To prevent oxidation of ultradisperse ferromagnetic particles in aqueous media, it is beneficial to coat their surface with carbon. Suitable protected metallic micro- and nano-particles can be produced by a variety of techniques (CVD, plasmachemistry, joint grinding, etc.). Ferro-carbon particles produced by plasmachemical technique have high sorption capacities for various organic and inorganic compounds (as well as for various cell metabolites), can be formed in rather stable aqueous suspensions, and be controlled (e.g., sedimented) by a magnetic field. This makes these particles a very interesting research tool. In our opinion, biological experiments with ferro-carbon nano-structured particles in microgravity will generate important scientific data and will allow creating new methods of negating the adverse effects of microgravity on living systems.

Untangling human development and natural gradients: implications of underlying correlation structure for linking landscapes and riverine ecosystems

Treesearch

Yasmin Lucero; E. Ashley Steel; Kelly M. Burnett; Kelly Christiansen

2011-01-01

Increasingly, ecologists seek to identify and quantify relationships between landscape gradients and aquatic ecosystems. Considerable statistical challenges emerge in this effort, some of which are attributable to multicollinearity between human development and landscape gradients. In this paper, we measure the covariation between human development—such as agriculture...

Integrating ecosystem sampling, gradient modeling, remote sensing, and ecosystem simulation to create spatially explicit landscape inventories

Treesearch

Robert E. Keane; Matthew G. Rollins; Cecilia H. McNicoll; Russell A. Parsons

2002-01-01

Presented is a prototype of the Landscape Ecosystem Inventory System (LEIS), a system for creating maps of important landscape characteristics for natural resource planning. This system uses gradient-based field inventories coupled with gradient modeling remote sensing, ecosystem simulation, and statistical analyses to derive spatial data layers required for ecosystem...

Environment-dependent microevolution in a Mediterranean pine (Pinus pinaster Aiton).

PubMed

Alía, Ricardo; Chambel, Regina; Notivol, Eduardo; Climent, José; González-Martínez, Santiago C

2014-09-23

A central question for understanding the evolutionary responses of plant species to rapidly changing environments is the assessment of their potential for short-term (in one or a few generations) genetic change. In our study, we consider the case of Pinus pinaster Aiton (maritime pine), a widespread Mediterranean tree, and (i) test, under different experimental conditions (growth chamber and semi-natural), whether higher recruitment in the wild from the most successful mothers is due to better performance of their offspring; and (ii) evaluate genetic change in quantitative traits across generations at two different life stages (mature trees and seedlings) that are known to be under strong selection pressure in forest trees. Genetic control was high for most traits (h2 = 0.137-0.876) under the milder conditions of the growth chamber, but only for ontogenetic change (0.276), total height (0.415) and survival (0.719) under the more stressful semi-natural conditions. Significant phenotypic selection gradients were found in mature trees for traits related to seed quality (germination rate and number of empty seeds). Moreover, female relative reproductive success was significantly correlated with offspring performance for specific leaf area (SLA) in the growth chamber experiment, and stem mass fraction (SMF) in the experiment under semi-natural conditions, two adaptive traits related to abiotic stress-response in pines. Selection gradients based on genetic covariance of seedling traits and responses to selection at this stage involved traits related to biomass allocation (SMF) and growth (as decomposed by a Gompertz model) or delayed ontogenetic change, depending also on the testing environment. Despite the evidence of microevolutionary change in adaptive traits in maritime pine, directional or disruptive changes are difficult to predict due to variable selection at different life stages and environments. At mature-tree stages, higher female effective reproductive success can be explained by differences in their production of offspring (due to seed quality) and, to a lesser extent, by seemingly better adapted seedlings. Selection gradients and responses to selection for seedlings also differed across experimental conditions. The distinct processes involved at the two life stages (mature trees or seedlings) together with environment-specific responses advice caution when predicting likely evolutionary responses to environmental change in Mediterranean forest trees.

A quasi two-dimensional benchmark experiment for the solidification of a tin lead binary alloy

NASA Astrophysics Data System (ADS)

Wang, Xiao Dong; Petitpas, Patrick; Garnier, Christian; Paulin, Jean-Pierre; Fautrelle, Yves

2007-05-01

A horizontal solidification benchmark experiment with pure tin and a binary alloy of Sn-10 wt.%Pb is proposed. The experiment consists in solidifying a rectangular sample using two lateral heat exchangers which allow the application a controlled horizontal temperature difference. An array of fifty thermocouples placed on the lateral wall permits the determination of the instantaneous temperature distribution. The cases with the temperature gradient G=0, and the cooling rates equal to 0.02 and 0.04 K/s are studied. The time evolution of the interfacial total heat flux and the temperature field are recorded and analyzed. This allows us to evaluate heat transfer evolution due to natural convection, as well as its influence on the solidification macrostructure. To cite this article: X.D. Wang et al., C. R. Mecanique 335 (2007).

BACTERIOPHAGE AND MICROSPHERE TRANSPORT IN SATURATED POROUS MEDIA: FORCED-GRADIENT EXPERIMENT AT BORDEN, ONTARIO

EPA Science Inventory

A two-well forced-gradient experiment involving virus and microsphere transport was carried out in a sandy aquifer in Borden, Ontario, Canada. Virus traveled at least a few meters in the experiment, but virus concentrations at observation points 1 and 2.54 m away from the injecti...

HPLC of the Polypeptides in a Hydrolyzate of Egg-White Lysozyme. An Experiment for the Undergraduate Biochemistry Laboratory.

ERIC Educational Resources Information Center

Richardson, W. S., III; Burns, L.

1988-01-01

Describes a simple high-performance liquid chromatography experiment for undergraduate biochemistry laboratories. The experiment illustrates the separation of polypeptides by a step gradient elution using a single pump instrument with no gradient attachments. Discusses instrumentation, analysis, a sample preparation, and results. (CW)

Scalar gradient trajectory measurements using high-frequency cinematographic planar Rayleigh scattering

NASA Astrophysics Data System (ADS)

Gampert, Markus; Narayanaswamy, Venkat; Peters, Norbert

2013-12-01

In this work, we perform an experimental investigation into statistics based on scalar gradient trajectories in a turbulent jet flow, which have been suggested as an alternative means to analyze turbulent flow fields by Wang and Peters (J Fluid Mech 554:457-475, 2006, 608:113-138, 2008). Although there are several numerical simulations and theoretical works that investigate the statistics along gradient trajectories, only few experiments in this area have been reported. To this end, high-frequency cinematographic planar Rayleigh scattering imaging is performed at different axial locations of a turbulent propane jet issuing into a CO2 coflow at nozzle-based Reynolds numbers Re 0 = 3,000-8,600. Taylor's hypothesis is invoked to obtain a three-dimensional reconstruction of the scalar field in which then the corresponding scalar gradient trajectories can be computed. These are then used to examine the local structure of the mixture fraction with a focus on the scalar turbulent/non-turbulent interface. The latter is a layer that is located between the fully turbulent part of the jet and the outer flow. Using scalar gradient trajectories, we partition the turbulent scalar field into these three regions according to an approach developed by Mellado et al. (J Fluid Mech 626:333-365, 2009). Based on the latter, we investigate the probability to find the respective regions as a function of the radial distance to the centerline, which turns out to reveal the meandering nature of the scalar T/NT interface layer as well as its impact on the local structure of the turbulent scalar field.

Measuring small compartment dimensions by probing diffusion dynamics via Non-uniform Oscillating-Gradient Spin-Echo (NOGSE) NMR.

PubMed

Shemesh, Noam; Alvarez, Gonzalo A; Frydman, Lucio

2013-12-01

Noninvasive measurements of microstructure in materials, cells, and in biological tissues, constitute a unique capability of gradient-assisted NMR. Diffusion-diffraction MR approaches pioneered by Callaghan demonstrated this ability; Oscillating-Gradient Spin-Echo (OGSE) methodologies tackle the demanding gradient amplitudes required for observing diffraction patterns by utilizing constant-frequency oscillating gradient pairs that probe the diffusion spectrum, D(ω). Here we present a new class of diffusion MR experiments, termed Non-uniform Oscillating-Gradient Spin-Echo (NOGSE), which dynamically probe multiple frequencies of the diffusion spectral density at once, thus affording direct microstructural information on the compartment's dimension. The NOGSE methodology applies N constant-amplitude gradient oscillations; N-1 of these oscillations are spaced by a characteristic time x, followed by a single gradient oscillation characterized by a time y, such that the diffusion dynamics is probed while keeping (N-1)x+y≡TNOGSE constant. These constant-time, fixed-gradient-amplitude, multi-frequency attributes render NOGSE particularly useful for probing small compartment dimensions with relatively weak gradients - alleviating difficulties associated with probing D(ω) frequency-by-frequency or with varying relaxation weightings, as in other diffusion-monitoring experiments. Analytical descriptions of the NOGSE signal are given, and the sequence's ability to extract small compartment sizes with a sensitivity towards length to the sixth power, is demonstrated using a microstructural phantom. Excellent agreement between theory and experiments was evidenced even upon applying weak gradient amplitudes. An MR imaging version of NOGSE was also implemented in ex vivo pig spinal cords and mouse brains, affording maps based on compartment sizes. The effects of size distributions on NOGSE are also briefly analyzed. Copyright © 2013 Elsevier Inc. All rights reserved.

Leveraging 35 years of Pinus taeda research in the southeastern US to constrain forest carbon cycle predictions: regional data assimilation using ecosystem experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, R. Quinn; Brooks, Evan B.; Jersild, Annika L.

Predicting how forest carbon cycling will change in response to climate change and management depends on the collective knowledge from measurements across environmental gradients, ecosystem manipulations of global change factors, and mathematical models. Formally integrating these sources of knowledge through data assimilation, or model–data fusion, allows the use of past observations to constrain model parameters and estimate prediction uncertainty. Data assimilation (DA) focused on the regional scale has the opportunity to integrate data from both environmental gradients and experimental studies to constrain model parameters. Here, we introduce a hierarchical Bayesian DA approach (Data Assimilation to Predict Productivity for Ecosystems and Regions,more » DAPPER) that uses observations of carbon stocks, carbon fluxes, water fluxes, and vegetation dynamics from loblolly pine plantation ecosystems across the southeastern US to constrain parameters in a modified version of the Physiological Principles Predicting Growth (3-PG) forest growth model. The observations included major experiments that manipulated atmospheric carbon dioxide (CO 2) concentration, water, and nutrients, along with nonexperimental surveys that spanned environmental gradients across an 8.6 × 10 5 km 2 region. We optimized regionally representative posterior distributions for model parameters, which dependably predicted data from plots withheld from the data assimilation. While the mean bias in predictions of nutrient fertilization experiments, irrigation experiments, and CO 2 enrichment experiments was low, future work needs to focus modifications to model structures that decrease the bias in predictions of drought experiments. Predictions of how growth responded to elevated CO 2 strongly depended on whether ecosystem experiments were assimilated and whether the assimilated field plots in the CO 2 study were allowed to have different mortality parameters than the other field plots in the region. We present predictions of stem biomass productivity under elevated CO 2, decreased precipitation, and increased nutrient availability that include estimates of uncertainty for the southeastern US. Overall, we (1) demonstrated how three decades of research in southeastern US planted pine forests can be used to develop DA techniques that use multiple locations, multiple data streams, and multiple ecosystem experiment types to optimize parameters and (2) developed a tool for the development of future predictions of forest productivity for natural resource managers that leverage a rich dataset of integrated ecosystem observations across a region.« less

Leveraging 35 years of Pinus taeda research in the southeastern US to constrain forest carbon cycle predictions: regional data assimilation using ecosystem experiments

DOE PAGES

Thomas, R. Quinn; Brooks, Evan B.; Jersild, Annika L.; ...

2017-07-26

Predicting how forest carbon cycling will change in response to climate change and management depends on the collective knowledge from measurements across environmental gradients, ecosystem manipulations of global change factors, and mathematical models. Formally integrating these sources of knowledge through data assimilation, or model–data fusion, allows the use of past observations to constrain model parameters and estimate prediction uncertainty. Data assimilation (DA) focused on the regional scale has the opportunity to integrate data from both environmental gradients and experimental studies to constrain model parameters. Here, we introduce a hierarchical Bayesian DA approach (Data Assimilation to Predict Productivity for Ecosystems and Regions,more » DAPPER) that uses observations of carbon stocks, carbon fluxes, water fluxes, and vegetation dynamics from loblolly pine plantation ecosystems across the southeastern US to constrain parameters in a modified version of the Physiological Principles Predicting Growth (3-PG) forest growth model. The observations included major experiments that manipulated atmospheric carbon dioxide (CO 2) concentration, water, and nutrients, along with nonexperimental surveys that spanned environmental gradients across an 8.6 × 10 5 km 2 region. We optimized regionally representative posterior distributions for model parameters, which dependably predicted data from plots withheld from the data assimilation. While the mean bias in predictions of nutrient fertilization experiments, irrigation experiments, and CO 2 enrichment experiments was low, future work needs to focus modifications to model structures that decrease the bias in predictions of drought experiments. Predictions of how growth responded to elevated CO 2 strongly depended on whether ecosystem experiments were assimilated and whether the assimilated field plots in the CO 2 study were allowed to have different mortality parameters than the other field plots in the region. We present predictions of stem biomass productivity under elevated CO 2, decreased precipitation, and increased nutrient availability that include estimates of uncertainty for the southeastern US. Overall, we (1) demonstrated how three decades of research in southeastern US planted pine forests can be used to develop DA techniques that use multiple locations, multiple data streams, and multiple ecosystem experiment types to optimize parameters and (2) developed a tool for the development of future predictions of forest productivity for natural resource managers that leverage a rich dataset of integrated ecosystem observations across a region.« less

Leveraging 35 years of Pinus taeda research in the southeastern US to constrain forest carbon cycle predictions: regional data assimilation using ecosystem experiments

NASA Astrophysics Data System (ADS)

Quinn Thomas, R.; Brooks, Evan B.; Jersild, Annika L.; Ward, Eric J.; Wynne, Randolph H.; Albaugh, Timothy J.; Dinon-Aldridge, Heather; Burkhart, Harold E.; Domec, Jean-Christophe; Fox, Thomas R.; Gonzalez-Benecke, Carlos A.; Martin, Timothy A.; Noormets, Asko; Sampson, David A.; Teskey, Robert O.

2017-07-01

Predicting how forest carbon cycling will change in response to climate change and management depends on the collective knowledge from measurements across environmental gradients, ecosystem manipulations of global change factors, and mathematical models. Formally integrating these sources of knowledge through data assimilation, or model-data fusion, allows the use of past observations to constrain model parameters and estimate prediction uncertainty. Data assimilation (DA) focused on the regional scale has the opportunity to integrate data from both environmental gradients and experimental studies to constrain model parameters. Here, we introduce a hierarchical Bayesian DA approach (Data Assimilation to Predict Productivity for Ecosystems and Regions, DAPPER) that uses observations of carbon stocks, carbon fluxes, water fluxes, and vegetation dynamics from loblolly pine plantation ecosystems across the southeastern US to constrain parameters in a modified version of the Physiological Principles Predicting Growth (3-PG) forest growth model. The observations included major experiments that manipulated atmospheric carbon dioxide (CO2) concentration, water, and nutrients, along with nonexperimental surveys that spanned environmental gradients across an 8.6 × 105 km2 region. We optimized regionally representative posterior distributions for model parameters, which dependably predicted data from plots withheld from the data assimilation. While the mean bias in predictions of nutrient fertilization experiments, irrigation experiments, and CO2 enrichment experiments was low, future work needs to focus modifications to model structures that decrease the bias in predictions of drought experiments. Predictions of how growth responded to elevated CO2 strongly depended on whether ecosystem experiments were assimilated and whether the assimilated field plots in the CO2 study were allowed to have different mortality parameters than the other field plots in the region. We present predictions of stem biomass productivity under elevated CO2, decreased precipitation, and increased nutrient availability that include estimates of uncertainty for the southeastern US. Overall, we (1) demonstrated how three decades of research in southeastern US planted pine forests can be used to develop DA techniques that use multiple locations, multiple data streams, and multiple ecosystem experiment types to optimize parameters and (2) developed a tool for the development of future predictions of forest productivity for natural resource managers that leverage a rich dataset of integrated ecosystem observations across a region.

A major locus controls local adaptation and adaptive life history variation in a perennial plant.

PubMed

Wang, Jing; Ding, Jihua; Tan, Biyue; Robinson, Kathryn M; Michelson, Ingrid H; Johansson, Anna; Nystedt, Björn; Scofield, Douglas G; Nilsson, Ove; Jansson, Stefan; Street, Nathaniel R; Ingvarsson, Pär K

2018-06-04

The initiation of growth cessation and dormancy represent critical life-history trade-offs between survival and growth and have important fitness effects in perennial plants. Such adaptive life-history traits often show strong local adaptation along environmental gradients but, despite their importance, the genetic architecture of these traits remains poorly understood. We integrate whole genome re-sequencing with environmental and phenotypic data from common garden experiments to investigate the genomic basis of local adaptation across a latitudinal gradient in European aspen (Populus tremula). A single genomic region containing the PtFT2 gene mediates local adaptation in the timing of bud set and explains 65% of the observed genetic variation in bud set. This locus is the likely target of a recent selective sweep that originated right before or during colonization of northern Scandinavia following the last glaciation. Field and greenhouse experiments confirm that variation in PtFT2 gene expression affects the phenotypic variation in bud set that we observe in wild natural populations. Our results reveal a major effect locus that determines the timing of bud set and that has facilitated rapid adaptation to shorter growing seasons and colder climates in European aspen. The discovery of a single locus explaining a substantial fraction of the variation in a key life-history trait is remarkable, given that such traits are generally considered to be highly polygenic. These findings provide a dramatic illustration of how loci of large-effect for adaptive traits can arise and be maintained over large geographical scales in natural populations.

The world is not flat: can people reorient using slope?

PubMed

Nardi, Daniele; Newcombe, Nora S; Shipley, Thomas F

2011-03-01

Studies of spatial representation generally focus on flat environments and visual input. However, the world is not flat, and slopes are part of most natural environments. In a series of 4 experiments, we examined whether humans can use a slope as a source of allocentric, directional information for reorientation. A target was hidden in a corner of a square, featureless enclosure tilted at a 5° angle. Finding it required using the vestibular, kinesthetic, and visual cues associated with the slope gradient. In Experiment 1, the overall sample performed above chance, showing that slope is sufficient for reorientation in a real environment. However, a sex difference emerged; men outperformed women by 1.4 SDs because they were more likely to use a slope-based strategy. In Experiment 2, attention was drawn to the slope, and participants were prompted to rely on it to solve the task; however, men still outperformed women, indicating a greater ability to use slope. In Experiment 3, we excluded the possibility that women's disadvantage was due to wearing heeled footwear. In Experiment 4, women required more time than men to identify the uphill direction of the slope gradient; this suggests that, in a bottom-up fashion, a perceptual or attentional difficulty underlies women's disadvantage in the ability to use slope and their decreased reliance on this cue. Overall, a bi-coordinate representation was used to find the goal: The target was encoded primarily with respect to the vertical axis and secondarily with respect to the orthogonal axis of the slope. 2011 APA, all rights reserved

Reproducing stone monument photosynthetic-based colonization under laboratory conditions.

PubMed

Miller, Ana Zélia; Laiz, Leonila; Gonzalez, Juan Miguel; Dionísio, Amélia; Macedo, Maria Filomena; Saiz-Jimenez, Cesareo

2008-11-01

In order to understand the biodeterioration process occurring on stone monuments, we analyzed the microbial communities involved in these processes and studied their ability to colonize stones under controlled laboratory experiments. In this study, a natural green biofilm from a limestone monument was cultivated, inoculated on stone probes of the same lithotype and incubated in a laboratory chamber. This incubation system, which exposes stone samples to intermittently sprinkling water, allowed the development of photosynthetic biofilms similar to those occurring on stone monuments. Denaturing gradient gel electrophoresis (DGGE) analysis was used to evaluate the major microbial components of the laboratory biofilms. Cyanobacteria, green microalgae, bacteria and fungi were identified by DNA-based molecular analysis targeting the 16S and 18S ribosomal RNA genes. The natural green biofilm was mainly composed by the Chlorophyta Chlorella, Stichococcus, and Trebouxia, and by Cyanobacteria belonging to the genera Leptolyngbya and Pleurocapsa. A number of bacteria belonging to Alphaproteobacteria, Bacteroidetes and Verrucomicrobia were identified, as well as fungi from the Ascomycota. The laboratory colonization experiment on stone probes showed a colonization pattern similar to that occurring on stone monuments. The methodology described in this paper allowed to reproduce a colonization equivalent to the natural biodeteriorating process.

Elemental, stable isotopic and biochemical characterization of soil organic matter alteration across a natural peatland gradient

NASA Astrophysics Data System (ADS)

Cowie, G.; Mowbray, S.; Belyea, L.; Laing, C.; Allton, K.; Abbott, G.; Muhammad, A.

2010-12-01

Northern peatlands store around one third of global soil C and thus represent a key reservoir. To elucidate how these systems might respond to climate change, field- and laboratory-based experimental incubation studies are being conducted at sites across a natural peatland gradient in the boreonemoral zone of central Sweden (Ryggmossen). The site comprises four successional stages, from edge to centre; Swamp Forest (SF), Lagg Fen (LF), Bog Margin (BM) and Bog Plateau (BP). The well-preserved succession shows strong decreases in mineral cations and pH, and distinct changes in vegetation and water-table depth. As an underpinning to these experiments, comprehensive characterization of natural soil organic matter (SOM) alteration has been carried out through detailed analyses of vegetation and downcore profiles at contrasting topographic sites (hummock vs hollow) in each of the four locations. As illustrated in Figure 1, while some similarities occur in downcore trends, contrasts are observed in C and N elemental and stable isotopic compositions, between stages and, in some cases, between microtopographic settings. Downcore trends and intersite differences are also observed in biochemical yields and molecular composition (carbohydrates, amino acids, phenols, lipids and D/L amino acid ratios). These reflect SOM decay and alteration combined with the effects of contrasting hydrologic, redox and nutrient regimes and differing vegetation and microbial inputs at each of the study sites. Multivariate analysis is used to to elucidate compositional patterns that characterize and delineate progressive SOM decay, specific vegetation types, and the effects of contrasting environmental conditions at the different sites. Figure 1. A. Organic carbon content (wt %), B. Atomic ratio of organic C to total N, C. Stable C isotopic composition of organic C (d13Corg), and D. Stable N isotopic composition of total nitrogen (d15N), all for core profiles from contrasting settings (hummock and hollow) at locations spanning a peatland gradient. Site locations are defined in the text.

The El Nino-Southern Oscillation in the second Hadley Centre coupled model and its response to greenhouse warming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, M.

This paper describes El Nino-Southern Oscillation (ENSO) interannual variability simulated in the second Handley Centre coupled model under control and greenhouse warming scenarios. The model produces a very reasonable simulation of ENSO in the control experiment--reproducing the amplitude, spectral characteristics, and phase locking to the annual cycle that are observed in nature. The mechanism for the model ENSO is shown to be a mixed SST-ocean dynamics mode that can be interpreted in terms of the ocean recharge paradigm of Jin. In experiments with increased levels of greenhouse gases, no statistically significant changes in ENSO are seen until these levels approachmore » four times preindustrial values. In these experiments, the model ENSO has an approximately 20% larger amplitude, a frequency that is approximately double that of the current ENSO (implying more frequent El Ninos and La Ninas), and phase locks to the annual cycle at a different time of year. It is shown that the increase in the vertical gradient of temperature in the thermocline region, associated with the model's response to increased greenhouse gases, is responsible for the increase in the amplitude of ENSO, while the increase in meridional temperature gradients on either side of the equator, again associated with the models response to increasing greenhouse gases, is responsible for the increased frequency of ENSO events.« less

Temperature logging of groundwater in bedrock wells for geothermal gradient characterization in New Hampshire, 2012

USGS Publications Warehouse

Degnan, James; Barker, Gregory; Olson, Neil; Wilder, Leland

2012-01-01

Maximum groundwater temperatures at the bottom of the logs were between 11.7 and 17.3 degrees Celsius. Geothermal gradients were generally higher than typically reported for other water wells in the United States. Some of the high gradients were associated with high natural gamma emissions. Groundwater flow was discernible in 5 of the 10 wells studied but only obscured the portion of the geothermal gradient signal where groundwater actually flowed through the well. Temperature gradients varied by mapped bedrock type but can also vary by differences in mineralogy or rock type within the wells.

Gradient Heating Facility. Experiment cartridges. Description and general specifications

NASA Technical Reports Server (NTRS)

Breton, J.

1982-01-01

Specifications that define experiment cartridges that are compatible with the furnace of the gradient heating facility on board the Spacelab are presented. They establish a standard cartridge design independent of the type of experiment to be conducted. By using them, experimenters can design, construct, and test the hot section of the cartridge, known as the high temperature nacelle.

Using an NMR Spectrometer to Do Magnetic Resonance Imaging: An Undergraduate Physical Chemistry Laboratory Experiment

ERIC Educational Resources Information Center

Steinmetz, Wayne E.; Maher, M. Cyrus

2007-01-01

A conventional Fourier-transform NMR spectrometer with a triple-axis gradient probe can function as a MRI imager. In this experiment students gain hands-on experience with MRI while they learn about important principles underlying the practice of NMR, such as gradients, multi-dimensional spectroscopy, and relaxation. Students image a biological…

Thermal-gradient migration of brine inclusions in salt crystals. [Synthetic single crystals of NaCl and KCl

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yagnik, S.K.

1982-09-01

It has been proposed that high-level nuclear waste be disposed in a geologic repository. Natural-salt deposits, which are being considered for this purpose, contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive-decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In this work, thermal gradient migration of bothmore » all-liquid and gas-liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot-stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusions were found to be dependent on temperature, temperature gradient, and inclusion shape and size. The velocities were also dictated by the interfacial mass transfer resistance at brine/solid interface. This interfacial resistance depends on the dislocation density in the crystal, which in turn, depends on the axial compressive loading of the crystal. At low axial loads, the dependence between the velocity and temperature gradient is non-linear.At high axial loads, however, the interfacial resistance is reduced and the migration velocity depends linearly on the temperature gradient. All-liquid inclusions filled with mixed brines were also studied. For gas-liquid inclusions, three different gas phases (helium, air and argon) were compared. Migration studies were also conducted on single crystallites of natural salt as well as in polycrystalline natural salt samples. The behavior of the inclusions at large angle grain boundaries was observed. 35 figures, 3 tables.« less

A global analysis of fine root production as affected by soil nitrogen and phosphorus.

PubMed

Yuan, Z Y; Chen, Han Y H

2012-09-22

Fine root production is the largest component of belowground production and plays substantial roles in the biogeochemical cycles of terrestrial ecosystems. The increasing availability of nitrogen (N) and phosphorus (P) due to human activities is expected to increase aboveground net primary production (ANNP), but the response of fine root production to N and P remains unclear. If roots respond to nutrients as ANNP, fine root production is anticipated to increase with increasing soil N and P. Here, by synthesizing data along the nutrient gradient from 410 natural habitats and from 469 N and/or P addition experiments, we showed that fine root production increased in terrestrial ecosystems with an average increase along the natural N gradient of up to 0.5 per cent with increasing soil N. Fine root production also increased with soil P in natural conditions, particularly at P < 300 mg kg(-1). With N, P and combined N + P addition, fine root production increased by a global average of 27, 21 and 40 per cent, respectively. However, its responses differed among ecosystems and soil types. The global average increases in fine root production are lower than those of ANNP, indicating that above- and belowground counterparts are coupled, but production allocation shifts more to aboveground with higher soil nutrients. Our results suggest that the increasing fertilizer use and combined N deposition at present and in the future will stimulate fine root production, together with ANPP, probably providing a significant influence on atmospheric CO(2) emissions.

Response of Phytoplankton Iron Contents to Gradients in Iron Availability in the California Current System

NASA Astrophysics Data System (ADS)

Twining, B. S.; Jacquot, J. E.; Rauschenberg, S.; Enright, J.; Marchetti, A.; Cohen, N.; Brown, M.; Parker, C.; Bruland, K. W.

2016-02-01

Iron is a critical micronutrient that controls primary production in large swaths of the global ocean. Experiments with laboratory cultures indicate that phytoplankton differ in their ability to compete for and store Fe in response to varying ambient Fe concentrations. However there are very few measurements of the physiological responses of natural phytoplankton populations to gradients in Fe availability. Incubation experiments were conducted off the coast of California and Oregon at two sites characterized by a 10-fold difference in dissolved Fe (0.3 and 3 nM). In each experiment, incubation water was amended with either dissolved Fe (5-10 nM), the model siderophore desferrioxamine B (DFB; 200 nM), or left unamended. Iron contents of three abundant diatom groups (Chaetoceros sp. and large and small pennate diatoms) were monitored by synchrotron X-ray fluorescence, along with dissolved and bulk particulate trace metals and macronutrients over the course of 3 days. Transcriptomic samples were also collected at daily timepoints to assess molecular responses. Added dissolved Fe was drawn down in both experiments, while DFB appeared to solubilize a fraction of ambient particulate Fe in the high-Fe experiment. Iron quotas of unamended diatoms were nearly 10-fold higher under high-Fe conditions. Quotas increased in response to added Fe in both experiments, but the magnitude of changes varied between diatom taxa. DFB additions resulted in reduced Fe quotas in the low-Fe incubation, since cells were presumably forced to use internal Fe stores to support growth. These data demonstrate significant plasticity in the abilities of phytoplankton to take advantage of changing micronutrient inputs. Quota data will be compared to transcript abundance data to ascertain mechanisms of Fe quota maintenance.

Proposed gravity-gradient dynamics experiments in lunar orbit using the RAE-B spacecraft

NASA Technical Reports Server (NTRS)

Blanchard, D. L.; Walden, H.

1973-01-01

A series of seven gravity-gradient dynamics experiments is proposed utilizing the Radio Astronomy Explorer (RAE-B) spacecraft in lunar orbit. It is believed that none of the experiments will impair the spacecraft structure or adversely affect the continuation of the scientific mission of the satellite. The first experiment is designed to investigate the spacecraft dynamical behavior in the absence of libration damper action and inertia. It requires stable gravity-gradient capture of the spacecraft in lunar orbit with small amplitude attitude librations as a prerequisite. Four subsequent experiments involve partial retraction, ultimately followed by full redeployment, of one or two of the 230-meter booms forming the lunar-directed Vee-antenna. These boom length change operations will induce moderate amplitude angular librations of the spacecraft.

Prolonged exposure does not increase soil microbial community compositional response to warming along geothermal gradients.

PubMed

Radujkovic, Dajana; Verbruggen, Erik; Sigurdsson, Bjarni D; Leblans, Niki I W; Janssens, Ivan A; Vicca, Sara; Weedon, James T

2018-02-01

Global change is expected to affect soil microbial communities through their responsiveness to temperature. It has been proposed that prolonged exposure to elevated temperatures may lead to progressively larger effects on soil microbial community composition. However, due to the relatively short-term nature of most warming experiments, this idea has been challenging to evaluate. The present study took the advantage of natural geothermal gradients (from +1°C to +19°C above ambient) in two subarctic grasslands to test the hypothesis that long-term exposure (>50 years) intensifies the effect of warming on microbial community composition compared to short-term exposure (5-7 years). Community profiles from amplicon sequencing of bacterial and fungal rRNA genes did not support this hypothesis: significant changes relative to ambient were observed only starting from the warming intensity of +9°C in the long term and +7°C/+3°C in the short term, for bacteria and fungi, respectively. Our results suggest that microbial communities in high-latitude grasslands will not undergo lasting shifts in community composition under the warming predicted for the coming 100 years (+2.2°C to +8.3°C). © FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Measuring diffusion-relaxation correlation maps using non-uniform field gradients of single-sided NMR devices.

PubMed

Nogueira d'Eurydice, Marcel; Galvosas, Petrik

2014-11-01

Single-sided NMR systems are becoming a relevant tool in industry and laboratory environments due to their low cost, low maintenance and capacity to evaluate quantity and quality of hydrogen based materials. The performance of such devices has improved significantly over the last decade, providing increased field homogeneity, field strength and even controlled static field gradients. For a class of these devices, the configuration of the permanent magnets provides a linear variation of the magnetic field and can be used in diffusion measurements. However, magnet design depends directly on its application and, according to the purpose, the field homogeneity may significantly be compromised. This may prevent the determination of diffusion properties of fluids based on the natural inhomogeneity of the field using known techniques. This work introduces a new approach that extends the applicability of diffusion-editing CPMG experiments to NMR devices with highly inhomogeneous magnetic fields, which do not vary linearly in space. Herein, we propose a method to determine a custom diffusion kernel based on the gradient distribution, which can be seen as a signature of each NMR device. This new diffusion kernel is then utilised in the 2D inverse Laplace transform (2D ILT) in order to determine diffusion-relaxation correlation maps of homogeneous multi-phasic fluids. The experiments were performed using NMR MObile Lateral Explore (MOLE), which is a single-sided NMR device designed to maximise the volume at the sweet spot with enhanced depth penetration. Copyright © 2014 Elsevier Inc. All rights reserved.

Autecology of an arsenite chemolithotroph: sulfide constraints on function and distribution in a geothermal spring.

PubMed

D'Imperio, Seth; Lehr, Corinne R; Breary, Michele; McDermott, Timothy R

2007-11-01

Previous studies in an acid-sulfate-chloride spring in Yellowstone National Park found that microbial arsenite [As(III)] oxidation is absent in regions of the spring outflow channel where H(2)S exceeds approximately 5 microM and served as a backdrop for continued efforts in the present study. Ex situ assays with microbial mat samples demonstrated immediate As(III) oxidation activity when H(2)S was absent or at low concentrations, suggesting the presence of As(III) oxidase enzymes that could be reactivated if H(2)S is removed. Cultivation experiments initiated with mat samples taken from along the H(2)S gradient in the outflow channel resulted in the isolation of an As(III)-oxidizing chemolithotroph from the low-H(2)S region of the gradient. The isolate was phylogenetically related to Acidicaldus and was characterized in vitro for spring-relevant properties, which were then compared to its distribution pattern in the spring as determined by denaturing gradient gel electrophoresis and quantitative PCR. While neither temperature nor oxygen requirements appeared to be related to the occurrence of this organism within the outflow channel, H(2)S concentration appeared to be an important constraint. This was verified by in vitro pure-culture modeling and kinetic experiments, which suggested that H(2)S inhibition of As(III) oxidation is uncompetitive in nature. In summary, the studies reported herein illustrate that H(2)S is a potent inhibitor of As(III) oxidation and will influence the niche opportunities and population distribution of As(III) chemolithotrophs.

Autecology of an Arsenite Chemolithotroph: Sulfide Constraints on Function and Distribution in a Geothermal Spring▿

PubMed Central

D'Imperio, Seth; Lehr, Corinne R.; Breary, Michele; McDermott, Timothy R.

2007-01-01

Previous studies in an acid-sulfate-chloride spring in Yellowstone National Park found that microbial arsenite [As(III)] oxidation is absent in regions of the spring outflow channel where H2S exceeds ∼5 μM and served as a backdrop for continued efforts in the present study. Ex situ assays with microbial mat samples demonstrated immediate As(III) oxidation activity when H2S was absent or at low concentrations, suggesting the presence of As(III) oxidase enzymes that could be reactivated if H2S is removed. Cultivation experiments initiated with mat samples taken from along the H2S gradient in the outflow channel resulted in the isolation of an As(III)-oxidizing chemolithotroph from the low-H2S region of the gradient. The isolate was phylogenetically related to Acidicaldus and was characterized in vitro for spring-relevant properties, which were then compared to its distribution pattern in the spring as determined by denaturing gradient gel electrophoresis and quantitative PCR. While neither temperature nor oxygen requirements appeared to be related to the occurrence of this organism within the outflow channel, H2S concentration appeared to be an important constraint. This was verified by in vitro pure-culture modeling and kinetic experiments, which suggested that H2S inhibition of As(III) oxidation is uncompetitive in nature. In summary, the studies reported herein illustrate that H2S is a potent inhibitor of As(III) oxidation and will influence the niche opportunities and population distribution of As(III) chemolithotrophs. PMID:17827309

Current and historical composition and size structure of upland forests across a soil gradient in north Mississippi

Treesearch

Sherry B. Surrette; Steven M. Aquilani; J. Stephen Brewer

2008-01-01

Comparisons of current and historical tree species composition and size structure along natural productivity gradients are useful for inferring effects of disturbance regimes and productivity on patterns of succession.

Enhanced sensitivity of DNA- and rRNA-based stable isotope probing by fractionation and quantitative analysis of isopycnic centrifugation gradients.

PubMed

Lueders, Tillmann; Manefield, Mike; Friedrich, Michael W

2004-01-01

Stable isotope probing (SIP) of nucleic acids allows the detection and identification of active members of natural microbial populations that are involved in the assimilation of an isotopically labelled compound into nucleic acids. SIP is based on the separation of isotopically labelled DNA or rRNA by isopycnic density gradient centrifugation. We have developed a highly sensitive protocol for the detection of 'light' and 'heavy' nucleic acids in fractions of centrifugation gradients. It involves the fluorometric quantification of total DNA or rRNA, and the quantification of either 16S rRNA genes or 16S rRNA in gradient fractions by real-time PCR with domain-specific primers. Using this approach, we found that fully 13C-labelled DNA or rRNA of Methylobacterium extorquens was quantitatively resolved from unlabelled DNA or rRNA of Methanosarcina barkeri by cesium chloride or cesium trifluoroacetate density gradient centrifugation respectively. However, a constant low background of unspecific nucleic acids was detected in all DNA or rRNA gradient fractions, which is important for the interpretation of environmental SIP results. Consequently, quantitative analysis of gradient fractions provides a higher precision and finer resolution for retrieval of isotopically enriched nucleic acids than possible using ethidium bromide or gradient fractionation combined with fingerprinting analyses. This is a prerequisite for the fine-scale tracing of microbial populations metabolizing 13C-labelled compounds in natural ecosystems.

Domain Derivatives in Dielectric Rough Surface Scattering

DTIC Science & Technology

2015-01-01

and require the gradient of the objective function in the unknown model parameter vector at each stage of iteration. For large N, finite...differencing becomes numerically intensive, and an efficient alternative is domain differentiation in which the full gradient is obtained by solving a single...derivative calculation of the gradient for a locally perturbed dielectric interface. The method is non-variational, and algebraic in nature in that it

Evaluation of multiple tracer methods to estimate low groundwater flow velocities

DOE PAGES

Reimus, Paul W.; Arnold, Bill W.

2017-02-20

Here, four different tracer methods were used to estimate groundwater flow velocity at a multiple-well site in the saturated alluvium south of Yucca Mountain, Nevada: (1) two single-well tracer tests with different rest or “shut-in” periods, (2) a cross-hole tracer test with an extended flow interruption, (3) a comparison of two tracer decay curves in an injection borehole with and without pumping of a downgradient well, and (4) a natural-gradient tracer test. Such tracer methods are potentially very useful for estimating groundwater velocities when hydraulic gradients are flat (and hence uncertain) and also when water level and hydraulic conductivity datamore » are sparse, both of which were the case at this test location. The purpose of the study was to evaluate the first three methods for their ability to provide reasonable estimates of relatively low groundwater flow velocities in such low-hydraulic-gradient environments. The natural-gradient method is generally considered to be the most robust and direct method, so it was used to provide a “ground truth” velocity estimate. However, this method usually requires several wells, so it is often not practical in systems with large depths to groundwater and correspondingly high well installation costs. The fact that a successful natural gradient test was conducted at the test location offered a unique opportunity to compare the flow velocity estimates obtained by the more easily deployed and lower risk methods with the ground-truth natural-gradient method. The groundwater flow velocity estimates from the four methods agreed very well with each other, suggesting that the first three methods all provided reasonably good estimates of groundwater flow velocity at the site. We discuss the advantages and disadvantages of the different methods, as well as some of the uncertainties associated with them.« less

Evaluation of multiple tracer methods to estimate low groundwater flow velocities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reimus, Paul W.; Arnold, Bill W.

Here, four different tracer methods were used to estimate groundwater flow velocity at a multiple-well site in the saturated alluvium south of Yucca Mountain, Nevada: (1) two single-well tracer tests with different rest or “shut-in” periods, (2) a cross-hole tracer test with an extended flow interruption, (3) a comparison of two tracer decay curves in an injection borehole with and without pumping of a downgradient well, and (4) a natural-gradient tracer test. Such tracer methods are potentially very useful for estimating groundwater velocities when hydraulic gradients are flat (and hence uncertain) and also when water level and hydraulic conductivity datamore » are sparse, both of which were the case at this test location. The purpose of the study was to evaluate the first three methods for their ability to provide reasonable estimates of relatively low groundwater flow velocities in such low-hydraulic-gradient environments. The natural-gradient method is generally considered to be the most robust and direct method, so it was used to provide a “ground truth” velocity estimate. However, this method usually requires several wells, so it is often not practical in systems with large depths to groundwater and correspondingly high well installation costs. The fact that a successful natural gradient test was conducted at the test location offered a unique opportunity to compare the flow velocity estimates obtained by the more easily deployed and lower risk methods with the ground-truth natural-gradient method. The groundwater flow velocity estimates from the four methods agreed very well with each other, suggesting that the first three methods all provided reasonably good estimates of groundwater flow velocity at the site. We discuss the advantages and disadvantages of the different methods, as well as some of the uncertainties associated with them.« less

OSMOSIS: A CAUSE OF APPARENT DEVIATIONS FROM DARCY'S LAW.

USGS Publications Warehouse

Olsen, Harold W.

1985-01-01

This review of the existing evidence shows that osmosis causes intercepts in flow rate versus hydraulic gradient relationships that are consistent with the observed deviations from Darcy's law at very low gradients. Moreover, it is suggested that a natural cause of osmosis in laboratory samples could be chemical reactions such as those involved in aging effects. This hypothesis is analogous to the previously proposed occurrence of electroosmosis in nature generated by geochemical weathering reactions. Refs.

Experimental and observational studies find contrasting responses of soil nutrients to climate change.

PubMed

Yuan, Z Y; Jiao, F; Shi, X R; Sardans, Jordi; Maestre, Fernando T; Delgado-Baquerizo, Manuel; Reich, Peter B; Peñuelas, Josep

2017-06-01

Manipulative experiments and observations along environmental gradients, the two most common approaches to evaluate the impacts of climate change on nutrient cycling, are generally assumed to produce similar results, but this assumption has rarely been tested. We did so by conducting a meta-analysis and found that soil nutrients responded differentially to drivers of climate change depending on the approach considered. Soil carbon, nitrogen, and phosphorus concentrations generally decreased with water addition in manipulative experiments but increased with annual precipitation along environmental gradients. Different patterns were also observed between warming experiments and temperature gradients. Our findings provide evidence of inconsistent results and suggest that manipulative experiments may be better predictors of the causal impacts of short-term (months to years) climate change on soil nutrients but environmental gradients may provide better information for long-term correlations (centuries to millennia) between these nutrients and climatic features. Ecosystem models should consequently incorporate both experimental and observational data to properly assess the impacts of climate change on nutrient cycling.

Product Distribution Theory and Semi-Coordinate Transformations

NASA Technical Reports Server (NTRS)

Airiau, Stephane; Wolpert, David H.

2004-01-01

Product Distribution (PD) theory is a new framework for doing distributed adaptive control of a multiagent system (MAS). We introduce the technique of "coordinate transformations" in PD theory gradient descent. These transformations selectively couple a few agents with each other into "meta-agents". Intuitively, this can be viewed as a generalization of forming binding contracts between those agents. Doing this sacrifices a bit of the distributed nature of the MAS, in that there must now be communication from multiple agents in determining what joint-move is finally implemented However, as we demonstrate in computer experiments, these transformations improve the performance of the MAS.

Studies of bacterial aerotaxis in a microfluidic device

PubMed Central

Adler, Micha; Erickstad, Michael; Gutierrez, Edgar; Groisman, Alex

2012-01-01

Aerotaxis, the directional motion of bacteria in gradients of oxygen, was discovered in late 19th century and has since been reported in a variety of bacterial species. Nevertheless, quantitative studies of aerotaxis have been complicated by the lack of tools for generation of stable gradients of oxygen concentration, [O2]. Here we report a series of experiments on aerotaxis of Escherichia coli in a specially built experimental setup consisting of a computer-controlled gas mixer and a two-layer microfluidic device made of polydimethylsiloxane (PDMS). The setup enables generation of a variety of stable linear profiles of [O2] across a long gradient channel, with characteristic [O2] ranging from aerobic to microaerobic conditions. A suspension of E. coli cells is perfused through the gradient channel at a low speed, allowing cells enough time to explore the [O2] gradient, and the distribution of cells across the channel is analyzed near the channel outlet at a throughput of >105 cells per hour. Aerotaxis experiments are performed in [O2] gradients with identical logarithmic slopes and varying mean concentrations, as well as in gradients with identical mean concentrations and varying slopes. Experiments in gradients with [O2] ranging from 0 to ~11.5% indicate that, in contrast to some previous reports, E. coli cells do not congregate at some intermediate level of [O2], but rather prefer the highest accessible [O2]. The presented technology can be applied to studies of aerotaxis of other aerobic and microaerobic bacteria. PMID:23010909

Experimental and Computational Studies of the Control of Convection of Non-Conducting Liquids During solidification by Means of a Magnetic Field Gradient

NASA Technical Reports Server (NTRS)

Seybert, C. D.; Evans, J. W.; Leslie, F.; Jones, W. K., Jr.

2001-01-01

The elimination of convection is essential in experimental investigations of diffusive transport (of heat and matter) during solidification. One classical approach to damping convection in a conducting liquid is the application of a magnetic field. The damping phenomenon is the induction, by the motion of a conductor in a magnetic field, of currents which interact with the field to produce Lorentz forces that oppose the flow. However, there are many liquids which are not sufficiently conducting to exploit this phenomenon; examples include the transparent liquids (such as succinonitrile-acetone) that are used as "model alloys" in fundamental solidification studies. There have been several investigations of the solidification of these liquids that have been carried out in orbiting laboratories to eliminate natural convection. The paper describes an investigation of an alternative approach whereby a magnetic field gradient is applied to the liquid. A magnetic body force then arises which is dependent on the susceptibility of the liquid and thereby on the temperature and or concentration. With the field gradient aligned vertically and of correct magnitude, the variation of gravitational body force due to temperature/concentration dependent density can be counterbalanced by a variation in magnetic body force. Experiments have been carried out in a super-conducting magnet at Marshall Space Flight Center to measure velocities in an aqueous manganese chloride solution. The solution was contained in a chamber with temperature controlled end walls and glass side walls. Velocities were measured by particle image velocimetry. Starting from zero current in the magnet (zero field gradient) flow driven by the temperature difference between the end walls was measured. At a critical current the flow was halted. At higher currents the normal convection was reversed. The experiments included ones where the solution was solidified and were accompanied by solution of the flow/transport equations using the software package FLUENT.

Local Adaptation Enhances Seedling Recruitment Along an Altitudinal Gradient in a High Mountain Mediterranean Plant

PubMed Central

Giménez-Benavides, Luis; Escudero, Adrián; Iriondo, José M.

2007-01-01

Background and Aims Germination and seedling establishment, which are critical stages in the regeneration process of plant populations, may be subjected to natural selection and adaptive evolution. The aims of this work were to assess the main limitations on offspring performance of Silene ciliata, a high mountain Mediterranean plant, and to test whether local adaptation at small spatial scales has a significant effect on the success of establishment. Methods Reciprocal sowing experiments were carried out among three populations of the species to test for evidence of local adaptation on seedling emergence, survival and size. Studied populations were located at the southernmost margin of the species' range, along the local elevation gradient that leads to a drought stress gradient. Key Results Drought stress in summer was the main cause of seedling mortality even though germination mainly occurred immediately after snowmelt to make the best use of soil moisture. The results support the hypothesis that species perform better at the centre of their altitudinal range than at the boundaries. Evidence was also found of local adaptation in seedling survival and growth along the whole gradient. Conclusions The local adaptation acting on seedling emergence and survival favours the persistence of remnant populations on the altitudinal and latitudinal margins of mountain species. In a global warming context, such processes may help to counteract the contraction of this species' ranges and the consequent loss of habitat area. PMID:17307775

Reduced-Reference Quality Assessment Based on the Entropy of DWT Coefficients of Locally Weighted Gradient Magnitudes.

PubMed

Golestaneh, S Alireza; Karam, Lina

2016-08-24

Perceptual image quality assessment (IQA) attempts to use computational models to estimate the image quality in accordance with subjective evaluations. Reduced-reference (RR) image quality assessment (IQA) methods make use of partial information or features extracted from the reference image for estimating the quality of distorted images. Finding a balance between the number of RR features and accuracy of the estimated image quality is essential and important in IQA. In this paper we propose a training-free low-cost RRIQA method that requires a very small number of RR features (6 RR features). The proposed RRIQA algorithm is based on the discrete wavelet transform (DWT) of locally weighted gradient magnitudes.We apply human visual system's contrast sensitivity and neighborhood gradient information to weight the gradient magnitudes in a locally adaptive manner. The RR features are computed by measuring the entropy of each DWT subband, for each scale, and pooling the subband entropies along all orientations, resulting in L RR features (one average entropy per scale) for an L-level DWT. Extensive experiments performed on seven large-scale benchmark databases demonstrate that the proposed RRIQA method delivers highly competitive performance as compared to the state-of-the-art RRIQA models as well as full reference ones for both natural and texture images. The MATLAB source code of REDLOG and the evaluation results are publicly available online at https://http://lab.engineering.asu.edu/ivulab/software/redlog/.

An empirical basis for Mach bands

PubMed Central

Lotto, R. Beau; Williams, S. Mark; Purves, Dale

1999-01-01

Mach bands, the illusory brightness maxima and minima perceived at the initiation and termination of luminance gradients, respectively, are generally considered a direct perceptual manifestation of lateral inhibitory interactions among retinal or other lower order visual neurons. Here we examine an alternative explanation, namely that Mach bands arise as a consequence of real-world luminance gradients. In this first of two companion papers, we analyze the natural sources of luminance gradients, demonstrating that real-world gradients arising from curved surfaces are ordinarily adorned by photometric highlights and lowlights in the position of the illusory bands. The prevalence of such gradients provides an empirical basis for the generation of this perceptual phenomenon. PMID:10220450

Geophysical logging of bedrock wells for geothermal gradient characterization in New Hampshire, 2013

USGS Publications Warehouse

Degnan, James R.; Barker, Gregory; Olson, Neil; Wilder, Leland

2014-01-01

Maximum groundwater temperatures at the bottom of the logs ranged from 11.2 to 15.4 degrees Celsius. Geothermal gradients were generally higher than those typically reported for other water wells in the United States. Some of the high gradients were associated with high natural gamma emissions. Groundwater flow was discernible in 4 of the 10 wells studied but only obscured the part of the geothermal gradient signal where groundwater actually flowed into, out of, or through the well. Temperature gradients varied by mapped bedrock type but can also vary by localized differences in mineralogy or rock type within the wells.

Theoretical approach to oxygen atom degradation of silver

NASA Technical Reports Server (NTRS)

Fromhold, Albert T., Jr.; Noh, Seung; Beshears, Ronald; Whitaker, Ann F.; Little, Sally A.

1987-01-01

Based on available Rutherford backscattering spectrometry (RBS), proton induced X-ray emission (PIXE) and ellipsometry data obtained on silver specimens subjected to atomic oxygen attack in low Earth orbit STS flight 41-G, a theory was developed to model the oxygen atom degradation of silver. The diffusion of atomic oxygen in a microscopically nonuniform medium is an essential constituent of the theory. The driving force for diffusion is the macroscopic electrochemical potential gradient developed between the specimen surface exposed to the ambient and the bulk of the silver specimen. The longitudinal electric effect developed parallel to the gradient is modified by space charge of the diffusing charged species. Lateral electric fields and concentration differences also exist due to the nonuniform nature of the medium. The lateral concentration differences are found to be more important than the lateral electric fields in modifying the diffusion rate. The model was evaluated numerically. Qualitative agreement exists between the kinetics predicted by the theory and kinetic data taken in ground-based experiments utilizing a plasma asher.

Study of high viscous multiphase phase flow in a horizontal pipe

NASA Astrophysics Data System (ADS)

Baba, Yahaya D.; Aliyu, Aliyu M.; Archibong, Archibong-Eso; Almabrok, Almabrok A.; Igbafe, A. I.

2018-03-01

Heavy oil accounts for a major portion of the world's total oil reserves. Its production and transportation through pipelines is beset with great challenges due to its highly viscous nature. This paper studies the effects of high viscosity on heavy oil two-phase flow characteristics such as pressure gradient, liquid holdup, slug liquid holdup, slug frequency and slug liquid holdup using an advanced instrumentation (i.e. Electrical Capacitance Tomography). Experiments were conducted in a horizontal flow loop with a pipe internal diameter (ID) of 0.0762 m; larger than most reported in the open literature for heavy oil flow. Mineral oil of 1.0-5.0 Pa.s viscosity range and compressed air were used as the liquid and gas phases respectively. Pressure gradient (measured by means differential pressure transducers) and mean liquid holdup was observed to increase as viscosity of oil is increased. Obtained results also revealed that increase in liquid viscosity has significant effects on flow pattern and slug flow features.

Changes in the selection differential exerted on a marine snail during the ontogeny of a predatory shore crab.

PubMed

Pakes, D; Boulding, E G

2010-08-01

Empirical estimates of selection gradients caused by predators are common, yet no one has quantified how these estimates vary with predator ontogeny. We used logistic regression to investigate how selection on gastropod shell thickness changed with predator size. Only small and medium purple shore crabs (Hemigrapsus nudus) exerted a linear selection gradient for increased shell-thickness within a single population of the intertidal snail (Littorina subrotundata). The shape of the fitness function for shell thickness was confirmed to be linear for small and medium crabs but was humped for large male crabs, suggesting no directional selection. A second experiment using two prey species to amplify shell thickness differences established that the selection differential on adult snails decreased linearly as crab size increased. We observed differences in size distribution and sex ratios among three natural shore crab populations that may cause spatial and temporal variation in predator-mediated selection on local snail populations.

In vitro quantitative analysis of Salmonella typhimurium preference for amino acids secreted by human breast tumor

NASA Astrophysics Data System (ADS)

Choi, Eunpyo; Maeng, Bohee; Lee, Jae-hun; Chang, Hyung-kwan; Park, Jungyul

2016-12-01

Bacterial therapies have been paid significant attentions by their ability to penetrate deep into the solid tumor tissue and its propensity to naturally accumulate in tumors of living animals. Understanding the actual mechanism for bacteria to target the tumor is therapeutically crucial but is poorly understood. We hypothesized that amino acids released from the specific tumors induced bacteria to those tumors and the experiments for chemotactic response of bacteria toward the cancer secreting amino acids was then performed by using the diffusion based multiple chemical gradient generator constructed by in situ self-assembly of microspheres. The quantitative analysis was carried out by comparison of intensity using green fluorescent protein (GFP) tagged Salmonella typhimurium ( S. typhimurium) in the gradient generator, which showed the clear preference to the released amino acids, especially from breast cancer patients. The understanding chemotaxis toward the cancer secreting amino acids is essential for controlling S. typhimurium targeting in tumors and will allow for the development of bacterial therapies.

Observation of 690 MV m -1 Electron Accelerating Gradient with a Laser-Driven Dielectric Microstructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wootton, K. P.; Wu, Z.; Cowan, B. M.

Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. In this work, experimental results are presented of relativistic electron acceleration with 690±100 MVm -1 gradient. This is a record-high accelerating gradient for a dielectric microstructure accelerator, nearly doubling the previous record gradient. To reach higher acceleration gradients the present experiment employs 90 fs duration laser pulses.

Chemotaxis of Molecular Dyes in Polymer Gradients in Solution.

PubMed

Guha, Rajarshi; Mohajerani, Farzad; Collins, Matthew; Ghosh, Subhadip; Sen, Ayusman; Velegol, Darrell

2017-11-08

Chemotaxis provides a mechanism for directing the transport of molecules along chemical gradients. Here, we show the chemotactic migration of dye molecules in response to the gradients of several different neutral polymers. The magnitude of chemotactic response depends on the structure of the monomer, polymer molecular weight and concentration, and the nature of the solvent. The mechanism involves cross-diffusion up the polymer gradient, driven by favorable dye-polymer interaction. Modeling allows us to quantitatively evaluate the strength of the interaction and the effect of the various parameters that govern chemotaxis.

Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds

NASA Astrophysics Data System (ADS)

Rodgers, K. B.; Mikaloff-Fletcher, S. E.; Bianchi, D.; Beaulieu, C.; Galbraith, E. D.; Gnanadesikan, A.; Hogg, A. G.; Iudicone, D.; Lintner, B. R.; Naegler, T.; Reimer, P. J.; Sarmiento, J. L.; Slater, R. D.

2011-10-01

Tree ring Δ14C data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric Δ14C varied on multi-decadal to centennial timescales, in both hemispheres, over the period between AD 950 and 1830. The Northern and Southern Hemispheric Δ14C records display similar variability, but from the data alone is it not clear whether these variations are driven by the production of 14C in the stratosphere (Stuiver and Quay, 1980) or by perturbations to exchanges between carbon reservoirs (Siegenthaler et al., 1980). As the sea-air flux of 14CO2 has a clear maximum in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the interhemispheric gradient. In this study, model simulations are used to show that Southern Ocean winds are likely a main driver of the observed variability in the interhemispheric gradient over AD 950-1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980-2004). This interpretation also implies that there may have been a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds at the Medieval Climate Anomaly to Little Ice Age transition remain unknown. Our process-focused suite of perturbation experiments with models raises the possibility that the current generation of coupled climate and earth system models may underestimate the natural background multi-decadal- to centennial-timescale variations in the winds over the Southern Ocean.

Field-scale Prediction of Enhanced DNAPL Dissolution Using Partitioning Tracers and Flow Pattern Effects

NASA Astrophysics Data System (ADS)

Wang, F.; Annable, M. D.; Jawitz, J. W.

2012-12-01

The equilibrium streamtube model (EST) has demonstrated the ability to accurately predict dense nonaqueous phase liquid (DNAPL) dissolution in laboratory experiments and numerical simulations. Here the model is applied to predict DNAPL dissolution at a PCE-contaminated dry cleaner site, located in Jacksonville, Florida. The EST is an analytical solution with field-measurable input parameters. Here, measured data from a field-scale partitioning tracer test were used to parameterize the EST model and the predicted PCE dissolution was compared to measured data from an in-situ alcohol (ethanol) flood. In addition, a simulated partitioning tracer test from a calibrated spatially explicit multiphase flow model (UTCHEM) was also used to parameterize the EST analytical solution. The ethanol prediction based on both the field partitioning tracer test and the UTCHEM tracer test simulation closely matched the field data. The PCE EST prediction showed a peak shift to an earlier arrival time that was concluded to be caused by well screen interval differences between the field tracer test and alcohol flood. This observation was based on a modeling assessment of potential factors that may influence predictions by using UTCHEM simulations. The imposed injection and pumping flow pattern at this site for both the partitioning tracer test and alcohol flood was more complex than the natural gradient flow pattern (NGFP). Both the EST model and UTCHEM were also used to predict PCE dissolution under natural gradient conditions, with much simpler flow patterns than the forced-gradient double five spot of the alcohol flood. The NGFP predictions based on parameters determined from tracer tests conducted with complex flow patterns underestimated PCE concentrations and total mass removal. This suggests that the flow patterns influence aqueous dissolution and that the aqueous dissolution under the NGFP is more efficient than dissolution under complex flow patterns.

Refractive index-based detection of gradient elution liquid chromatography using chip-integrated microring resonator arrays.

PubMed

Wade, James H; Bailey, Ryan C

2014-01-07

Refractive index-based sensors offer attractive characteristics as nondestructive and universal detectors for liquid chromatographic separations, but a small dynamic range and sensitivity to minor thermal perturbations limit the utility of commercial RI detectors for many potential applications, especially those requiring the use of gradient elutions. As such, RI detectors find use almost exclusively in sample abundant, isocratic separations when interfaced with high-performance liquid chromatography. Silicon photonic microring resonators are refractive index-sensitive optical devices that feature good sensitivity and tremendous dynamic range. The large dynamic range of microring resonators allows the sensors to function across a wide spectrum of refractive indices, such as that encountered when moving from an aqueous to organic mobile phase during a gradient elution, a key analytical advantage not supported in commercial RI detectors. Microrings are easily configured into sensor arrays, and chip-integrated control microrings enable real-time corrections of thermal drift. Thermal controls allow for analyses at any temperature and, in the absence of rigorous temperature control, obviates extended detector equilibration wait times. Herein, proof of concept isocratic and gradient elution separations were performed using well-characterized model analytes (e.g., caffeine, ibuprofen) in both neat buffer and more complex sample matrices. These experiments demonstrate the ability of microring arrays to perform isocratic and gradient elutions under ambient conditions, avoiding two major limitations of commercial RI-based detectors and maintaining comparable bulk RI sensitivity. Further benefit may be realized in the future through selective surface functionalization to impart degrees of postcolumn (bio)molecular specificity at the detection phase of a separation. The chip-based and microscale nature of microring resonators also make it an attractive potential detection technology that could be integrated within lab-on-a-chip and microfluidic separation devices.

Personal semantic and episodic autobiographical memories in Korsakoff syndrome: A comparison of interview methods.

PubMed

Rensen, Yvonne C M; Kessels, Roy P C; Migo, Ellen M; Wester, Arie J; Eling, Paul A T M; Kopelman, Michael D

2017-08-01

The temporal gradient in patients with Korsakoff's syndrome has been of particular interest in the literature, as many studies have found evidence for a steep temporal gradient, but others have observed more uniform remote memory impairment across all past time periods. Inconsistencies might be the result of the nature of remote memory impairment under study (i.e., nonpersonal or autobiographical memory) and of methodological differences in the examination of remote memory loss. The aim of this study was to examine whether differences between autobiographical memory interview (AMI) and autobiographical interview (AI) procedures influence the presence of a temporal gradient in semantic and episodic autobiographical memory in Korsakoff patients. The procedure used in the present study combined the AMI and AI into one study session. We compared the performance of 20 patients with Korsakoff's syndrome and 27 healthy controls. First, participants were asked to recall knowledge from different life periods. Second, participants were asked to recall memories from five life periods. Thirdly, participants were asked to rate their subjective experience of each event recalled on a 5-point scale. Finally, we analyzed the findings in terms of all the memories recalled versus the first memory from each life-period only. Both the AMI and the AI showed a temporally graded retrograde amnesia in the Korsakoff patients for personal semantic and episodic autobiographical memories. The pattern of amnesia in Korsakoff patients was not affected by examining only one event per life-period. Subjective ratings of recalled memories were largely comparable between the groups. The findings were generally consistent across the AMI and AI. Varying the number of events did not affect the pattern of the gradient. Hence, the temporal gradient in Korsakoff patients is not an artefact of either the AMI or the AI method.

Microbial mediated soil structure formation under wetting and drying cycles along a climate gradient (arid to humid) on hillslopes in Chile

NASA Astrophysics Data System (ADS)

Bernhard, Nadine; Moskwa, Lisa-Marie; Kühn, Peter; Mueller, Carsten W.; Wagner, Dirk; Scholten, Thomas

2017-04-01

It is well-known that the land surface resistance against erosion is largely controlled by the structure stability of the soil given by its inherent properties. Microbial activity plays a vital role in soil structure development, and thus affecting soil physical parameters. Accordingly the influence of biota shaping the earth's surface has been described through mechanisms such as mineral weathering, formation of ions and biofilms controlling land surface resistance against erosion. However the role of microorganisms for the development of soil stabilizing properties is still unclear and a precise quantitative understanding of the mechanisms under different climate conditions is widely missing. The objectives of our study are to examine to which extend microbiological processes control soil structure formation and stability and whether this is influenced by climate and topographic position. Soil samples were taken along a climate gradient and from different topographic positions of hillslopes in the Chilean Coastal Cordillera in austral autumn 2016. The variables of lithology, human disturbances and relief were held as far as possible constant whereas climate varies along the transect. We implemented 10 wet-dry cycles on air dried and sieved natural and sterile samples to enhance particle aggregation and increase structure stability. Throughout the entire experiment temperature is held constant at 20 °C to avoid changes in microbial activity. Samples are moistened and dried and each kept at the same respective pF-values for the same duration to add the same stress to each sample. Aggregate stability will be measured using wet sieving, ultrasonic dispersion and simulated rainfall. The results will be compared with on-site rainfall simulation experiments on hillslopes in the Chilean Coastal Cordillera to link laboratory results with natural field conditions. The experiment gives first insight into the aggregate formation process over time with and without microorganisms (sterilized samples). Furthermore it allows to qualify and quantify the contribution of biota to soil structure formation and stability.

Atmospheric gradients from very long baseline interferometry observations

NASA Technical Reports Server (NTRS)

Macmillan, D. S.

1995-01-01

Azimuthal asymmetries in the atmospheric refractive index can lead to errors in estimated vertical and horizontal station coordinates. Daily average gradient effects can be as large as 50 mm of delay at a 7 deg elevation. To model gradients, the constrained estimation of gradient paramters was added to the standard VLBI solution procedure. Here the analysis of two sets of data is summarized: the set of all geodetic VLBI experiments from 1990-1993 and a series of 12 state-of-the-art R&D experiments run on consecutive days in January 1994. In both cases, when the gradient parameters are estimated, the overall fit of the geodetic solution is improved at greater than the 99% confidence level. Repeatabilities of baseline lengths ranging up to 11,000 km are improved by 1 to 8 mm in a root-sum-square sense. This varies from about 20% to 40% of the total baseline length scatter without gradient modeling for the 1990-1993 series and 40% to 50% for the January series. Gradients estimated independently for each day as a piecewise linear function are mostly continuous from day to day within their formal uncertainties.

Transverse spin relaxation and diffusion-constant measurements of spin-polarized 129Xe nuclei in the presence of a magnetic field gradient

PubMed Central

Liu, Xiaohu; Chen, Chang; Qu, Tianliang; Yang, Kaiyong; Luo, Hui

2016-01-01

The presence of a magnetic field gradient in a sample cell containing spin-polarized 129Xe atoms will cause an increased relaxation rate. We measured the transverse spin relaxation time of 129Xe verse the applied magnetic field gradient and the cell temperature. We then compared the different transverse spin relaxation behavior of dual isotopes of xenon (129Xe and 131Xe) due to magnetic field gradient in the same cell. The experiment results show the residual magnetic field gradient can be measured and compensated by applying a negative magnetic gradient in the sample cell. The transverse spin relaxation time of 129Xe could be increased 2–7 times longer when applying an appropriate magnetic field gradient. The experiment results can also be used to determine the diffusion constant of 129Xe in H2 and N2 to be 0.4 ± 0.26 cm2/sec and 0.12 ± 0.02 cm2/sec. The results are close with theoretical calculation. PMID:27049237

Transport of Chemotactic Bacteria in Porous Media with Structured Heterogeneity

NASA Astrophysics Data System (ADS)

Ford, R. M.; Wang, M.; Liu, J.; Long, T.

2008-12-01

Chemical contaminants that become trapped in low permeability zones (e.g. clay lenses) are difficult to remediate using conventional pump-and-treat approaches. Chemotactic bacteria that are transported by groundwater through more permeable regions may migrate toward these less permeable zones in response to chemical gradients created by contaminant diffusion from the low permeability source, thereby enhancing the remediation process by directing bacteria to the contaminants they degrade. What effect does the heterogeneity associated with coarse- and fine-grained layers that are characteristic of natural groundwater environments have on the transport of microorganisms and their chemotactic response? To address this question experiments were conducted over a range of scales from a single capillary tube to a laboratory- scale column in both static and flowing systems with and without chemoattractant gradients. In static capillary assays, motile bacteria accumulated at the interface between an aqueous solution and a suspension of agarose particulates. In microfluidic devices with an array of staggered cylinders, chemotactic bacteria migrated transverse to flow in response to a chemoattractant gradient. In sand columns packed with a coarse-grained core and surrounded by a fine-grained annulus, chemotactic bacteria migrated preferentially toward a chemoattractant source along the centerline. Mathematical models and computer simulations were developed to analyze the experimental observations in terms of transport parameters from the advection- disperson-sorption equation.

Deviation from niche optima affects the nature of plant–plant interactions along a soil acidity gradient

PubMed Central

He, Lei; Cheng, Lulu; Hu, Liangliang; Tang, Jianjun; Chen, Xin

2016-01-01

There is increasing recognition of the importance of niche optima in the shift of plant–plant interactions along environmental stress gradients. Here, we investigate whether deviation from niche optima would affect the outcome of plant–plant interactions along a soil acidity gradient (pH = 3.1, 4.1, 5.5 and 6.1) in a pot experiment. We used the acid-tolerant species Lespedeza formosa Koehne as the neighbouring plant and the acid-tolerant species Indigofera pseudotinctoria Mats. or acid-sensitive species Medicago sativa L. as the target plants. Biomass was used to determine the optimal pH and to calculate the relative interaction index (RII). We found that the relationships between RII and the deviation of soil pH from the target's optimal pH were linear for both target species. Both targets were increasingly promoted by the neighbour as pH values deviated from their optima; neighbours benefitted target plants by promoting soil symbiotic arbuscular mycorrhizal fungi, increasing soil organic matter or reducing soil exchangeable aluminium. Our results suggest that the shape of the curve describing the relationship between soil pH and facilitation/competition depends on the soil pH optima of the particular species. PMID:26740568

Cannibalism and activity rate in larval damselflies increase along a latitudinal gradient as a consequence of time constraints.

PubMed

Sniegula, Szymon; Golab, Maria J; Johansson, Frank

2017-07-14

Predation is ubiquitous in nature. One form of predation is cannibalism, which is affected by many factors such as size structure and resource density. However, cannibalism may also be influenced by abiotic factors such as seasonal time constraints. Since time constraints are greater at high latitudes, cannibalism could be stronger at such latitudes, but we know next to nothing about latitudinal variation in cannibalism. In this study, we examined cannibalism and activity in larvae of the damselfly Lestes sponsa along a latitudinal gradient across Europe. We did this by raising larvae from the egg stage at different temperatures and photoperiods corresponding to different latitudes. We found that the more seasonally time-constrained populations in northern latitudes and individuals subjected to greater seasonal time constraints exhibited a higher level of cannibalism. We also found that activity was higher at north latitude conditions, and thus correlated with cannibalism, suggesting that this behaviour mediates higher levels of cannibalism in time-constrained animals. Our results go counter to the classical latitude-predation pattern which predicts higher predation at lower latitudes, since we found that predation was stronger at higher latitudes. The differences in cannibalism might have implications for population dynamics along the latitudinal gradients, but further experiments are needed to explore this.

Supercritical Fluid Chromatography of Drugs: Parallel Factor Analysis for Column Testing in a Wide Range of Operational Conditions

PubMed Central

Al-Degs, Yahya; Andri, Bertyl; Thiébaut, Didier; Vial, Jérôme

2017-01-01

Retention mechanisms involved in supercritical fluid chromatography (SFC) are influenced by interdependent parameters (temperature, pressure, chemistry of the mobile phase, and nature of the stationary phase), a complexity which makes the selection of a proper stationary phase for a given separation a challenging step. For the first time in SFC studies, Parallel Factor Analysis (PARAFAC) was employed to evaluate the chromatographic behavior of eight different stationary phases in a wide range of chromatographic conditions (temperature, pressure, and gradient elution composition). Design of Experiment was used to optimize experiments involving 14 pharmaceutical compounds present in biological and/or environmental samples and with dissimilar physicochemical properties. The results showed the superiority of PARAFAC for the analysis of the three-way (column × drug × condition) data array over unfolding the multiway array to matrices and performing several classical principal component analyses. Thanks to the PARAFAC components, similarity in columns' function, chromatographic trend of drugs, and correlation between separation conditions could be simply depicted: columns were grouped according to their H-bonding forces, while gradient composition was dominating for condition classification. Also, the number of drugs could be efficiently reduced for columns classification as some of them exhibited a similar behavior, as shown by hierarchical clustering based on PARAFAC components. PMID:28695040

Cover of coastal vegetation as an indicator of eutrophication along environmental gradients.

PubMed

Wikström, Sofia A; Carstensen, Jacob; Blomqvist, Mats; Krause-Jensen, Dorte

2016-01-01

Coastal vegetation communities are important for primary production, biodiversity, coastal protection, carbon and nutrient cycling which, in combination with their sensitivity to eutrophication, render them potential indicators of environmental status for environmental policies like the EU Water and Marine Strategy Framework Directives. We evaluated one potential indicator for coastal vegetation, the cumulative cover at depths where the vegetation is light limited, by investigating its response to eutrophication along gradients in natural conditions. We used a large data set covering the Swedish coastline, spanning broad gradients in nutrient level, water clarity, seabed substrate, physical exposure and climate in addition to a salinity gradient from 0.5 to 30.5. Macroalgal cover increased significantly along gradients of declining nutrient concentration and increasing water clarity when we had accounted for diver effects, spatio-temporal sampling variability, salinity gradients, wave exposure and latitude. The developed empirical model explained 79% of the variation in algal cover across 130 areas. Based on this, we identified macroalgal cover as a promising indicator across the Baltic Sea, Kattegat and Skagerrak. A parallel analysis of soft-substrate macrophytes similarly identified significant increases in cover with decreasing concentrations of total nitrogen and increasing salinity, but the resulting empirical model explained only 52% of the variation in cover, probably due to the spatially more variable nature of soft-substrate vegetation. The identified general responses of vegetation cover to gradients of eutrophication across wide ranges in environmental settings may be useful for monitoring and management of marine vegetation in areas with strong environmental gradients.

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. Copyright © 2011. Published by Elsevier Ltd.

Floristic composition and across-track reflectance gradient in Landsat images over Amazonian forests

NASA Astrophysics Data System (ADS)

Muro, Javier; doninck, Jasper Van; Tuomisto, Hanna; Higgins, Mark A.; Moulatlet, Gabriel M.; Ruokolainen, Kalle

2016-09-01

Remotely sensed image interpretation or classification of tropical forests can be severely hampered by the effects of the bidirectional reflection distribution function (BRDF). Even for narrow swath sensors like Landsat TM/ETM+, the influence of reflectance anisotropy can be sufficiently strong to introduce a cross-track reflectance gradient. If the BRDF could be assumed to be linear for the limited swath of Landsat, it would be possible to remove this gradient during image preprocessing using a simple empirical method. However, the existence of natural gradients in reflectance caused by spatial variation in floristic composition of the forest can restrict the applicability of such simple corrections. Here we use floristic information over Peruvian and Brazilian Amazonia acquired through field surveys, complemented with information from geological maps, to investigate the interaction of real floristic gradients and the effect of reflectance anisotropy on the observed reflectances in Landsat data. In addition, we test the assumption of linearity of the BRDF for a limited swath width, and whether different primary non-inundated forest types are characterized by different magnitudes of the directional reflectance gradient. Our results show that a linear function is adequate to empirically correct for view angle effects, and that the magnitude of the across-track reflectance gradient is independent of floristic composition in the non-inundated forests we studied. This makes a routine correction of view angle effects possible. However, floristic variation complicates the issue, because different forest types have different mean reflectances. This must be taken into account when deriving the correction function in order to avoid eliminating natural gradients.

Nucleation and particle coagulation experiments in microgravity

NASA Technical Reports Server (NTRS)

Nuth, J.

1987-01-01

Measurements of the conditions under which carbon, aluminum oxide, and silicon carbide smokes condense and of the morphology and crystal structure of the resulting grains are essential if the nature of the materials ejected into the interstellar medium and the nature of the grains which eventually became part of the proto solar nebular are to be understood. Little information is currently available on the vapor-solid phase transitions of refractory metals and solids. What little experimental data do exist are, however, not in agreement with currently accepted models of the nucleation process for more volatile materials. The major obstacle to performing such experiments in earth-based laboratories is the susceptibility of these systems to convection. Evaporation of refractory materials into a low-pressure environment with a carefully controlled temperature gradient will produce refractory smokes when the critical supersaturation of the system is exceeded. Measurement of the point at which nucleation occurs, via light scattering or extinction, can not only yield nucleation data but also, information on the chemical composition and crystal structure of the condensate. Experimental requirements are presented.

The Phase Rule in a System Subject to a Pressure Gradient

NASA Astrophysics Data System (ADS)

Podladchikov, Yuri; Connolly, James; Powell, Roger; Aardvark, Alberto

2015-04-01

It can be shown by diligent application of Lagrange's method of undetermined multipliers that the phase rule in a system subject to a pressure gradient is: � + 赑 ≥ ρ. We explore the consequence of this important relationship for natural systems.

Sex differences in cue perception in a visual scene: investigation of cue type.

PubMed

Barkley, Cynthia L; Gabriel, Kara I

2007-04-01

Sex differences in spatial navigation indicate that women may focus on positional, landmark cues whereas men favor Euclidean, directional cues. Some studies have investigated sex differences in proximal and distal cue use; however, sex differences in gradient (i.e., graded features) and pinpoint (i.e., single, defined) cue perception remain unexamined. In the current experiments, paired photographs were presented in which the 2nd photograph showed the same scene with cues removed (Experiment 1) or isolated (Experiment 2) from the 1st photograph. In Experiment 1, women showed less disruption of task performance than men showed following cue removal but were slowest after proximal pinpoint cue removal. Male performance was slowed by distal gradient and proximal pinpoint cue removal. In Experiment 2, women were faster than men at identifying isolated proximal and distal pinpoint cues and were more accurate at identifying isolated distal gradient and distal pinpoint cues. Better pinpoint cue perception and memory in women indicates one possible mechanism underlying female preference for landmark-based navigation strategies. Findings also show that whereas men may preferentially rely on distal gradient cues they are not better at perceiving those cues than are women. (c) 2007 APA, all rights reserved

Phylogenetic structure of arbuscular mycorrhizal fungal communities along an elevation gradient.

PubMed

Egan, Cameron P; Callaway, Ragan M; Hart, Miranda M; Pither, Jason; Klironomos, John

2017-04-01

Despite the importance of arbuscular mycorrhizal (AM) fungi within terrestrial ecosystems, we know little about how natural AM fungal communities are structured. To date, the majority of studies examining AM fungal community diversity have focused on single habitats with similar environmental conditions, with relatively few studies having assessed the diversity of AM fungi over large-scale environmental gradients. In this study, we characterized AM fungal communities in the soil along a high-elevation gradient in the North American Rocky Mountains. We focused on phylogenetic patterns of AM fungal communities to gain insight into how AM fungal communities are naturally assembled. We found that alpine AM fungal communities had lower phylogenetic diversity relative to lower elevation communities, as well as being more heterogeneous in composition than either treeline or subalpine communities. AM fungal communities were phylogenetically clustered at all elevations sampled, suggesting that environmental filtering, either selection by host plants or fungal niches, is the primary ecological process structuring communities along the gradient.

Observations of reduced electron Gyroscale fluctuations in national spherical torus experiment H-mode plasmas with large ExB flow shear.

PubMed

Smith, D R; Kaye, S M; Lee, W; Mazzucato, E; Park, H K; Bell, R E; Domier, C W; Leblanc, B P; Levinton, F M; Luhmann, N C; Menard, J E; Yuh, H

2009-06-05

Electron gyroscale fluctuation measurements in National Spherical Torus Experiment H-mode plasmas with large toroidal rotation reveal fluctuations consistent with electron temperature gradient (ETG) turbulence. Large toroidal rotation in National Spherical Torus Experiment plasmas with neutral beam injection generates ExB flow shear rates comparable to ETG linear growth rates. Enhanced fluctuations occur when the electron temperature gradient is marginally stable with respect to the ETG linear critical gradient. Fluctuation amplitudes decrease when the ExB flow shear rate exceeds ETG linear growth rates. The observations indicate that ExB flow shear can be an effective suppression mechanism for ETG turbulence.

Erosion of volcanic ocean islands: insights from modeling, topographic analyses, and cosmogenic exposure dating

NASA Astrophysics Data System (ADS)

Huppert, K.; Perron, J. T.; Ferrier, K.; Mukhopadhyay, S.; Rosener, M.; Douglas, M.

2016-12-01

With homogeneous bedrock, dramatic rainfall gradients, paleoshorelines, and datable remnant topography, volcanic ocean islands provide an exceptional natural experiment in landscape evolution. Analyses traversing gradients in island climate and bedrock age have the potential to advance our understanding of landscape evolution in a diverse range of continental settings. However, as small, conical, dominantly subsiding, and initially highly permeable landmasses, islands are unique, and it remains unclear how these properties influence their erosional history. We use a landscape evolution model and observations from the Hawaiian island of Kaua'i and other islands to characterize the topographic evolution of volcanic ocean islands. We present new measurements of helium-3 concentrations in detrital olivine from 20 rivers on Kaua'i. These measurements indicate that minimum erosion rates over the past 3 to 48 kyr are on average 2.6 times faster than erosion rates averaged over the past 3.9 to 4.4 Myr estimated from the volume of river canyons. This apparent acceleration of erosion rates on Kaua'i is consistent with observations on other islands; erosion rates estimated from the volume of river canyons on 31 islands worldwide, combined with observations of minimal incision on young island volcanoes, suggest a progressive increase in erosion rates over the first few million years of island landscape development. Using a landscape evolution model, we perform a set of experiments to quantify the contribution of subsidence, climate change, and initial geometry to changes in island erosion rates through time. We base these experiments on the evolution of Kaua'i, and we use measured erosion rates and the observed topography to calibrate the model. We find that progressive steepening of island topography by canyon incision drives an acceleration of erosion rates over time. Increases in mean channel and hillslope gradient with island age in the global compilation suggest this may be a general trend in the topographic evolution of volcanic ocean islands.

Neuroperformance Imaging

DTIC Science & Technology

2012-10-01

EMBC10.1722. 10. Mitra, P.P., Halperin, B.I.: Effects of finite gradient-pulse widths in pulsed- field - gradient diffusion measurements . Journal of Magnetic ...December 2011 ABSTRACT: The addition of a pair of magnetic field gradient pulses had initially enabled the measurement of spin motion to nuclear mag- netic...introduced a pair of (homogenous) magnetic field gradients into the spin echo experi- ment with the purpose of accurately measuring the scalar diffusion

Application of the conjugate-gradient method to ground-water models

USGS Publications Warehouse

Manteuffel, T.A.; Grove, D.B.; Konikow, Leonard F.

1984-01-01

The conjugate-gradient method can solve efficiently and accurately finite-difference approximations to the ground-water flow equation. An aquifer-simulation model using the conjugate-gradient method was applied to a problem of ground-water flow in an alluvial aquifer at the Rocky Mountain Arsenal, Denver, Colorado. For this application, the accuracy and efficiency of the conjugate-gradient method compared favorably with other available methods for steady-state flow. However, its efficiency relative to other available methods depends on the nature of the specific problem. The main advantage of the conjugate-gradient method is that it does not require the use of iteration parameters, thereby eliminating this partly subjective procedure. (USGS)

The influence of double-diffusive processes on the melting of ice in the Arctic Ocean: laboratory analogue experiments and their interpretation

NASA Astrophysics Data System (ADS)

Turner, J. S.; Veronis, G.

2004-03-01

This study has been motivated by two oceanographic observations: an increased rate of melting of sea ice in the Arctic Ocean, and the advance of an anomalously warm tongue of Atlantic water across the Arctic below the halocline over the last few decades. A series of laboratory experiments has been carried out in order to explore the physical principles underlying these phenomena, and the possibility that the extra heating at depth is responsible for the enhanced melting rate. A tank was filled with salt solution having various constant vertical density gradients. A block of ice one third of the length of the tank was floated on the surface at one end, and the rest of the surface and the walls of the tank were insulated. When no extra heat was supplied the melting rate (loss of weight of the ice in 1 h) systematically decreased as the stratification was changed from homogeneous fluid to increasingly large density gradients, while keeping the salinity of the solution in contact with the ice constant. An analogue of the intruding Atlantic water was produced by heating the lower portion of the vertical end wall at the end of the tank opposite to the ice end, keeping its temperature constant, and using the same range of salinity gradients as in the unheated experiments. Again the melting rate decreased as the density gradient was increased, but for low gradients it was larger than that in the unheated experiments. Above a certain intermediate gradient there was no significant difference in melting rate between the unheated and heated runs. The melting data were supplemented by photographs and vertical temperature and salinity profiles. The upward transfer of heat from the body of the fluid to melt the ice was clearly double-diffusive: overturning layers, separated by 'diffusive' interfaces, were visible on shadowgraphs, and the thickness of the layers decreased as the density gradient increased. The mean thickness of the layers through the depth of the tank also systematically decreased as the density gradient increased. With weak gradients an extra heat flux to the ice came from the intruding heated layer, but at large gradients this tongue of warm water at depth did not add to the flux near the surface. Though they were obtained in a simple, arbitrary and fixed geometry, we believe that the results of these experiments can be used as the basis for a better physical understanding of the melting rates of ice in the Arctic under various conditions.

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)

The Goldilocks Principle and Rapid Evolution of Antibiotic Resistance in Bacteria

NASA Astrophysics Data System (ADS)

Zhang, Qiucen; Austin, Robert

2011-03-01

Goldilocks sampled the three bear's wares for the ``just right'' combination of taste, fit and comfort. Like Goldilocks's need for the just right parameters, evolution proceeds most rapidly when there is the just right combination of a large number of mutants and rapid fixation of the mutants. We show here using a two-dimensional micro-ecology that it is possible to fix resistance to the powerful antibiotic ciprofloxacin (Cipro) in wild-type E. coli in 10 hours through a combination of extremely high population gradients, which generate rapid fixation, convolved with the just right level of antibiotic which generates a large number of mutants and the motility of the organism. Although evolution occurs in well-stirred chemostats without such Goldilocks conditions, natural environments are rarely well stirred in nature.For complex environments such as the Galapagos Islands, spatial population gradients and movement of mutants along these population gradients can be as important as genomic heterogeneity in setting the speed of evolution. The design of our micro-ecology is unique in that it provides two overlapping gradients, one an emergent and self generated bacterial population gradient due to food restriction and the other a mutagenic antibiotic gradient. Further, it exploits the motility of the bacteria moving across these gradients to drive the rate of resistance to Cipro to extraordinarily high rates. The research described was supported by Award Number U54CA143803 from the National Cancer Institute.

Experimental and observational studies find contrasting responses of soil nutrients to climate change

PubMed Central

Yuan, ZY; Jiao, F; Shi, XR; Sardans, Jordi; Maestre, Fernando T; Delgado-Baquerizo, Manuel; Reich, Peter B; Peñuelas, Josep

2017-01-01

Manipulative experiments and observations along environmental gradients, the two most common approaches to evaluate the impacts of climate change on nutrient cycling, are generally assumed to produce similar results, but this assumption has rarely been tested. We did so by conducting a meta-analysis and found that soil nutrients responded differentially to drivers of climate change depending on the approach considered. Soil carbon, nitrogen, and phosphorus concentrations generally decreased with water addition in manipulative experiments but increased with annual precipitation along environmental gradients. Different patterns were also observed between warming experiments and temperature gradients. Our findings provide evidence of inconsistent results and suggest that manipulative experiments may be better predictors of the causal impacts of short-term (months to years) climate change on soil nutrients but environmental gradients may provide better information for long-term correlations (centuries to millennia) between these nutrients and climatic features. Ecosystem models should consequently incorporate both experimental and observational data to properly assess the impacts of climate change on nutrient cycling. DOI: http://dx.doi.org/10.7554/eLife.23255.001 PMID:28570219

Minimising the Residual Field and Field Gradient in a Magnetically Shielded Room for an nEDM experiment at Los Alamos National Laboratory

NASA Astrophysics Data System (ADS)

Amarasinghe, Chamindu; LANL nEDM Collaboration

2017-09-01

The LANL neutron Electric Dipole Moment (nEDM) experiment is an effort to set a sensitivity limit of 3.2 × 10-27 e cm on the electric dipole moment of the neutron, an order of magnitude smaller than the current upper limit. This measurement uses Ramsey's method of oscillating magnetic fields. The magnetic field and field gradient have to be low enough to avoid the smearing of the Ramsey fringes and to increase the neutron dephasing time respectively. The experiment is enclosed in a two layer Mu-metal magnetically shielded room (MSR) to null any external magnetic fields from the environment. The MSR is degaussed to sufficiently reduce its residual magnetic field and field gradient. The MSR is designed for residual fields as low as 30 nT. The experiment further requires a field gradient of 1 nT/m or smaller. Here we report on the degaussing procedure and the resulting improvement in the shielding prowess of the MSR. Funded by an NSF Grant.

Experiments on Electron-Plasma Vortex Motion Driven by a Background Vorticity Gradient.

NASA Astrophysics Data System (ADS)

Kabantsev, A. A.; Driscoll, C. F.

2000-10-01

The interaction of self-trapped vortices with a background vorticity gradient plays an important role in 2D hydrodynamics, including various aspects of relaxation and self-organization of 2D turbulence. In the present experiments, electron plasma columns with monotonically decreasing density profiles provide a vorticity background with (negative) shear in the rotational flow. Clumps of extra electrons are then retrograde vortices, rotating against the background shear; and regions with a deficit of electrons (holes) are prograde vortices. Theory predicts that clumps move up the background gradient, and holes move down the gradient, with velocities which depend differently on the ratio of the vortex trapping length to vortex radius, l / r_v. The present experiments show quantitative agreement with recent theory and simulations,(D.A. Schecter and D.H.E. Dubin, Phys. Rev. Lett. 83), 2191 (1999). for the accessible regime of 0.2 < l/rv < 2. The experiments also show that moving clumps leave a spiral density wake, and that instability of these wakes results in a large number of long-lived holes.

Local adaptation to temperature conserves top-down control in a grassland food web.

PubMed

Barton, Brandon T

2011-10-22

A fundamental limitation in many climate change experiments is that tests represent relatively short-term 'shock' experiments and so do not incorporate the phenotypic plasticity or evolutionary change that may occur during the gradual process of climate change. However, capturing this aspect of climate change effects in an experimental design is a difficult challenge that few studies have accomplished. I examined the effect of temperature and predator climate history in food webs composed of herbaceous plants, generalist grasshopper herbivores and spider predators across a natural 4.8°C temperature gradient spanning 500 km in northeastern USA. In these grasslands, the effects of rising temperatures on the plant community are indirect and arise via altered predator-herbivore interactions. Experimental warming had no direct effect on grasshoppers, but reduced predation risk effects by causing spiders from all study sites to seek thermal refuge lower in the plant canopy. However, spider thermal tolerance corresponded to spider origin such that spiders from warmer study sites tolerated higher temperatures than spiders from cooler study sites. As a consequence, the magnitude of the indirect effect of spiders on plants did not differ along the temperature gradient, although a reciprocal transplant experiment revealed significantly different effects of spider origin on the magnitude of top-down control. These results suggest that variation in predator response to warming may maintain species interactions and associated food web processes when faced with long term, chronic climate warming.

¹⁴N Quadrupole Resonance line broadening due to the earth magnetic field, occuring only in the case of an axially symmetric electric field gradient tensor.

PubMed

Aissani, Sarra; Guendouz, Laouès; Marande, Pierre-Louis; Canet, Daniel

2015-01-01

As demonstrated before, the application of a weak static B0 magnetic field (less than 10 G) may produce definite effects on the ¹⁴N Quadrupole Resonance line when the electric field gradient tensor at the nitrogen nucleus level is of axial symmetry. Here, we address more precisely the problem of the relative orientation of the two magnetic fields (the static field and the radio-frequency field of the pure NQR experiment). For a field of 6G, the evolution of the signal intensity, as a function of this relative orientation, is in very good agreement with the theoretical predictions. There is in particular an intensity loss by a factor of three when going from the parallel configuration to the perpendicular configuration. By contrast, when dealing with a very weak magnetic field (as the earth field, around 0.5 G), this effect drops to ca. 1.5 in the case Hexamethylenetetramine (HMT).This is explained by the fact that the Zeeman shift (due to the very weak magnetic field) becomes comparable to the natural line-width. The latter can therefore be determined by accounting for this competition. Still in the case of HMT, the estimated natural line-width is half the observed line-width. The extra broadening is thus attributed to earth magnetic field. The latter constitutes therefore the main cause of the difference between the natural transverse relaxation time (T₂) and the transverse relaxation time derived from the observed line-width (T₂(⁎)). Copyright © 2015 Elsevier Inc. All rights reserved.

Birth-order differences can drive natural selection on aging.

PubMed

Gillespie, Duncan O S; Trotter, Meredith V; Krishna-Kumar, Siddharth; Tuljapurkar, Shripad D

2014-03-01

Senescence-the deterioration of survival and reproductive capacity with increasing age-is generally held to be an evolutionary consequence of the declining strength of natural selection with increasing age. The diversity in rates of aging observed in nature suggests that the rate at which age-specific selection weakens is determined by species-specific ecological factors. We propose that, in iteroparous species, relationships between parental age, offspring birth order, and environment may affect selection on senescence. Later-born siblings have, on average, older parents than do first borns. Offspring born to older parents may experience different environments in terms of family support or inherited resources, factors often mediated by competition from siblings. Thus, age-specific selection on parents may change if the environment produces birth-order related gradients in reproductive success. We use an age-and-stage structured population model to investigate the impact of sibling environmental inequality on the expected evolution of senescence. We show that accelerated senescence evolves when later-born siblings are likely to experience an environment detrimental to lifetime reproduction. In general, sibling inequality is likely to be of particular importance for the evolution of senescence in species such as humans, where family interactions and resource inheritance have important roles in determining lifetime reproduction. © 2013 The Author(s). Evolution © 2013 The Society for the Study of Evolution.

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)

Inequalities in dental caries experience among 4-year-old New Zealand children.

PubMed

Shackleton, Nichola; Broadbent, Jonathan M; Thornley, Simon; Milne, Barry J; Crengle, Sue; Exeter, Daniel J

2018-06-01

To investigate ethnic-specific deprivation gradients in early childhood dental caries experience considering different domains of deprivation. We used cross-sectional near whole population-level data on 318 321 four-year-olds attending the "B4 School check," a national health and development check in New Zealand, across 6 fiscal years (2010/2011 to 2015/2016). The "lift the lip" screening tool was used to estimate experience of any caries and severe caries. We investigated deprivation gradients using the Index of Multiple Deprivation (IMD), which measures seven domains of deprivation across 5958 geographical areas ("data zones"). Ethnicity was categorized into five groups: (i) Māori, (ii) Pacific, (iii) Asian, (iv) Middle Eastern, Latin American and African (MELAA) and (v) European & Other (combined). We used a random intercepts model to estimate mutually adjusted associations between deprivation, ethnicity, age, fiscal year, and evidence of any dental caries experience. Reports of any caries experience decreased from 15.8% (95% CI: 15.7; 15.9%) to 14.7% 95% CI: 14.4; 14.8%), while reports of severe caries experience increased from 3.0% (95% CI: 3.0; 3.1%) to 4.4% (95% CI: 4.3; 4.5%) from 2010/2011 to 2015/2016. This varied by ethnicity with larger increases in severe caries for Pacific children from 7.1% (95% CI: 6.8; 7.4%) to 14.1% (95% CI: 13.7; 14.5%). There were deprivation gradients in dental caries experience with considerable variation by ethnicity and by domain of deprivation. The association between deprivation and dental caries experience was weakest for Asian children and was most pronounced for Pacific and Māori children. Socioeconomic gradients in dental caries experience are evident by age 4 years, and these gradients vary by ethnicity and domain of deprivation. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Drought as a modifier of interaction between adult beech and spruce - impacts on tree water use, C budgets and biotic interactions above- and belowground

NASA Astrophysics Data System (ADS)

Grams, Thorsten

2017-04-01

Understanding biotic interactions among tree species with their microbial associates under drought will be crucial for silviculture in meeting ecological challenges of the future. This contribution gives an overview on a project integrating a throughfall-exclusion experiment (TEE) on adult trees with a natural precipitation gradient (PGR) in central European forests. Focus is on drought affecting species interaction above and belowground, including associated ectomycorrhizal (ECM) communities. Study objects are pure and mixed forests dominated by adult European beech and Norway spruce trees (c. 70-years old). At the throughfall-exclusion experiment (TEE), trees are readily accessible via scaffolding and canopy crane (Kranzberg Forest, southern Germany). Effects of experimentally induced, repeated summer drought are assessed with roughly 100 trees assigned to a total of 12 plots (Kranzberg forest ROOF experiment, kroof.wzw.tum.de). The summer drought treatment started in 2014 and was repeated in 2015 and 2106. The focus on species interaction is intensified by a parallel study along a natural precipitation gradient with plot triplets of monocultures and mixed cultures of European beech and Norway spruce at each of the five study sites. Complementary resource use, effects of competitive vs. facilitation and related changes in ECM communities are exemplified for the two tree species of contrasting foliage (i.e. deciduous vs. evergreen) and stomatal sensitivity to drought (i.e. an-isohydric vs. isohydric behavior). At the TEE site, precipitation throughfall was completely excluded from early spring to late fall (i.e. March to November), resulting in pre-dawn leaf water potentials of both beech and spruce as low as -2.5 MPa. Despite significant reductions in growth and rate of photosynthesis by up to 80% under drought, NSC budget of trees was hardly affected. Moreover, phloem functionality, tested as phloem transport velocity through 13C-labeling of recent photoassimilates, remained unaffected. The link between photosynthesis and stem cellulose (DBH) was assessed based on natural abundance of delta13C and delta18O. Under drought, mixing of recent photoassimilates with older carbohydrates during phloem transport significantly affected isotopic signatures of transported sucrose, diminishing the impact of drought. A quantitative relationship of this mixing effect (i.e. uncoupling of photosynthetic fractionation at the leaf level and isotopic signatures in stem cellulose) was established. Belowground, a distinct decline in fine root biomass, in particular in spruce, was observed. Along that line, repeated summer drought affected species composition of associated ECM fungi in both species. In particular, changes of ECM exploration types (i.e. contact/short-distance vs. long distance) may be related to C shortage of trees. Along the natural precipitation gradient (PGR), basal area increment of tree stems (DBH) was related to 13C discrimination in tree rings. Carbon isotope signatures proved to be a more sensible indicator of tree responses to drought that BAI. Sensitivity of trees was significantly affected by growth conditions, i.e. growth in mono- vs. mixed culture. Higher drought resistance was displayed by spruce on drier sites (i.e. habituation effect) and, conversely, by beech on moist sites, in particular when grown in mixture with spruce.

Composite pulsed field gradients with refocused chemical shifts and short recovery time.

PubMed

Hu, H; Shaka, A J

1999-01-01

An improved self-compensating pulsed field gradient (PFG) technique that combines antiphase gradient pairs with broadband frequency-modulated 180 degrees pulses is proposed. The antiphase gradient pairs lead to superb system recovery. In addition, evolution under chemical shift and heteronuclear J coupling are refocused during the PFG, making it appear effectively instantaneous. This new approach makes it possible to obtain high-resolution phase-sensitive 2D spectra for the PFG version of many experiments such as COSY, DQF-COSY, and HSQC without adding extra compensating delays or pulses. While reasonable suppression of unwanted magnetization is achieved, this method also gives satisfactory retention of desired signals. As a bonus, the field-frequency lock is not perturbed during the experiments. Copyright 1999 Academic Press.

Photosynthetic Acclimation of Symbiodinium in hospite Depends on Vertical Position in the Tissue of the Scleractinian Coral Montastrea curta

PubMed Central

Lichtenberg, Mads; Larkum, Anthony W. D.; Kühl, Michael

2016-01-01

Coral photophysiology has been studied intensively from the colony scale down to the scale of single fluorescent pigment granules as light is one of the key determinants for coral health. We studied the photophysiology of the oral and aboral symbiont band of scleractinian coral Montastrea curta to investigate if different acclimation to light exist in hospite on a polyp scale. By combined use of electrochemical and fiber-optic microsensors for O2, scalar irradiance and variable chlorophyll fluorescence, we could characterize the physical and chemical microenvironment experienced by the symbionts and, for the first time, estimate effective quantum yields of PSII photochemistry and rates of electron transport at the position of the zooxanthellae corrected for the in-tissue gradient of scalar irradiance. The oral- and aboral Symbiodinium layers received ∼71% and ∼33% of surface scalar irradiance, respectively, and the two symbiont layers experience considerable differences in light exposure. Rates of gross photosynthesis did not differ markedly between the oral- and aboral layer and curves of PSII electron transport rates corrected for scalar irradiance in hospite, showed that the light use efficiency under sub-saturating light conditions were similar between the two layers. However, the aboral Symbiodinium band did not experience photosynthetic saturation, even at the highest investigated irradiance where the oral layer was clearly saturated. We thus found a different light acclimation response for the oral and aboral symbiont bands in hospite, and discuss whether such response could be shaped by spectral shifts caused by tissue gradients of scalar irradiance. Based on our experimental finding, combined with previous knowledge, we present a conceptual model on the photophysiology of Symbiodinium residing inside living coral tissue under natural gradients of light and chemical parameters. PMID:26955372

Photosynthetic Acclimation of Symbiodinium in hospite Depends on Vertical Position in the Tissue of the Scleractinian Coral Montastrea curta.

PubMed

Lichtenberg, Mads; Larkum, Anthony W D; Kühl, Michael

2016-01-01

Coral photophysiology has been studied intensively from the colony scale down to the scale of single fluorescent pigment granules as light is one of the key determinants for coral health. We studied the photophysiology of the oral and aboral symbiont band of scleractinian coral Montastrea curta to investigate if different acclimation to light exist in hospite on a polyp scale. By combined use of electrochemical and fiber-optic microsensors for O2, scalar irradiance and variable chlorophyll fluorescence, we could characterize the physical and chemical microenvironment experienced by the symbionts and, for the first time, estimate effective quantum yields of PSII photochemistry and rates of electron transport at the position of the zooxanthellae corrected for the in-tissue gradient of scalar irradiance. The oral- and aboral Symbiodinium layers received ∼71% and ∼33% of surface scalar irradiance, respectively, and the two symbiont layers experience considerable differences in light exposure. Rates of gross photosynthesis did not differ markedly between the oral- and aboral layer and curves of PSII electron transport rates corrected for scalar irradiance in hospite, showed that the light use efficiency under sub-saturating light conditions were similar between the two layers. However, the aboral Symbiodinium band did not experience photosynthetic saturation, even at the highest investigated irradiance where the oral layer was clearly saturated. We thus found a different light acclimation response for the oral and aboral symbiont bands in hospite, and discuss whether such response could be shaped by spectral shifts caused by tissue gradients of scalar irradiance. Based on our experimental finding, combined with previous knowledge, we present a conceptual model on the photophysiology of Symbiodinium residing inside living coral tissue under natural gradients of light and chemical parameters.

Linear solvation energy relationships in normal phase chromatography based on gradient separations.

PubMed

Wu, Di; Lucy, Charles A

2017-09-22

Coupling the modified Soczewiñski model and one gradient run, a gradient method was developed to build a linear solvation energy relationship (LSER) for normal phase chromatography. The gradient method was tested on dinitroanilinopropyl (DNAP) and silica columns with hexane/dichloromethane (DCM) mobile phases. LSER models built based on the gradient separation agree with those derived from a series of isocratic separations. Both models have similar LSER coefficients and comparable goodness of fit, but the LSER model based on gradient separation required fewer trial and error experiments. Copyright © 2017 Elsevier B.V. All rights reserved.

Hand-Portable Gradient Capillary Liquid Chromatography Pumping System.

PubMed

Sharma, Sonika; Plistil, Alex; Barnett, Hal E; Tolley, H Dennis; Farnsworth, Paul B; Stearns, Stanley D; Lee, Milton L

2015-10-20

In this work, a novel splitless nanoflow gradient generator integrated with a stop-flow injector was developed and evaluated using an on-column UV-absorption detector. The gradient pumping system consisted of two nanoflow pumps controlled by micro stepper motors, a mixer connected to a serpentine tube, and a high-pressure valve. The gradient system weighed only 4 kg (9 lbs) and could generate up to 55 MPa (8000 psi) pressure. The system could operate using a 24 V DC battery and required 1.2 A for operation. The total volume capacity of the pump was 74 μL, and a sample volume of 60 nL could be injected. The system provided accurate nanoflow rates as low as 10 nL/min without employing a splitter, making it ideal for capillary column use. The gradient dwell volume was calculated to be 1.3 μL, which created a delay of approximately 4 min with a typical flow rate of 350 nL/min. Gradient performance was evaluated for gradient step accuracy, and excellent reproducibility was obtained in day-to-day experiments (RSD < 1.2%, n = 4). Linear gradient reproducibility was tested by separating a three-component pesticide mixture on a poly(ethylene glycol) diacrylate (PEGDA) monolithic column. The retention time reproducibility was very good in run-to-run experiments (RSD < 1.42%, n = 4). Finally, excellent separation of five phenols was demonstrated using the nanoflow gradient system.

A z-gradient array for simultaneous multi-slice excitation with a single-band RF pulse.

PubMed

Ertan, Koray; Taraghinia, Soheil; Sadeghi, Alireza; Atalar, Ergin

2018-07-01

Multi-slice radiofrequency (RF) pulses have higher specific absorption rates, more peak RF power, and longer pulse durations than single-slice RF pulses. Gradient field design techniques using a z-gradient array are investigated for exciting multiple slices with a single-band RF pulse. Two different field design methods are formulated to solve for the required current values of the gradient array elements for the given slice locations. The method requirements are specified, optimization problems are formulated for the minimum current norm and an analytical solution is provided. A 9-channel z-gradient coil array driven by independent, custom-designed gradient amplifiers is used to validate the theory. Performance measures such as normalized slice thickness error, gradient strength per unit norm current, power dissipation, and maximum amplitude of the magnetic field are provided for various slice locations and numbers of slices. Two and 3 slices are excited by a single-band RF pulse in simulations and phantom experiments. The possibility of multi-slice excitation with a single-band RF pulse using a z-gradient array is validated in simulations and phantom experiments. Magn Reson Med 80:400-412, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

A robust holographic autofocusing criterion based on edge sparsity: comparison of Gini index and Tamura coefficient for holographic autofocusing based on the edge sparsity of the complex optical wavefront

NASA Astrophysics Data System (ADS)

Tamamitsu, Miu; Zhang, Yibo; Wang, Hongda; Wu, Yichen; Ozcan, Aydogan

2018-02-01

The Sparsity of the Gradient (SoG) is a robust autofocusing criterion for holography, where the gradient modulus of the complex refocused hologram is calculated, on which a sparsity metric is applied. Here, we compare two different choices of sparsity metrics used in SoG, specifically, the Gini index (GI) and the Tamura coefficient (TC), for holographic autofocusing on dense/connected or sparse samples. We provide a theoretical analysis predicting that for uniformly distributed image data, TC and GI exhibit similar behavior, while for naturally sparse images containing few high-valued signal entries and many low-valued noisy background pixels, TC is more sensitive to distribution changes in the signal and more resistive to background noise. These predictions are also confirmed by experimental results using SoG-based holographic autofocusing on dense and connected samples (such as stained breast tissue sections) as well as highly sparse samples (such as isolated Giardia lamblia cysts). Through these experiments, we found that ToG and GoG offer almost identical autofocusing performance on dense and connected samples, whereas for naturally sparse samples, GoG should be calculated on a relatively small region of interest (ROI) closely surrounding the object, while ToG offers more flexibility in choosing a larger ROI containing more background pixels.

Monitoring Streambed Scour/Deposition Under Nonideal Temperature Signal and Flood Conditions

NASA Astrophysics Data System (ADS)

DeWeese, Timothy; Tonina, Daniele; Luce, Charles

2017-12-01

Streambed erosion and deposition are fundamental geomorphic processes in riverbeds, and monitoring their evolution is important for ecological system management and in-stream infrastructure stability. Previous research showed proof of concept that analysis of paired temperature signals of stream and pore waters can simultaneously provide monitoring scour and deposition, stream sediment thermal regime, and seepage velocity information. However, it did not address challenges often associated with natural systems, including nonideal temperature variations (low-amplitude, nonsinusoidal signal, and vertical thermal gradients) and natural flooding conditions on monitoring scour and deposition processes over time. Here we addressed this knowledge gap by testing the proposed thermal scour-deposition chain (TSDC) methodology, with laboratory experiments to test the impact of nonideal temperature signals under a range of seepage velocities and with a field application during a pulse flood. Both analyses showed excellent match between surveyed and temperature-derived bed elevation changes even under very low temperature signal amplitudes (less than 1°C), nonideal signal shape (sawtooth shape), and strong and changing vertical thermal gradients (4°C/m). Root-mean-square errors on predicting the change in streambed elevations were comparable with the median grain size of the streambed sediment. Future research should focus on improved techniques for temperature signal phase and amplitude extractions, as well as TSDC applications over long periods spanning entire hydrographs.

Percolation and transport in a sandy soil under a natural hydraulic gradient

USGS Publications Warehouse

Green, Christopher T.; Stonestrom, David A.; Bekins, Barbara A.; Akstin, Katherine C.; Schulz, Marjorie S.

2005-01-01

Unsaturated flow and transport under a natural hydraulic gradient in a Mediterranean climate were investigated with a field tracer experiment combined with laboratory analyses and numerical modeling. Bromide was applied to the surface of a sandy soil during the dry season. During the subsequent rainy season, repeated sediment sampling tracked the movement of bromide through the profile. Analysis of data on moisture content, matric pressure, unsaturated hydraulic conductivity, bulk density, and soil texture and structure provides insights into parameterization and use of the advective‐dispersive modeling approach. Capturing the gross features of tracer and moisture movement with model simulations required an order‐of‐magnitude increase in laboratory‐measured hydraulic conductivity. Wetting curve characteristics better represented field results, calling into question the routine estimation of hydraulic characteristics based only on drying conditions. Measured increases in profile moisture exceeded cumulative precipitation in early winter, indicating that gains from dew drip can exceed losses from evapotranspiration during periods of heavy (“Tule”) fog. A single‐continuum advective‐dispersive modeling approach could not reproduce a peak of bromide that was retained near the soil surface for over 3 years. Modeling of this feature required slow exchange of solute at a transfer rate of 0.5–1 × 10−4 d−1 with an immobile volume approaching the residual moisture content.

Fast Depiction Invariant Visual Similarity for Content Based Image Retrieval Based on Data-driven Visual Similarity using Linear Discriminant Analysis

NASA Astrophysics Data System (ADS)

Wihardi, Y.; Setiawan, W.; Nugraha, E.

2018-01-01

On this research we try to build CBIRS based on Learning Distance/Similarity Function using Linear Discriminant Analysis (LDA) and Histogram of Oriented Gradient (HoG) feature. Our method is invariant to depiction of image, such as similarity of image to image, sketch to image, and painting to image. LDA can decrease execution time compared to state of the art method, but it still needs an improvement in term of accuracy. Inaccuracy in our experiment happen because we did not perform sliding windows search and because of low number of negative samples as natural-world images.

Enhanced peripheral nerve regeneration through asymmetrically porous nerve guide conduit with nerve growth factor gradient.

PubMed

Oh, Se Heang; Kang, Jun Goo; Kim, Tae Ho; Namgung, Uk; Song, Kyu Sang; Jeon, Byeong Hwa; Lee, Jin Ho

2018-01-01

In this study, we fabricated a nerve guide conduit (NGC) with nerve growth factor (NGF) gradient along the longitudinal direction by rolling a porous polycaprolactone membrane with NGF concentration gradient. The NGF immobilized on the membrane was continuously released for up to 35 days, and the released amount of the NGF from the membrane gradually increased from the proximal to distal NGF ends, which may allow a neurotrophic factor gradient in the tubular NGC for a sufficient period. From the in vitro cell culture experiment, it was observed that the PC12 cells sense the NGF concentration gradient on the membrane for the cell proliferation and differentiation. From the in vivo animal experiment using a long gap (20 mm) sciatic nerve defect model of rats, the NGC with NGF concentration gradient allowed more rapid nerve regeneration through the NGC than the NGC itself and NGC immobilized with uniformly distributed NGF. The NGC with NGF concentration gradient seems to be a promising strategy for the peripheral nerve regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 52-64, 2018. © 2017 Wiley Periodicals, Inc.

Theory of an experiment in an orbiting space laboratory to determine the gravitational constant.

NASA Technical Reports Server (NTRS)

Vinti, J. P.

1972-01-01

An experiment is discussed for determining the gravitational constant with the aid of an isolated system consisting of an artificial satellite moving around an artificial planet. The experiment is to be conducted in a spherical laboratory traveling in an orbit around the earth. Difficulties due to the gravity-gradient term are considered, and the three-tunnel method proposed by Wilk (1969) is examined. The rotation of the sphere is discussed together with aspects of the reference systems used, the equations of motion of the spacecraft and of the test objects, the field from the earth's gravity gradient at the test object, higher harmonic terms in the gravity gradient force, gravitational effects of the spacecraft itself, and a computer simulation.

Magnetic Control of Concentration Gradient in Microgravity

NASA Technical Reports Server (NTRS)

Leslie, Fred; Ramachandran, Narayanan

2005-01-01

A report describes a technique for rapidly establishing a fluid-concentration gradient that can serve as an initial condition for an experiment on solutal instabilities associated with crystal growth in microgravity. The technique involves exploitation of the slight attractive or repulsive forces exerted on most fluids by a magnetic-field gradient. Although small, these forces can dominate in microgravity and therefore can be used to hold fluids in position in preparation for an experiment. The magnetic field is applied to a test cell, while a fluid mixture containing a concentration gradient is prepared by introducing an undiluted solution into a diluting solution in a mixing chamber. The test cell is then filled with the fluid mixture. Given the magnetic susceptibilities of the undiluted and diluting solutions, the magnetic-field gradient must be large enough that the magnetic force exceeds both (1) forces associated with the flow of the fluid mixture during filling of the test cell and (2) forces imposed by any residual gravitation and fluctuations thereof. Once the test cell has been filled with the fluid mixture, the magnetic field is switched off so that the experiment can proceed, starting from the proper initial conditions.

Nonequilibrium Interfacial Tension in Simple and Complex Fluids

NASA Astrophysics Data System (ADS)

Truzzolillo, Domenico; Mora, Serge; Dupas, Christelle; Cipelletti, Luca

2016-10-01

Interfacial tension between immiscible phases is a well-known phenomenon, which manifests itself in everyday life, from the shape of droplets and foam bubbles to the capillary rise of sap in plants or the locomotion of insects on a water surface. More than a century ago, Korteweg generalized this notion by arguing that stresses at the interface between two miscible fluids act transiently as an effective, nonequilibrium interfacial tension, before homogenization is eventually reached. In spite of its relevance in fields as diverse as geosciences, polymer physics, multiphase flows, and fluid removal, experiments and theoretical works on the interfacial tension of miscible systems are still scarce, and mostly restricted to molecular fluids. This leaves crucial questions unanswered, concerning the very existence of the effective interfacial tension, its stabilizing or destabilizing character, and its dependence on the fluid's composition and concentration gradients. We present an extensive set of measurements on miscible complex fluids that demonstrate the existence and the stabilizing character of the effective interfacial tension, unveil new regimes beyond Korteweg's predictions, and quantify its dependence on the nature of the fluids and the composition gradient at the interface. We introduce a simple yet general model that rationalizes nonequilibrium interfacial stresses to arbitrary mixtures, beyond Korteweg's small gradient regime, and show that the model captures remarkably well both our new measurements and literature data on molecular and polymer fluids. Finally, we briefly discuss the relevance of our model to a variety of interface-driven problems, from phase separation to fracture, which are not adequately captured by current approaches based on the assumption of small gradients.

Comparison of retention models for polymers 1. Poly(ethylene glycol)s.

PubMed

Bashir, Mubasher A; Radke, Wolfgang

2006-10-27

The suitability of three different retention models to predict the retention times of poly(ethylene glycol)s (PEGs) in gradient and isocratic chromatography was investigated. The models investigated were the linear (LSSM) and the quadratic solvent strength model (QSSM). In addition, a model describing the retention behaviour of polymers was extended to account for gradient elution (PM). It was found that all models are suited to properly predict gradient retention volumes provided the extraction of the analyte specific parameters is performed from gradient experiments as well. The LSSM and QSSM on principle cannot describe retention behaviour under critical or SEC conditions. Since the PM is designed to cover all three modes of polymer chromatography, it is therefore superior to the other models. However, the determination of the analyte specific parameters, which are needed to calibrate the retention behaviour, strongly depend on the suitable selection of initial experiments. A useful strategy for a purposeful selection of these calibration experiments is proposed.

Motion of Drops on Surfaces with Wettability Gradients

NASA Technical Reports Server (NTRS)

Subramanian, R. Shankar; McLaughlin, John B.; Moumen, Nadjoua; Qian, Dongying

2002-01-01

A liquid drop present on a solid surface can move because of a gradient in wettability along the surface, as manifested by a gradient in the contact angle. The contact angle at a given point on the contact line between a solid and a liquid in a gaseous medium is the angle between the tangent planes to the liquid and the solid surfaces at that point and is measured within the liquid side, by convention. The motion of the drop occurs in the direction of increasing wettability. The cause of the motion is the net force exerted on the drop by the solid surface because of the variation of the contact angle around the periphery. This force causes acceleration of an initially stationary drop, and leads to its motion in the direction of decreasing contact angle. The nature of the motion is determined by the balance between the motivating force and the resisting hydrodynamic force from the solid surface and the surrounding gaseous medium. A wettability gradient can be chemically induced as shown by Chaudhury and Whitesides who provided unambiguous experimental evidence that drops can move in such gradients. The phenomenon can be important in heat transfer applications in low gravity, such as when condensation occurs on a surface. Daniel et al have demonstrated that the velocity of a drop on a surface due to a wettability gradient in the presence of condensation can be more than two orders of magnitude larger than that observed in the absence of condensation. In the present research program, we have begun to study the motion of a drop in a wettability gradient systematically using a model system. Our initial efforts will be restricted to a system in which no condensation occurs. The experiments are performed as follows. First, a rectangular strip of approximate dimensions 10 x 20 mm is cut out of a silicon wafer. The strip is cleaned thoroughly and its surface is exposed to the vapor from an alkylchlorosilane for a period lasting between one and two minutes inside a desiccator. This is done using an approximate line source of the vapor in the form of a string soaked in the alkylchlorosilane. Ordinarily, many fluids, including water, wet the surface of silicon quite well. This means that the contact angle is small. But the silanized surface resists wetting, with contact angles that are as large as 100 degs. Therefore, a gradient of wettability is formed on the silicon surface. The region near the string is highly hydrophobic, and the contact angle decreases gradually toward a small value at the hydrophilic end away from this region. The change in wettability occurs over a distance of several mm. The strip is placed on a platform within a Plexiglas cell. Drops of a suitable liquid are introduced on top of the strip near the hydrophobic end. An optical system attached to a video camera is trained on the drop so that images of the moving drop can be captured on videotape for subsequent analysis. We have performed preliminary experiments with water as well as ethylene glycol drops. Results from these experiments will be presented in the poster. Future plans include the refinement of the experimental system so as to permit images to be recorded from the side as well as the top, and the conduct of a systematic study in which the drop size is varied over a good range. Experiments will be conducted with different fluids so as to obtain the largest possible range of suitably defined Reynolds and Capillary numbers. Also, an effort will be initiated on theoretical modeling of this motion. The challenges in the development of the theoretical description lie in the proper analysis of the region in the vicinity of the contact line, as well as in the free boundary nature of the problem. It is known that continuum models assuming the no slip condition all the way to the contact line fail by predicting that the stress on the solid surface becomes singular as the contact line is approached. One approach for dealing with this issue has been to relax the no-slip boundary condition using the Navier model. Molecular dynamics simulations of the contact line region show that for a non-polar liquid on a solid surface, the no-slip boundary condition is in fact incorrect near the contact line. Furthermore, the same simulations also show that the usual relationship between stress and the rate of deformation breaks down in the vicinity of the contact line. In developing continuum theoretical models of the system, we shall accommodate this knowledge to the extent possible.

Sound control by temperature gradients

NASA Astrophysics Data System (ADS)

Sánchez-Dehesa, José; Angelov, Mitko I.; Cervera, Francisco; Cai, Liang-Wu

2009-11-01

This work reports experiments showing that airborne sound propagation can be controlled by temperature gradients. A system of two heated tubes is here used to demonstrate the collimation and focusing of an ultrasonic beam by the refractive index profile created by the temperature gradients existing around the tubes. Numerical simulations supporting the experimental findings are also reported.

Quantitative separation of the anisotropic magnetothermopower and planar Nernst effect by the rotation of an in-plane thermal gradient

NASA Astrophysics Data System (ADS)

Reimer, Oliver; Meier, Daniel; Bovender, Michel; Helmich, Lars; Dreessen, Jan-Oliver; Krieft, Jan; Shestakov, Anatoly S.; Back, Christian H.; Schmalhorst, Jan-Michael; Hütten, Andreas; Reiss, Günter; Kuschel, Timo

2017-01-01

A thermal gradient as the driving force for spin currents plays a key role in spin caloritronics. In this field the spin Seebeck effect (SSE) is of major interest and was investigated in terms of in-plane thermal gradients inducing perpendicular spin currents (transverse SSE) and out-of-plane thermal gradients generating parallel spin currents (longitudinal SSE). Up to now all spincaloric experiments employ a spatially fixed thermal gradient. Thus, anisotropic measurements with respect to well defined crystallographic directions were not possible. Here we introduce a new experiment that allows not only the in-plane rotation of the external magnetic field, but also the rotation of an in-plane thermal gradient controlled by optical temperature detection. As a consequence, the anisotropic magnetothermopower and the planar Nernst effect in a permalloy thin film can be measured simultaneously. Thus, the angular dependence of the magnetothermopower with respect to the magnetization direction reveals a phase shift, that allows the quantitative separation of the thermopower, the anisotropic magnetothermopower and the planar Nernst effect.

Preliminary Experimental Examination Of Controls On Methane Expulsion During Melting Of Natural Gas Hydrate Systems

NASA Astrophysics Data System (ADS)

Kneafsey, T. J.; Flemings, P. B.; Bryant, S. L.; You, K.; Polito, P. J.

2013-12-01

Global climate change will cause warming of the oceans and land. This will affect the occurrence, behavior, and location of subseafloor and subterranean methane hydrate deposits. We suggest that in many natural systems local salinity, elevated by hydrate formation or freshened by hydrate dissociation, may control gas transport through the hydrate stability zone. We are performing experiments and modeling the experiments to explore this behavior for different warming scenarios. Initially, we are exploring hydrate association/dissociation in saline systems with constant water mass. We compare experiments run with saline (3.5 wt. %) water vs. distilled water in a sand mixture at an initial water saturation of ~0.5. We increase the pore fluid (methane) pressure to 1050 psig. We then stepwise cool the sample into the hydrate stability field (~3 degrees C), allowing methane gas to enter as hydrate forms. We measure resistivity and the mass of methane consumed. We are currently running these experiments and we predict our results from equilibrium thermodynamics. In the fresh water case, the modeled final hydrate saturation is 63% and all water is consumed. In the saline case, the modeled final hydrate saturation is 47%, the salinity is 12.4 wt. %, and final water saturation is 13%. The fresh water system is water-limited: all the water is converted to hydrate. In the saline system, pore water salinity is elevated and salt is excluded from the hydrate structure during hydrate formation until the salinity drives the system to three phase equilibrium (liquid, gas, hydrate) and no further hydrate forms. In our laboratory we can impose temperature gradients within the column, and we will use this to investigate equilibrium conditions in large samples subjected to temperature gradients and changing temperature. In these tests, we will quantify the hydrate saturation and salinity over our meter-long sample using spatially distributed temperature sensors, spatially distributed resistivity probes, compressional wave velocities, and X-ray computed tomography scanning. Modeling of hydrate formation and dissociation for these conditions indicates that the transport of bulk fluid phases (gas and water) plays a crucial role in the overall behavior, and we will explore open-system boundary conditions in the experiments to test this prediction.

Glassy dynamics of landscape evolution

PubMed Central

Ortiz, Carlos P.; Jerolmack, Douglas J.

2018-01-01

Soil creeps imperceptibly downhill, but also fails catastrophically to create landslides. Despite the importance of these processes as hazards and in sculpting landscapes, there is no agreed-upon model that captures the full range of behavior. Here we examine the granular origins of hillslope soil transport by discrete element method simulations and reanalysis of measurements in natural landscapes. We find creep for slopes below a critical gradient, where average particle velocity (sediment flux) increases exponentially with friction coefficient (gradient). At critical gradient there is a continuous transition to a dense-granular flow rheology. Slow earthflows and landslides thus exhibit glassy dynamics characteristic of a wide range of disordered materials; they are described by a two-phase flux equation that emerges from grain-scale friction alone. This glassy model reproduces topographic profiles of natural hillslopes, showing its promise for predicting hillslope evolution over geologic timescales. PMID:29686102

From Chemical Gardens to Fuel Cells: Generation of Electrical Potential and Current Across Self-Assembling Iron Mineral Membranes.

PubMed

Barge, Laura M; Abedian, Yeghegis; Russell, Michael J; Doloboff, Ivria J; Cartwright, Julyan H E; Kidd, Richard D; Kanik, Isik

2015-07-06

We examine the electrochemical gradients that form across chemical garden membranes and investigate how self-assembling, out-of-equilibrium inorganic precipitates-mimicking in some ways those generated in far-from-equilibrium natural systems-can generate electrochemical energy. Measurements of electrical potential and current were made across membranes precipitated both by injection and solution interface methods in iron-sulfide and iron-hydroxide reaction systems. The battery-like nature of chemical gardens was demonstrated by linking multiple experiments in series which produced sufficient electrical energy to light an external light-emitting diode (LED). This work paves the way for determining relevant properties of geological precipitates that may have played a role in hydrothermal redox chemistry at the origin of life, and materials applications that utilize the electrochemical properties of self-organizing chemical systems. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Vegetation recovery in tidal marshes reveals critical slowing down under increased inundation

PubMed Central

van Belzen, Jim; van de Koppel, Johan; Kirwan, Matthew L.; van der Wal, Daphne; Herman, Peter M. J.; Dakos, Vasilis; Kéfi, Sonia; Scheffer, Marten; Guntenspergen, Glenn R.; Bouma, Tjeerd J.

2017-01-01

A declining rate of recovery following disturbance has been proposed as an important early warning for impending tipping points in complex systems. Despite extensive theoretical and laboratory studies, this ‘critical slowing down' remains largely untested in the complex settings of real-world ecosystems. Here, we provide both observational and experimental support of critical slowing down along natural stress gradients in tidal marsh ecosystems. Time series of aerial images of European marsh development reveal a consistent lengthening of recovery time as inundation stress increases. We corroborate this finding with transplantation experiments in European and North American tidal marshes. In particular, our results emphasize the power of direct observational or experimental measures of recovery over indirect statistical signatures, such as spatial variance or autocorrelation. Our results indicate that the phenomenon of critical slowing down can provide a powerful tool to probe the resilience of natural ecosystems. PMID:28598430

Interaction of feel system and flight control system dynamics on lateral flying qualities

NASA Technical Reports Server (NTRS)

Bailey, Randall E.; Powers, Bruce G.; Shafer, Mary F.

1988-01-01

An investigation of feel system and flight control system dynamics on lateral flying qualities was conducted using the variable stability USAF NT-33 aircraft. Experimental variations in feel system natural frequency, force-deflection gradient, control system command architecture type, flight control system filter frequency, and control system delay were made. The experiment data include pilot ratings using the Cooper-Harper (1969) rating scale, pilot comments, and tracking performance statistic. Three test pilots served as evaluators. The data indicate that as the feel system natural frequency is reduced lateral flying qualities degrade. At the slowest feel system frequency, the closed-loop response becomes nonlinear with a 'bobweight' effect apparent in the feel system. Feel system influences were essentially independent of the control system architecture. The flying qualities influence due to the feel system was different than when the identical dynamic systenm was used as a flight control system element.

Vegetation recovery in tidal marshes reveals critical slowing down under increased inundation

NASA Astrophysics Data System (ADS)

van Belzen, Jim; van de Koppel, Johan; Kirwan, Matthew L.; van der Wal, Daphne; Herman, Peter M. J.; Dakos, Vasilis; Kéfi, Sonia; Scheffer, Marten; Guntenspergen, Glenn R.; Bouma, Tjeerd J.

2017-06-01

A declining rate of recovery following disturbance has been proposed as an important early warning for impending tipping points in complex systems. Despite extensive theoretical and laboratory studies, this `critical slowing down' remains largely untested in the complex settings of real-world ecosystems. Here, we provide both observational and experimental support of critical slowing down along natural stress gradients in tidal marsh ecosystems. Time series of aerial images of European marsh development reveal a consistent lengthening of recovery time as inundation stress increases. We corroborate this finding with transplantation experiments in European and North American tidal marshes. In particular, our results emphasize the power of direct observational or experimental measures of recovery over indirect statistical signatures, such as spatial variance or autocorrelation. Our results indicate that the phenomenon of critical slowing down can provide a powerful tool to probe the resilience of natural ecosystems.

Vegetation recovery in tidal marshes reveals critical slowing down under increased inundation.

PubMed

van Belzen, Jim; van de Koppel, Johan; Kirwan, Matthew L; van der Wal, Daphne; Herman, Peter M J; Dakos, Vasilis; Kéfi, Sonia; Scheffer, Marten; Guntenspergen, Glenn R; Bouma, Tjeerd J

2017-06-09

A declining rate of recovery following disturbance has been proposed as an important early warning for impending tipping points in complex systems. Despite extensive theoretical and laboratory studies, this 'critical slowing down' remains largely untested in the complex settings of real-world ecosystems. Here, we provide both observational and experimental support of critical slowing down along natural stress gradients in tidal marsh ecosystems. Time series of aerial images of European marsh development reveal a consistent lengthening of recovery time as inundation stress increases. We corroborate this finding with transplantation experiments in European and North American tidal marshes. In particular, our results emphasize the power of direct observational or experimental measures of recovery over indirect statistical signatures, such as spatial variance or autocorrelation. Our results indicate that the phenomenon of critical slowing down can provide a powerful tool to probe the resilience of natural ecosystems.

Magnetic field of longitudinal gradient bend

NASA Astrophysics Data System (ADS)

Aiba, Masamitsu; Böge, Michael; Ehrlichman, Michael; Streun, Andreas

2018-06-01

The longitudinal gradient bend is an effective method for reducing the natural emittance in light sources. It is, however, not a common element. We have analyzed its magnetic field and derived a set of formulae. Based on the derivation, we discuss how to model the longitudinal gradient bend in accelerator codes that are used for designing electron storage rings. Strengths of multipole components can also be evaluated from the formulae, and we investigate the impact of higher order multipole components in a very low emittance lattice.

Peak-Seeking Control Using Gradient and Hessian Estimates

NASA Technical Reports Server (NTRS)

Ryan, John J.; Speyer, Jason L.

2010-01-01

A peak-seeking control method is presented which utilizes a linear time-varying Kalman filter. Performance function coordinate and magnitude measurements are used by the Kalman filter to estimate the gradient and Hessian of the performance function. The gradient and Hessian are used to command the system toward a local extremum. The method is naturally applied to multiple-input multiple-output systems. Applications of this technique to a single-input single-output example and a two-input one-output example are presented.

Preparation, testing and analysis of zinc diffusion samples, NASA Skylab experiment M-558

NASA Technical Reports Server (NTRS)

Braski, D. N.; Kobisk, E. H.; Odonnell, F. R.

1974-01-01

Transport mechanisms of zinc atoms in molten zinc were investigated by radiotracer techniques in unit and in near-zero gravity environments. Each melt in the Skylab flight experiments was maintained in a thermal gradient of 420 C to 790 C. Similar tests were performed in a unit gravity environment for comparison. After melting in the gradient furnace followed by a thermal soak period (the latter was used for flight samples only), the samples were cooled and analyzed for Zn-65 distribution. All samples melted in a unit gravity environment were found to have uniform Zn-65 distribution - no concentration gradient was observed even when the sample was brought rapidly to melting and then quenched. Space-melted samples, however, showed textbook distributions, obviously the result of diffusion. It was evident that convection phenomena were the dominant factors influencing zinc transport in unit gravity experiments, while diffusion was the dominant factor in near-zero gravity experiments.

Adaptive evolution of Escherichia coli to Ciprofloxacin in controlled stress environments: emergence of resistance in continuous and step-wise gradients

NASA Astrophysics Data System (ADS)

Deng, J.; Zhou, L.; Dong, Y.; Sanford, R. A.; Shechtman, L. A.; Alcalde, R.; Werth, C. J.; Fouke, B. W.

2017-12-01

Microorganisms in nature have evolved in response to a variety of environmental stresses, including gradients in pH, flow and chemistry. While environmental stresses are generally considered to be the driving force of adaptive evolution, the impact and extent of any specific stress needed to drive such changes has not been well characterized. In this study, a microfluidic diffusion chamber (MDC) and a batch culturing system were used to systematically study the effects of continuous versus step-wise stress increments on adaptation of E. coli to the antibiotic ciprofloxacin. In the MDC, a diffusion gradient of ciprofloxacin was established across a microfluidic well array to microscopically observe changes in Escherichia coli strain 307 replication and migration patterns that would indicate emergence of resistance due to genetic mutations. Cells recovered from the MDC only had resistance of 50-times the original minimum inhibition concentration (MICoriginal) of ciprofloxacin, although minimum exposure concentrations were over 80 × MICoriginal by the end of the experiment. In complementary batch experiments, E. coli 307 were exposed to step-wise daily increases of ciprofloxacin at rates equivalent to 0.1×, 0.2×, 0.4× or 0.8× times MICoriginal/day. Over a period of 18 days, E. coli cells were able to acquire resistance of up to 225 × MICoriginal, with exposure to ciprofloxacin concentration up to only 14.9 × MIC­original. The different levels of acquired resistance in the continuous MDC versus step-wise batch increment experiments suggests that the intrinsic rate of E. coli adaptation was exceeded in the MDC, while the step-wise experiments favor adaptation to the highest ciprofloxacin experiments. Genomic analyses of E. coli DNA extracted from the microfluidic cell and batch cultures indicated four single nucleotide polymorphism (SNP) mutations of amino acid 82, 83 and 87 in the gyrA gene. The progression of adaptation in the step-wise increments of ciprofloxacin indicate that the Ser83-Leu mutation gradually becomes dominant over other gyrA mutations with increased antibiotic resistance. Co-existence of the Ser83-Leu and Asp87—Gly mutations appear to provide the greatest level of resistance (i.e., 85 × to 225 × MICoriginal), and only emerged after the whole community acquired the Ser83—Leu mutation.

Phytoextraction potential of poplar (Populus alba L. var. pyramidalis Bunge) from calcareous agricultural soils contaminated by cadmium.

PubMed

Hu, Yahu; Nan, Zhongren; Jin, Cheng; Wang, Ning; Luo, Huanzhang

2014-01-01

To investigate the phytoextraction potential of Populus alba L. var. pyramidalis Bunge for cadmium (Cd) contaminated calcareous soils, a concentration gradient experiment and a field sampling experiment (involving poplars of different ages) were conducted. The translocation factors for all experiments and treatments were greater than 1. The bioconcentration factor decreased from 2.37 to 0.25 with increasing soil Cd concentration in the concentration gradient experiment and generally decreased with stand age under field conditions. The Cd concentrations in P. pyramidalis organs decreased in the order of leaves > stems > roots. The shoot biomass production in the concentration gradient experiment was not significantly reduced with soil Cd concentrations up to or slightly over 50 mg kg(-1). The results show that the phytoextraction efficiency of P. pyramidalis depends on both the soil Cd concentration and the tree age. Populus pyramidalis is most suitable for remediation of slightly Cd contaminated calcareous soils through the combined harvest of stems and leaves under actual field conditions.

Bubble Formation and Transport during Microgravity Materials Processing: Model Experiments on the Space Station

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

2003-01-01

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

Bubble Formation and Transport during Microgravity Materials Processing: Model Experiments on the International Space Station

NASA Technical Reports Server (NTRS)

Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

2003-01-01

Flow Visualization experiments on the controlled melting and solidification of succinonitrile were conducted in the glovebox facility of the International Space Station (ISS). The experimental samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) under 450 millibar of nitrogen. Porosity in the samples arose from natural shrinkage, and in some cases by direct insertion of nitrogen bubbles, during solidification of the liquid SCN. The samples were processed in the Pore Formation and Mobility Investigation (PFMI) apparatus that is placed in the glovebox facility (GBX) aboard the ISS. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. During the experiments, the sample is first subjected to a unidirectional melt back, generally at 10 microns per second, with a constant temperature gradient ahead of the melting interface. The temperatures in the sample are monitored by six in situ thermocouples. Real time visualization of the controlled directional melt back shows bubbles of different sizes initiating at the melt interface and, upon dislodging from the melting solid, migrating at different speeds into the temperature field ahead of them, before coming to rest. The thermocapillary flow field set up in the melt, ahead of the interface, is dramatic in the context of the large bubbles, and plays a major role in dislodging the bubble. A preliminary analysis of the observed bubble formation and mobility during melt back and its implication to future microgravity experiments is presented and discussed.

Role of spatial averaging in multicellular gradient sensing.

PubMed

Smith, Tyler; Fancher, Sean; Levchenko, Andre; Nemenman, Ilya; Mugler, Andrew

2016-05-20

Gradient sensing underlies important biological processes including morphogenesis, polarization, and cell migration. The precision of gradient sensing increases with the length of a detector (a cell or group of cells) in the gradient direction, since a longer detector spans a larger range of concentration values. Intuition from studies of concentration sensing suggests that precision should also increase with detector length in the direction transverse to the gradient, since then spatial averaging should reduce the noise. However, here we show that, unlike for concentration sensing, the precision of gradient sensing decreases with transverse length for the simplest gradient sensing model, local excitation-global inhibition. The reason is that gradient sensing ultimately relies on a subtraction of measured concentration values. While spatial averaging indeed reduces the noise in these measurements, which increases precision, it also reduces the covariance between the measurements, which results in the net decrease in precision. We demonstrate how a recently introduced gradient sensing mechanism, regional excitation-global inhibition (REGI), overcomes this effect and recovers the benefit of transverse averaging. Using a REGI-based model, we compute the optimal two- and three-dimensional detector shapes, and argue that they are consistent with the shapes of naturally occurring gradient-sensing cell populations.

Role of spatial averaging in multicellular gradient sensing

NASA Astrophysics Data System (ADS)

Smith, Tyler; Fancher, Sean; Levchenko, Andre; Nemenman, Ilya; Mugler, Andrew

2016-06-01

Gradient sensing underlies important biological processes including morphogenesis, polarization, and cell migration. The precision of gradient sensing increases with the length of a detector (a cell or group of cells) in the gradient direction, since a longer detector spans a larger range of concentration values. Intuition from studies of concentration sensing suggests that precision should also increase with detector length in the direction transverse to the gradient, since then spatial averaging should reduce the noise. However, here we show that, unlike for concentration sensing, the precision of gradient sensing decreases with transverse length for the simplest gradient sensing model, local excitation-global inhibition. The reason is that gradient sensing ultimately relies on a subtraction of measured concentration values. While spatial averaging indeed reduces the noise in these measurements, which increases precision, it also reduces the covariance between the measurements, which results in the net decrease in precision. We demonstrate how a recently introduced gradient sensing mechanism, regional excitation-global inhibition (REGI), overcomes this effect and recovers the benefit of transverse averaging. Using a REGI-based model, we compute the optimal two- and three-dimensional detector shapes, and argue that they are consistent with the shapes of naturally occurring gradient-sensing cell populations.

Regulators of coastal wetland methane production and responses to simulated global change

Treesearch

Carmella Vizza; William E. West; Stuart E. Jones; Julia A. Hart; Gary A. Lamberti

2017-01-01

Wetlands are the largest natural source of methane (CH4) emissions to the atmosphere, which vary along salinity and productivity gradients. Global change has the potential to reshape these gradients and therefore alter future contributions of wetlands to the global CH4 budget. Our study examined CH4...

Chemical diffusion during isobaric degassing of magma

NASA Astrophysics Data System (ADS)

von Aulock, Felix W.; Kennedy, Ben M.; Lavallée, Yan; Henton-de Angelis, Sarah; Oze, Christopher; Morgan, Daniel J.; Clesham, Steve

2014-05-01

During ascent of magma, volatiles exsolve and bubbles form. Volatiles can either escape through a permeable network of bubbles in an open system or be trapped in non-connected pores during closed system degassing. Geochemical studies have shown that in most cases both- open system and closed system degassing take place at the same time. During cooling of the melt, diffusion slows down and eventually diffusional gradients get frozen in, preserving a history of degassing and rehydration during bubble growth, bubble collapse and crystal growth. We present data from experiments in which natural obsidian was degassed at atmospheric pressures at 950ºC over timescales of 3-24h. During bubble growth, a skin formed, at the outer edge of the sample, effectively prohibiting any degassing of its interior. Diffusion gradients were measured across the glass surrounding vesicles, and across this impermeable skin. Water contents were analyzed with synchrotron sourced Fourier transform infrared spectroscopy and several major, minor and trace elements were mapped using synchrotron sourced X-ray fluorescence spectroscopy. The samples show a dimpled surface, as well as signs of oxidation and growth of submicroscopic crystals. Water contents around bubbles decrease in simple heating experiments (from ~0.13 wt. % down to ~0.1 wt. %), whereas slight rehydration of the vesicle wall can be observed when a second, cooler step at 850ºC follows the initial 950ºC. Water gradients towards the outside of the sample decrease linearly to a minimum of ~0.045 wt. %, far below the solubility of water in melts at these temperatures. We mapped the distribution of K, Ca, Fe, Ti, Mn, Rb, Sr, Y and Zr. Especially the trace elements show a decrease towards the outside of the sample, whereas K, Fe, Ca and Ti generally do not show significant partitioning between melt and gas/crystal phase. Several effects could attribute to the distribution of these elements, such as the crystal growth and exchange with atmospheric oxygen, and detailed models of the diffusion of these elements will have to verify the mechanisms of elemental partitioning during degassing Our experiments show that even on a small scale, open system and closed system degassing inherently coexist. This manifests itself in different elemental distribution in the quenched glass. Water distribution gradients can be explained with diffusion during exsolution and rehydration during cooling, however, the surface of the sample is undersaturated in water. Some trace elements follow the same pattern, even though they might not be considered as volatile. Therefore we suggest that chemical gradients may be partially induced by the growth of sub-microscopic crystals and by exchange with the atmosphere. Crystal rich, volatile poor outer skins, as produced in the experiments of this study, have locally drastically increased viscosities and can therefore withstand higher pressures during foaming of the interior of the sample. This self sealing of magma could be an important process on different scales of magma degassing, from bread crust bombs to rising magma in conduits.

A study on Rayleigh wave dispersion in bone according to Mindlin's Form II gradient elasticity.

PubMed

Vavva, Maria G; Gergidis, Leonidas N; Protopappas, Vasilios C; Charalambopoulos, Antonios; Polyzos, Demosthenes; Fotiadis, Dimitrios I

2014-05-01

The classical elasticity cannot effectively describe bone's mechanical behavior since only homogeneous media and local stresses are assumed. Additionally, it cannot predict the dispersive nature of the Rayleigh wave which has been reported in experimental studies and was also demonstrated in a previous computational study by adopting Mindlin's Form II gradient elasticity. In this work Mindlin's theory is employed to analytically determine the dispersion of Rayleigh waves in a strain gradient elastic half-space. An isotropic semi-infinite space is considered with properties equal to those of bone and dynamic behavior suffering from microstructural effects. Microstructural effects are considered by incorporating four intrinsic parameters in the stress analysis. The results are presented in the form of group and phase velocity dispersion curves and compared with existing computational results and semi-analytical curves calculated for a simpler case of Rayleigh waves in dipolar gradient elastic half-spaces. Comparisons are also performed with the velocity of the first-order antisymmetric mode propagating in a dipolar plate so as to observe the Rayleigh asymptotic behavior. It is shown that Mindlin's Form II gradient elasticity can effectively describe the dispersive nature of Rayleigh waves. This study could be regarded as a step toward the ultrasonic characterization of bone.

Simplification of arboreal marsupial assemblages in response to increasing urbanization.

PubMed

Isaac, Bronwyn; White, John; Ierodiaconou, Daniel; Cooke, Raylene

2014-01-01

Arboreal marsupials play an essential role in ecosystem function including regulating insect and plant populations, facilitating pollen and seed dispersal and acting as a prey source for higher-order carnivores in Australian environments. Primarily, research has focused on their biology, ecology and response to disturbance in forested and urban environments. We used presence-only species distribution modelling to understand the relationship between occurrences of arboreal marsupials and eco-geographical variables, and to infer habitat suitability across an urban gradient. We used post-proportional analysis to determine whether increasing urbanization affected potential habitat for arboreal marsupials. The key eco-geographical variables that influenced disturbance intolerant species and those with moderate tolerance to disturbance were natural features such as tree cover and proximity to rivers and to riparian vegetation, whereas variables for disturbance tolerant species were anthropogenic-based (e.g., road density) but also included some natural characteristics such as proximity to riparian vegetation, elevation and tree cover. Arboreal marsupial diversity was subject to substantial change along the gradient, with potential habitat for disturbance-tolerant marsupials distributed across the complete gradient and potential habitat for less tolerant species being restricted to the natural portion of the gradient. This resulted in highly-urbanized environments being inhabited by a few generalist arboreal marsupial species. Increasing urbanization therefore leads to functional simplification of arboreal marsupial assemblages, thus impacting on the ecosystem services they provide.

Simplification of Arboreal Marsupial Assemblages in Response to Increasing Urbanization

PubMed Central

Isaac, Bronwyn; White, John; Ierodiaconou, Daniel; Cooke, Raylene

2014-01-01

Arboreal marsupials play an essential role in ecosystem function including regulating insect and plant populations, facilitating pollen and seed dispersal and acting as a prey source for higher-order carnivores in Australian environments. Primarily, research has focused on their biology, ecology and response to disturbance in forested and urban environments. We used presence-only species distribution modelling to understand the relationship between occurrences of arboreal marsupials and eco-geographical variables, and to infer habitat suitability across an urban gradient. We used post-proportional analysis to determine whether increasing urbanization affected potential habitat for arboreal marsupials. The key eco-geographical variables that influenced disturbance intolerant species and those with moderate tolerance to disturbance were natural features such as tree cover and proximity to rivers and to riparian vegetation, whereas variables for disturbance tolerant species were anthropogenic-based (e.g., road density) but also included some natural characteristics such as proximity to riparian vegetation, elevation and tree cover. Arboreal marsupial diversity was subject to substantial change along the gradient, with potential habitat for disturbance-tolerant marsupials distributed across the complete gradient and potential habitat for less tolerant species being restricted to the natural portion of the gradient. This resulted in highly-urbanized environments being inhabited by a few generalist arboreal marsupial species. Increasing urbanization therefore leads to functional simplification of arboreal marsupial assemblages, thus impacting on the ecosystem services they provide. PMID:24608165

Overview of the Frontal Air-Sea Interaction Experiment (FASINEX) - A study of air-sea interaction in a region of strong oceanic gradients

NASA Technical Reports Server (NTRS)

Weller, Robert A.

1991-01-01

From 1984 to 1986 the cooperative Frontal Air-Sea Interaction Experiment (FASINEX) was conducted in the subtropical convergence zone southwest of Bermuda. The overall objective of the experiment was to study air-sea interaction on 1- to 100-km horizontal scales in a region of the open ocean characterized by strong horizontal gradients in upper ocean and sea surface properties. Ocean fronts provided both large spatial gradients in sea surface temperature and strong jetlike flows in the upper ocean. The motivation for and detailed objectives of FASINEX are reviewed. Then the components of the field program are summarized. Finally, selected results are presented in order to provide an overview of the outcome of FASINEX.

Latest Results of ILC High-Gradient R&D 9-cell Cavities at JLAB

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geng, Rongli

2008-02-11

It has been over a year since JLAB started processing and testing ILC 9-cell cavities in the frame work of ILC high-gradient cavity R&D, aiming at the goal of a 35 MV/m gradient at a Q of 1E10 with a yield of 90%. The necessary cavity processing steps include field flatness tuning, electropolishing (EP), hydrogen out-gassing under vacuum, high-pressure water rinsing, clean room assembly, and low temperature bake. These are followed by RF test at 2 Kelvin. Ultrasonic cleaning with Micro-90, an effective post-EP rinsing recipe discovered at JLAB, is routinely used. Seven industry manufactured 9-cell TESLAshape cavities are processedmore » and tested repeatedly. So far, 33 EP cycles are accumulated, corresponding to more than 65 hours of active EP time. An emphasis put on RF testing is to discern cavity quench characteristics, including its nature and its location. Often times, the cavity performance is limited by thermal-magnetic quench instead of field emission. The quench field in some cavities is lower than 20 MV/m and remains unchanged despite repeated EP, implying material and/or fabrication defects. The quench field in some other cavities is high but changes unpredictably after repeated EP, suggesting processing induced defects. Based on our experience and results, several areas are identified where improvement is needed to improve cavity performance as well as yield.« less

Dynamics of arbuscular mycorrhizal fungal community structure and functioning along a nitrogen enrichment gradient in an alpine meadow ecosystem.

PubMed

Jiang, Shengjing; Liu, Yongjun; Luo, Jiajia; Qin, Mingsen; Johnson, Nancy Collins; Öpik, Maarja; Vasar, Martti; Chai, Yuxing; Zhou, Xiaolong; Mao, Lin; Du, Guozhen; An, Lizhe; Feng, Huyuan

2018-03-30

Nitrogen (N) availability is increasing dramatically in many ecosystems, but the influence of elevated N on the functioning of arbuscular mycorrhizal (AM) fungi in natural ecosystems is not well understood. We measured AM fungal community structure and mycorrhizal function simultaneously across an experimental N addition gradient in an alpine meadow that is limited by N but not by phosphorus (P). AM fungal communities at both whole-plant-community (mixed roots) and single-plant-species (Elymus nutans roots) scales were described using pyro-sequencing, and the mycorrhizal functioning was quantified using a mycorrhizal-suppression treatment in the field (whole-plant-community scale) and a glasshouse inoculation experiment (single-plant-species scale). Nitrogen enrichment progressively reduced AM fungal abundance, changed AM fungal community composition, and shifted mycorrhizal functioning towards parasitism at both whole-plant-community and E. nutans scales. N-induced shifts in AM fungal community composition were tightly linked to soil N availability and/or plant species richness, whereas the shifts in mycorrhizal function were associated with the communities of specific AM fungal lineages. The observed changes in both AM fungal community structure and functioning across an N enrichment gradient highlight that N enrichment of ecosystems that are not P-limited can induce parasitic mycorrhizal functioning and influence plant community structure and ecosystem sustainability. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Anaerobic electron acceptor chemotaxis in Shewanella putrefaciens

NASA Technical Reports Server (NTRS)

Nealson, K. H.; Moser, D. P.; Saffarini, D. A.

1995-01-01

Shewanella putrefaciens MR-1 can grow either aerobically or anaerobically at the expense of many different electron acceptors and is often found in abundance at redox interfaces in nature. Such redox interfaces are often characterized by very strong gradients of electron acceptors resulting from rapid microbial metabolism. The coincidence of S. putrefaciens abundance with environmental gradients prompted an examination of the ability of MR-1 to sense and respond to electron acceptor gradients in the laboratory. In these experiments, taxis to the majority of the electron acceptors that S. putrefaciens utilizes for anaerobic growth was seen. All anaerobic electron acceptor taxis was eliminated by the presence of oxygen, nitrate, nitrite, elemental sulfur, or dimethyl sulfoxide, even though taxis to the latter was very weak and nitrate and nitrite respiration was normal in the presence of dimethyl sulfoxide. Studies with respiratory mutants of MR-1 revealed that several electron acceptors that could not be used for anaerobic growth nevertheless elicited normal anaerobic taxis. Mutant M56, which was unable to respire nitrite, showed normal taxis to nitrite, as well as the inhibition of taxis to other electron acceptors by nitrite. These results indicate that electron acceptor taxis in S. putrefaciens does not conform to the paradigm established for Escherichia coli and several other bacteria. Carbon chemo-taxis was also unusual in this organism: of all carbon compounds tested, the only positive response observed was to formate under anaerobic conditions.

A Dissolved Oxygen Threshold for Shifts in Bacterial Community Structure in a Seasonally Hypoxic Estuary.

PubMed

Spietz, Rachel L; Williams, Cheryl M; Rocap, Gabrielle; Horner-Devine, M Claire

2015-01-01

Pelagic ecosystems can become depleted of dissolved oxygen as a result of both natural processes and anthropogenic effects. As dissolved oxygen concentration decreases, energy shifts from macrofauna to microorganisms, which persist in these hypoxic zones. Oxygen-limited regions are rapidly expanding globally; however, patterns of microbial communities associated with dissolved oxygen gradients are not yet well understood. To assess the effects of decreasing dissolved oxygen on bacteria, we examined shifts in bacterial community structure over space and time in Hood Canal, Washington, USA-a glacial fjord-like water body that experiences seasonal low dissolved oxygen levels known to be detrimental to fish and other marine organisms. We found a strong negative association between bacterial richness and dissolved oxygen. Bacterial community composition across all samples was also strongly associated with the dissolved oxygen gradient, and significant changes in bacterial community composition occurred at a dissolved oxygen concentration between 5.18 and 7.12 mg O2 L(-1). This threshold value of dissolved oxygen is higher than classic definitions of hypoxia (<2.0 mg O2 L(-1)), suggesting that changes in bacterial communities may precede the detrimental effects on ecologically and economically important macrofauna. Furthermore, bacterial taxa responsible for driving whole community changes across the oxygen gradient are commonly detected in other oxygen-stressed ecosystems, suggesting that the patterns we uncovered in Hood Canal may be relevant in other low oxygen ecosystems.

Complementary ecosystem services provided by pest predators and pollinators increase quantity and quality of coffee yields

PubMed Central

Classen, Alice; Peters, Marcell K.; Ferger, Stefan W.; Helbig-Bonitz, Maria; Schmack, Julia M.; Maassen, Genevieve; Schleuning, Matthias; Kalko, Elisabeth K. V.; Böhning-Gaese, Katrin; Steffan-Dewenter, Ingolf

2014-01-01

Wild animals substantially support crop production by providing ecosystem services, such as pollination and natural pest control. However, the strengths of synergies between ecosystem services and their dependencies on land-use management are largely unknown. Here, we took an experimental approach to test the impact of land-use intensification on both individual and combined pollination and pest control services in coffee production systems at Mount Kilimanjaro. We established a full-factorial pollinator and vertebrate exclosure experiment along a land-use gradient from traditional homegardens (agroforestry systems), shaded coffee plantations to sun coffee plantations (total sample size = 180 coffee bushes). The exclusion of vertebrates led to a reduction in fruit set of ca 9%. Pollinators did not affect fruit set, but significantly increased fruit weight of coffee by an average of 7.4%. We found no significant decline of these ecosystem services along the land-use gradient. Pest control and pollination service were thus complementary, contributing to coffee production by affecting the quantity and quality of a major tropical cash crop across different coffee production systems at Mount Kilimanjaro. PMID:24500173

Complementary ecosystem services provided by pest predators and pollinators increase quantity and quality of coffee yields.

PubMed

Classen, Alice; Peters, Marcell K; Ferger, Stefan W; Helbig-Bonitz, Maria; Schmack, Julia M; Maassen, Genevieve; Schleuning, Matthias; Kalko, Elisabeth K V; Böhning-Gaese, Katrin; Steffan-Dewenter, Ingolf

2014-03-22

Wild animals substantially support crop production by providing ecosystem services, such as pollination and natural pest control. However, the strengths of synergies between ecosystem services and their dependencies on land-use management are largely unknown. Here, we took an experimental approach to test the impact of land-use intensification on both individual and combined pollination and pest control services in coffee production systems at Mount Kilimanjaro. We established a full-factorial pollinator and vertebrate exclosure experiment along a land-use gradient from traditional homegardens (agroforestry systems), shaded coffee plantations to sun coffee plantations (total sample size = 180 coffee bushes). The exclusion of vertebrates led to a reduction in fruit set of ca 9%. Pollinators did not affect fruit set, but significantly increased fruit weight of coffee by an average of 7.4%. We found no significant decline of these ecosystem services along the land-use gradient. Pest control and pollination service were thus complementary, contributing to coffee production by affecting the quantity and quality of a major tropical cash crop across different coffee production systems at Mount Kilimanjaro.

Rational and Efficient Preparative Isolation of Natural Products by MPLC-UV-ELSD based on HPLC to MPLC Gradient Transfer.

PubMed

Challal, Soura; Queiroz, Emerson Ferreira; Debrus, Benjamin; Kloeti, Werner; Guillarme, Davy; Gupta, Mahabir Prashad; Wolfender, Jean-Luc

2015-11-01

In natural product research, the isolation of biomarkers or bioactive compounds from complex natural extracts represents an essential step for de novo identification and bioactivity assessment. When pure natural products have to be obtained in milligram quantities, the chromatographic steps are generally labourious and time-consuming. In this respect, an efficient method has been developed for the reversed-phase gradient transfer from high-performance liquid chromatography to medium-performance liquid chromatography for the isolation of pure natural products at the level of tens of milligrams from complex crude natural extracts. The proposed method provides a rational way to predict retention behaviour and resolution at the analytical scale prior to medium-performance liquid chromatography, and guarantees similar performances at both analytical and preparative scales. The optimisation of the high-performance liquid chromatography separation and system characterisation allows for the prediction of the gradient at the medium-performance liquid chromatography scale by using identical stationary phase chemistries. The samples were introduced in medium-performance liquid chromatography using a pressure-resistant aluminium dry load cell especially designed for this study to allow high sample loading while maintaining a maximum achievable flow rate for the separation. The method has been validated with a mixture of eight natural product standards. Ultraviolet and evaporative light scattering detections were used in parallel for a comprehensive monitoring. In addition, post-chromatographic mass spectrometry detection was provided by high-throughput ultrahigh-performance liquid chromatography time-of-flight mass spectrometry analyses of all fractions. The processing of all liquid chromatography-mass spectrometry data in the form of an medium-performance liquid chromatography x ultra high-performance liquid chromatography time-of-flight mass spectrometry matrix enabled an efficient localisation of the compounds of interest in the generated fractions. The methodology was successfully applied for the separation of three different plant extracts that contain many diverse secondary metabolites. The advantages and limitations of this approach and the theoretical chromatographic background that rules such as liquid chromatography gradient transfer are presented from a practical viewpoint. Georg Thieme Verlag KG Stuttgart · New York.

A large-scale forest fragmentation experiment: the Stability of Altered Forest Ecosystems Project.

PubMed

Ewers, Robert M; Didham, Raphael K; Fahrig, Lenore; Ferraz, Gonçalo; Hector, Andy; Holt, Robert D; Kapos, Valerie; Reynolds, Glen; Sinun, Waidi; Snaddon, Jake L; Turner, Edgar C

2011-11-27

Opportunities to conduct large-scale field experiments are rare, but provide a unique opportunity to reveal the complex processes that operate within natural ecosystems. Here, we review the design of existing, large-scale forest fragmentation experiments. Based on this review, we develop a design for the Stability of Altered Forest Ecosystems (SAFE) Project, a new forest fragmentation experiment to be located in the lowland tropical forests of Borneo (Sabah, Malaysia). The SAFE Project represents an advance on existing experiments in that it: (i) allows discrimination of the effects of landscape-level forest cover from patch-level processes; (ii) is designed to facilitate the unification of a wide range of data types on ecological patterns and processes that operate over a wide range of spatial scales; (iii) has greater replication than existing experiments; (iv) incorporates an experimental manipulation of riparian corridors; and (v) embeds the experimentally fragmented landscape within a wider gradient of land-use intensity than do existing projects. The SAFE Project represents an opportunity for ecologists across disciplines to participate in a large initiative designed to generate a broad understanding of the ecological impacts of tropical forest modification.

A large-scale forest fragmentation experiment: the Stability of Altered Forest Ecosystems Project

PubMed Central

Ewers, Robert M.; Didham, Raphael K.; Fahrig, Lenore; Ferraz, Gonçalo; Hector, Andy; Holt, Robert D.; Kapos, Valerie; Reynolds, Glen; Sinun, Waidi; Snaddon, Jake L.; Turner, Edgar C.

2011-01-01

Opportunities to conduct large-scale field experiments are rare, but provide a unique opportunity to reveal the complex processes that operate within natural ecosystems. Here, we review the design of existing, large-scale forest fragmentation experiments. Based on this review, we develop a design for the Stability of Altered Forest Ecosystems (SAFE) Project, a new forest fragmentation experiment to be located in the lowland tropical forests of Borneo (Sabah, Malaysia). The SAFE Project represents an advance on existing experiments in that it: (i) allows discrimination of the effects of landscape-level forest cover from patch-level processes; (ii) is designed to facilitate the unification of a wide range of data types on ecological patterns and processes that operate over a wide range of spatial scales; (iii) has greater replication than existing experiments; (iv) incorporates an experimental manipulation of riparian corridors; and (v) embeds the experimentally fragmented landscape within a wider gradient of land-use intensity than do existing projects. The SAFE Project represents an opportunity for ecologists across disciplines to participate in a large initiative designed to generate a broad understanding of the ecological impacts of tropical forest modification. PMID:22006969

Gravity dependent processes and intracellular motion

NASA Technical Reports Server (NTRS)

Todd, Paul

1991-01-01

Most organelles large enough to sediment or to undergo isothermal settling within eukaryotic cells are held in position by one or more components of the cytoskeleton. The interior of eukaryotic cells is considered to be very crowded, and the evaluation of natural-convective processes is very difficult. In a most simple view, the cell may be considered as consisting of four immiscible phases among which solutes are exchanged causing steep concentration gradients and thermodynamic conditions far from equilibrium. Extracellular gravity-related forces may include natural convection due to solute gradients external to single cells or the work performed by swimming, ciliated, or elongating cells.

[Maintaining mechanism of species diversity of land plant communities].

PubMed

Shang, Wenyan; Wu, Gang; Fu, Xiao; Liu, Yang

2005-03-01

The maintaining mechanism of species diversity of land plant communities is a key and advancing edge in biodiversity study. Botanists and ecologists have presented many hypotheses and theories with controversies, and no general theory system was available. In this paper, the problem was reviewed mainly on two scales. The first was big spatial scale, aiming at the physical and natural factors that affect the species diversity, including histories and ages of plant communities, gradient changes such as latitude gradient, water gradient, altitude gradient and soil nutrients gradient, area effect, and isolation; and the second was concentrated on a special plant community, and mainly discussed the relationships of biodiversity with biotic factors (primary productivity, relationship between species, and gap dynamics) and abiotic factors (succession, disturbance and spatial heterogeneity, and human activity).

A simple method for MR elastography: a gradient-echo type multi-echo sequence.

PubMed

Numano, Tomokazu; Mizuhara, Kazuyuki; Hata, Junichi; Washio, Toshikatsu; Homma, Kazuhiro

2015-01-01

To demonstrate the feasibility of a novel MR elastography (MRE) technique based on a conventional gradient-echo type multi-echo MR sequence which does not need additional bipolar magnetic field gradients (motion encoding gradient: MEG), yet is sensitive to vibration. In a gradient-echo type multi-echo MR sequence, several images are produced from each echo of the train with different echo times (TEs). If these echoes are synchronized with the vibration, each readout's gradient lobes achieve a MEG-like effect, and the later generated echo causes a greater MEG-like effect. The sequence was tested for the tissue-mimicking agarose gel phantoms and the psoas major muscles of healthy volunteers. It was confirmed that the readout gradient lobes caused an MEG-like effect and the later TE images had higher sensitivity to vibrations. The magnitude image of later generated echo suffered the T2 decay and the susceptibility artifacts, but the wave image and elastogram of later generated echo were unaffected by these effects. In in vivo experiments, this method was able to measure the mean shear modulus of the psoas major muscle. From the results of phantom experiments and volunteer studies, it was shown that this method has clinical application potential. Copyright © 2014 Elsevier Inc. All rights reserved.

Evaluation of the qualitative and quantitative effectiveness of three media of centrifugation (Maxifreeze, Cushion Fluid Equine, and PureSperm 100) in preparation of fresh or frozen-thawed brown bear spermatozoa.

PubMed

Nicolas, M; Alvarez, M; Borragán, S; Martinez-Pastor, F; Chamorro, C A; Alvarez-Rodriguez, M; de Paz, P; Anel, L

2012-04-01

Centrifugation is a crucial procedure in sperm cryopreservation protocols of brown bear (Ursus arctos), because the semen must be processed to increase sperm concentration and/or clean urine-contaminated samples. The efficacy of three media for centrifugation (Maxifreeze [IMV technologies, L'Aigle, France], Cushion Fluid Equine (Minitübe, Tiefenbach, Germany), and PureSperm [Nidacon, Gothenburg, Sweden]) on the quality of bear spermatozoa was evaluated. In experiment one, two cushioned media used for protecting against mechanical stress during centrifugation were analyzed. In experiment two, a density gradient based on PureSperm was assessed in relation to the maximum retrieval and the quality of fresh spermatozoa, and the freezability of the spermatozoa selected in this density gradient was studied in experiment three. Finally, the selection of frozen-thawed sperm using PureSperm was analyzed in experiment four. Our results indicate that the use of dense isotonic cushion solutions (Maxifreeze, Cushion Fluid Equine) in centrifugation did not improve the quality of recovered spermatozoa compared with standard centrifugation. However, a density gradient prepared with PureSperm improved the quality of spermatozoa in fresh semen and frozen-thawed semen, but the spermatozoa selected from the fresh sample with this density gradient did not show a better resistance to freezing with this density gradient in comparison with the control sample. Copyright © 2012 Elsevier Inc. All rights reserved.

Temperature Gradients on the Cell Wall in the Critical Viscosity Experiment

NASA Technical Reports Server (NTRS)

Berg, Robert F.; Moldover, Michael R.

1993-01-01

Because of the diverging susceptibility delta rho/delta Tau near the liquid-vapor critical point, temperature gradients must be kept small to maintain adequate sample homogeneity. In our Science Requirements Document we paid particular attention to radial density gradients caused by equilibration of the xenon sample. Axial density gradients were addressed through the requirement that the cell's copper wall have a gradient less than 22 microK/m. This report re-examines the cell wall's temperature distribution in more detail by estimating all known significant contributions to temperature differences on the cell's wall.

High gradient RF test results of S-band and C-band cavities for medical linear accelerators

NASA Astrophysics Data System (ADS)

Degiovanni, A.; Bonomi, R.; Garlasché, M.; Verdú-Andrés, S.; Wegner, R.; Amaldi, U.

2018-05-01

TERA Foundation has proposed and designed hadrontherapy facilities based on novel linacs, i.e. high gradient linacs which accelerate either protons or light ions. The overall length of the linac, and therefore its cost, is almost inversely proportional to the average accelerating gradient. With the scope of studying the limiting factors for high gradient operation and to optimize the linac design, TERA, in collaboration with the CLIC Structure Development Group, has conducted a series of high gradient experiments. The main goals were to study the high gradient behavior and to evaluate the maximum gradient reached in 3 and 5.7 GHz structures to direct the design of medical accelerators based on high gradient linacs. This paper summarizes the results of the high power tests of 3.0 and 5.7 GHz single-cell cavities.

A bioenergetic basis for membrane divergence in archaea and bacteria.

PubMed

Sojo, Víctor; Pomiankowski, Andrew; Lane, Nick

2014-08-01

Membrane bioenergetics are universal, yet the phospholipid membranes of archaea and bacteria-the deepest branches in the tree of life-are fundamentally different. This deep divergence in membrane chemistry is reflected in other stark differences between the two domains, including ion pumping and DNA replication. We resolve this paradox by considering the energy requirements of the last universal common ancestor (LUCA). We develop a mathematical model based on the premise that LUCA depended on natural proton gradients. Our analysis shows that such gradients can power carbon and energy metabolism, but only in leaky cells with a proton permeability equivalent to fatty acid vesicles. Membranes with lower permeability (equivalent to modern phospholipids) collapse free-energy availability, precluding exploitation of natural gradients. Pumping protons across leaky membranes offers no advantage, even when permeability is decreased 1,000-fold. We hypothesize that a sodium-proton antiporter (SPAP) provided the first step towards modern membranes. SPAP increases the free energy available from natural proton gradients by ∼60%, enabling survival in 50-fold lower gradients, thereby facilitating ecological spread and divergence. Critically, SPAP also provides a steadily amplifying advantage to proton pumping as membrane permeability falls, for the first time favoring the evolution of ion-tight phospholipid membranes. The phospholipids of archaea and bacteria incorporate different stereoisomers of glycerol phosphate. We conclude that the enzymes involved took these alternatives by chance in independent populations that had already evolved distinct ion pumps. Our model offers a quantitatively robust explanation for why membrane bioenergetics are universal, yet ion pumps and phospholipid membranes arose later and independently in separate populations. Our findings elucidate the paradox that archaea and bacteria share DNA transcription, ribosomal translation, and ATP synthase, yet differ in equally fundamental traits that depend on the membrane, including DNA replication.

Glassy dynamics of landscape evolution.

PubMed

Ferdowsi, Behrooz; Ortiz, Carlos P; Jerolmack, Douglas J

2018-05-08

Soil creeps imperceptibly downhill, but also fails catastrophically to create landslides. Despite the importance of these processes as hazards and in sculpting landscapes, there is no agreed-upon model that captures the full range of behavior. Here we examine the granular origins of hillslope soil transport by discrete element method simulations and reanalysis of measurements in natural landscapes. We find creep for slopes below a critical gradient, where average particle velocity (sediment flux) increases exponentially with friction coefficient (gradient). At critical gradient there is a continuous transition to a dense-granular flow rheology. Slow earthflows and landslides thus exhibit glassy dynamics characteristic of a wide range of disordered materials; they are described by a two-phase flux equation that emerges from grain-scale friction alone. This glassy model reproduces topographic profiles of natural hillslopes, showing its promise for predicting hillslope evolution over geologic timescales. Copyright © 2018 the Author(s). Published by PNAS.

Graphite to diamond transformation during sediment-peridotite interaction at 7.5 and 10.5 GPa

NASA Astrophysics Data System (ADS)

Girnis, A. V.; Brey, G. P.; Bulatov, V. K.; Höfer, H. E.; Woodland, A. B.

2018-06-01

Diamond nucleation and growth were investigated experimentally at 7.5 and 10.5 GPa and temperatures up to 1500 °C. Samples consisted of two layers: i) H2O- and CO2-bearing model sediment and ii) graphite-bearing garnet harzburgite comprising natural minerals. Two experimental series were conducted, one under a controlled temperature gradient with the sedimentary layer usually in the cold zone and the other under isothermal conditions. In the latter case, diamond seeds were added to the sedimentary mixture. During the experiments, the sedimentary layer partially or completely melted, with the melt percolating and interacting with the adjacent harzburgite. The graphite-to-diamond transition in the peridotite was observed above 1300 °C at 7.5 GPa and 1200 °C at 10.5 GPa in the temperature-gradient experiments, and at temperatures 100 °C lower in the isothermal experiments with diamond seeds. Newly formed diamond occurs mostly as individual grains up to 10 μm in size and is separate from graphite aggregates. In some cases, an association of diamond with magnesite was observed. Diamond nucleation occurs in hydrous and CO2-bearing silicate melt following graphite dissolution and recrystallization. In the case of the diamond-magnesite association, diamond was probably formed through carbonate reduction coupled with graphite oxidation. The composition of the melts ranged from "carbonatitic" with 10 wt% SiO2 and >50 wt% volatiles to hydrous silicate with 40 wt% SiO2 and <10 wt% volatiles. This variation has no strong effect on diamond nucleation or growth.

Influence of surface wettability on transport mechanisms governing water droplet evaporation.

PubMed

Pan, Zhenhai; Weibel, Justin A; Garimella, Suresh V

2014-08-19

Prediction and manipulation of the evaporation of small droplets is a fundamental problem with importance in a variety of microfluidic, microfabrication, and biomedical applications. A vapor-diffusion-based model has been widely employed to predict the interfacial evaporation rate; however, its scope of applicability is limited due to incorporation of a number of simplifying assumptions of the physical behavior. Two key transport mechanisms besides vapor diffusion-evaporative cooling and natural convection in the surrounding gas-are investigated here as a function of the substrate wettability using an augmented droplet evaporation model. Three regimes are distinguished by the instantaneous contact angle (CA). In Regime I (CA ≲ 60°), the flat droplet shape results in a small thermal resistance between the liquid-vapor interface and substrate, which mitigates the effect of evaporative cooling; upward gas-phase natural convection enhances evaporation. In Regime II (60 ≲ CA ≲ 90°), evaporative cooling at the interface suppresses evaporation with increasing contact angle and counterbalances the gas-phase convection enhancement. Because effects of the evaporative cooling and gas-phase convection mechanisms largely neutralize each other, the vapor-diffusion-based model can predict the overall evaporation rates in this regime. In Regime III (CA ≳ 90°), evaporative cooling suppresses the evaporation rate significantly and reverses entirely the direction of natural convection induced by vapor concentration gradients in the gas phase. Delineation of these counteracting mechanisms reconciles previous debate (founded on single-surface experiments or models that consider only a subset of the governing transport mechanisms) regarding the applicability of the classic vapor-diffusion model. The vapor diffusion-based model cannot predict the local evaporation flux along the interface for high contact angle (CA ≥ 90°) when evaporative cooling is strong and the temperature gradient along the interface determines the peak local evaporation flux.

Large Eddy Simulations of Compositional Density Currents Flowing Over a Mobile Bed

NASA Astrophysics Data System (ADS)

Kyrousi, Foteini; Zordan, Jessica; Leonardi, Alessandro; Juez, Carmelo; Zanello, Francesca; Armenio, Vincenzo; Franca, Mário J.

2017-04-01

Density currents are a ubiquitous phenomenon caused by natural events or anthropogenic activities, and play an important role in the global sediment cycle; they are agents of long distance sediment transport in lakes, seas and oceans. Density gradients induced by salinity, temperature differences, or by the presence of suspended material are all possible triggers of a current. Such flows can travel long distances while eroding or depositing bed materials. This can provoke rapid topological changes, which makes the estimation of their transport capacity of prime interest for environmental engineering. Despite their relevance, field data regarding their dynamics is limited due to density currents scattered and unpredictable occurrence in nature. For this reason, laboratory experiments and numerical simulations have been a preferred way to investigate sediment transport processes associated to density currents. The study of entrainment and deposition processes requires detailed data of velocities spatial and temporal distributions in the boundary layer and bed shear stress, which are troublesome to obtain in laboratory. Motivated by this, we present 3D wall-resolved Large Eddy Simulations (LES) of density currents generated by lock-exchange. The currents travel over a smooth flat bed, which includes a section composed by erodible fine sediment susceptible of eroding. Several sediment sizes and initial density gradients are considered. The grid is set to resolve the velocity field within the boundary layer of the current (a tiny fraction of the total height), which in turn allows to obtain predictions of the bed shear stress. The numerical outcomes are compared with experimental data obtained with an analogous laboratory setting. In laboratory experiments salinity was chosen for generating the initial density gradient in order to facilitate the identification of entrained particles, since salt does not hinder the possibility to track suspended particles. Under these circumstances, it is possible to focus alone on the effect of the dynamics of the current on the particles entrainment. To achieve this, LES-filtered Navier-Stokes equations are coupled with two scalar transport equations: one for salinity and one for sediment concentration. We discuss the use of different sediment pick-up and settling formulations, which are key factors in reproducing the correct erosion and sedimentation mechanisms. The simulations show the emergence of longitudinal bed forms, and highlight the role of turbulent structures in the entrainment pattern for different regions within the current.

Nitrogen mineralization across an atmospheric nitrogen deposition gradient in Southern California deserts

Treesearch

L.E. Rao; D.R. Parker; Andrzej Bytnerowicz; E.B. Allen

2009-01-01

Dry nitrogen deposition is common in arid ecosystems near urban and agricultural centers, yet its impacts on natural environments are relatively understudied. We examined the effects of N deposition on soil N mineralization across a depositional gradient at Joshua Tree National Park. We hypothesized that N deposition affects N mineralization by promoting...

Near-field Development of a Turbulent Mixing Layer Periodically Forced by a Bimorph PVDF Film Actuator

NASA Astrophysics Data System (ADS)

Naka, Yoshitsugu; Tsuboi, Ken-Ichiro; Kametani, Yukinori; Fukagata, Koji; Obi, Shinnosuke

We have performed experiments in a turbulent mixing layer with periodic forcing introduced by a Piezo Film Actuator (PFA). Three different lengths of PFAs have been used, and the effects of various combinations of forcing amplitudes and frequencies are investigated. The forcing at the first and second sub-harmonic frequencies against the natural frequency enhances the development of the thickness of the mixing layer: the mixing layer spreads due to the forcing. On the other hand, the forcing near the natural frequency suppresses the development: the mean velocity gradient becomes steeper than the no control case. The vector pattern of the periodic velocity components indicated the formation of the vortical structure. By forcing at the natural and its first sub-harmonic frequencies, two counter-rotating vortices are clearly observed in one period of forcing. By forcing at second sub-harmonic frequency, the vortical structure is found only in the downstream region. The distribution of the periodic Reynolds shear stress significantly varies with the forcing frequency and it takes a positive value when forcing occurs near the natural frequency. However, the total value of the Reynolds shear stress remains negative due to the contribution of the turbulent components.

Salinity Gradients for Sustainable Energy: Primer, Progress, and Prospects.

PubMed

Yip, Ngai Yin; Brogioli, Doriano; Hamelers, Hubertus V M; Nijmeijer, Kitty

2016-11-15

Combining two solutions of different composition releases the Gibbs free energy of mixing. By using engineered processes to control the mixing, chemical energy stored in salinity gradients can be harnessed for useful work. In this critical review, we present an overview of the current progress in salinity gradient power generation, discuss the prospects and challenges of the foremost technologies - pressure retarded osmosis (PRO), reverse electrodialysis (RED), and capacitive mixing (CapMix) and provide perspectives on the outlook of salinity gradient power generation. Momentous strides have been made in technical development of salinity gradient technologies and field demonstrations with natural and anthropogenic salinity gradients (for example, seawater-river water and desalination brine-wastewater, respectively), but fouling persists to be a pivotal operational challenge that can significantly ebb away cost-competitiveness. Natural hypersaline sources (e.g., hypersaline lakes and salt domes) can achieve greater concentration difference and, thus, offer opportunities to overcome some of the limitations inherent to seawater-river water. Technological advances needed to fully exploit the larger salinity gradients are identified. While seawater desalination brine is a seemingly attractive high salinity anthropogenic stream that is otherwise wasted, actual feasibility hinges on the appropriate pairing with a suitable low salinity stream. Engineered solutions are foulant-free and can be thermally regenerative for application in low-temperature heat utilization. Alternatively, PRO, RED, and CapMix can be coupled with their analog separation process (reverse osmosis, electrodialysis, and capacitive deionization, respectively) in salinity gradient flow batteries for energy storage in chemical potential of the engineered solutions. Rigorous techno-economic assessments can more clearly identify the prospects of low-grade heat conversion and large-scale energy storage. While research attention is squarely focused on efficiency and power improvements, efforts to mitigate fouling and lower membrane and electrode cost will be equally important to reduce levelized cost of salinity gradient energy production and, thus, boost PRO, RED, and CapMix power generation to be competitive with other renewable technologies. Cognizance of the recent key developments and technical progress on the different technological fronts can help steer the strategic advancement of salinity gradient as a sustainable energy source.

Experimental Study of Instantaneous Evolution of A Scalar Gradient With Small-scale Anisotropic Injection In A 2d, Periodic Flow

NASA Astrophysics Data System (ADS)

Godard, G.; Paranthoen, P.; Gonzalez, M.

Anisotropic small-scale injection of a scalar (e.g. heat) in a turbulent medium can be performed by means of a small-diameter line source as already done in a turbulent plane jet and a turbulent boundary layer (Rosset et al., Phys. Fluids 13, 3729, 2001). In such conditions, however, experiment is revealed delicate especially, as regard to temperature gradient measurements in the near-field of the source. In the present study, we get rid of previous difficulties by setting up the heated line source in a simpler flow namely, a Bénard-von Kármán street. Under this situation, owing to a phase reference, the history of the instantaneous temperature gradient can be scrutinized from the vicinity of the source. Gradient statistics (second-order mo- ments, skewness, kurtosis ...) is derived which allows us to follow the evolution of anisotropy downstream of the line source. Alignment of temperature gradient with respect to strain principal axes is also analyzed. This experiment provides a precise knowledge of the way in which a scalar gradient evolves under the combined actions of strain, vorticity and molecular diffusion.

Opposing environmental gradients govern vegetation zonation in an intermountain playa

USGS Publications Warehouse

Sanderson, J.S.; Kotliar, N.B.; Steingraeber, D.A.

2008-01-01

Vegetation zonation was investigated at an intermountain playa wetland (Mishak Lakes) in the San Luis Valley (SLV) of southern Colorado. Plant composition and abiotic conditions were quantified in six vegetation zones. Reciprocal transplants were performed to test the importance of abiotic factors in governing zonation. Abiotic conditions differed among several vegetation zones. Prolonged inundation led to anaerobic soils in the Eleocharis palustris and the submerged aquatics zones, on the low end of the site's 1.25 m elevation gradient. On the high end of the gradient, soil salinity and sodicity (a measure of exchangeable sodium) were high in the Distichlis spicata zone (electrical conductivity, EC = 5.3 dS/m, sodium absorption ratio, SAR = 44.0) and extreme in the Sarcobatus vermiculatus zone (EC = 21 dS/m, SAR = 274). Transplanted species produced maximum biomass in the zone where they originated, not in any other higher or lower vegetation zone. The greatest overall transplant effect occurred for E. palustris, which experienced a ??? 77% decline in productivity when transplanted to other zones. This study provides evidence that physical factors are a major determinant of vegetation zone composition and distribution across the entire elevation gradient at Mishak Lakes. Patterns at Mishak Lakes arise from counter-directional stress gradients: a gradient from anaerobic to well-oxygenated from basin bottom to upland and a gradient from extremely high salinity to low salinity in the opposing direction. Because abiotic conditions dominate vegetation zonation, restoration of the altered hydrologic regime of this wetland to a natural hydrologic regime may be sufficient to re-establish many of the natural biodiversity functions provided by these wetlands. ?? 2008 The Society of Wetland Scientists.

Influence of convection on eutectic microstructure

NASA Technical Reports Server (NTRS)

Baskaran, V.; Eisa, G. F.; Wilcox, W. R.

1985-01-01

When the MnBi-Bi eutectic is directionally solidified, it forms fibers of MnBi in a matrix of bismuth. When the material solidified in space at rates of 30 and 50 cm/hr, the average fiber spacing lambda was about one half of the value obtained in cases in which the same material solidified on earth. Neither an altered temperature gradient nor a fluctuating freezing rate are apparently responsible for the change in lambda, and the possibility is studied that natural convection increases lambda on earth by perturbing the compositional field in the melt ahead of the growing solid. A theoretical analysis is conducted along with some experiments. On the basis of the theoretical results for lamellar growth, it is concluded that the spacing lambda increases with increasing stirring, especially at small freezing rates. The experiments indicate that at low growth rates the cross-sectional area of the MnBi blades increases with increased stirring and with decreased growth rate.

High-pressure structural, elastic, and electronic properties of the scintillator host material KMgF3

NASA Astrophysics Data System (ADS)

Vaitheeswaran, G.; Kanchana, V.; Kumar, Ravhi S.; Cornelius, A. L.; Nicol, M. F.; Svane, A.; Delin, A.; Johansson, B.

2007-07-01

The high-pressure structural behavior of the fluoroperovskite KMgF3 is investigated by theory and experiment. Density functional calculations were performed within the local density approximation and the generalized gradient approximation for exchange and correlation effects, as implemented within the full-potential linear muffin-tin orbital method. In situ high-pressure powder x-ray diffraction experiments were performed up to a maximum pressure of 40GPa using synchrotron radiation. We find that the cubic Pm3¯m crystal symmetry persists throughout the pressure range studied. The calculated ground state properties—the equilibrium lattice constant, bulk modulus, and elastic constants—are in good agreement with experimental results. By analyzing the ratio between the bulk and shear moduli, we conclude that KMgF3 is brittle in nature. Under ambient conditions, KMgF3 is found to be an indirect gap insulator, with the gap increasing under pressure.

Turbulent Transport of Fast Ions in the Large Plasma Device (LAPD)

NASA Astrophysics Data System (ADS)

Zhou, Shu; Heidbrink, William; McWilliams, Roger; Boehmer, Heinrich; Carter, Troy; Popovich, Pavel; Tripathi, Shreekrishna; Vincena, Steve; Jenko, Frank

2010-11-01

Due to gyroradius averaging and drift-orbit averaging, the transport of fast ions by microturbulence is often smaller than for thermal ions. In this experiment, Strong drift wave turbulence is observed in LAPD on gradients produced by a plate obstacle. Energetic lithium ions orbit through the turbulent region. Scans with a collimated analyzer and with probes give detailed profiles of the fast ion spatial distribution and of the fluctuating fields. The fast-ion transport decreases rapidly with increasing fast-ion gyroradius. Unlike the diffusive transport caused by Coulomb collisions, in this case the turbulent transport is non-diffusive. Analysis and simulation suggest that the fast ions interact ballistically with stationary two-dimensional electrostatic turbulence. The energy dependence of the transport is well explained by gyro-averaging theory. In new experiments, different sources and obstacles alter the drift-wave turbulence to modify the nature of the transport.

Mirage is an image in a flat ground surface.

PubMed

Tavassoly, M Taghi; Osanloo, Soghra; Salehpour, Ali

2015-04-01

Mirage is a fascinating phenomenon that has attracted many scientists to report their observations and descriptions about it. There are two different approaches to mirage formation. The more popular one is attributed to total internal reflection that occurs in the near ground air layers on hot sunny days. According to the other approach, mirage is an image in a rough surface that is observed at grazing angles of incidence. Most of the existing descriptions are qualitative and some include calculations based on guessing temperature change with no concrete experiments. In this report, first we show that Fermat's principle also concerns the wave nature of light and covers the constructive and destructive interference that is essential for image formation. Then, we provide a brief review of the image formation theory in a rough plane and demonstrate by experiments in the lab and deserts that the temperature gradient in the near ground air layers does not lead to mirage formation.

Open forum

NASA Technical Reports Server (NTRS)

1973-01-01

Some experiments on turbulent free shear layers in pressure gradients are discussed. Topics covered in the discussion include: (1) two dimensional vortex structures, (2) the effect of channel walls, and (3) the case of a mixing layer in pressure gradient.

Evidence of Magnetic Breakdown on the Defects With Thermally Suppressed Critical Field in High Gradient SRF Cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eremeev, Grigory; Palczewski, Ari

2013-09-01

At SRF 2011 we presented the study of quenches in high gradient SRF cavities with dual mode excitation technique. The data differed from measurements done in 80's that indicated thermal breakdown nature of quenches in SRF cavities. In this contribution we present analysis of the data that indicates that our recent data for high gradient quenches is consistent with the magnetic breakdown on the defects with thermally suppressed critical field. From the parametric fits derived within the model we estimate the critical breakdown fields.

Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruiz Ruiz, J.; White, A. E.; Ren, Y.

2015-12-15

Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the electron gyro-scale, k{sub ⊥}ρ{sub e} ≲ 1, can be responsible for anomalous electron thermal transport in NSTX. Electron scale (high-k) turbulence is diagnosed in NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report on stabilization effects of the electron density gradient on electron-scale density fluctuations in a set of neutral beam injection heated H-mode plasmas. We found that the absence of high-k density fluctuations from measurements is correlated with large equilibrium density gradient, which ismore » shown to be consistent with linear stabilization of ETG modes due to the density gradient using the analytical ETG linear threshold in F. Jenko et al. [Phys. Plasmas 8, 4096 (2001)] and linear gyrokinetic simulations with GS2 [M. Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)]. We also found that the observed power of electron-scale turbulence (when it exists) is anti-correlated with the equilibrium density gradient, suggesting density gradient as a nonlinear stabilizing mechanism. Higher density gradients give rise to lower values of the plasma frame frequency, calculated based on the Doppler shift of the measured density fluctuations. Linear gyrokinetic simulations show that higher values of the electron density gradient reduce the value of the real frequency, in agreement with experimental observation. Nonlinear electron-scale gyrokinetic simulations show that high electron density gradient reduces electron heat flux and stiffness, and increases the ETG nonlinear threshold, consistent with experimental observations.« less

RNA polymerase activity is associated with viral particles isolated from Leishmania braziliensis subsp. guyanensis.

PubMed Central

Widmer, G; Keenan, M C; Patterson, J L

1990-01-01

Viral particles purified from species of the protozoan parasite Leishmania braziliensis subsp. guyanensis by centrifugation in CsCl gradients were examined for the presence of viral polymerase. We demonstrated that RNA-dependent RNA polymerase is associated with viral particles. Viral transcription was studied in vitro with pulse-chase experiments and by assaying the RNase sensitivity of the viral transcripts. Viral polymerase synthesized full-length transcripts within 1 h. Double-strained, genome-length, and single-stranded RNAs were produced in this system. The nature of the RNA extracted from virions was also tested by RNase protection assays; both single-stranded and double-stranded RNAs were found. Images PMID:2370680

Rheology, tectonics, and the structure of the Venus lithosphere

NASA Technical Reports Server (NTRS)

Zuber, M. T.

1994-01-01

Given the absence of ground truth information on seismic structure, heat flow, and rock strength, or short wavelength gravity or magnetic data for Venus, information on the thermal, mechanical and compositional nature of the shallow interior must be obtained by indirect methods. Using pre-Magellan data, theoretical models constrained by the depths of impact craters and the length scales of tectonic features yielded estimates on the thickness of Venus' brittle-elastic lithosphere and the allowable range of crustal thickness and surface thermal gradient. The purpose of this study is to revisit the question of the shallow structure of Venus based on Magellan observations of the surface and recent experiments that address Venus' crustal rheology.

The Earth: Kinda like a Mai Tai?

NASA Astrophysics Data System (ADS)

Jellinek, M.

2005-12-01

Many problems in the Earth sciences involve fluid flow. Examples include the formation and differentiation of planets, mantle convection, plate tectonics, the generation of planetary magnetic fields, the generation, rise, and chemical differentiation of magmas, crystal nucleation and growth, sedimentation and mechanical erosion at riverbeds, and circulation in the atmosphere and oceans. In each of these situations fluid motions arise as a result of balances among body forces (e.g. effects of gravitational and magnetic fields) and (or) surface forces (e.g. effects of surface tension, shear and pressure gradients). Processes in which such force balance arise naturally are examples of ``Natural convection''. Familiar examples of natural convection include thermally-driven motions above a radiator in a cold room or inside a pot of pasta sauce warmed on a stove. Analog fluid mechanics experiments are a useful and fun way to isolate and learn about the mechanics of such processes. Experiments need not be done in a fluid dynamics laboratory. Indeed some of the most interesting occur in your favorite cocktails. In this demonstration I first use household materials from the kitchen and from the liquor cabinet to isolate and build understanding of individual examples of convection driven by thermal, compositional and surface tension effects over a range of conditions. Next, using more complicated experiments with actual and analog bar drinks I will present and analyze a number of coupled convective processes and also address the role of the rheology of the working fluids. In particular, the structure, transport and mixing properties of the motions are investigated.

On-chip gradient generation in 256 microfluidic cell cultures: simulation and experimental validation.

PubMed

Somaweera, Himali; Haputhanthri, Shehan O; Ibraguimov, Akif; Pappas, Dimitri

2015-08-07

A microfluidic diffusion diluter was used to create a stable concentration gradient for dose response studies. The microfluidic diffusion diluter used in this study consisted of 128 culture chambers on each side of the main fluidic channel. A calibration method was used to find unknown concentrations with 12% error. Flow rate dependent studies showed that changing the flow rates generated different gradient patterns. Mathematical simulations using COMSOL Multi-physics were performed to validate the experimental data. The experimental data obtained for the flow rate studies agreed with the simulation results. Cells could be loaded into culture chambers using vacuum actuation and cultured for long times under low shear stress. Decreasing the size of the culture chambers resulted in faster gradient formation (20 min). Mass transport into the side channels of the microfluidic diffusion diluter used in this study is an important factor in creating the gradient using diffusional mixing as a function of the distance. To demonstrate the device's utility, an H2O2 gradient was generated while culturing Ramos cells. Cell viability was assayed in the 256 culture chambers, each at a discrete H2O2 concentration. As expected, the cell viability for the high concentration side channels increased (by injecting H2O2) whereas the cell viability in the low concentration side channels decreased along the chip due to diffusional mixing as a function of distance. COMSOL simulations were used to identify the effective concentration of H2O2 for cell viability in each side chamber at 45 min. The gradient effects were confirmed using traditional H2O2 culture experiments. Viability of cells in the microfluidic device under gradient conditions showed a linear relationship with the viability of the traditional culture experiment. Development of the microfluidic device used in this study could be used to study hundreds of concentrations of a compound in a single experiment.

Biodegradation of PCE and TCE in landfill leachate predicted from concentrations of molecular hydrogen: a case study.

PubMed

Gonsoulin, Mary E; Wilson, Barbara H; Wilson, John T

2004-12-01

The Refuse Hideaway Landfill (23-acre) received municipal, commercial, and industrial waste between 1974 and 1988. It was designed as a "natural attenuation" landfill and no provision was made to collect and treat contaminated water. Natural biological degradation through sequential reductive dechlorination had been an important mechanism for natural attenuation at the site. We used the concentration of hydrogen to forecast whether reductive dechlorination would continue over time at particular locations in the plume. Based on published literature, reductive dechlorination and natural attenuation of PCE, TCE, and cis-DCE can be expected in the aquifer if the concentration of molecular hydrogen in monitoring wells are adequate (> 1 nanomolar). Reductive dechlorination can be expected to continue as the ground water moves down gradient. Natural attenuation through reductive dechlorination is not expected in flow paths that originate at down gradient monitoring wells with low concentrations of molecular hydrogen (< 1 nanomolar). In three monitoring wells at the margin of the landfill and in five monitoring wells down gradient of the landfill, ground water maintained a molecular hydrogen concentration, ranging from 1.30 to 9.17 nanomolar, that is adequate for reductive dechlorination. In three of the monitoring wells far down gradient of the landfill, the concentration of molecular hydrogen (0.33 to 0.83 nanomolar) was not adequate to support reductive dechlorination. In wells with adequate concentrations of hydrogen, the concentrations of chlorinated volatile organic compounds were attenuated over time, or concentrations of chlorinated volatile organics were below the detection limit. In wells with inadequate concentrations of hydrogen, the concentrations of chlorinated organic compounds attenuated at a slower rate over time. In wells with adequate hydrogen the first order rate of attenuation of PCE, TCE, cis-DCE and total chlorinated volatile organic compounds varies from 0.38 to 0.18 per year. In wells without adequate hydrogen the rate varies from 0.015 to 0.006 per year.

Generation of animal form by the Chordin/Tolloid/BMP gradient: 100 years after D'Arcy Thompson.

PubMed

De Robertis, Edward M; Moriyama, Yuki; Colozza, Gabriele

2017-09-01

The classic book "On Growth and Form" by naturalist D'Arcy Thompson was published 100 years ago. To celebrate this landmark, we present experiments in the Xenopus embryo that provide a framework for understanding how simple, quantitative transformations of a morphogen gradient might have affected evolution and morphological diversity of organisms. D'Arcy Thompson proposed that different morphologies might be generated by modifying physical parameters in an underlying system of Cartesian coordinates that pre-existed in Nature and arose during evolutionary history. Chordin is a BMP antagonist secreted by the Spemann organizer located on the dorsal side of the gastrula. Chordin generates a morphogen gradient as first proposed by mathematician Alan Turing. The rate-limiting step of this dorsal-ventral (D-V) morphogen is the degradation of Chordin by the Tolloid metalloproteinase in the ventral side. Chordin is expressed at gastrula on the dorsal side where BMP signaling is low, while at the opposite side peak levels of BMP signaling are reached. In fishes, amphibians, reptiles and birds, high BMP signaling in the ventral region induces transcription of a secreted inhibitor of Tolloid called Sizzled. By depleting Sizzled exclusively in the ventral half of the embryo we were able to expand the ventro-posterior region in an otherwise normal embryo. Conversely, ventral depletion of Tolloid, which stabilizes Chordin, decreased ventral and tail structures, phenocopying the tolloid zebrafish mutation. We explain how historical constraints recorded in the language of DNA become subject to the universal laws of physics when an ancestral reaction-diffusion morphogen gradient dictates form. © 2017 Japanese Society of Developmental Biologists.

Bubble behavior in molten glass in a temperature gradient. [in reduced gravity rocket experiment

NASA Technical Reports Server (NTRS)

Meyyappan, M.; Subramanian, R. S.; Wilcox, W. R.; Smith, H.

1982-01-01

Gas bubble motion in a temperature gradient was observed in a sodium borate melt in a reduced gravity rocket experiment under the NASA SPAR program. Large bubbles tended to move faster than smaller ones, as predicted by theory. When the bubbles contacted a heated platinum strip, motion virtually ceased because the melt only imperfectly wets platinum. In some cases bubble diameter increased noticeably with time.

Bird species turnover is related to changing predation risk along a vegetation gradient

USGS Publications Warehouse

LaManna, Joseph A.; Hemenway, Amy B.; Boccadori, Vanna; Martin, Thomas E.

2015-01-01

Turnover in animal species along vegetation gradients is often assumed to reflect adaptive habitat preferences that are narrower than the full gradient. Specifically, animals may decline in abundance where their reproductive success is low, and these poor-quality locations differ among species. Yet habitat use does not always appear adaptive. The crucial tests of how abundances and demographic costs of animals vary along experimentally manipulated vegetation gradients are lacking. We examined habitat use and nest predation rates for 16 bird species that exhibited turnover with shifts in deciduous and coniferous vegetation. For most bird species, decreasing abundance was associated with increasing predation rates along both natural and experimentally modified vegetation gradients. This landscape-scale approach strongly supports the idea that vegetation-mediated effects of predation are associated with animal distributions and species turnover.

High gradient RF test results of S-band and C-band cavities for medical linear accelerators

DOE PAGES

Degiovanni, A.; Bonomi, R.; Garlasche, M.; ...

2018-02-09

TERA Foundation has proposed and designed hadrontherapy facilities based on novel linacs, i.e. high gradient linacs which accelerate either protons or light ions. The overall length of the linac, and therefore its cost, is almost inversely proportional to the average accelerating gradient. With the scope of studying the limiting factors for high gradient operation and to optimize the linac design, TERA, in collaboration with the CLIC Structure Development Group, has conducted a series of high gradient experiments. The main goals were to study the high gradient behavior and to evaluate the maximum gradient reached in 3 and 5.7 GHz structuresmore » to direct the design of medical accelerators based on high gradient linacs. Lastly, this paper summarizes the results of the high power tests of 3.0 and 5.7 GHz single-cell cavities.« less

High gradient RF test results of S-band and C-band cavities for medical linear accelerators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Degiovanni, A.; Bonomi, R.; Garlasche, M.

TERA Foundation has proposed and designed hadrontherapy facilities based on novel linacs, i.e. high gradient linacs which accelerate either protons or light ions. The overall length of the linac, and therefore its cost, is almost inversely proportional to the average accelerating gradient. With the scope of studying the limiting factors for high gradient operation and to optimize the linac design, TERA, in collaboration with the CLIC Structure Development Group, has conducted a series of high gradient experiments. The main goals were to study the high gradient behavior and to evaluate the maximum gradient reached in 3 and 5.7 GHz structuresmore » to direct the design of medical accelerators based on high gradient linacs. Lastly, this paper summarizes the results of the high power tests of 3.0 and 5.7 GHz single-cell cavities.« less

Simultaneous schlieren photography and soot foil in the study of detonation phenomena

NASA Astrophysics Data System (ADS)

Kellenberger, Mark; Ciccarelli, Gaby

2017-10-01

The use of schlieren photography has been essential in unravelling the complex nature of high-speed combustion phenomena, but its line-of-sight integration makes it difficult to decisively determine the nature of multi-dimensional combustion wave propagation. Conventional schlieren alone makes it impossible to determine in what plane across the channel an observed structure may exist. To overcome this, a technique of simultaneous high-speed schlieren photography and soot foils was demonstrated that can be applied to the study of detonation phenomena. Using a kerosene lamp, soot was deposited on a glass substrate resulting in a semi-transparent sheet through which schlieren source light could pass. In order to demonstrate the technique, experiments were carried out in mixtures of stoichiometric hydrogen-oxygen at initial pressures between 10 and 15 kPa. Compared to schlieren imaging obtained without a sooted foil, high-speed video results show schlieren images with a small reduction of contrast with density gradients remaining clear. Areas of high temperature cause soot lofted from the foil to incandescence strongly, resulting in the ability to track hot spots and flame location. Post-processing adjustments were demonstrated to make up for camera sensitivity limitations to enable viewing of schlieren density gradients. High-resolution glass soot foils were produced that enable direct coupling of schlieren video to triple-point trajectories seen on the soot foils, allowing for the study of three-dimensional propagation mechanisms of detonation waves.

BlochSolver: A GPU-optimized fast 3D MRI simulator for experimentally compatible pulse sequences

NASA Astrophysics Data System (ADS)

Kose, Ryoichi; Kose, Katsumi

2017-08-01

A magnetic resonance imaging (MRI) simulator, which reproduces MRI experiments using computers, has been developed using two graphic-processor-unit (GPU) boards (GTX 1080). The MRI simulator was developed to run according to pulse sequences used in experiments. Experiments and simulations were performed to demonstrate the usefulness of the MRI simulator for three types of pulse sequences, namely, three-dimensional (3D) gradient-echo, 3D radio-frequency spoiled gradient-echo, and gradient-echo multislice with practical matrix sizes. The results demonstrated that the calculation speed using two GPU boards was typically about 7 TFLOPS and about 14 times faster than the calculation speed using CPUs (two 18-core Xeons). We also found that MR images acquired by experiment could be reproduced using an appropriate number of subvoxels, and that 3D isotropic and two-dimensional multislice imaging experiments for practical matrix sizes could be simulated using the MRI simulator. Therefore, we concluded that such powerful MRI simulators are expected to become an indispensable tool for MRI research and development.

B1 gradient coherence selection using a tapered stripline.

PubMed

van Meerten, S G J; Tijssen, K C H; van Bentum, P J M; Kentgens, A P M

2018-01-01

Pulsed-field gradients are common in modern liquid state NMR pulse sequences. They are often used instead of phase cycles for the selection of coherence pathways, thereby decreasing the time required for the NMR experiment. Soft off-resonance pulses with a B 1 gradient result in a spatial encoding similar to that created by pulsed-field (B 0 ) gradients. In this manuscript we show that pulse sequences with pulsed-field gradients can easily be converted to one which uses off-resonance B 1 field gradient (OFFBEAT) pulses. The advantage of B 1 gradient pulses for coherence selection is that the chemical shift evolution during the pulses is (partially) suppressed. Therefore no refocusing echos are required to correct for evolution during the gradient pulses. A tapered stripline is shown to be a convenient tool for creating a well-defined gradient in the B 1 field strength. B 1 gradient coherence selection using a tapered stripline is a simple and cheap alternative to B 0 pulsed-field gradients. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Reptile Embryos Lack the Opportunity to Thermoregulate by Moving within the Egg.

PubMed

Telemeco, Rory S; Gangloff, Eric J; Cordero, Gerardo A; Mitchell, Timothy S; Bodensteiner, Brooke L; Holden, Kaitlyn G; Mitchell, Sarah M; Polich, Rebecca L; Janzen, Fredric J

2016-07-01

Historically, egg-bound reptile embryos were thought to passively thermoconform to the nest environment. However, recent observations of thermal taxis by embryos of multiple reptile species have led to the widely discussed hypothesis that embryos behaviorally thermoregulate. Because temperature affects development, such thermoregulation could allow embryos to control their fate far more than historically assumed. We assessed the opportunity for embryos to behaviorally thermoregulate in nature by examining thermal gradients within natural nests and eggs of the common snapping turtle (Chelydra serpentina; which displays embryonic thermal taxis) and by simulating thermal gradients within nests across a range of nest depths, egg sizes, and soil types. We observed little spatial thermal variation within nests, and thermal gradients were poorly transferred to eggs. Furthermore, thermal gradients sufficiently large and constant for behavioral thermoregulation were not predicted to occur in our simulations. Gradients of biologically relevant magnitude have limited global occurrence and reverse direction twice daily when they do exist, which is substantially faster than embryos can shift position within the egg. Our results imply that reptile embryos will rarely, if ever, have the opportunity to behaviorally thermoregulate by moving within the egg. We suggest that embryonic thermal taxis instead represents a play behavior, which may be adaptive or selectively neutral, and results from the mechanisms for behavioral thermoregulation in free-living stages coming online prior to hatching.

A comprehensive study on rotation reversal in KSTAR: experimental observations and modelling

NASA Astrophysics Data System (ADS)

Na, D. H.; Na, Yong-Su; Angioni, C.; Yang, S. M.; Kwon, J. M.; Jhang, Hogun; Camenen, Y.; Lee, S. G.; Shi, Y. J.; Ko, W. H.; Lee, J. A.; Hahm, T. S.; KSTAR Team

2017-12-01

Dedicated experiments have been performed in KSTAR Ohmic plasmas to investigate the detailed physics of the rotation reversal phenomena. Here we adapt the more general definition of rotation reversal, a large change of the intrinsic toroidal rotation gradient produced by minor changes in the control parameters (Camenen et al 2017 Plasma Phys. Control. Fusion 59 034001), which is commonly observed in KSTAR regardless of the operating conditions. The two main phenomenological features of the rotation reversal are the normalized toroidal rotation gradient ({{u}\\prime} ) change in the gradient region and the existence of an anchor point. For the KSTAR Ohmic plasma database including the experiment results up to the 2016 experimental campaign, both features were investigated. First, the observations show that the locations of the gradient and the anchor point region are dependent on {{q}95} . Second, a strong dependence of {{u}\\prime} on {νeff} is clearly observed in the gradient region, whereas the dependence on R/{{L}{{Ti}}} , R/{{L}{{Te}}} , and R/{{L}{{ne}}} is unclear considering the usual variation of the normalized gradient length in KSTAR. The experimental observations were compared against several theoretical models. The rotation reversal might not occur due to the transition of the dominant turbulence from the trapped electron mode to the ion temperature gradient mode or the neoclassical equilibrium effect in KSTAR. Instead, it seems that the profile shearing effects associated with a finite ballooning tilting well reproduce the experimental observations of both the gradient region and the anchor point; the difference seems to be related to the magnetic shear and the q value. Further analysis implies that the increase of {{u}\\prime} in the gradient region with the increase of the collisionality would occur when the reduction of the momentum diffusivity is comparatively larger than the reduction of the residual stress. It is supported by the perturbative analysis of the experiments and the nonlinear gyrokinetic simulations. The absence of the sign change of {{u}\\prime} even when a much lower collisionality is produced by additional electron cyclotron heating brings further experimental support to this interpretation.

Suppressing Electron Turbulence and Triggering Internal Transport Barriers with Reversed Magnetic Shear in the National Spherical Torus Experiment

NASA Astrophysics Data System (ADS)

Peterson, Jayson Luc

2011-10-01

Observations in the National Spherical Torus Experiment (NSTX) have found electron temperature gradients that greatly exceed the linear threshold for the onset for electron temperature gradient-driven (ETG) turbulence. These discharges, deemed electron internal transport barriers (e-ITBs), coincide with a reversal in the shear of the magnetic field and with a reduction in electron-scale density fluctuations, qualitatively consistent with earlier gyrokinetic predictions. To investigate this phenomenon further, we numerically model electron turbulence in NSTX reversed-shear plasmas using the gyrokinetic turbulence code GYRO. These first-of-a-kind nonlinear gyrokinetic simulations of NSTX e-ITBs confirm that reversing the magnetic shear can allow the plasma to reach electron temperature gradients well beyond the critical gradient for the linear onset of instability. This effect is very strong, with the nonlinear threshold for significant transport approaching three times the linear critical gradient in some cases, in contrast with moderate shear cases, which can drive significant ETG turbulence at much lower gradients. In addition to the experimental implications of this upshifted nonlinear critical gradient, we explore the behavior of ETG turbulence during reversed shear discharges. This work is supported by the SciDAC Center for the Study of Plasma Microturbulence, DOE Contract DE-AC02-09CH11466, and used the resources of NCCS at ORNL and NERSC at LBNL. M. Ono et al., Nucl. Fusion 40, 557 (2000).

The Effect of Concomitant Fields in Fast Spin Echo Acquisition on Asymmetric MRI Gradient Systems

PubMed Central

Tao, Shengzhen; Weavers, Paul T.; Trzasko, Joshua D.; Huston, John; Shu, Yunhong; Gray, Erin M.; Foo, Thomas K.F.; Bernstein, Matt A.

2017-01-01

Purpose To investigate the effect of the asymmetric gradient concomitant fields (CF) with zeroth and first-order spatial dependence on fast/turbo spin-echo acquisitions, and to demonstrate the effectiveness of their real-time compensation. Methods After briefly reviewing the CF produced by asymmetric gradients, the effects of the additional zeroth and first-order CFs on these systems are investigated using extended-phase graph simulations. Phantom and in vivo experiments are performed to corroborate the simulation. Experiments are performed before and after the real-time compensations using frequency tracking and gradient pre-emphasis to demonstrate their effectiveness in correcting the additional CFs. The interaction between the CFs and prescan-based correction to compensate for eddy currents is also investigated. Results It is demonstrated that, unlike the second-order CFs on conventional gradients, the additional zeroth/first-order CFs on asymmetric gradients cause substantial signal loss and dark banding in fast spin-echo acquisitions within a typical brain-scan field of view. They can confound the prescan correction for eddy currents and degrade image quality. Performing real-time compensation successfully eliminates the artifacts. Conclusions We demonstrate that the zeroth/first-order CFs specific to asymmetric gradients can cause substantial artifacts, including signal loss and dark bands for brain imaging. These effects can be corrected using real-time compensation. PMID:28643408

Climate impacts on soil carbon processes along an elevation gradient in the tropical Luquillo Experimental Forest

Treesearch

Dingfang Chen; Mei Yu; Grizelle González; Xiaoming Zou; Qiong Gao

2017-01-01

Tropical forests play an important role in regulating the global climate and the carbon cycle. With the changing temperature and moisture along the elevation gradient, the Luquillo Experimental Forest in Northeastern Puerto Rico provides a natural approach to understand tropical forest ecosystems under climate change. In this study, we conducted a soil translocation...

Holocene vegetation and fire history of the Coast Range, western Oregon, USA

Treesearch

Colin J. Long; Cathy Whitlock; Patrick J. Bartlein

2007-01-01

Pollen and high-resolution charcoal records from three lakes were examined to reconstruct the vegetation and fire history of the Oregon Coast Range for the last 9000 years. The sites are located along a north to- south effective precipitation gradient and changes in vegetation and fire activity provided information on the nature of this gradient in the past. The...

Regional patterns in foliar 15N across a gradient of nitrogen deposition in the northeastern US

Treesearch

Linda H. Pardo; Steven G. McNulty; Johnny L. Boggs; Sara Duke

2007-01-01

Recent studies have demonstrated that natural abundance 15N can be a useful tool for assessing nitrogen saturation, because as nitrification and nitrate loss increase, d15N of foliage and soil also increases. We measured foliar d15N at 11 high-elevation spruce-fir stands along an N deposition gradient...

Regional patterns in foliar 15N across a gradient of nitrogen deposition in the northeastern US

Treesearch

Linda H. Pardo; Steven G. McNulty; Johnny L. Boggs; Sara Duke

2007-01-01

Recent studies have demonstrated that natural abundance 15N can be a useful tool for assessing nitrogen saturation, because as nitrification and nitrate loss increase, a15N of foliage and soil also increases. We measured foliar a15N at 11 high-elevation spruce-fir stands along an N deposition gradient...

A numerical experiment that provides new results regarding the inception of separation in the flow around a circular cylinder

NASA Astrophysics Data System (ADS)

Malamataris, Nikolaos; Liakos, Anastasios

2015-11-01

The exact value of the Reynolds number regarding the inception of separation in the flow around a circular cylinder is still a matter of research. This work connects the inception of separation with the calculation of a positive pressure gradient around the circumference of the cylinder. The hypothesis is that inception of separation occurs when the pressure gradient becomes positive around the circumference. From the most cited laboratory experiments that have dealt with that subject of inception of separation only Thom has measured the pressure gradient there at very low Reynolds numbers (up to Re=3.5). For this reason, the experimental conditions of his tunnel are simulated in a new numerical experiment. The full Navier Stokes equations in both two and three dimensions are solved with a home made code that utilizes Galerkin finite elements. In the two dimensional numerical experiment, inception of separation is observed at Re=4.3, which is the lowest Reynolds number where inception has been reported computationally. Currently, the three dimensional experiment is under way, in order to compare if there are effects of three dimensional theory of separation in the conditions of Thom's experiments.

No-reference image quality assessment based on natural scene statistics and gradient magnitude similarity

NASA Astrophysics Data System (ADS)

Jia, Huizhen; Sun, Quansen; Ji, Zexuan; Wang, Tonghan; Chen, Qiang

2014-11-01

The goal of no-reference/blind image quality assessment (NR-IQA) is to devise a perceptual model that can accurately predict the quality of a distorted image as human opinions, in which feature extraction is an important issue. However, the features used in the state-of-the-art "general purpose" NR-IQA algorithms are usually natural scene statistics (NSS) based or are perceptually relevant; therefore, the performance of these models is limited. To further improve the performance of NR-IQA, we propose a general purpose NR-IQA algorithm which combines NSS-based features with perceptually relevant features. The new method extracts features in both the spatial and gradient domains. In the spatial domain, we extract the point-wise statistics for single pixel values which are characterized by a generalized Gaussian distribution model to form the underlying features. In the gradient domain, statistical features based on neighboring gradient magnitude similarity are extracted. Then a mapping is learned to predict quality scores using a support vector regression. The experimental results on the benchmark image databases demonstrate that the proposed algorithm correlates highly with human judgments of quality and leads to significant performance improvements over state-of-the-art methods.

Isotopic composition of water vapor near the air-water interface

NASA Astrophysics Data System (ADS)

Zannoni, Daniele; Bergamasco, Andrea; Peschiutta, Mirco; Rampazzo, Giancarlo; Stenni, Barbara

2017-04-01

Evaporation is a key process in water cycle that links liquid water to the atmosphere. In the last fifty years stable isotopes of hydrogen and oxygen have been intensively used to describe climate processes related to evaporation and precipitation, ranging in different spatial and temporal scales. Evaporation introduces large isotopic effects in the phases involved. The well known Craig-Gordon model (Craig & Gordon, 1965) describes those isotopic effects involving several steps and different processes, moving from the air-water interface to the free atmosphere. However, very few works in literature have tested the vertical behavior of the Craig-Gordon model in natural conditions on both fresh and marine waters. In this work we present the results from four field experiments aimed to describe the vertical variability of δ18O and δD in the first few meters over a large water body (the coastal lagoon of Venice, northern Italy) and to test the Craig-Gordon model in such conditions. Each experiment involved cryotrapping of water vapor at different height over the water surface (0.1m, 2m and 4m) and the sampling of the liquid water at two depth (surface and 0.5m). During the experiments, water vapor was also sampled in the nearest mainland (˜2.5 km from gradient measurements) to determine the isotopic composition of background water vapor. Liquid samples were then analyzed with a Picarro L1102-i and Thermo-Fisher Delta Plus Advantage for water vapor and lagoon water, respectively. The last two experiments have also involved simultaneous measurements of relative humidity using commercially-available humidity probes at each height. This approach was used to determine a reference scale in order to compare observations to modeled estimates. Despite the coarse time resolution due to cryotrapping method (measurements are averaged over 1.5 hours), preliminary results show measurable differences in the isotopic composition of water vapor along the vertical gradient and good agreement between observations and predicted values from the model. Even if this work is an exploratory phase it shows an interesting potential to grow our understanding of the processes involved as well as a useful implementation for future studies focused on fractionation of water isotopes due to evaporation in natural conditions. References Craig, H., & Gordon, L. I. (1965). Deuterium and oxygen 18 variations in the ocean and the marine atmosphere.

Diffusion pore imaging with generalized temporal gradient profiles.

PubMed

Laun, Frederik B; Kuder, Tristan A

2013-09-01

In porous material research, one main interest of nuclear magnetic resonance diffusion (NMR) experiments is the determination of the shape of pores. While it has been a longstanding question if this is in principle achievable, it has been shown recently that it is indeed possible to perform NMR-based diffusion pore imaging. In this work we present a generalization of these previous results. We show that the specific temporal gradient profiles that were used so far are not unique as more general temporal diffusion gradient profiles may be used. These temporal gradient profiles may consist of any number of "short" gradient pulses, which fulfil the short-gradient approximation. Additionally, "long" gradient pulses of small amplitude may be present, which can be used to fulfil the rephasing condition for the complete profile. Some exceptions exist. For example, classical q-space gradients consisting of two short gradient pulses of opposite sign cannot be used as the phase information is lost due to the temporal antisymmetry of this profile. Copyright © 2013 Elsevier Inc. All rights reserved.

Surface Tension Gradients Induced by Temperature: The Thermal Marangoni Effect

ERIC Educational Resources Information Center

Gugliotti, Marcos; Baptisto, Mauricio S.; Politi, Mario J.

2004-01-01

Surface tensions gradients were generated in a thin liquid film because of the local increase in temperature, for demonstration purposes. This is performed using a simple experiment and allows different alternatives for heat generation to be used.

Extraction of espresso coffee by using gradient of temperature. Effect on physicochemical and sensorial characteristics of espresso.

PubMed

Salamanca, C Alejandra; Fiol, Núria; González, Carlos; Saez, Marc; Villaescusa, Isabel

2017-01-01

Espresso extraction is generally carried out at a fixed temperature within the range 85-95°C. In this work the extraction of the espressos was made in a new generation coffee machine that enables temperature profiling of the brewing water. The effect of using gradient of temperature to brew espressos on physicochemical and sensorial characteristics of the beverage has been investigated. Three different extraction temperature profiles were tested: updrawn gradient (88-93°C), downdrawn gradient (93-88°C) and fixed temperature (90°C). The coffee species investigated were Robusta, Arabica natural and Washed Arabica. Results proved that the use of gradient temperature for brewing espressos allows increasing or decreasing the extraction of some chemical compounds from coffee grounds. Moreover an appropriate gradient of temperature can highlight or hide some sensorial attributes. In conclusion, the possibility of programming gradient of temperature in the coffee machines recently introduced in the market opens new expectations in the field of espresso brewing. Copyright © 2016 Elsevier Ltd. All rights reserved.

Se Isotopes as groundwater redox indicators: Detecting natural attenuation of Se at an in situ recovery U mine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anirban, Basu; Schilling, Kathrin; Brown, Shaun T.

One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. Here in this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradientmore » wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ 82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ 82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of $-$2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Moreover, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.« less

Se Isotopes as groundwater redox indicators: Detecting natural attenuation of Se at an in situ recovery U mine

DOE PAGES

Anirban, Basu; Schilling, Kathrin; Brown, Shaun T.; ...

2016-08-22

One of the major ecological concerns associated with the in situ recovery (ISR) of uranium (U) is the environmental release of soluble, toxic selenium (Se) oxyanions generated by mining. Post-mining natural attenuation by the residual reductants in the ore body and reduced down-gradient sediments should mitigate the risk of Se contamination in groundwater. Here in this work, we investigate the Se concentrations and Se isotope systematics of groundwater and of U ore bearing sediments from an ISR site at Rosita, TX, USA. Our results show that selenate (Se(VI)) is the dominant Se species in Rosita groundwater, and while several up-gradientmore » wells have elevated Se(VI), the majority of the ore zone and down-gradient wells have little or no Se oxyanions. In addition, the δ 82SeVI of Rosita groundwater is generally elevated relative to the U ore up to +6.14‰, with the most enriched values observed in the ore-zone wells. Increasing δ 82Se with decreasing Se(VI) conforms to a Rayleigh type distillation model with an ε of $-$2.25‰ ± 0.61‰, suggesting natural Se(VI) reduction occurring along the hydraulic gradient at the Rosita ISR site. Moreover, our results show that Se isotopes are excellent sensors for detecting and monitoring post-mining natural attenuation of Se oxyanions at ISR sites.« less

The influence of natural and anthropic environmental variables on the structure and spatial distribution along longitudinal gradient of macroinvertebrate communities in southern Brazilian streams

PubMed Central

Batalla Salvarrey, Andrea Vanessa; Kotzian, Carla Bender; Spies, Márcia Regina; Braun, Bruna

2014-01-01

Abstract Southern Brazilian rivers and streams have been intensively affected by human activities, especially agriculture and the release of untreated domestic sewage. However, data about the aquatic macroinvertebrates in these streams are scarce and limited to only certain groups. In addition, studies focusing on the structure and spatial distribution of these communities are lacking. This study analyzed the effects of natural and anthropic variables on the community structure of macroinvertebrates along a longitudinal gradient in three microbasins located in a region of landscape transition in the state of Rio Grande do Sul, Brazil. Sampling was conducted in the Vacacaí-Mirim River (August 2008) and in the Ibicuí-Mirim and Tororaipí rivers (August 2009) following an environmental gradient including 1 st , 2 nd , 3 rd , and 4 th order segments. Local natural factors that were analyzed include water temperature, pH, electrical conductivity, dissolved oxygen, substrate granulometry, and the presence of aquatic vegetation. Anthropic variables that were analyzed include including bank erosion, land use, urbanization, riparian deforestation, and fine sediments input. A total of 42 families and 129 taxa were found, with predominance of environmentally tolerant taxa. Geological context (landscape transition and large hydrographic basins) tended to influence natural environmental factors along the rivers’ longitudinal gradients. However, changes in anthropic variables were not affected by these geological differences and therefore did not correlate with patterns of spatial distribution in macroinvertebrate communities. Only 1 st order stream segments showed a community composition with high richness of taxa intolerant to anthropic disturbance. Richness as a whole tended to be higher in 3 rd to 4 th order set of segments, but this trend was a result of local anthropic environmental disturbances. Future inventories conducted in similar landscape transition regions of Brazil, for conservation purposes, must consider stream segments of different orders, microbasins, and major basins in order to obtain data that faithfully reflect the regional diversity. Additionally, it is necessary to consider environmental gradients of land use and anthropic impacts in order to suggest appropriate strategies for conserving the environmental integrity of streams. PMID:25373160

The Borden Micrometeorological Experiment 2009 (BMW09): Micrometeorology and Stable Isotopes for Carbon Cycle Studies

NASA Astrophysics Data System (ADS)

Warland, J. S.; Wagner-Riddle, C.; Staebler, R. M.; Lee, X.; Bartlett, P. A.; Brown, S. E.; Kim, K.; Santos, E. A.; Chang, K.

2009-12-01

A large collaborative experiment took place during summer 2009 at the Environment Canada tower site on CFB Borden in southern Ontario. The site is a long-term flux monitoring station, instrumented for eddy covariance measurements of CO2 and H2O, soil respiration, canopy profiles of CO2, H2O and temperature, net radiation, and standard meteorological variables. During BMW09, we brought to the site additional instrumentation to monitor gradients of stable isotopes of CO2 and H2O, turbulence profiles in the canopy and additional soil respiration data. Tunable diode laser trace gas analyzers were used to make continuous, high-frequency measurements of 12CO2, 13CO2 and C16O18O and H216O, HDO and H218O. Measurements were made of gradients of these isotopes above the canopy and in the understory. Profiles of CO2, H2O, temperature and turbulence statistics were measured for inverse Lagrangian analysis, where concentration profiles are used to determine source strength profiles through the canopy, thus separating soil, understory and overstory components of the net exchange made by eddy covariance. The project combines stable isotope measurements with novel micrometeorological techniques with the goal of developing improved operational measurements and gaining new insight into carbon and water cycles through this two-pronged approach. The overall goal of this intensive measurement campaign was to provide detailed data on the carbon and water cycles within this natural ecosystem for use in model testing and improvement. Specifically, the project will use this data with the C&N-CLASS model (the Canadian Land Surface Scheme with additional carbon and nitrogen routines) to improve its ability to predict changes to natural ecosystems under a changing climate when used within GCM simulations. This poster will present an overview of the project, highlight preliminary results, and illustrate how these disparate datasets will be tied together to provide new insight into carbon cycling.

[Fast optimization of stepwise gradient conditions for ternary mobile phase in reversed-phase high performance liquid chromatography].

PubMed

Shan, Yi-chu; Zhang, Yu-kui; Zhao, Rui-huan

2002-07-01

In high performance liquid chromatography, it is necessary to apply multi-composition gradient elution for the separation of complex samples such as environmental and biological samples. Multivariate stepwise gradient elution is one of the most efficient elution modes, because it combines the high selectivity of multi-composition mobile phase and shorter analysis time of gradient elution. In practical separations, the separation selectivity of samples can be effectively adjusted by using ternary mobile phase. For the optimization of these parameters, the retention equation of samples must be obtained at first. Traditionally, several isocratic experiments are used to get the retention equation of solute. However, it is time consuming especially for the separation of complex samples with a wide range of polarity. A new method for the fast optimization of ternary stepwise gradient elution was proposed based on the migration rule of solute in column. First, the coefficients of retention equation of solute are obtained by running several linear gradient experiments, then the optimal separation conditions are searched according to the hierarchical chromatography response function which acts as the optimization criterion. For each kind of organic modifier, two initial linear gradient experiments are used to obtain the primary coefficients of retention equation of each solute. For ternary mobile phase, only four linear gradient runs are needed to get the coefficients of retention equation. Then the retention times of solutes under arbitrary mobile phase composition can be predicted. The initial optimal mobile phase composition is obtained by resolution mapping for all of the solutes. A hierarchical chromatography response function is used to evaluate the separation efficiencies and search the optimal elution conditions. In subsequent optimization, the migrating distance of solute in the column is considered to decide the mobile phase composition and sustaining time of the latter steps until all the solutes are eluted out. Thus the first stepwise gradient elution conditions are predicted. If the resolution of samples under the predicted optimal separation conditions is satisfactory, the optimization procedure is stopped; otherwise, the coefficients of retention equation are adjusted according to the experimental results under the previously predicted elution conditions. Then the new stepwise gradient elution conditions are predicted repeatedly until satisfactory resolution is obtained. Normally, the satisfactory separation conditions can be found only after six experiments by using the proposed method. In comparison with the traditional optimization method, the time needed to finish the optimization procedure can be greatly reduced. The method has been validated by its application to the separation of several samples such as amino acid derivatives, aromatic amines, in which satisfactory separations were obtained with predicted resolution.

Few multiyear precipitation-reduction experiments find a shift in the productivity-precipitation relationship.

PubMed

Estiarte, Marc; Vicca, Sara; Peñuelas, Josep; Bahn, Michael; Beier, Claus; Emmett, Bridget A; Fay, Philip A; Hanson, Paul J; Hasibeder, Roland; Kigel, Jaime; Kröel-Dulay, Gyorgy; Larsen, Klaus Steenberg; Lellei-Kovács, Eszter; Limousin, Jean-Marc; Ogaya, Romà; Ourcival, Jean-Marc; Reinsch, Sabine; Sala, Osvaldo E; Schmidt, Inger Kappel; Sternberg, Marcelo; Tielbörger, Katja; Tietema, Albert; Janssens, Ivan A

2016-07-01

Well-defined productivity-precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity-precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation-reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effects of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation-manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity-precipitation relationship downward the spatial fit. The majority of experiments (72%) showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land-model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation-reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid. © 2016 John Wiley & Sons Ltd.

Designing gradient coils with reduced hot spot temperatures.

PubMed

While, Peter T; Forbes, Larry K; Crozier, Stuart

2010-03-01

Gradient coil temperature is an important concern in the design and construction of MRI scanners. Closely spaced gradient coil windings cause temperature hot spots within the system as a result of Ohmic heating associated with large current being driven through resistive material, and can strongly affect the performance of the coils. In this paper, a model is presented for predicting the spatial temperature distribution of a gradient coil, including the location and extent of temperature hot spots. Subsequently, a method is described for designing gradient coils with improved temperature distributions and reduced hot spot temperatures. Maximum temperature represents a non-linear constraint and a relaxed fixed point iteration routine is proposed to adjust coil windings iteratively to minimise this coil feature. Several examples are considered that assume different thermal material properties and cooling mechanisms for the gradient system. Coil winding solutions are obtained for all cases considered that display a considerable drop in hot spot temperature (>20%) when compared to standard minimum power gradient coils with equivalent gradient homogeneity, efficiency and inductance. The method is semi-analytical in nature and can be adapted easily to consider other non-linear constraints in the design of gradient coils or similar systems. Crown Copyright (c) 2009. Published by Elsevier Inc. All rights reserved.

Sensitivity to ocean acidification parallels natural pCO2 gradients experienced by Arctic copepods under winter sea ice

PubMed Central

Lewis, Ceri N.; Brown, Kristina A.; Edwards, Laura A.; Cooper, Glenn; Findlay, Helen S.

2013-01-01

The Arctic Ocean already experiences areas of low pH and high CO2, and it is expected to be most rapidly affected by future ocean acidification (OA). Copepods comprise the dominant Arctic zooplankton; hence, their responses to OA have important implications for Arctic ecosystems, yet there is little data on their current under-ice winter ecology on which to base future monitoring or make predictions about climate-induced change. Here, we report results from Arctic under-ice investigations of copepod natural distributions associated with late-winter carbonate chemistry environmental data and their response to manipulated pCO2 conditions (OA exposures). Our data reveal that species and life stage sensitivities to manipulated OA conditions were correlated with their vertical migration behavior and with their natural exposures to different pCO2 ranges. Vertically migrating adult Calanus spp. crossed a pCO2 range of >140 μatm daily and showed only minor responses to manipulated high CO2. Oithona similis, which remained in the surface waters and experienced a pCO2 range of <75 μatm, showed significantly reduced adult and nauplii survival in high CO2 experiments. These results support the relatively untested hypothesis that the natural range of pCO2 experienced by an organism determines its sensitivity to future OA and highlight that the globally important copepod species, Oithona spp., may be more sensitive to future high pCO2 conditions compared with the more widely studied larger copepods. PMID:24297880

Influence of the Latitudinal Temperature Gradient on Soil Dust Concentration and Deposition in Greenland

NASA Technical Reports Server (NTRS)

Tegen, Ina; Rind, David

2000-01-01

To investigate the effects of changes in the latitudinal temperature gradient and the global mean temperature on dust concentration in the Northern Hemisphere, experiments with the Goddard Institute for Space Studies General Circulation Model (GISS GCM) are performed. The dust concentration over Greenland is calculated from sources in central and eastern Asia, which are integrated on-line in the model. The results show that an increase in the latitudinal temperature gradient increases both the Asian dust source strength and the concentration over Greenland. The source increase is the result of increased surface winds, and to a minor extent, the increase in Greenland dust is also associated with increased northward transport. Cooling the climate in addition to this increased gradient leads to a decrease in precipitation scavenging, which helps produce a further (slight) increase in Greenland dust in this experiment. Reducing the latitudinal gradient reduces the surface wind and hence the dust source, with a subsequent reduction in Greenland dust concentrations. Warming the climate in addition to this reduced gradient leads to a further reduction in Greenland dust due to enhanced precipitation scavenging. These results can be used to evaluate the relationship of Greenland ice core temperature changes to changes in the latitudinal and global temperatures.

Thermal-gradient migration of brine inclusions in salt crystals

NASA Astrophysics Data System (ADS)

Yagnik, S. K.

1982-09-01

High level nuclear waste disposal in a geologic repository was proposed. Natural salt deposits which are considered contain a small volume fraction of water in the form of brine inclusions distributed throughout the salt. Radioactive decay heating of the nuclear wastes will impose a temperature gradient on the surrounding salt which mobilizes the brine inclusions. Inclusions filled completely with brine migrate up the temperature gradient and eventually accumulate brine near the buried waste forms. The brine may slowly corrode or degrade the waste forms which is undesirable. In this work, thermal gradient migration of both all liquid and gas liquid inclusions was experimentally studied in synthetic single crystals of NaCl and KCl using a hot stage attachment to an optical microscope which was capable of imposing temperature gradients and axial compressive loads on the crystals. The migration velocities of the inclusion shape and size are discussed.

A study on the unsteady flow of two immiscible micropolar and Newtonian fluids through a horizontal channel: A numerical approach

NASA Astrophysics Data System (ADS)

Devakar, M.; Raje, Ankush

2018-05-01

The unsteady flow of two immiscible micropolar and Newtonian fluids through a horizontal channel is considered. In addition to the classical no-slip and hyper-stick conditions at the boundary, it is assumed that the fluid velocities and shear stresses are continuous across the fluid-fluid interface. Three cases for the applied pressure gradient are considered to study the problem: one with constant pressure gradient and the other two cases with time-dependent pressure gradients, viz. periodic and decaying pressure gradient. The Crank-Nicolson approach has been used to obtain numerical solutions for fluid velocity and microrotation for diverse sets of fluid parameters. The nature of fluid velocities and microrotation with various values of pressure gradient, Reynolds number, ratio of viscosities, micropolarity parameter and time is illustrated through graphs. It has been observed that micropolarity parameter and ratio of viscosities reduce the fluid velocities.

Morphology of melt-rich channels formed during reaction infiltration experiments on partially molten mantle rocks

NASA Astrophysics Data System (ADS)

Pec, Matej; Holtzman, Benjamin; Zimmerman, Mark; Kohlstedt, David

2016-04-01

Geochemical, geophysical and geological observations suggest that melt extraction from the partially molten mantle occurs by some sort of channelized flow. Melt-solid reactions can lead to melt channelization due to a positive feedback between melt flow and reaction. If a melt-solid reaction increases local permeability, subsequent flow is increased as well and promotes further reaction. This process can lead to the development of high-permeability channels which emerge from background flow. In nature, anastomozing tabular dunite bodies within peridotitic massifs are thought to represent fossilized channels that formed by reactive flow. The conditions under which such channels can emerge are treated by the reaction infiltration instability (RII) theory (e.g. Szymczak and Ladd 2014). In this contribution, we report the results of a series of Darcy type experiments designed to study the development of channels due to RII in mantle lithologies (Pec et al. 2015). We sandwiched a partially molten rock between a melt source and a porous sink and annealed it at high-pressures (P = 300 MPa) and high-temperatures (T = 1200° or 1250° C) under a controlled pressure gradient (∇P = 0-100 MPa/mm) for up to 5 hours. The partially molten rock is formed by 50:50 mixtures of San Carlos olivine (Ol, Fo ˜ 88) and clinopyroxene (Cpx) with either 4, 10 or 20 vol% of alkali basalt added. The source and sink are disks of alkali basalt and porous alumina, respectively. During the experiments, silica undersaturated melt from the melt source dissolves Cpx and precipitates an iron rich Ol (Fo ˜ 82) thereby forming a Cpx-free reaction layer at the melt source - partially molten rock interface. The melt fraction in the reaction layer increases significantly (40% melt) compared to the protolith, confirming that the reaction increases the permeability of the partially molten rock. In experiments annealed under a low pressure gradient (and hence slow melt flow velocity) the reaction layer is planar and no channels develop. However, if the melt migration velocity exceeds ˜5 μm/s the reaction layer locally protrudes into the partially molten rock forming finger-like melt-rich channels. The morphology and spacing of the channels depends on the initial melt fraction. With 20 vol% melt, multiple and voluminous channels with an elliptical core formed of pure melt develop. At lower melt contents, fewer and thinner channels develop. Our experiments demonstrate that melt-rock reactions can lead to melt channelization in mantle lithologies. The morphology of the channels seems to depend on the initial permeability perturbations present in the starting material. The observed lithological transformations are in broad agreement with natural observations. However, the resulting channels lack the tabular anastomozing shapes which are likely caused by shear deformation in nature. Therefore, both reaction-driven as well as stress-driven melt segregation have to interact in nature to form the observed dunite channels. Szymczak, P., and A. J. C. Ladd (2014), Reactive-infiltration instabilities in rocks. Part 2. Dissolution of a porous matrix, J. Fluid Mech., 738, 591-630. Pec, M., B. K. Holtzman, M. Zimmerman, and D. L. Kohlstedt (2015), Reaction infiltration instabilities in experiments on partially molten mantle rocks, Geology, 43(7), 575-578, doi:10.1130/G36611.1.

A general strategy for performing temperature-programming in high performance liquid chromatography--prediction of segmented temperature gradients.

PubMed

Wiese, Steffen; Teutenberg, Thorsten; Schmidt, Torsten C

2011-09-28

In the present work it is shown that the linear elution strength (LES) model which was adapted from temperature-programming gas chromatography (GC) can also be employed to predict retention times for segmented-temperature gradients based on temperature-gradient input data in liquid chromatography (LC) with high accuracy. The LES model assumes that retention times for isothermal separations can be predicted based on two temperature gradients and is employed to calculate the retention factor of an analyte when changing the start temperature of the temperature gradient. In this study it was investigated whether this approach can also be employed in LC. It was shown that this approximation cannot be transferred to temperature-programmed LC where a temperature range from 60°C up to 180°C is investigated. Major relative errors up to 169.6% were observed for isothermal retention factor predictions. In order to predict retention times for temperature gradients with different start temperatures in LC, another relationship is required to describe the influence of temperature on retention. Therefore, retention times for isothermal separations based on isothermal input runs were predicted using a plot of the natural logarithm of the retention factor vs. the inverse temperature and a plot of the natural logarithm of the retention factor vs. temperature. It could be shown that a plot of lnk vs. T yields more reliable isothermal/isocratic retention time predictions than a plot of lnk vs. 1/T which is usually employed. Hence, in order to predict retention times for temperature-gradients with different start temperatures in LC, two temperature gradient and two isothermal measurements have been employed. In this case, retention times can be predicted with a maximal relative error of 5.5% (average relative error: 2.9%). In comparison, if the start temperature of the simulated temperature gradient is equal to the start temperature of the input data, only two temperature-gradient measurements are required. Under these conditions, retention times can be predicted with a maximal relative error of 4.3% (average relative error: 2.2%). As an example, the systematic method development for an isothermal as well as a temperature gradient separation of selected sulfonamides by means of the adapted LES model is demonstrated using a pure water mobile phase. Both methods are compared and it is shown that the temperature-gradient separation provides some advantages over the isothermal separation in terms of limits of detection and analysis time. Copyright © 2011 Elsevier B.V. All rights reserved.

A Dissolved Oxygen Threshold for Shifts in Bacterial Community Structure in a Seasonally Hypoxic Estuary

PubMed Central

Spietz, Rachel L.; Williams, Cheryl M.; Rocap, Gabrielle; Horner-Devine, M. Claire

2015-01-01

Pelagic ecosystems can become depleted of dissolved oxygen as a result of both natural processes and anthropogenic effects. As dissolved oxygen concentration decreases, energy shifts from macrofauna to microorganisms, which persist in these hypoxic zones. Oxygen-limited regions are rapidly expanding globally; however, patterns of microbial communities associated with dissolved oxygen gradients are not yet well understood. To assess the effects of decreasing dissolved oxygen on bacteria, we examined shifts in bacterial community structure over space and time in Hood Canal, Washington, USA−a glacial fjord-like water body that experiences seasonal low dissolved oxygen levels known to be detrimental to fish and other marine organisms. We found a strong negative association between bacterial richness and dissolved oxygen. Bacterial community composition across all samples was also strongly associated with the dissolved oxygen gradient, and significant changes in bacterial community composition occurred at a dissolved oxygen concentration between 5.18 and 7.12 mg O2 L-1. This threshold value of dissolved oxygen is higher than classic definitions of hypoxia (<2.0 mg O2 L-1), suggesting that changes in bacterial communities may precede the detrimental effects on ecologically and economically important macrofauna. Furthermore, bacterial taxa responsible for driving whole community changes across the oxygen gradient are commonly detected in other oxygen-stressed ecosystems, suggesting that the patterns we uncovered in Hood Canal may be relevant in other low oxygen ecosystems. PMID:26270047

Pulsed field gradients in simulations of one- and two-dimensional NMR spectra.

PubMed

Meresi, G H; Cuperlovic, M; Palke, W E; Gerig, J T

1999-03-01

A method for the inclusion of the effects of z-axis pulsed field gradients in computer simulations of an arbitrary pulsed NMR experiment with spin (1/2) nuclei is described. Recognizing that the phase acquired by a coherence following the application of a z-axis pulsed field gradient bears a fixed relation to its order and the spatial position of the spins in the sample tube, the sample is regarded as a collection of volume elements, each phase-encoded by a characteristic, spatially dependent precession frequency. The evolution of the sample's density matrix is thus obtained by computing the evolution of the density matrix for each volume element. Following the last gradient pulse, these density matrices are combined to form a composite density matrix which evolves through the rest of the experiment to yield the observable signal. This approach is implemented in a program which includes capabilities for rigorous inclusion of spin relaxation by dipole-dipole, chemical shift anisotropy, and random field mechanisms, plus the effects of arbitrary RF fields. Mathematical procedures for accelerating these calculations are described. The approach is illustrated by simulations of representative one- and two-dimensional NMR experiments. Copyright 1999 Academic Press.

Predictive mapping of forest composition and structure with direct gradient analysis and nearest neighbor imputation in coastal Oregon, U.S.A.

Treesearch

Janet L. Ohmann; Matthew J. Gregory

2002-01-01

Spatially explicit information on the species composition and structure of forest vegetation is needed at broad spatial scales for natural resource policy analysis and ecological research. We present a method for predictive vegetation mapping that applies direct gradient analysis and nearest-neighbor imputation to ascribe detailed ground attributes of vegetation to...

Natural abundance 15N in soil and litter across a nitrate-output gradient in New Hampshire

Treesearch

L.H. Pardo; H.F. Hemond; J.P. Montoya; J. Pett-Ridge

2007-01-01

Stable isotopes of nitrogen are potentially a valuable tool for regional assessments of nitrogen saturation because they provide an integrated measure of the past nitrogen cycling history of a site. We measured δ15N of soil and litter, as well as net nitrification potential, at three sites across a nitrate-loss gradient in the White...

A landscape model for predicting potential natural vegetation of the Olympic Peninsula USA using boundary equations and newly developed environmental variables.

Treesearch

Jan A. Henderson; Robin D. Lesher; David H. Peter; Chris D. Ringo

2011-01-01

A gradient-analysis-based model and grid-based map are presented that use the potential vegetation zone as the object of the model. Several new variables are presented that describe the environmental gradients of the landscape at different scales. Boundary algorithms are conceptualized, and then defined, that describe the environmental boundaries between vegetation...

Diffusion with chemical reaction: An attempt to explain number density anomalies in experiments involving alkali vapor

NASA Technical Reports Server (NTRS)

Snow, W. L.

1974-01-01

The mutual diffusion of two reacting gases is examined which takes place in a bath of inert gas atoms. Solutions are obtained between concentric spheres, each sphere acting as a source for one of the reactants. The calculational model is used to illustrate severe number density gradients observed in absorption experiments with alkali vapor. Severe gradients result when sq root k/D R is approximately 5 where k, D, and R are respectively the second order rate constant, the multicomponent diffusion constant, and the geometrical dimension of the experiment.

Natural convection in binary gases driven by combined horizontal thermal and vertical solutal gradients

NASA Technical Reports Server (NTRS)

Weaver, J. A.; Viskanta, Raymond

1992-01-01

An investigation of natural convection is presented to examine the influence of a horizontal temperature gradient and a concentration gradient occurring from the bottom to the cold wall in a cavity. As the solutal buoyancy force changes from augmenting to opposing the thermal buoyancy force, the fluid motion switches from unicellular to multicellular flow (fluid motion is up the cold wall and down the hot wall for the bottom counterrotating flow cell). Qualitatively, the agreement between predicted streamlines and smoke flow patterns is generally good. In contrast, agreement between measured and predicted temperature and concentration distributions ranges from fair to poor. Part of the discrepancy can be attributed to experimental error. However, there remains considerable discrepancy between data and predictions due to the idealizations of the mathematical model, which examines only first-order physical effects. An unsteady flow, variable thermophysical properties, conjugate effects, species interdiffusion, and radiation were not accounted for in the model.

The evolution of distributed sensing and collective computation in animal populations

PubMed Central

Hein, Andrew M; Rosenthal, Sara Brin; Hagstrom, George I; Berdahl, Andrew; Torney, Colin J; Couzin, Iain D

2015-01-01

Many animal groups exhibit rapid, coordinated collective motion. Yet, the evolutionary forces that cause such collective responses to evolve are poorly understood. Here, we develop analytical methods and evolutionary simulations based on experimental data from schooling fish. We use these methods to investigate how populations evolve within unpredictable, time-varying resource environments. We show that populations evolve toward a distinctive regime in behavioral phenotype space, where small responses of individuals to local environmental cues cause spontaneous changes in the collective state of groups. These changes resemble phase transitions in physical systems. Through these transitions, individuals evolve the emergent capacity to sense and respond to resource gradients (i.e. individuals perceive gradients via social interactions, rather than sensing gradients directly), and to allocate themselves among distinct, distant resource patches. Our results yield new insight into how natural selection, acting on selfish individuals, results in the highly effective collective responses evident in nature. DOI: http://dx.doi.org/10.7554/eLife.10955.001 PMID:26652003

Riparian rehabilitation planning in an urban-rural gradient: Integrating social needs and ecological conditions.

PubMed

Guida-Johnson, Bárbara; Zuleta, Gustavo A

2017-09-01

In the present context of global change and search for sustainability, we detected a gap between restoration and society: local communities are usually only considered as threats or disturbances when planning for restoration. To bridge this gap, we propose a landscape design framework for planning riparian rehabilitation in an urban-rural gradient. A spatial multi-criteria analysis was used to assess the priority of riversides by considering two rehabilitation objectives simultaneously-socio-environmental and ecological-and two sets of criteria were designed according to these objectives. The assessment made it possible to identify 17 priority sites for riparian rehabilitation that were associated with different conditions along the gradient. The double goal setting enabled a dual consideration of citizens, both as beneficiaries and potential impacts to rehabilitation, and the criteria selected incorporated the multi-dimensional nature of the environment. This approach can potentially be adapted and implemented in any other anthropic-natural interface throughout the world.

ASSESSING ABUNDANCE DISTRIBUTIONS IN NATURAL COMMUNITIES OF ECTOMYCORRHIZAS ALONG AN ENVIRONMENTAL GRADIENT

EPA Science Inventory

Alpha diversity indices often fail to distinguish between natural populations that a more detailed investigation of the distribution of ramets among types would show are quite different. We studied the effectiveness of applying SHE analyses to morphotype classifications of ectom...

Adaptations between ecotypes and along environmental gradients in Panicum virgatum

USDA-ARS?s Scientific Manuscript database

Determining the patterns and mechanisms of adaptation to different habitats across the natural landscape is of fundamental importance to understanding the differentiation of populations and the evolution of new species. Most recent studies of habitat-mediated natural selection in the wild have focus...

Enigmatic Extinction: An Investigation of the 2175Å Extinction Bump in M101

NASA Astrophysics Data System (ADS)

Danowski, Meredith E.; Cook, Timothy; Gordon, Karl D.; Chakrabarti, Supriya; Lawton, Brandon L.; Misselt, Karl A.

2014-06-01

Evidence from studies of starburst galaxies indicates that active formation of high mass stars modifies the UV dust extinction curve as seen by a lack of the characteristic 2175Å bump. For over 45 years, the source of the 2175Å extinction feature has yet to be positively identified. Small aromatic/PAH grains are suggested as a leading contender in dust grain models. The face-on spiral galaxy M101 is an ideal laboratory for the study of dust, with many well-studied HII regions and a steep metallicity and ionization gradient.The Interstellar Medium Absorption Gradient Experiment Rocket (IMAGER) probes the correlation between dust extinction, and the metallicity and radiation environment in M101 at ultraviolet wavelengths. IMAGER simultaneously images M101 in three 400Å-wide bandpasses, measuring the apparent strength of the 2175Å bump and the UV continuum.Combining data from IMAGER with high S/N far- and near- UV observations from the MAMA detectors on the Hubble STIS instrument, we examine the apparent strength of the 2175Å bump in HII regions of M101. With additional infrared data from Spitzer, the DIRTY radiative transfer model, and stellar evolution models, we probe the correlation between the 2175Å feature and the aromatic/PAH features across HII regions of varying metallicity and radiation field hardness. The results of this experiment will directly impact our understanding of the nature of dust and our ability to accurately account for the effects of dust on observations at all redshifts.

Investigation of the magnetic properties of Si-gradient steel sheet by comparison with 6.5%Si steel sheet

NASA Astrophysics Data System (ADS)

Hiratani, T.; Zaizen, Y.; Oda, Y.; Yoshizaki, S.; Senda, K.

2018-05-01

In this study, we investigated the magnetic properties of Si-gradient steel sheet produced by CVD (chemical vapor deposition) siliconizing process, comparing with 6.5% Si steel sheet. The Si-gradient steel sheet having silicon concentration gradient in the thickness direction, has larger hysteresis loss and smaller eddy current loss than the 6.5% Si steel sheet. In such a loss configuration, the iron loss of the Si-gradient steel sheet becomes lower than that of the 6.5% Si steel sheet at high frequencies. The experiment suggests that tensile stress is formed at the surface layer and compressive stress is formed at the inner layer in the Si gradient steel sheet. The magnetic anisotropy is induced by the internal stress and it is considered to affect the magnetization behavior of the Si-gradient steel sheet. The small eddy current loss of Si-gradient steel sheet can be explained as an effect of magnetic flux concentration on the surface layer.

Reduced calcification and lack of acclimatization by coral colonies growing in areas of persistent natural acidification.

PubMed

Crook, Elizabeth D; Cohen, Anne L; Rebolledo-Vieyra, Mario; Hernandez, Laura; Paytan, Adina

2013-07-02

As the surface ocean equilibrates with rising atmospheric CO2, the pH of surface seawater is decreasing with potentially negative impacts on coral calcification. A critical question is whether corals will be able to adapt or acclimate to these changes in seawater chemistry. We use high precision CT scanning of skeletal cores of Porites astreoides, an important Caribbean reef-building coral, to show that calcification rates decrease significantly along a natural gradient in pH and aragonite saturation (Ωarag). This decrease is accompanied by an increase in skeletal erosion and predation by boring organisms. The degree of sensitivity to reduced Ωarag measured on our field corals is consistent with that exhibited by the same species in laboratory CO2 manipulation experiments. We conclude that the Porites corals at our field site were not able to acclimatize enough to prevent the impacts of local ocean acidification on their skeletal growth and development, despite spending their entire lifespan in low pH, low Ωarag seawater.

Few multi-year precipitation-reduction experiments find a shift in the productivity-precipitation relationship

DOE PAGES

Estiarte, Marc; Vicca, Sara; Penuelas, Josep; ...

2016-04-06

Well-defined productivity–precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity–precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation–reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effectsmore » of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation–manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity–precipitation relationship downward the spatial fit. Seventy two percent of expiriments showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land-model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation–reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid.« less

Few multi-year precipitation-reduction experiments find a shift in the productivity-precipitation relationship

DOE Office of Scientific and Technical Information (OSTI.GOV)

Estiarte, Marc; Vicca, Sara; Penuelas, Josep

Well-defined productivity–precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity–precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation–reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effectsmore » of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation–manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity–precipitation relationship downward the spatial fit. Seventy two percent of expiriments showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land-model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation–reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid.« less

Probing of molecular replication and accumulation in shallow heat gradients through numerical simulations.

PubMed

Keil, Lorenz; Hartmann, Michael; Lanzmich, Simon; Braun, Dieter

2016-07-27

How can living matter arise from dead matter? All known living systems are built around information stored in RNA and DNA. To protect this information against molecular degradation and diffusion, the second law of thermodynamics imposes the need for a non-equilibrium driving force. Following a series of successful experiments using thermal gradients, we have shown that heat gradients across sub-millimetre pores can drive accumulation, replication, and selection of ever longer molecules, implementing all the necessary parts for Darwinian evolution. For these lab experiments to proceed with ample speed, however, the temperature gradients have to be quite steep, reaching up to 30 K per 100 μm. Here we use computer simulations based on experimental data to show that 2000-fold shallower temperature gradients - down to 100 K over one metre - can still drive the accumulation of protobiomolecules. This finding opens the door for various environments to potentially host the origins of life: volcanic, water-vapour, or hydrothermal settings. Following the trajectories of single molecules in simulation, we also find that they are subjected to frequent temperature oscillations inside these pores, facilitating e.g. template-directed replication mechanisms. The tilting of the pore configuration is the central strategy to achieve replication in a shallow temperature gradient. Our results suggest that shallow thermal gradients across porous rocks could have facilitated the formation of evolutionary machines, significantly increasing the number of potential sites for the origin of life on young rocky planets.

Limited-memory trust-region methods for sparse relaxation

NASA Astrophysics Data System (ADS)

Adhikari, Lasith; DeGuchy, Omar; Erway, Jennifer B.; Lockhart, Shelby; Marcia, Roummel F.

2017-08-01

In this paper, we solve the l2-l1 sparse recovery problem by transforming the objective function of this problem into an unconstrained differentiable function and applying a limited-memory trust-region method. Unlike gradient projection-type methods, which uses only the current gradient, our approach uses gradients from previous iterations to obtain a more accurate Hessian approximation. Numerical experiments show that our proposed approach eliminates spurious solutions more effectively while improving computational time.

Studies of turbulent round jets through experimentation, simulation, and modeling

NASA Astrophysics Data System (ADS)

Keedy, Ryan

This thesis studies the physics of the turbulent round jet. In particular, it focuses on three different problems that have the turbulent round jet as their base flow. The first part of this thesis examines a compressible turbulent round jet at its sonic condition. We investigate the shearing effect such a jet has when impinging on a solid surface that is perpendicular to the flow direction. We report on experiments to evaluate the jet's ability to remove different types of explosive particles from a glass surface. Theoretical analysis revealed trends and enabled modeling to improve the predictability of particle removal for various jet conditions. The second part of thesis aims at developing a non-intrusive measurement technique for free-shear turbulent flows in nature. Most turbulent jet investigations in the literature, both in the laboratory and in the field, required specialized intrusive instrumentation and/or complex optical setups. There are many situations in naturally-occurring flows where the environment may prove too hostile or remote for existing instrumentation. We have developed a methodology for analyzing video of the exterior of a naturally-occurring flow and calculating the flow velocity. We found that the presence of viscosity gradients affects the velocity analysis. While these effects produce consistent, predictable changes, we became interested in the mechanism by which the viscosity gradients affect the mixing and development of the turbulent round jet. We conducted a stability analysis of the axisymmetric jet when a viscosity gradient is present. Finally, the third problem addressed in this thesis is the growth of liquid droplets by condensation in a turbulent round jet. A vapor-saturated turbulent jet issues into a cold, dry environment. The resulting mixing produces highly inhomogeneous regions of supersaturation, where droplets grow and evaporate. Non-linear interactions between the droplet growth rate and the supersaturation field make analysis computationally taxing. A Probability Density Function (PDF) model for the concentration of scalars, as well as for the droplet number in different size bins, is developed. The growth of droplets as they evolve along the jet, for different downstream and radial positions, compared favorably with experimental measurements in the literature. We utilized a graphical processing unit with the PDF method to more efficiently compute the statistics of the droplet diameter in the non-uniform supersaturation field.

Genetic diversity in natural populations of a soil bacterium across a landscape gradient

PubMed Central

McArthur, J. Vaun; Kovacic, David A.; Smith, Michael H.

1988-01-01

Genetic diversity in natural populations of the bacterium Pseudomonas cepacia was surveyed in 10 enzymes from 70 clones isolated along a landscape gradient. Estimates of genetic diversity, ranging from 0.54 to 0.70, were higher than any previously reported values of which we are aware and were positively correlated with habitat variability. Patterns of bacterial genetic diversity were correlated with habitat variability. Findings indicate that the source of strains used in genetic engineering will greatly affect the outcome of planned releases in variable environments. Selection of generalist strains may confer a large advantage to engineered populations, while selection of laboratory strains may result in quick elimination of the engineered strains. PMID:16594009

Evolution of a Planar Wake in Adverse Pressure Gradient

NASA Technical Reports Server (NTRS)

Driver, David M.; Mateer, George G.

2016-01-01

In the interest of improving the predictability of high-lift systems at maximum lift conditions, a series of fundamental experiments were conducted to study the effects of adverse pressure gradient on a wake flow. Mean and fluctuating velocities were measured with a two-component laser-Doppler velocimeter. Data were obtained for several cases of adverse pressure gradient, producing flows ranging from no reversed flow to massively reversed flow. While the turbulent Reynolds stresses increase with increasing size of the reversed flow region, the gradient of Reynolds stress does not. Computations using various turbulence models were unable to reproduce the reversed flow.

AmeriFlux US-SCd Southern California Climate Gradient - Sonoran Desert

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goulden, Mike

This is the AmeriFlux version of the carbon flux data for the site US-SCd Southern California Climate Gradient - Sonoran Desert. Site Description - Half hourly data are available at https://www.ess.uci.edu/~california/. This site is one of six Southern California Climate Gradient flux towers operated along an elevation gradient (sites are US-SCg, US-SCs, US-SCf, US-SCw, US-SCc, US-SCd). This site is a low desert site in Southern California's rain shadow; the climate is extremely dry and hot. The site has experience repeated droughts, with negligible rainfall during several years of the record.

A fast random walk algorithm for computing the pulsed-gradient spin-echo signal in multiscale porous media.

PubMed

Grebenkov, Denis S

2011-02-01

A new method for computing the signal attenuation due to restricted diffusion in a linear magnetic field gradient is proposed. A fast random walk (FRW) algorithm for simulating random trajectories of diffusing spin-bearing particles is combined with gradient encoding. As random moves of a FRW are continuously adapted to local geometrical length scales, the method is efficient for simulating pulsed-gradient spin-echo experiments in hierarchical or multiscale porous media such as concrete, sandstones, sedimentary rocks and, potentially, brain or lungs. Copyright © 2010 Elsevier Inc. All rights reserved.

Isotopic evidence for reductive immobilization of uranium across a roll-front mineral deposit

DOE PAGES

Brown, Shaun T.; Basu, Anirban; Christensen, John N.; ...

2016-05-20

We use uranium (U) isotope ratios to detect and quantify the extent of natural U reduction in groundwater across a roll front redox gradient. Our study was conducted at the Smith Ranch-Highland in situ recovery (ISR) U mine in eastern Wyoming, USA, where economic U deposits occur in the Paleocene Fort Union formation. To evaluate the fate of aqueous U in and adjacent to the ore body, we investigated the chemical composition and isotope ratios of groundwater samples from the roll-front type ore body and surrounding monitoring wells of a previously mined area. The 238U/ 235U of groundwater varies bymore » approximately 3‰ and is correlated with U concentrations. Fluid samples down-gradient of the ore zone are the most depleted in 238U and have the lowest U concentrations. Activity ratios of 234U/ 238U are ~5.5 up-gradient of the ore zone, ~1.0 in the ore zone, and between 2.3 and 3.7 in the down-gradient monitoring wells. High-precision measurements of 234U/ 238U and 238U/ 235U allow for development of a conceptual model that evaluates both the migration of U from the ore body and the extent of natural attenuation due to reduction. We find that the premining migration of U down-gradient of the delineated ore body is minimal along eight transects due to reduction in or adjacent to the ore body, whereas two other transects show little or no sign of reduction in the down-gradient region. Lastly, these results suggest that characterization of U isotopic ratios at the mine planning stage, in conjunction with routine geochemical analyses, can be used to identify where more or less postmining remediation will be necessary.« less

Convective Electrokinetic Instability With Conductivity Gradients

NASA Astrophysics Data System (ADS)

Chen, Chuan-Hua; Lin, Hao; Lele, Sanjiva; Santiago, Juan

2003-11-01

Electrokinetic flow instability has been experimentally identified and quantified in a glass T-junction microchannel system with a cross section of 11 um x 155 um. In this system, buffers of different conductivities were electrokinetically driven into a common mixing channel by a DC electric field. A convective instability was observed with a threshold electric field of 0.45 kV/cm for a 10:1 conductivity ratio. A physical model has been developed which consists of a modified Ohmic model formulation for electrolyte solutions and the Navier-Stokes equations with an electric body force term. The model and experiments show that bulk charge accumulation in regions of conductivity gradients is the key mechanism of such instabilities. A linear stability analysis was performed in a convective framework, and Briggs-Bers criteria were applied to determine the nature of instability. The analysis shows the instability is governed by two key parameters: the ratio of molecular diffusion to electroviscous time scale which governs the onset of instability, and the ratio of electroviscous to electroosmotic velocity which governs whether the instability is convective or absolute. The model predicted critical electric field, growth rate, wavelength, and phase speed which were comparable to experimental data.

Modelling the multidimensional niche by linking functional traits to competitive performance

PubMed Central

Maynard, Daniel S.; Leonard, Kenneth E.; Drake, John M.; Hall, David W.; Crowther, Thomas W.; Bradford, Mark A.

2015-01-01

Linking competitive outcomes to environmental conditions is necessary for understanding species' distributions and responses to environmental change. Despite this importance, generalizable approaches for predicting competitive outcomes across abiotic gradients are lacking, driven largely by the highly complex and context-dependent nature of biotic interactions. Here, we present and empirically test a novel niche model that uses functional traits to model the niche space of organisms and predict competitive outcomes of co-occurring populations across multiple resource gradients. The model makes no assumptions about the underlying mode of competition and instead applies to those settings where relative competitive ability across environments correlates with a quantifiable performance metric. To test the model, a series of controlled microcosm experiments were conducted using genetically related strains of a widespread microbe. The model identified trait microevolution and performance differences among strains, with the predicted competitive ability of each organism mapped across a two-dimensional carbon and nitrogen resource space. Areas of coexistence and competitive dominance between strains were identified, and the predicted competitive outcomes were validated in approximately 95% of the pairings. By linking trait variation to competitive ability, our work demonstrates a generalizable approach for predicting and modelling competitive outcomes across changing environmental contexts. PMID:26136444

Solution-Adaptive Cartesian Cell Approach for Viscous and Inviscid Flows

NASA Technical Reports Server (NTRS)

Coirier, William J.; Powell, Kenneth G.

1996-01-01

A Cartesian cell-based approach for adaptively refined solutions of the Euler and Navier-Stokes equations in two dimensions is presented. Grids about geometrically complicated bodies are generated automatically, by the recursive subdivision of a single Cartesian cell encompassing the entire flow domain. Where the resulting cells intersect bodies, polygonal cut cells are created using modified polygon-clipping algorithms. The grid is stored in a binary tree data structure that provides a natural means of obtaining cell-to-cell connectivity and of carrying out solution-adaptive mesh refinement. The Euler and Navier-Stokes equations are solved on the resulting grids using a finite volume formulation. The convective terms are upwinded: A linear reconstruction of the primitive variables is performed, providing input states to an approximate Riemann solver for computing the fluxes between neighboring cells. The results of a study comparing the accuracy and positivity of two classes of cell-centered, viscous gradient reconstruction procedures is briefly summarized. Adaptively refined solutions of the Navier-Stokes equations are shown using the more robust of these gradient reconstruction procedures, where the results computed by the Cartesian approach are compared to theory, experiment, and other accepted computational results for a series of low and moderate Reynolds number flows.

GPU-based stochastic-gradient optimization for non-rigid medical image registration in time-critical applications

NASA Astrophysics Data System (ADS)

Bhosale, Parag; Staring, Marius; Al-Ars, Zaid; Berendsen, Floris F.

2018-03-01

Currently, non-rigid image registration algorithms are too computationally intensive to use in time-critical applications. Existing implementations that focus on speed typically address this by either parallelization on GPU-hardware, or by introducing methodically novel techniques into CPU-oriented algorithms. Stochastic gradient descent (SGD) optimization and variations thereof have proven to drastically reduce the computational burden for CPU-based image registration, but have not been successfully applied in GPU hardware due to its stochastic nature. This paper proposes 1) NiftyRegSGD, a SGD optimization for the GPU-based image registration tool NiftyReg, 2) random chunk sampler, a new random sampling strategy that better utilizes the memory bandwidth of GPU hardware. Experiments have been performed on 3D lung CT data of 19 patients, which compared NiftyRegSGD (with and without random chunk sampler) with CPU-based elastix Fast Adaptive SGD (FASGD) and NiftyReg. The registration runtime was 21.5s, 4.4s and 2.8s for elastix-FASGD, NiftyRegSGD without, and NiftyRegSGD with random chunk sampling, respectively, while similar accuracy was obtained. Our method is publicly available at https://github.com/SuperElastix/NiftyRegSGD.

Study on transient beam loading compensation for China ADS proton linac injector II

NASA Astrophysics Data System (ADS)

Gao, Zheng; He, Yuan; Wang, Xian-Wu; Chang, Wei; Zhang, Rui-Feng; Zhu, Zheng-Long; Zhang, Sheng-Hu; Chen, Qi; Powers, Tom

2016-05-01

Significant transient beam loading effects were observed during beam commissioning tests of prototype II of the injector for the accelerator driven sub-critical (ADS) system, which took place at the Institute of Modern Physics, Chinese Academy of Sciences, between October and December 2014. During these tests experiments were performed with continuous wave (CW) operation of the cavities with pulsed beam current, and the system was configured to make use of a prototype digital low level radio frequency (LLRF) controller. The system was originally operated in pulsed mode with a simple proportional plus integral and deviation (PID) feedback control algorithm, which was not able to maintain the desired gradient regulation during pulsed 10 mA beam operations. A unique simple transient beam loading compensation method which made use of a combination of proportional and integral (PI) feedback and feedforward control algorithm was implemented in order to significantly reduce the beam induced transient effect in the cavity gradients. The superconducting cavity field variation was reduced to less than 1.7% after turning on this control algorithm. The design and experimental results of this system are presented in this paper. Supported by National Natural Science Foundation of China (91426303, 11525523)

Local plant adaptation across a subarctic elevational gradient

PubMed Central

Kardol, Paul; De Long, Jonathan R.; Wardle, David A.

2014-01-01

Predicting how plants will respond to global warming necessitates understanding of local plant adaptation to temperature. Temperature may exert selective effects on plants directly, and also indirectly through environmental factors that covary with temperature, notably soil properties. However, studies on the interactive effects of temperature and soil properties on plant adaptation are rare, and the role of abiotic versus biotic soil properties in plant adaptation to temperature remains untested. We performed two growth chamber experiments using soils and Bistorta vivipara bulbil ecotypes from a subarctic elevational gradient (temperature range: ±3°C) in northern Sweden to disentangle effects of local ecotype, temperature, and biotic and abiotic properties of soil origin on plant growth. We found partial evidence for local adaption to temperature. Although soil origin affected plant growth, we did not find support for local adaptation to either abiotic or biotic soil properties, and there were no interactive effects of soil origin with ecotype or temperature. Our results indicate that ecotypic variation can be an important driver of plant responses to the direct effects of increasing temperature, while responses to covariation in soil properties are of a phenotypic, rather than adaptive, nature. PMID:26064553

How does pedogenesis drive plant diversity?

USGS Publications Warehouse

Laliberté, Etienne; Grace, James B.; Huston, Michael A.; Lambers, Hans; Teste, François P.; Turner, Benjamin L.; Wardle, David A.

2013-01-01

Some of the most species-rich plant communities occur on ancient, strongly weathered soils, whereas those on recently developed soils tend to be less diverse. Mechanisms underlying this well-known pattern, however, remain unresolved. Here, we present a conceptual model describing alternative mechanisms by which pedogenesis (the process of soil formation) might drive plant diversity. We suggest that long-term soil chronosequences offer great, yet largely untapped, potential as 'natural experiments' to determine edaphic controls over plant diversity. Finally, we discuss how our conceptual model can be evaluated quantitatively using structural equation modeling to advance multivariate theories about the determinants of local plant diversity. This should help us to understand broader-scale diversity patterns, such as the latitudinal gradient of plant diversity.

Nonlinear analogue of the May−Wigner instability transition

PubMed Central

Fyodorov, Yan V.; Khoruzhenko, Boris A.

2016-01-01

We study a system of N≫1 degrees of freedom coupled via a smooth homogeneous Gaussian vector field with both gradient and divergence-free components. In the absence of coupling, the system is exponentially relaxing to an equilibrium with rate μ. We show that, while increasing the ratio of the coupling strength to the relaxation rate, the system experiences an abrupt transition from a topologically trivial phase portrait with a single equilibrium into a topologically nontrivial regime characterized by an exponential number of equilibria, the vast majority of which are expected to be unstable. It is suggested that this picture provides a global view on the nature of the May−Wigner instability transition originally discovered by local linear stability analysis. PMID:27274077

Testing thermal gradient driving force for grain boundary migration using molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xian-Ming; Zhang, Yongfeng; Tonks, Michael R.

2015-02-01

Strong thermal gradients in low-thermal-conductivity ceramics may drive extended defects, such as grain boundaries and voids, to migrate in preferential directions. In this work, molecular dynamics simulations are conducted to study thermal gradient driven grain boundary migration and to verify a previously proposed thermal gradient driving force equation, using uranium dioxide as a model system. It is found that a thermal gradient drives grain boundaries to migrate up the gradient and the migration velocity increases under a constant gradient owing to the increase in mobility with temperature. Different grain boundaries migrate at very different rates due to their different intrinsicmore » mobilities. The extracted mobilities from the thermal gradient driven simulations are compared with those calculated from two other well-established methods and good agreement between the three different methods is found, demonstrating that the theoretical equation of the thermal gradient driving force is valid, although a correction of one input parameter should be made. The discrepancy in the grain boundary mobilities between modeling and experiments is also discussed.« less

Three-dimensional Macroscopic Scaffolds With a Gradient in Stiffness for Functional Regeneration of Interfacial Tissues

PubMed Central

Singh, Milind; Dormer, Nathan; Salash, Jean R.; Christian, Jordan M.; Moore, David S.; Berkland, Cory; Detamore, Michael S.

2010-01-01

A novel approach has been demonstrated to construct biocompatible, macroporous 3-D tissue engineering scaffolds containing a continuous macroscopic gradient in composition that yields a stiffness gradient along the axis of the scaffold. Polymeric microspheres, made of poly(d,l-lactic-co-glycolic acid) (PLGA), and composite microspheres encapsulating a higher stiffness nano-phase material (PLGA encapsulating CaCO3 or TiO2 nanoparticles) were used for the construction of microsphere-based scaffolds. Using controlled infusion of polymeric and composite microspheres, gradient scaffolds displaying an anisotropic macroscopic distribution of CaCO3/TiO2 were fabricated via an ethanol sintering technique. The controllable mechanical characteristics and biocompatible nature of these scaffolds warrants further investigation for interfacial tissue engineering applications. PMID:20336753

Reexamining X-mode suppression and fine structure in artificial E region field-aligned plasma density irregularities

NASA Astrophysics Data System (ADS)

Miceli, R. J.; Hysell, D. L.; Munk, J.; McCarrick, M.; Huba, J. D.

2013-09-01

Artificial field-aligned plasma density irregularities (FAIs) were generated in the E region of the ionosphere above the High Frequency Active Auroral Research Program facility during campaigns in May and August of 2012 and observed using a 30 MHz coherent scatter radar imager in Homer, Alaska. The purpose of this ionospheric modification experiment was to measure the threshold pump power required to excite thermal parametric instabilities by O-mode heating and to investigate the suppression of the FAIs by simultaneous X-mode heating. We find that the threshold pump power for irregularity excitation was consistent with theoretical predictions and increased by approximately a factor of 2 when X-mode heating was present. A modified version of the Another Model of the Ionosphere (SAMI2) ionospheric model was used to simulate the threshold experiments and suggested that the increase was entirely due to enhanced D region absorption associated with X-mode heating. Additionally, a remarkable degree of fine structure possibly caused by natural gradient drift instability in the heater-modified volume was observed in experiments performed during geomagnetically active conditions.

Continuing Climate Warming Will Result in Failure of Post-Harvest Natural Regeneration across the Landscape in Interior Alaska

NASA Astrophysics Data System (ADS)

Morimoto, M.; Juday, G. P.; Huettmann, F.

2016-12-01

Following forest disturbance, the stand initiation stage decisively influences future forest structure. Understanding post-harvest regeneration, especially under climate change, is essential to predicting future carbon stores in this extensive forest biome. We apply IPCC B1, A1B, and A2 climate scenarios to generate plausible future forest conditions under different management. We recorded presence of white spruce, birch, and aspen in 726 plots on 30 state forest white spruce harvest units. We built spatially explicit models and scenarios of species presence/absence using TreeNet (Stochastic Gradient Boosting). Post-harvest tree regeneration predictions in calibration data closely matched the validation set, indicating tree regeneration scenarios are reliable. Early stage post-harvest regeneration is similar to post-fire regeneration and matches the pattern of long-term natural vegetation distribution, confirming that site environmental factors are more important than management practices. Post-harvest natural regeneration of tree species increases under moderate warming scenarios, but fails under strong warming scenarios in landscape positions with high temperatures and low precipitation. Under all warming scenarios, the most successful regenerating species following white spruce harvest is white spruce. Birch experiences about 30% regeneration failure under A2 scenario by 2050. White spruce and aspen are projected to regenerate more successfully when site preparation is applied. Although white spruce has been the major managed species, birch may require more intensive management. Sites likely to experience regeneration failure of current tree species apparently will experience biome shift, although adaptive migration of existing or new species might be an option. Our scenario modeling tool allows resource managers to forecast tree regeneration on productive managed sites that have made a disproportionate contribution to carbon flux in a critical region.

A magnetic gradient induced force in NMR restricted diffusion experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ghadirian, Bahman; Stait-Gardner, Tim; Castillo, Reynaldo

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 magneticmore » 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.« less

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. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Feeding selectivity of Calanus finmarchicus in the Trondheimsfjord

NASA Astrophysics Data System (ADS)

Leiknes, Øystein; Striberny, Anja; Tokle, Nils Egil; Olsen, Yngvar; Vadstein, Olav; Sommer, Ulrich

2014-01-01

The feeding selectivity of Calanus finmarchicus was studied by carrying out three incubation experiments; two experiments with natural seawater sampled during spring bloom (Exp. 1) and post-bloom conditions (Exp. 2) and a third experiment with cultured dinoflagellates and ciliates (Exp. 3). In the first two experiments a gradient in ciliate concentration was created to investigate the potential for prey density dependent selective feeding of C. finmarchicus. Results of microplankton counts indicated C. finmarchicus to be omnivorous. Diatoms contributed chiefly to the diet during spring bloom conditions. Despite the high microphytoplankton biomass during the spring bloom (Exp. 1), ciliates were selected positively by C. finmarchicus when the ciliate biomass exceeded 6.5 μg C L- 1. A selection in favor of large conic ciliates such as Laboea sp. and Strombidium conicum was indicated by positive selectivity indices. Ciliates were throughout positively selected by C. finmarchicus during Exp. 2, and selectivity indices indicated a negative selection of diatoms. The results from Exp. 3 showed that C. finmarchicus has the ability to switch from dinoflagellates to ciliates as sole food source, even if the dinoflagellate was offered in surplus. This suggests that other factors, such as nutrition may be of significance for the feeding selectivity of C. finmarchicus.

Short-scale turbulent fluctuations driven by the electron-temperature gradient in the national spherical torus experiment.

PubMed

Mazzucato, E; Smith, D R; Bell, R E; Kaye, S M; Hosea, J C; LeBlanc, B P; Wilson, J R; Ryan, P M; Domier, C W; Luhmann, N C; Yuh, H; Lee, W; Park, H

2008-08-15

Measurements with coherent scattering of electromagnetic waves in plasmas of the National Spherical Torus Experiment indicate the existence of turbulent fluctuations in the range of wave numbers k perpendicular rho(e)=0.1-0.4, corresponding to a turbulence scale length nearly equal to the collisionless skin depth. Experimental observations and agreement with numerical results from a linear gyrokinetic stability code support the conjecture that the observed turbulence is driven by the electron-temperature gradient.

Dynamics of a gravity-gradient stabilized flexible spacecraft

NASA Technical Reports Server (NTRS)

Meirovitch, L.; Juang, J. N.

1974-01-01

The dynamics of gravity-gradient stabilized flexible satellite in the neighborhood of a deformed equilibrium configuration are discussed. First the equilibrium configuration was determined by solving a set of nonlinear differential equations. Then stability of motion about the deformed equilibrium was tested by means of the Liapunov direct method. The natural frequencies of oscillation of the complete structure were calculated. The analysis is applicable to the RAE/B satellite.

Density-Gradient Theory: A Macroscopic Approach to Quantum Confinement and Tunneling in Semiconductor Devices

DTIC Science & Technology

2011-01-01

that are attractive as luminescent biolabels, and possibly also for optoelectronic devices and solar cells . The equilibrium nature of such situations...The boundary layers as- sociated with the diffusion and Debye lengths are familiar, while that of LQ defines the layer in which the quantum in...circuits, transmission lines Diffusion -drift, density-gradient Semi-classical electron dynamics, Boltzmann transport Schrödinger, density- matrix, Wigner

Modeling energy flow and nutrient cycling in natural semiarid grassland ecosystems with the aid of thematic mapper data

NASA Technical Reports Server (NTRS)

Lewis, James K.

1987-01-01

Energy flow and nutrient cycling were modeled as affected by herbivory on selected intensive sites along gradients of precipitation and soils, validating the model output by monitoring selected parameters with data derived from the Thematic Mapper (TM). Herbivore production was modeled along the gradient of soils and herbivory, and validated with data derived from TM in a spatial data base.

Driving bubbles out of glass

NASA Technical Reports Server (NTRS)

Mattox, D. M.

1981-01-01

Surface tension gradient in melt forces gas bubbles to surface, increasing glass strength and transparency. Conventional chemical and buoyant fining are extremely slow in viscous glasses, but tension gradient method moves 250 um bubbles as rapidly as 30 um/s. Heat required for high temperature part of melt is furnished by stationary electrical or natural-gas heater; induction and laser heating are also possible. Method has many applications in industry processes.

On the Myths of Indicator Species: Issues and Further Consideration in the Use of Static Concepts for Ecological Applications

PubMed Central

Zettler, Michael L.; Proffitt, C. Edward; Darr, Alexander; Degraer, Steven; Devriese, Lisa; Greathead, Clare; Kotta, Jonne; Magni, Paolo; Martin, Georg; Reiss, Henning; Speybroeck, Jeroen; Tagliapietra, Davide; Van Hoey, Gert; Ysebaert, Tom

2013-01-01

The use of static indicator species, in which species are expected to have a similar sensitivity or tolerance to either natural or human-induced stressors, does not account for possible shifts in tolerance along natural environmental gradients and between biogeographic regions. Their indicative value may therefore be considered at least questionable. In this paper we demonstrate how species responses (i.e. abundance) to changes in sediment grain size and organic matter (OM) alter along a salinity gradient and conclude with a plea for prudency when interpreting static indicator-based quality indices. Six model species (three polychaetes, one amphipod and two bivalves) from the North Sea, Baltic Sea and the Mediterranean Sea region were selected. Our study demonstrated that there were no generic relationships between environment and biota and half of the studied species showed different responses in different seas. Consequently, the following points have to be carefully considered when applying static indicator-based quality indices: (1) species tolerances and preferences may change along environmental gradients and between different biogeographic regions, (2) as environment modifies species autecology, there is a need to adjust indicator species lists along major environmental gradients and (3) there is a risk of including sibling or cryptic species in calculating the index value of a species. PMID:24147123

Gelatin freeze casting of biomimetic titanium alloy with anisotropic and gradient pore structure.

PubMed

Zhang, Lei; Le Coz-Botrel, Ronan; Beddoes, Charlotte; Sjöström, Terje; Su, Bo

2017-01-17

Titanium is a material commonly used for dental and orthopaedic implants. However, due to large differences in properties between the titanium metal and the natural bone, stress shielding has been observed in the surrounding area, resulting in bone atrophy, and thus has raised concerns of the use of this material. Ideally implant materials should possess similar properties to the surrounding tissues in order to distribute the load as the joint would naturally, while also possessing a similar porous structure to the bone to enable interaction with the surrounding material. In this paper we report the formation of aligned porous titanium alloy scaffolds with the use of unidirectional freeze casting with a temperature gradient. The resulting scaffolds had a dense bottom part with sufficient strength for loading, while the top part remaining porous in order to allow bone growth in the scaffold and fully integrating with the surrounding tissue. The anisotropic nature of the pores within the titanium alloy samples were observed via micro computed tomography, where a gradient structure similar to bone was observed. The compressive strength of the fabricated scaffolds was found to be up to 427 MPa when measured with the pores aligned with the applied load, depending on the pore density. This is within the range of cortical bone.

Natural learning in NLDA networks.

PubMed

González, Ana; Dorronsoro, José R

2007-07-01

Non Linear Discriminant Analysis (NLDA) networks combine a standard Multilayer Perceptron (MLP) transfer function with the minimization of a Fisher analysis criterion. In this work we will define natural-like gradients for NLDA network training. Instead of a more principled approach, that would require the definition of an appropriate Riemannian structure on the NLDA weight space, we will follow a simpler procedure, based on the observation that the gradient of the NLDA criterion function J can be written as the expectation nablaJ(W)=E[Z(X,W)] of a certain random vector Z and defining then I=E[Z(X,W)Z(X,W)(t)] as the Fisher information matrix in this case. This definition of I formally coincides with that of the information matrix for the MLP or other square error functions; the NLDA J criterion, however, does not have this structure. Although very simple, the proposed approach shows much faster convergence than that of standard gradient descent, even when its costlier complexity is taken into account. While the faster convergence of natural MLP batch training can be also explained in terms of its relationship with the Gauss-Newton minimization method, this is not the case for NLDA training, as we will see analytically and numerically that the hessian and information matrices are different.

Global-change drivers of ecosystem functioning modulated by natural variability and saturating responses.

PubMed

Flombaum, Pedro; Yahdjian, Laura; Sala, Osvaldo E

2017-02-01

Humans are altering global environment at an unprecedented rate through changes in biodiversity, climate, nitrogen cycle, and land use. To address their effects on ecosystem functioning, experiments most frequently explore one driver at a time and control as many confounding factors as possible. Yet, which driver exerts the largest influence on ecosystem functioning and whether their relative importance changes among systems remain unclear. We analyzed experiments in the Patagonian steppe that evaluated the aboveground net primary production (ANPP) response to manipulated gradients of species richness, precipitation, temperature, nitrogen fertilization (N), and grazing intensity. We compared the effect on ANPP relative to ambient conditions considering intensity and direction of manipulations for each driver. The ranking of responses to drivers with comparable manipulation intensity was as follows: biodiversity>grazing>precipitation>N. For a similar intensity of manipulation, the effect of biodiversity loss was 4.0, 3.6, and 1.5, times larger than N deposition, decreased precipitation, and increased grazing intensity. We interpreted our results considering two hypotheses. First, the response of ANPP to changes in precipitation and biodiversity is saturating, so we expected larger effects when the driver was reduced, relative to ambient conditions, than when it was increased. Experimental manipulations that reduced ambient levels had larger effects than those that increased them. Second, the sensitivity of ANPP to each driver is inversely related to the natural variability of the driver. In Patagonia, the ranking of natural variability of drivers is as follows: precipitation>grazing>temperature>biodiversity>N. So, in general, the ecosystem was most sensitive to drivers that varied the least. Comparable results from Cedar Creek (MN) support both hypotheses and suggest that sensitivity to drivers varies among ecosystem types. Given the importance of understanding ecosystem sensitivity to predict global-change impacts, it is necessary to design new experiments located in regions with contrasting natural variability and that include the full range of drivers. © 2016 John Wiley & Sons Ltd.

Merging metagenomics and geochemistry reveals environmental controls on biological diversity and evolution.

PubMed

Alsop, Eric B; Boyd, Eric S; Raymond, Jason

2014-05-28

The metabolic strategies employed by microbes inhabiting natural systems are, in large part, dictated by the physical and geochemical properties of the environment. This study sheds light onto the complex relationship between biology and environmental geochemistry using forty-three metagenomes collected from geochemically diverse and globally distributed natural systems. It is widely hypothesized that many uncommonly measured geochemical parameters affect community dynamics and this study leverages the development and application of multidimensional biogeochemical metrics to study correlations between geochemistry and microbial ecology. Analysis techniques such as a Markov cluster-based measure of the evolutionary distance between whole communities and a principal component analysis (PCA) of the geochemical gradients between environments allows for the determination of correlations between microbial community dynamics and environmental geochemistry and provides insight into which geochemical parameters most strongly influence microbial biodiversity. By progressively building from samples taken along well defined geochemical gradients to samples widely dispersed in geochemical space this study reveals strong links between the extent of taxonomic and functional diversification of resident communities and environmental geochemistry and reveals temperature and pH as the primary factors that have shaped the evolution of these communities. Moreover, the inclusion of extensive geochemical data into analyses reveals new links between geochemical parameters (e.g. oxygen and trace element availability) and the distribution and taxonomic diversification of communities at the functional level. Further, an overall geochemical gradient (from multivariate analyses) between natural systems provides one of the most complete predictions of microbial taxonomic and functional composition. Clustering based on the frequency in which orthologous proteins occur among metagenomes facilitated accurate prediction of the ordering of community functional composition along geochemical gradients, despite a lack of geochemical input. The consistency in the results obtained from the application of Markov clustering and multivariate methods to distinct natural systems underscore their utility in predicting the functional potential of microbial communities within a natural system based on system geochemistry alone, allowing geochemical measurements to be used to predict purely biological metrics such as microbial community composition and metabolism.

Cell–cell communication enhances the capacity of cell ensembles to sense shallow gradients during morphogenesis

PubMed Central

Ellison, David; Mugler, Andrew; Brennan, Matthew D.; Lee, Sung Hoon; Huebner, Robert J.; Shamir, Eliah R.; Woo, Laura A.; Kim, Joseph; Amar, Patrick; Nemenman, Ilya; Ewald, Andrew J.; Levchenko, Andre

2016-01-01

Collective cell responses to exogenous cues depend on cell–cell interactions. In principle, these can result in enhanced sensitivity to weak and noisy stimuli. However, this has not yet been shown experimentally, and little is known about how multicellular signal processing modulates single-cell sensitivity to extracellular signaling inputs, including those guiding complex changes in the tissue form and function. Here we explored whether cell–cell communication can enhance the ability of cell ensembles to sense and respond to weak gradients of chemotactic cues. Using a combination of experiments with mammary epithelial cells and mathematical modeling, we find that multicellular sensing enables detection of and response to shallow epidermal growth factor (EGF) gradients that are undetectable by single cells. However, the advantage of this type of gradient sensing is limited by the noisiness of the signaling relay, necessary to integrate spatially distributed ligand concentration information. We calculate the fundamental sensory limits imposed by this communication noise and combine them with the experimental data to estimate the effective size of multicellular sensory groups involved in gradient sensing. Functional experiments strongly implicated intercellular communication through gap junctions and calcium release from intracellular stores as mediators of collective gradient sensing. The resulting integrative analysis provides a framework for understanding the advantages and limitations of sensory information processing by relays of chemically coupled cells. PMID:26792522

Global gyrokinetic simulations of intrinsic rotation in ASDEX Upgrade Ohmic L-mode plasmas

NASA Astrophysics Data System (ADS)

Hornsby, W. A.; Angioni, C.; Lu, Z. X.; Fable, E.; Erofeev, I.; McDermott, R.; Medvedeva, A.; Lebschy, A.; Peeters, A. G.; The ASDEX Upgrade Team

2018-05-01

Non-linear, radially global, turbulence simulations of ASDEX Upgrade (AUG) plasmas are performed and the nonlinear generated intrinsic flow shows agreement with the intrinsic flow gradients measured in the core of Ohmic L-mode plasmas at nominal parameters. Simulations utilising the kinetic electron model show hollow intrinsic flow profiles as seen in a predominant number of experiments performed at similar plasma parameters. In addition, significantly larger flow gradients are seen than in a previous flux-tube analysis (Hornsby et al 2017 Nucl. Fusion 57 046008). Adiabatic electron model simulations can show a flow profile with opposing sign in the gradient with respect to a kinetic electron simulation, implying a reversal in the sign of the residual stress due to kinetic electrons. The shaping of the intrinsic flow is strongly determined by the density gradient profile. The sensitivity of the residual stress to variations in density profile curvature is calculated and seen to be significantly stronger than to neoclassical flows (Hornsby et al 2017 Nucl. Fusion 57 046008). This variation is strong enough on its own to explain the large variations in the intrinsic flow gradients seen in some AUG experiments. Analysis of the symmetry breaking properties of the turbulence shows that profile shearing is the dominant mechanism in producing a finite parallel wave-number, with turbulence gradient effects contributing a smaller portion of the parallel wave-vector.

SAGRAD: A Program for Neural Network Training with Simulated Annealing and the Conjugate Gradient Method.

PubMed

Bernal, Javier; Torres-Jimenez, Jose

2015-01-01

SAGRAD (Simulated Annealing GRADient), a Fortran 77 program for computing neural networks for classification using batch learning, is discussed. Neural network training in SAGRAD is based on a combination of simulated annealing and Møller's scaled conjugate gradient algorithm, the latter a variation of the traditional conjugate gradient method, better suited for the nonquadratic nature of neural networks. Different aspects of the implementation of the training process in SAGRAD are discussed, such as the efficient computation of gradients and multiplication of vectors by Hessian matrices that are required by Møller's algorithm; the (re)initialization of weights with simulated annealing required to (re)start Møller's algorithm the first time and each time thereafter that it shows insufficient progress in reaching a possibly local minimum; and the use of simulated annealing when Møller's algorithm, after possibly making considerable progress, becomes stuck at a local minimum or flat area of weight space. Outlines of the scaled conjugate gradient algorithm, the simulated annealing procedure and the training process used in SAGRAD are presented together with results from running SAGRAD on two examples of training data.

Peanut seed vigor elavuation using a thermal gradient

USDA-ARS?s Scientific Manuscript database

Experiments were conducted from 2007 to 2009 to evaluate the seed germination response of multiple peanut cultivars using a continuous temperature gradient ranging from 14 to 35 C (1.0 C increments). Growing degree day (GDD) accumulation for each temperature increment was measured. Two indices, maxi...

Flight Tests of a Supersonic Natural Laminar Flow Airfoil

NASA Technical Reports Server (NTRS)

Frederick, Mike; Banks, Dan; Garzon, Andres; Matisheck, Jason

2014-01-01

IR thermography was used to characterize the transition front on a S-NLF test article at chord Reynolds numbers in excess of 30 million Changes in transition due to Mach number, Reynolds number, and surface roughness were investigated - Regions of laminar flow in excess of 80% chord at chord Reynolds numbers greater than 14 million IR thermography clearly showed the transition front and other flow features such as shock waves impinging upon the surface A series of parallel oblique shocks, of yet unknown origin, were found to cause premature transition at higher Reynolds numbers. NASA has a current goal to eliminate barriers to the development of practical supersonic transport aircraft Drag reduction through the use of supersonic natural laminar flow (S-NLF) is currently being explored as a means of increasing aerodynamic efficiency - Tradeoffs work best for business jet class at M<2 Conventional high-speed designs minimize inviscid drag at the expense of viscous drag - Existence of strong spanwise pressure gradient leads to crossflow (CF) while adverse chordwise pressure gradients amplifies and Tollmien-Schlichting (TS) instabilities Aerion Corporation has patented a S-NLF wing design (US Patent No. 5322242) - Low sweep to control CF - dp/dx < 0 on both wing surfaces to stabilize TS - Thin wing with sharp leading edge to minimize wave drag increase due to reduction in sweep NASA and Aerion have partnered to study S-NLF since 1999 Series of S-NLF experiments flown on the NASA F-15B research test bed airplane Infrared (IR) thermography used to characterize transition - Non-intrusive, global, good spatial resolution - Captures significant flow features well

Heart valve bioprosthesis durability: a challenge to the new generation of porcine valves.

PubMed

Valente, M; Minarini, M; Maizza, A F; Bortolotti, U; Thiene, G

1992-01-01

Long-term experience with first generation porcine valve xenografts enabled identification of the major limitations to their durability: (1) prosthetic-ventricular mismatch due to the high profile of the stent in patients with mitral stenosis and a small left ventricle; (2) high-pressure fixation with loss of natural collagen crimping in the fibrosa, and wash-out of proteoglycans in the spongiosa; (3) xenograft tissue autolysis, due to the long interval between animal slaughter and aortic valve removal fixation; (4) muscle shelf in the right coronary cusp, which created a gradient and could undergo accelerated calcification and/or spontaneous perforation with time; (5) a flexible polypropylene stent, which could creep or even fracture with consequent inward bending of the stent; (6) progressive time-related dystrophic calcification; (7) host fibrous tissue ingrowth. An awareness of these limitations stimulated technical modifications, which frequently brought about distinct improvements: (1) the reduction of the stent profile eliminated the problem of mismatch, but resulted in a higher tendency towards cusp prolapse and earlier commissural tearing; (2) natural collagen waviness, proteoglycans and cusp extensibility were preserved by employing low or even zero pressure during the fixation process; (3) earlier valve fixation enabled preservation of cell integrity; (4) a new orifice for small valves was designed by replacing the right muscular cusp, thus achieving less gradient and avoiding muscle-shelf-related complications; (5) polypropylene was replaced by Delrin as stent material; (6) calcium-retarding agents like T6 and toluidine blue were applied during commercial processing and storage in order to mitigate tissue mineralization.(ABSTRACT TRUNCATED AT 250 WORDS)

Revisiting the homogenization of dammed rivers in the southeastern US

Treesearch

Ryan A. McManamay; Donald J. Orth; Charles A. Dolloff

2012-01-01

For some time, ecologists have attempted to make generalizations concerning how disturbances influence natural ecosystems, especially river systems. The existing literature suggests that dams homogenize the hydrologic variability of rivers. However, this might insinuate that dams affect river systems similarly despite a large gradient in natural hydrologic character....

Piecewise Disassembly of a Large-Herbivore Community across a Rainfall Gradient: The UHURU Experiment

PubMed Central

Palmer, Todd M.; Charles, Grace K.; Helgen, Kristofer M.; Kinyua, Stephen N.; Maclean, Janet E.; Turner, Benjamin L.; Young, Hillary S.

2013-01-01

Large mammalian herbivores (LMH) strongly influence plant communities, and these effects can propagate indirectly throughout food webs. Most existing large-scale manipulations of LMH presence/absence consist of a single exclusion treatment, and few are replicated across environmental gradients. Thus, important questions remain about the functional roles of different LMH, and how these roles depend on abiotic context. In September 2008, we constructed a series of 1-ha herbivore-exclusion plots across a 20-km rainfall gradient in central Kenya. Dubbed "UHURU" (Ungulate Herbivory Under Rainfall Uncertainty), this experiment aims to illuminate the ecological effects of three size classes of LMH, and how rainfall regimes shape the direction and magnitude of these effects. UHURU consists of four treatments: total-exclusion (all ungulate herbivores), mesoherbivore-exclusion (LMH >120-cm tall), megaherbivore-exclusion (elephants and giraffes), and unfenced open plots. Each treatment is replicated three times at three locations (“sites”) along the rainfall gradient: low (440 mm/year), intermediate (580 mm/year), and high (640 mm/year). There was limited variation across sites in soil attributes and LMH activity levels. Understory-plant cover was greater in plots without mesoherbivores, but did not respond strongly to the exclusion of megaherbivores, or to the additional exclusion of dik-dik and warthog. Eleven of the thirteen understory plant species that responded significantly to exclusion treatment were more common in exclusion plots than open ones. Significant interactions between site and treatment on plant communities, although uncommon, suggested that differences between treatments may be greater at sites with lower rainfall. Browsers reduced densities of several common overstory species, along with growth rates of the three dominant Acacia species. Small-mammal densities were 2–3 times greater in total-exclusion than in open plots at all sites. Although we expect patterns to become clearer with time, results from 2008–2012 show that the effects of excluding successively smaller-bodied subsets of the LMH community are generally non-additive for a given response variable, and inconsistent across response variables, indicating that the different LMH size classes are not functionally redundant. Several response variables showed significant treatment-by-site interactions, suggesting that the nature of plant-herbivore interactions can vary across restricted spatial scales. PMID:23405122

Piecewise disassembly of a large-herbivore community across a rainfall gradient: the UHURU experiment.

PubMed

Goheen, Jacob R; Palmer, Todd M; Charles, Grace K; Helgen, Kristofer M; Kinyua, Stephen N; Maclean, Janet E; Turner, Benjamin L; Young, Hillary S; Pringle, Robert M

2013-01-01

Large mammalian herbivores (LMH) strongly influence plant communities, and these effects can propagate indirectly throughout food webs. Most existing large-scale manipulations of LMH presence/absence consist of a single exclusion treatment, and few are replicated across environmental gradients. Thus, important questions remain about the functional roles of different LMH, and how these roles depend on abiotic context. In September 2008, we constructed a series of 1-ha herbivore-exclusion plots across a 20-km rainfall gradient in central Kenya. Dubbed "UHURU" (Ungulate Herbivory Under Rainfall Uncertainty), this experiment aims to illuminate the ecological effects of three size classes of LMH, and how rainfall regimes shape the direction and magnitude of these effects. UHURU consists of four treatments: total-exclusion (all ungulate herbivores), mesoherbivore-exclusion (LMH >120-cm tall), megaherbivore-exclusion (elephants and giraffes), and unfenced open plots. Each treatment is replicated three times at three locations ("sites") along the rainfall gradient: low (440 mm/year), intermediate (580 mm/year), and high (640 mm/year). There was limited variation across sites in soil attributes and LMH activity levels. Understory-plant cover was greater in plots without mesoherbivores, but did not respond strongly to the exclusion of megaherbivores, or to the additional exclusion of dik-dik and warthog. Eleven of the thirteen understory plant species that responded significantly to exclusion treatment were more common in exclusion plots than open ones. Significant interactions between site and treatment on plant communities, although uncommon, suggested that differences between treatments may be greater at sites with lower rainfall. Browsers reduced densities of several common overstory species, along with growth rates of the three dominant Acacia species. Small-mammal densities were 2-3 times greater in total-exclusion than in open plots at all sites. Although we expect patterns to become clearer with time, results from 2008-2012 show that the effects of excluding successively smaller-bodied subsets of the LMH community are generally non-additive for a given response variable, and inconsistent across response variables, indicating that the different LMH size classes are not functionally redundant. Several response variables showed significant treatment-by-site interactions, suggesting that the nature of plant-herbivore interactions can vary across restricted spatial scales.

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.

Plasma Streamwise Vortex Generators in an Adverse Pressure Gradient

NASA Astrophysics Data System (ADS)

Kelley, Christopher; Corke, Thomas; Thomas, Flint

2013-11-01

A wind tunnel experiment was conducted to compare plasma streamwise vortex generators (PSVGs) and passive vortex generators (VGs). These devices were installed on a wing section by which the angle of attack could be used to vary the streamwise pressure gradient. The experiment was performed for freestream Mach numbers 0.1-0.2. Three-dimensional velocity components were measured using a 5-hole Pitot probe in the boundary layer. These measurements were used to quantify the production of streamwise vorticity and the magnitude of the reorientation term from the vorticity transport equation. The effect of Mach number, pressure gradient, operating voltage, and electrode length was then investigated for the PSVGs. The results indicate that the PSVGs could easily outperform the passive VGs and provide a suitable alternative for flow control.

Evaluation of force generation mechanisms in natural, passive hydraulic actuators

NASA Astrophysics Data System (ADS)

Le Duigou, A.; Castro, M.

2016-01-01

Pine cones are well known natural actuators that can move their scales upon humidity gradient. The mechanism manifests itself through a displacement easily observable by the naked eye, but coupled with stress generation. In ancient Egypt, wooden wedges were used to break soft blocks of stone by the generated swelling stress. The purpose of the present study is to evaluate the ability of pine cone scales to generate forces while being wetted. In our experiments, a blocking force of around 3N is measured depending on the position on the pine cone where the scales are extracted. A fairly good agreement is obtained when theoretical results based on bimetallic strip systems are compared with experimental data, even if overestimation is observed arising from the input data considered for dry tissues. Inspired by a simplified pine cone microstructure, a biocomposite analogue is manufactured and tested. Although an adequate blocking force can be generated, it has a lower value compared to natural pine cones which benefit from optimized swelling tissue content and interfacial bond strength between them. This study provides new insights to understand the generation of force by pine cones as well as to develop novel biocomposite functionalities.

Role of a texture gradient in the perception of relative size.

PubMed

Tozawa, Junko

2010-01-01

Two theories regarding the role of a texture gradient in the perception of the relative size of objects are compared. Relational theory states that relative size is directly specified by the projective ratio of the numbers of texture elements spanned by objects. Distance calibration theory assumes that relative size is a product of visual angle and distance, once the distance is specified by the texture. Experiment 1 involved three variables: background (no texture, texture gradient patterns), the ratio of heights of the comparison stimulus to a standard (three levels), and angular vertical separation of the standard stimulus below the horizon (two levels). The effect of the retinal length of the comparison stimulus was examined in experiment 2. In both experiments, participants judged both the apparent size and distance of a comparison stimulus relative to a standard stimulus. Results suggest that the cues selected by observers to judge relative size were to some degree different from those used to judge relative distance. Relative size was strongly affected by a texture gradient and the retinal length of a comparison stimulus whereas relative distance perception was affected by relative height. When dominant cues that specify size are different from those which specify distance, relational theory might provide a better account of relative size perception than distance calibration theory.

Nonisothermal Brownian motion: Thermophoresis as the macroscopic manifestation of thermally biased molecular motion.

PubMed

Brenner, Howard

2005-12-01

A quiescent single-component gravity-free gas subject to a small steady uniform temperature gradient T, despite being at rest, is shown to experience a drift velocity UD=-D* gradient ln T, where D* is the gas's nonisothermal self-diffusion coefficient. D* is identified as being the gas's thermometric diffusivity alpha. The latter differs from the gas's isothermal isotopic self-diffusion coefficient D, albeit only slightly. Two independent derivations are given of this drift velocity formula, one kinematical and the other dynamical, both derivations being strictly macroscopic in nature. Within modest experimental and theoretical uncertainties, this virtual drift velocity UD=-alpha gradient ln T is shown to be constitutively and phenomenologically indistinguishable from the well-known experimental and theoretical formulas for the thermophoretic velocity U of a macroscopic (i.e., non-Brownian) non-heat-conducting particle moving under the influence of a uniform temperature gradient through an otherwise quiescent single-component rarefied gas continuum at small Knudsen numbers. Coupled with the size independence of the particle's thermophoretic velocity, the empirically observed equality, U=UD, leads naturally to the hypothesis that these two velocities, the former real and the latter virtual, are, in fact, simply manifestations of the same underlying molecular phenomenon, namely the gas's Brownian movement, albeit biased by the temperature gradient. This purely hydrodynamic continuum-mechanical equality is confirmed by theoretical calculations effected at the kinetic-molecular level on the basis of an existing solution of the Boltzmann equation for a quasi-Lorentzian gas, modulo small uncertainties pertaining to the choice of collision model. Explicitly, this asymptotically valid molecular model allows the virtual drift velocity UD of the light gas and the thermophoretic velocity U of the massive, effectively non-Brownian, particle, now regarded as the tracer particle of the light gas's drift velocity, to each be identified with the Chapman-Enskog "thermal diffusion velocity" of the quasi-Lorentzian gas, here designated by the symbol UM/M, as calculated by de la Mora and Mercer. It is further pointed out that, modulo the collective uncertainties cited above, the common velocities UD,U, and UM/M are identical to the single-component gas's diffuse volume current jv, the latter representing yet another, independent, strictly continuum-mechanical concept. Finally, comments are offered on the extension of the single-component drift velocity notion to liquids, and its application towards rationalizing Soret thermal-diffusion separation phenomena in quasi-Lorentzian liquid-phase binary mixtures composed of disparately sized solute and solvent molecules, with the massive Brownian solute molecules (e.g., colloidal particles) present in disproportionately small amounts relative to that of the solvent.

Massive hydraulic fracture mapping and characterization program. Surface potential data for Wattenberg 1975--1976 experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCann, R.P.; Bartel, L.C.; Keck, L.J.

1977-08-01

Three massive hydraulic fracture experiments for natural gas stimulation were conducted by Halliburton for AMOCO in the Wattenberg field northeast of Denver, Colorado. The experiments were conducted on three wells--Martin Hart ''E'' No. 1, Salazar G.U. No. 1, and UPRR-22P. All three wells were open hole and the fracture zone was located at a depth of approximately 8000 ft. All were treated with approximately 300,000 gal of fluid and 600,000 lb of proppant. The surface electrical potential technique was used to attempt characterization and mapping of the fracture. The noise perturbating the system consists of telluric currents, currents from industrialmore » sources, and natural local currents. It is difficult to determine the exact signal-to-noise ratio or the exact origin of the noise without exhaustive field measurements and data analysis. However, improvements have been made in the surface potential gradient technique since the early developmental stage of the diagnostic program. To aid in the interpretation of the field data, mathematical modeling efforts have been undertaken. The model utilizes the Green's function integral equation approach where the so-called half-space Green's function is used. The model calculates the potential difference that exists at the surface as a function of fracturing conditions. Data analysis indicates that the fracture orientation for all three wells lies in a SE to NW direction and that the fractures are asymmetric.« less

Increased seedling establishment via enemy release at the upper elevational range limit of sugar maple.

PubMed

Urli, Morgane; Brown, Carissa D; Narváez Perez, Rosela; Chagnon, Pierre-Luc; Vellend, Mark

2016-11-01

The enemy release hypothesis is frequently invoked to explain invasion by nonnative species, but studies focusing on the influence of enemies on natural plant range expansion due to climate change remain scarce. We combined multiple approaches to study the influence of plant-enemy interactions on the upper elevational range limit of sugar maple (Acer saccharum) in southeastern Québec, Canada, where a previous study had demonstrated intense seed predation just beyond the range limit. Consistent with the hypothesis of release from natural enemies at the range limit, data from both natural patterns of regeneration and from seed and seedling transplant experiments showed higher seedling densities at the range edge than in the core of the species' distribution. A growth chamber experiment manipulating soil origin and temperature indicated that this so-called "happy edge" was not likely caused by temperature (i.e., the possibility that climate warming has made high elevation temperatures optimal for sugar maple) or by abiotic soil factors that vary along the elevational gradient. Finally, an insect-herbivore-exclusion experiment showed that insect herbivory was a major cause of seedling mortality in the core of sugar maple's distribution, whereas seedlings transplanted at or beyond the range edge experienced minimal herbivory (i.e., enemy release). Insect herbivory did not completely explain the high levels of seedling mortality in the core of the species' distribution, suggesting that seedlings at or beyond the range edge may also experience release from pathogens. In sum, while some effects of enemies are magnified beyond range edges (e.g., seed predation), others are dampened at and beyond the range edge (e.g., insect herbivory), such that understanding the net outcome of different biotic interactions within, at and beyond the edge of distribution is critical to predicting species' responses to global change. © 2016 by the Ecological Society of America.

Determination of Acidity Constants by Gradient Flow-Injection Titration

ERIC Educational Resources Information Center

Conceicao, Antonio C. L.; Minas da Piedade, Manuel E.

2006-01-01

A three-hour laboratory experiment, designed for an advanced undergraduate course in instrumental analysis that illustrates the application of the gradient chamber flow-injection titration (GCFIT) method with spectrophotometric detection to determine acidity constants is presented. The procedure involves the use of an acid-base indicator to obtain…

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…

Numerical and Experimental Investigation of the Effects of Acceleration Disturbances on Microgravity Experiments

NASA Technical Reports Server (NTRS)

Ramachandran, Narayanan

2000-01-01

Normal vibrational modes on large spacecraft are excited by crew activity, operating machinery, and other mechanical disturbances. Periodic engine burns for maintaining vehicle attitude and random impulse type disturbances also contribute to the acceleration environment of a Spacecraft. Accelerations from these vibrations (often referred to as g-jitter) are several orders of magnitude larger than the residual accelerations from atmospheric drag and gravity gradient effects. Naturally, the effects of such accelerations have been a concern to prospective experimenters wishing to take advantage of the microgravity environment offered by spacecraft operating in low Earth orbit and the topic has been studied extensively, both numerically and analytically. However, these studies have not produced a general theory that predicts the effects of multi-spectral periodic accelerations on a general class of experiments nor have they produced scaling laws that a prospective experimenter could use to assess how his/her experiment might be affected by this acceleration environment. Furthermore, there are no actual flight experimental data that correlates heat or mass transport with measurements of the periodic acceleration environment. The present investigation approaches this problem with carefully conducted terrestrial experiments and rigorous numerical modeling thereby providing comparative theoretical and experimental data. The modeling, it is hoped will provide a predictive tool that can be used for assessing experiment response to Spacecraft vibrations.

The role of the meridional sea surface temperature gradient in controlling the Caribbean low-level jet

NASA Astrophysics Data System (ADS)

Maldonado, Tito; Rutgersson, Anna; Caballero, Rodrigo; Pausata, Francesco S. R.; Alfaro, Eric; Amador, Jorge

2017-06-01

The Caribbean low-level jet (CLLJ) is an important modulator of regional climate, especially precipitation, in the Caribbean and Central America. Previous work has inferred, due to their semiannual cycle, an association between CLLJ strength and meridional sea surface temperature (SST) gradients in the Caribbean Sea, suggesting that the SST gradients may control the intensity and vertical shear of the CLLJ. In addition, both the horizontal and vertical structure of the jet have been related to topographic effects via interaction with the mountains in Northern South America (NSA), including funneling effects and changes in the meridional geopotential gradient. Here we test these hypotheses, using an atmospheric general circulation model to perform a set of sensitivity experiments to examine the impact of both SST gradients and topography on the CLLJ. In one sensitivity experiment, we remove the meridional SST gradient over the Caribbean Sea and in the other, we flatten the mountains over NSA. Our results show that the SST gradient and topography have little or no impact on the jet intensity, vertical, and horizontal wind shears, contrary to previous works. However, our findings do not discount a possible one-way coupling between the SST and the wind over the Caribbean Sea through friction force. We also examined an alternative approach based on barotropic instability to understand the CLLJ intensity, vertical, and horizontal wind shears. Our results show that the current hypothesis about the CLLJ must be reviewed in order to fully understand the atmospheric dynamics governing the Caribbean region.

Determination of the electric field gradient in RbCaF3 near the phase transition

NASA Astrophysics Data System (ADS)

Hepp, M. A.; Man, P. P.; Trokiner, A.; Zanni, H.; Fraissard, J.

1992-12-01

The fluoroperovskite, RbCaF 3 undergoes a phase transition at 195.5K from a cubic to a tetragonal phase. The order parameter for this transition is directly related to the electric field gradient which arises in the tetragonal phase. In this work, we have used three NMR methods to measure the electric field gradient at the 87Rb site in a single crystal of RbCaF 3, very near this transition. These experiments are based on recent theoretical developments which allow the measurement of quadrupole parameters even for nuclei in a weak electric field gradient.

AmeriFlux US-SCf Southern California Climate Gradient - Oak/Pine Forest

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goulden, Mike

This is the AmeriFlux version of the carbon flux data for the site US-SCf Southern California Climate Gradient - Oak/Pine Forest. Site Description - Half hourly data are available at https://www.ess.uci.edu/~california/. This site is one of six Southern California Climate Gradient flux towers operated along an elevation gradient (sites are US-SCg, US-SCs, US-SCf, US-SCw, US-SCc, US-SCd). This site is a mixed oak/pine forest. The site experiences episodic severe drought and mortality, and has also experienced occasional logging and wildfire. Drought and mortality was especially severe in the early 2000s.

Ultra-High Gradient S-band Linac for Laboratory and Industrial Applications

NASA Astrophysics Data System (ADS)

Faillace, L.; Agustsson, R.; Dolgashev, V.; Frigola, P.; Murokh, A.; Rosenzweig, J.; Yakimenko, V.

2010-11-01

A strong demand for high gradient structures arises from the limited real estate available for linear accelerators. RadiaBeam Technologies is developing a Doubled Energy Compact Accelerator (DECA) structure: an S-band standing wave electron linac designed to operate at accelerating gradients of up to 50 MV/m. In this paper, we present the radio-frequency design of the DECA S-band accelerating structure, operating at 2.856 GHz in the π-mode. The structure design is heavily influenced by NLC collaboration experience with ultra high gradient X-band structures; S-band, however, is chosen to take advantage of commonly available high power S-band klystrons.

Numerical experience with a class of algorithms for nonlinear optimization using inexact function and gradient information

NASA Technical Reports Server (NTRS)

Carter, Richard G.

1989-01-01

For optimization problems associated with engineering design, parameter estimation, image reconstruction, and other optimization/simulation applications, low accuracy function and gradient values are frequently much less expensive to obtain than high accuracy values. Here, researchers investigate the computational performance of trust region methods for nonlinear optimization when high accuracy evaluations are unavailable or prohibitively expensive, and confirm earlier theoretical predictions when the algorithm is convergent even with relative gradient errors of 0.5 or more. The proper choice of the amount of accuracy to use in function and gradient evaluations can result in orders-of-magnitude savings in computational cost.

Nonlinear Analyte Concentration Gradients for One-Step Kinetic Analysis Employing Optical Microring Resonators

PubMed Central

Marty, Michael T.; Kuhnline Sloan, Courtney D.; Bailey, Ryan C.; Sligar, Stephen G.

2012-01-01

Conventional methods to probe the binding kinetics of macromolecules at biosensor surfaces employ a stepwise titration of analyte concentrations and measure the association and dissociation to the immobilized ligand at each concentration level. It has previously been shown that kinetic rates can be measured in a single step by monitoring binding as the analyte concentration increases over time in a linear gradient. We report here the application of nonlinear analyte concentration gradients for determining kinetic rates and equilibrium binding affinities in a single experiment. A versatile nonlinear gradient maker is presented, which is easily applied to microfluidic systems. Simulations validate that accurate kinetic rates can be extracted for a wide range of association and dissociation rates, gradient slopes and curvatures, and with models for mass transport. The nonlinear analyte gradient method is demonstrated with a silicon photonic microring resonator platform to measure prostate specific antigen-antibody binding kinetics. PMID:22686186

Nonlinear analyte concentration gradients for one-step kinetic analysis employing optical microring resonators.

PubMed

Marty, Michael T; Sloan, Courtney D Kuhnline; Bailey, Ryan C; Sligar, Stephen G

2012-07-03

Conventional methods to probe the binding kinetics of macromolecules at biosensor surfaces employ a stepwise titration of analyte concentrations and measure the association and dissociation to the immobilized ligand at each concentration level. It has previously been shown that kinetic rates can be measured in a single step by monitoring binding as the analyte concentration increases over time in a linear gradient. We report here the application of nonlinear analyte concentration gradients for determining kinetic rates and equilibrium binding affinities in a single experiment. A versatile nonlinear gradient maker is presented, which is easily applied to microfluidic systems. Simulations validate that accurate kinetic rates can be extracted for a wide range of association and dissociation rates, gradient slopes, and curvatures, and with models for mass transport. The nonlinear analyte gradient method is demonstrated with a silicon photonic microring resonator platform to measure prostate specific antigen-antibody binding kinetics.

NIST torsion oscillator viscometer response: Performance on the LeRC active vibration isolation platform

NASA Technical Reports Server (NTRS)

Berg, Robert F.; Grodsinsky, Carlos M.

1992-01-01

Critical point viscosity measurements are limited to their reduced temperature approach to T(sub c) in an Earth bound system, because of density gradients imposed by gravity. Therefore, these classes of experiments have been proposed as good candidates for 'microgravity' science experiments where this limitation is not present. The nature of these viscosity measurements dictate hardware that is sensitive to low frequency excitations. Because of the vibratory acceleration sensitivity of a torsion oscillator viscometer, used to acquire such measurements, a vibration isolation sensitivity test was performed on candidate 'microgravity' hardware to study the possibility of meeting the stringent oscillatory sensitivity requirements of a National Institute of Standards and Technology (NIST) torsion oscillator viscometer. A prototype six degree of freedom active magnetic isolation system, developed at NASA Lewis Research Center, was used as the isolation system. The ambient acceleration levels of the platform were reduced to the noise floor levels of its control sensors, about one microgravity in the 0.1 to 10 Hz bandwidth.

Guanylyl cyclase-dependent chemotaxis of endothelial cells in response to nitric oxide gradients.

PubMed

Isenberg, Jeff S; Ridnour, Lisa A; Thomas, Douglas D; Wink, David A; Roberts, David D; Espey, Michael Graham

2006-03-15

Nitric oxide (NO) is an important regulator of angiogenesis and neovascularization. The nature of endothelial cell motility responses to NO was examined using a Boyden chamber method. NO generated via decomposition of either DEA/NO or DETA/NO produced increases in human umbilical vein endothelial cell (HUVEC) chemotaxis, which were completely abrogated by ODQ, a soluble guanylyl cyclase inhibitor. Measurements of NO either directly by chemiluminescence or its chemistry with diaminofluorescein revealed that chemotaxis was driven by subtle NO gradients between the lower and the upper wells in this system. In addition to diffusion and volatilization from the upper chambers, the data showed that HUVEC consumption of NO contributed to these sustained gradients. Comparison of DEA/NO- and DETA/NO-mediated responses suggested that the persistence of spatial NO gradients is as significant as the absolute magnitude of NO exposure per unit time. The findings suggest that subnanomolar NO gradients are sufficient to mobilize endothelial cell migration into hypoxic tissue during neovascularization events, such as in wound healing and cancer.

The skylight gradient of luminance helps sandhoppers in sun and moon identification.

PubMed

Ugolini, Alberto; Galanti, Giuditta; Mercatelli, Luca

2012-08-15

To return to the ecologically optimal zone of the beach, the sandhopper Talitrus saltator (Montagu) maintains a constant sea-land direction based on the sun and moon compasses. In this study, we investigated the role of the skylight gradient of luminance in sun and moon identification under natural and artificial conditions of illumination. Clock-shifted (inverted) sandhoppers tested under the sun (during their subjective night) and under the full moon (during their subjective day) exhibit orientation in accordance with correct identification of the sun and the moon at night. Tested in artificial conditions of illumination at night without the artificial gradient of luminance, the artificial astronomical cue is identified as the moon even when the conditions of illumination allow sun compass orientation during the day. When the artificial gradient of luminance is added, the artificial astronomical cue is identified as the sun. The role of the sky gradient of luminance in sun and moon identification is discussed on the basis of present and past findings.

Altering the axial light gradient affects photomorphogenesis in emerging seedlings of Zea mays L

NASA Technical Reports Server (NTRS)

Parks, B. M.; Poff, K. L.

1986-01-01

The axial (longitudinal) red light gradient (632 nanometers) of 4 day old dark-grown maize seedlings is increased by staining the peripheral cells of the coleoptile. The magnitude of increase in the light gradient is dependent solely on the light-absorbing qualities of the stain used. Metanil yellow has no effect on the axial red-light gradient, while methylene blue causes a large increase in this light gradient. These stains did not affect growth in darkness or the sensitivity of mesocotyl elongation to red light. However, mesocotyl elongation was altered for the dark-grown seedlings stained with methylene blue when these seedlings were transplanted, covered with soil, and permitted to emerge under natural lighting conditions. These observations are consistent with the idea that there is a single perceptive site below the coleoptilar node, and suggest that this perceptive site gives the actinic light which has traveled downward through the length of the shoot from an entry point in the plant tip region.

Large polarization gradients and temperature-stable responses in compositionally-graded ferroelectrics

DOE PAGES

Damodaran, Anoop R.; Pandya, Shishir; Qi, Yubo; ...

2017-05-10

A range of modern applications require large and tunable dielectric, piezoelectric or pyroelectric response of ferroelectrics. Such effects are intimately connected to the nature of polarization and how it responds to externally applied stimuli. Ferroelectric susceptibilities are, in general, strongly temperature dependent, diminishing rapidly as one transitions away from the ferroelectric phase transition (T C). In turn, researchers seek new routes to manipulate polarization to simultaneously enhance susceptibilities and broaden operational temperature ranges. Here, we demonstrate such a capability by creating composition and strain gradients in Ba 1-xSr xTiO 3 films which result in spatial polarization gradients as large asmore » 35 μC cm -2 across a 150 nm thick film. These polarization gradients allow for large dielectric permittivity with low loss (ε r≈775, tan δ<0.05), negligible temperature-dependence (13% deviation over 500 °C) and high-dielectric tunability (greater than 70% across a 300 °C range). The role of space charges in stabilizing polarization gradients is also discussed.« less

Large polarization gradients and temperature-stable responses in compositionally-graded ferroelectrics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Damodaran, Anoop R.; Pandya, Shishir; Qi, Yubo

A range of modern applications require large and tunable dielectric, piezoelectric or pyroelectric response of ferroelectrics. Such effects are intimately connected to the nature of polarization and how it responds to externally applied stimuli. Ferroelectric susceptibilities are, in general, strongly temperature dependent, diminishing rapidly as one transitions away from the ferroelectric phase transition (T C). In turn, researchers seek new routes to manipulate polarization to simultaneously enhance susceptibilities and broaden operational temperature ranges. Here, we demonstrate such a capability by creating composition and strain gradients in Ba 1-xSr xTiO 3 films which result in spatial polarization gradients as large asmore » 35 μC cm -2 across a 150 nm thick film. These polarization gradients allow for large dielectric permittivity with low loss (ε r≈775, tan δ<0.05), negligible temperature-dependence (13% deviation over 500 °C) and high-dielectric tunability (greater than 70% across a 300 °C range). The role of space charges in stabilizing polarization gradients is also discussed.« less

Optimum gradient of mountain paths.

PubMed

Minetti, A E

1995-11-01

By combining the experiment results of R. Margaria (Atti Accad. Naz. Lincei Memorie 7: 299-368, 1938), regarding the metabolic cost of gradient locomotion, together with recent insights on gait biomechanics, a prediction about the most economical gradient of mountain paths (approximately 25%) is obtained and interpreted. The pendulum-like mechanism of walking produces a waste of mechanical work against gravity within the gradient range of up to 15% (the overall efficiency is dominated by the low transmission efficiency), whereas for steeper values only the muscular efficiency is responsible for the (slight) metabolic change (per meter of vertical displacement) with respect to gradient. The speeds at the optimum gradient turned out to be approximately 0.65 m/s (+0.16 m/s vertical) and 1.50 m/s (-0.36 m/s vertical), for uphill and downhill walking, respectively, and the ascensional energy expenditure was 0.4 and 2.0 ml O2.kg body mass-1.vertical m-1 climbed or descended. When the metabolic power becomes a burden, as in high-altitude mountaineering, the optimum gradient should be reduced. A sample of real mountain path gradients, experimentally measured, mimics the obtained predictions.

EARTHSHINE ON A YOUNG MOON: EXPLAINING THE LUNAR FARSIDE HIGHLANDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roy, Arpita; Wright, Jason T.; Sigurðsson, Steinn

2014-06-20

The lunar farside highlands problem refers to the curious and unexplained fact that the farside lunar crust is thicker, on average, than the nearside crust. Here we recognize the crucial influence of Earthshine, and propose that it naturally explains this hemispheric dichotomy. Since the accreting Moon rapidly achieved synchronous rotation, a surface and atmospheric thermal gradient was imposed by the proximity of the hot, post-giant impact Earth. This gradient guided condensation of atmospheric and accreting material, preferentially depositing crust-forming refractories on the cooler farside, resulting in a primordial bulk chemical inhomogeneity that seeded the crustal asymmetry. Our model provides amore » causal solution to the lunar highlands problem: the thermal gradient created by Earthshine produced the chemical gradient responsible for the crust thickness dichotomy that defines the lunar highlands.« less

Structure and Composition of Vegetation of Longleaf Pine Plantations Compared to Natural Stands Occurring Along an Environmental Gradient at the Savannah River Site

Treesearch

Gregory P. Smith; Victor B. Shelburne; Joan L. Walker

2002-01-01

Fifty-four plots in 33-43 year old longleaf pine plantations were compared to 30 remnant plots in longleaf stands on the Savannah River Site in South Carolina. Within these stands, the structure and composition of primarily the herb layer relative to a presumed soil moisture or soil texture gradient was studied using the North Carolina Vegetation Survey methodology....

Implementation of a Balance Operator in NCOM

DTIC Science & Technology

2016-04-07

the background temperature Tb and salinity Sb fields do), f is the Coriolis parameter, k is the vertical unit vector, ∇ is the horizontal gradient, p... effectively used as a natural metric in the space of cost function gradients. The associated geometry inhibits descent in the unbalanced directions...28) where f is the local Coriolis parameter, ∆yv is the local grid spacing in the y direction at a v point, and the overbars indicates horizontal

Tree Leaf Bacterial Community Structure and Diversity Differ along a Gradient of Urban Intensity

PubMed Central

Messier, Christian; Kembel, Steven W.

2017-01-01

ABSTRACT Tree leaf-associated microbiota have been studied in natural ecosystems but less so in urban settings, where anthropogenic pressures on trees could impact microbial communities and modify their interaction with their hosts. Additionally, trees act as vectors spreading bacterial cells in the air in urban environments due to the density of microbial cells on aerial plant surfaces. Characterizing tree leaf bacterial communities along an urban gradient is thus key to understand the impact of anthropogenic pressures on urban tree-bacterium interactions and on the overall urban microbiome. In this study, we aimed (i) to characterize phyllosphere bacterial communities of seven tree species in urban environments and (ii) to describe the changes in tree phyllosphere bacterial community structure and diversity along a gradient of increasing urban intensity and at two degrees of tree isolation. Our results indicate that, as anthropogenic pressures increase, urban leaf bacterial communities show a reduction in the abundance of the dominant class in the natural plant microbiome, the Alphaproteobacteria. Our work in the urban environment here reveals that the structures of leaf bacterial communities differ along the gradient of urban intensity. The diversity of phyllosphere microbial communities increases at higher urban intensity, also displaying a greater number and variety of associated indicator taxa than the low and medium urban gradient sites. In conclusion, we find that urban environments influence tree bacterial community composition, and our results suggest that feedback between human activity and plant microbiomes could shape urban microbiomes. IMPORTANCE In natural forests, tree leaf surfaces host diverse bacterial communities whose structure and composition are primarily driven by host species identity. Tree leaf bacterial diversity has also been shown to influence tree community productivity, a key function of terrestrial ecosystems. However, most urban microbiome studies have focused on the built environment, improving our understanding of indoor microbial communities but leaving much to be understood, especially in the nonbuilt microbiome. Here, we provide the first multiple-species comparison of tree phyllosphere bacterial structures and diversity along a gradient of urban intensity. We demonstrate that urban trees possess characteristic bacterial communities that differ from those seen with trees in nonurban environments, with microbial community structure on trees influenced by host species identity but also by the gradient of urban intensity and by the degree of isolation from other trees. Our results suggest that feedback between human activity and plant microbiomes could shape urban microbiomes. PMID:29238751

Tree Leaf Bacterial Community Structure and Diversity Differ along a Gradient of Urban Intensity.

PubMed

Laforest-Lapointe, Isabelle; Messier, Christian; Kembel, Steven W

2017-01-01

Tree leaf-associated microbiota have been studied in natural ecosystems but less so in urban settings, where anthropogenic pressures on trees could impact microbial communities and modify their interaction with their hosts. Additionally, trees act as vectors spreading bacterial cells in the air in urban environments due to the density of microbial cells on aerial plant surfaces. Characterizing tree leaf bacterial communities along an urban gradient is thus key to understand the impact of anthropogenic pressures on urban tree-bacterium interactions and on the overall urban microbiome. In this study, we aimed (i) to characterize phyllosphere bacterial communities of seven tree species in urban environments and (ii) to describe the changes in tree phyllosphere bacterial community structure and diversity along a gradient of increasing urban intensity and at two degrees of tree isolation. Our results indicate that, as anthropogenic pressures increase, urban leaf bacterial communities show a reduction in the abundance of the dominant class in the natural plant microbiome, the Alphaproteobacteria . Our work in the urban environment here reveals that the structures of leaf bacterial communities differ along the gradient of urban intensity. The diversity of phyllosphere microbial communities increases at higher urban intensity, also displaying a greater number and variety of associated indicator taxa than the low and medium urban gradient sites. In conclusion, we find that urban environments influence tree bacterial community composition, and our results suggest that feedback between human activity and plant microbiomes could shape urban microbiomes. IMPORTANCE In natural forests, tree leaf surfaces host diverse bacterial communities whose structure and composition are primarily driven by host species identity. Tree leaf bacterial diversity has also been shown to influence tree community productivity, a key function of terrestrial ecosystems. However, most urban microbiome studies have focused on the built environment, improving our understanding of indoor microbial communities but leaving much to be understood, especially in the nonbuilt microbiome. Here, we provide the first multiple-species comparison of tree phyllosphere bacterial structures and diversity along a gradient of urban intensity. We demonstrate that urban trees possess characteristic bacterial communities that differ from those seen with trees in nonurban environments, with microbial community structure on trees influenced by host species identity but also by the gradient of urban intensity and by the degree of isolation from other trees. Our results suggest that feedback between human activity and plant microbiomes could shape urban microbiomes.

A New Kind of Single-Well Tracer Test for Assessing Subsurface Heterogeneity

NASA Astrophysics Data System (ADS)

Hansen, S. K.; Vesselinov, V. V.; Lu, Z.; Reimus, P. W.; Katzman, D.

2017-12-01

Single-well injection-withdrawal (SWIW) tracer tests have historically been interpreted using the idealized assumption of tracer path reversibility (i.e., negligible background flow), with background flow due to natural hydraulic gradient being an un-modeled confounding factor. However, we have recently discovered that it is possible to use background flow to our advantage to extract additional information about the subsurface. To wit: we have developed a new kind of single-well tracer test that exploits flow due to natural gradient to estimate the variance of the log hydraulic conductivity field of a heterogeneous aquifer. The test methodology involves injection under forced gradient and withdrawal under natural gradient, and makes use of a relationship, discovered using a large-scale Monte Carlo study and machine learning techniques, between power law breakthrough curve tail exponent and log-hydraulic conductivity variance. We will discuss how we performed the computational study and derived this relationship and then show an application example in which our new single-well tracer test interpretation scheme was applied to estimation of heterogeneity of a formation at the chromium contamination site at Los Alamos National Laboratory. Detailed core hole records exist at the same site, from which it was possible to estimate the log hydraulic conductivity variance using a Kozeny-Carman relation. The variances estimated using our new tracer test methodology and estimated by direct inspection of core were nearly identical, corroborating the new methodology. Assessment of aquifer heterogeneity is of critical importance to deployment of amendments associated with in-situ remediation strategies, since permeability contrasts potentially reduce the interaction between amendment and contaminant. Our new tracer test provides an easy way to obtain this information.

Thermotropism by primary roots of maize

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fortin, M.-C.; Poff, K.L.

1990-05-01

Sensing in the roots of higher plants has long been recognized to be restricted mainly to gravitropism and thigmotropism. However, root responses to temperature gradients have not been extensively studied. We have designed experiments under controlled conditions to test if and how root direction of maize can be altered by thermal gradients perpendicular to the gravity vector. Primary roots of maize grown on agar plates exhibit positive thermotropism (curvature toward the warmer temperature) when exposed to gradients of 0.5 to 4.2{degree}C cm{sup {minus}1}. The extent of thermotropism depends on the temperature gradient and the temperature at which the root ismore » placed within the gradient. The curvature cannot be accounted for by differential growth as a direct effect of temperature on each side of the root.« less

A new smoothing modified three-term conjugate gradient method for [Formula: see text]-norm minimization problem.

PubMed

Du, Shouqiang; Chen, Miao

2018-01-01

We consider a kind of nonsmooth optimization problems with [Formula: see text]-norm minimization, which has many applications in compressed sensing, signal reconstruction, and the related engineering problems. Using smoothing approximate techniques, this kind of nonsmooth optimization problem can be transformed into a general unconstrained optimization problem, which can be solved by the proposed smoothing modified three-term conjugate gradient method. The smoothing modified three-term conjugate gradient method is based on Polak-Ribière-Polyak conjugate gradient method. For the Polak-Ribière-Polyak conjugate gradient method has good numerical properties, the proposed method possesses the sufficient descent property without any line searches, and it is also proved to be globally convergent. Finally, the numerical experiments show the efficiency of the proposed method.

Experiment study of mud to the moving process influent about viscous debris flow along slope

NASA Astrophysics Data System (ADS)

Jun, JiXian; Ying, Liang; Li, Pan Hua; Qiang, OuGuo

2018-01-01

Mud is the main component of viscous debris flow. The physical model experiments of viscous debris flow were carried out through the mixing mud with different density and fixed components of coarse particles. The width, longitudinal movement distance and motion velocity were recorded by video cameras during experiment. Through viscous debris flow physical model experiments, the influence of mud to transverse width, longitudinal movement distance and motion velocity was discussed. The physical model experiment results show that the motion forms change from inviscid particle flow to viscous debris flow and to the whole mass sliding with the increase of mud density; the width and the length along the slope decrease with mud density increasing; the movement process has classified phenomena about viscous debris flow composed by different mud densities: the velocity increases rapidly with time and the change gradient is steady when the density of mud is lower than 1.413g/cm3; the movement process can be divided into two stages when the density of mud is higher than 1.413g/cm3: the movement velocity is lower and the gradient change is small in the initial stage; but in the second stage, the movement velocity increases quickly, and the gradient is higher than the first stage, and with steady value.

Experiment, monitoring, and gradient methods used to infer climate change effects on plant communities yield consistent patterns.

PubMed

Elmendorf, Sarah C; Henry, Gregory H R; Hollister, Robert D; Fosaa, Anna Maria; Gould, William A; Hermanutz, Luise; Hofgaard, Annika; Jónsdóttir, Ingibjörg S; Jónsdóttir, Ingibjörg I; Jorgenson, Janet C; Lévesque, Esther; Magnusson, Borgþór; Molau, Ulf; Myers-Smith, Isla H; Oberbauer, Steven F; Rixen, Christian; Tweedie, Craig E; Walker, Marilyn D; Walker, Marilyn

2015-01-13

Inference about future climate change impacts typically relies on one of three approaches: manipulative experiments, historical comparisons (broadly defined to include monitoring the response to ambient climate fluctuations using repeat sampling of plots, dendroecology, and paleoecology techniques), and space-for-time substitutions derived from sampling along environmental gradients. Potential limitations of all three approaches are recognized. Here we address the congruence among these three main approaches by comparing the degree to which tundra plant community composition changes (i) in response to in situ experimental warming, (ii) with interannual variability in summer temperature within sites, and (iii) over spatial gradients in summer temperature. We analyzed changes in plant community composition from repeat sampling (85 plant communities in 28 regions) and experimental warming studies (28 experiments in 14 regions) throughout arctic and alpine North America and Europe. Increases in the relative abundance of species with a warmer thermal niche were observed in response to warmer summer temperatures using all three methods; however, effect sizes were greater over broad-scale spatial gradients relative to either temporal variability in summer temperature within a site or summer temperature increases induced by experimental warming. The effect sizes for change over time within a site and with experimental warming were nearly identical. These results support the view that inferences based on space-for-time substitution overestimate the magnitude of responses to contemporary climate warming, because spatial gradients reflect long-term processes. In contrast, in situ experimental warming and monitoring approaches yield consistent estimates of the magnitude of response of plant communities to climate warming.

Influence on cell death of high frequency motion of magnetic nanoparticles during magnetic hyperthermia experiments

NASA Astrophysics Data System (ADS)

Hallali, N.; Clerc, P.; Fourmy, D.; Gigoux, V.; Carrey, J.

2016-07-01

Studies with transplanted tumors in animals and clinical trials have provided the proof-of-concept of magnetic hyperthermia (MH) therapy of cancers using iron oxide nanoparticles. Interestingly, in several studies, the application of an alternating magnetic field (AMF) to tumor cells having internalized and accumulated magnetic nanoparticles (MNPs) into their lysosomes can induce cell death without detectable temperature increase. To explain these results, among other hypotheses, it was proposed that cell death could be due to the high-frequency translational motion of MNPs under the influence of the AMF gradient generated involuntarily by most inductors. Such mechanical actions of MNPs might cause cellular damages and participate in the induction of cell death under MH conditions. To test this hypothesis, we developed a setup maximizing this effect. It is composed of an anti-Helmholtz coil and two permanent magnets, which produce an AMF gradient and a superimposed static MF. We have measured the MNP heating power and treated tumor cells by a standard AMF and by an AMF gradient, on which was added or not a static magnetic field. We showed that the presence of a static magnetic field prevents MNP heating and cell death in standard MH conditions. The heating power of MNPs in an AMF gradient is weak, position-dependent, and related to the presence of a non-zero AMF. Under an AMF gradient and a static field, no MNP heating and cell death were measured. Consequently, the hypothesis that translational motions could be involved in cell death during MH experiments is ruled out by our experiments.

Magnetic Field Gradient Calibration as an Experiment to Illustrate Magnetic Resonance Imaging

ERIC Educational Resources Information Center

Seedhouse, Steven J.; Hoffmann, Markus M.

2008-01-01

A nuclear magnetic resonance (NMR) spectroscopy experiment for the undergraduate physical chemistry laboratory is described that encompasses both qualitative and quantitative pedagogical goals. Qualitatively, the experiment illustrates how images are obtained in magnetic resonance imaging (MRI). Quantitatively, students experience the…

Impact of Salinity Gradients on Ammonia Bioattenuation Processes in a Photosynthetic Wetland Biomat

NASA Astrophysics Data System (ADS)

Vega, M.; Jones, Z.; Sharp, J.

2017-12-01

Shallow, open water treatment wetlands may be able to offset challenges associated with the reclamation of impaired waters (e.g., membrane fouling, aeration costs, etc.) due to natural biogeochemical fluctuations produced by a benthic, photoactive biomat. This diatomaceous, redox-stratified biomat has demonstrated significant nitrate and trace organic removal from municipal wastewater streams and the microbial community has been thoroughly characterized. However, research is required to predict shifts in community structure and function in response to the excess salinity, ammonia, and metal gradients of impaired waters. Batch microcosm studies inoculating biomat from an active open water treatment wetland with incremental dilutions of hydraulic fracturing produced water were conducted in a light chamber with oscillating twelve-hour light and dark cycles to assess the effect of an impaired water matrix on biomat functionality. Diurnal photosynthetic signatures and ammonia removal kinetics were quantified in various experiments probing the effects of oscillating light conditions, biomat depth, water column isolation, nitrogen source, and salinity gradients in conjunction with phylogenetic profiles and morphological characterization. Diurnal pH and dissolved oxygen fluctuations were present at all produced water permutations, perhaps indicating stabilization of photosynthetic communities. Ammonia attenuation results suggest that the biomat is effective at removing ammonia, although first order rate constants decrease with increasing produced water abundance. Microbial community diversity appears to decrease with increasing salinity, and it is likely that these shifts correspond to variation in ecosystem function and thus treatment effectiveness. The application of shallow, open water treatment wetlands to remediate impaired waters has the potential to address societally relevant problems while discerning fundamental biogeochemical phenomena.

Susceptibility to a metal under global warming is shaped by thermal adaptation along a latitudinal gradient.

PubMed

Dinh Van, Khuong; Janssens, Lizanne; Debecker, Sara; De Jonge, Maarten; Lambret, Philippe; Nilsson-Örtman, Viktor; Bervoets, Lieven; Stoks, Robby

2013-09-01

Global warming and contamination represent two major threats to biodiversity that have the potential to interact synergistically. There is the potential for gradual local thermal adaptation and dispersal to higher latitudes to mitigate the susceptibility of organisms to contaminants and global warming at high latitudes. Here, we applied a space-for-time substitution approach to study the thermal dependence of the susceptibility of Ischnura elegans damselfly larvae to zinc in a common garden warming experiment (20 and 24 °C) with replicated populations from three latitudes spanning >1500 km in Europe. We observed a striking latitude-specific effect of temperature on the zinc-induced mortality pattern; local thermal adaptation along the latitudinal gradient made Swedish, but not French, damselfly larvae more susceptible to zinc at 24 °C. Latitude- and temperature-specific differences in zinc susceptibility may be related to the amount of energy available to defend against and repair damage since Swedish larvae showed a much stronger zinc-induced reduction of food intake at 24 °C. The pattern of local thermal adaptation indicates that the predicted temperature increase of 4 °C by 2100 will strongly magnify the impact of a contaminant such as zinc at higher latitudes unless there is thermal evolution and/or migration of lower latitude genotypes. Our results underscore the critical importance of studying the susceptibility to contaminants under realistic warming scenarios taking into account local thermal adaptation across natural temperature gradients. © 2013 John Wiley & Sons Ltd.

Using two classification schemes to develop vegetation indices of biological integrity for wetlands in West Virginia, USA.

PubMed

Veselka, Walter; Rentch, James S; Grafton, William N; Kordek, Walter S; Anderson, James T

2010-11-01

Bioassessment methods for wetlands, and other bodies of water, have been developed worldwide to measure and quantify changes in "biological integrity." These assessments are based on a classification system, meant to ensure appropriate comparisons between wetland types. Using a local site-specific disturbance gradient, we built vegetation indices of biological integrity (Veg-IBIs) based on two commonly used wetland classification systems in the USA: One based on vegetative structure and the other based on a wetland's position in a landscape and sources of water. The resulting class-specific Veg-IBIs were comprised of 1-5 metrics that varied in their sensitivity to the disturbance gradient (R2=0.14-0.65). Moreover, the sensitivity to the disturbance gradient increased as metrics from each of the two classification schemes were combined (added). Using this information to monitor natural and created wetlands will help natural resource managers track changes in biological integrity of wetlands in response to anthropogenic disturbance and allows the use of vegetative communities to set ecological performance standards for mitigation banks.

Analysis of vortical structures in turbulent natural convection

NASA Astrophysics Data System (ADS)

Park, Sangro; Lee, Changhoon

2014-11-01

Natural convection of fluid within two parallel walls, Rayleigh-Bénard convection, is studied by direct numerical simulation using a spectral method. The flow is in soft turbulence regime with Rayleigh number 106, 107, 108, Prandtl number 0 . 7 and aspect ratio 4. We investigate the relations between thermal plumes and vortical structures through manipulating the evolution equations of vorticity and velocity gradient tensor. According to simulation results, horizontal vorticity occurs near the wall and changes into vertical vorticity by vertical stretching of fluid element which is caused by vertical movement of the thermal plume. Additionally, eigenvalues, eigenvectors and invariants of velocity gradient tensor show the topologies of vortical structures, including how vortical structures are tilted or stretched. Difference of velocity gradient tensor between inside thermal plumes and background region is also investigated, and the result indicates that thermal plumes play an important role in changing the distribution of vortical structures. The results of this study are consistent with other researches which suggest that vertical vorticity is stronger in high Rayleigh number flows. Details will be presented in the meeting.

Stellar metallicity variations across spiral arms in disk galaxies with multiple populations

NASA Astrophysics Data System (ADS)

Khoperskov, S.; Di Matteo, P.; Haywood, M.; Combes, F.

2018-03-01

This Letter studies the formation of azimuthal metallicity variations in the disks of spiral galaxies in the absence of initial radial metallicity gradients. Using high-resolution N-body simulations, we model composite stellar discs, made of kinematically cold and hot stellar populations, and study their response to spiral arm perturbations. We find that, as expected, disk populations with different kinematics respond differently to a spiral perturbation, with the tendency for dynamically cooler populations to show a larger fractional contribution to spiral arms than dynamically hotter populations. By assuming a relation between kinematics and metallicity, namely the hotter the population, the more metal-poor it is, this differential response to the spiral arm perturbations naturally leads to azimuthal variations in the mean metallicity of stars in the simulated disk. Thus, azimuthal variations in the mean metallicity of stars across a spiral galaxy are not necessarily a consequence of the reshaping, by radial migration, of an initial radial metallicity gradient. They indeed arise naturally also in stellar disks which have initially only a negative vertical metallicity gradient.

A multi-year comparison of IPCI scores for prairie pothole wetlands: implications of temporal and spatial variation

USGS Publications Warehouse

Euliss, Ned H.; Mushet, David M.

2011-01-01

In the prairie pothole region of North America, development of Indices of Biotic Integrity (IBIs) to detect anthropogenic impacts on wetlands has been hampered by naturally dynamic inter-annual climate fluctuations. Of multiple efforts to develop IBIs for prairie pothole wetlands, only one, the Index of Plant Community Integrity (IPCI), has reported success. We evaluated the IPCI and its ability to distinguish between natural and anthropogenic variation using plant community data collected from 16 wetlands over a 4-year-period. We found that under constant anthropogenic influence, IPCI metric scores and condition ratings varied annually in response to environmental variation driven primarily by natural climate variation. Artificially forcing wetlands that occur along continuous hydrologic gradients into a limited number of discrete classes (e.g., temporary, seasonal, and semi-permanent) further confounded the utility of IPCI metrics. Because IPCI scores vary significantly due to natural climate dynamics as well as human impacts, methodology must be developed that adequately partitions natural and anthropogenically induced variation along continuous hydrologic gradients. Until such methodology is developed, the use of the IPCI to evaluate prairie pothole wetlands creates potential for misdirected corrective or regulatory actions, impairment of natural wetland functional processes, and erosion of public confidence in the wetland sciences.

Development and validation of a critical gradient energetic particle driven Alfven eigenmode transport model for DIII-D tilted neutral beam experiments

DOE PAGES

Waltz, Ronald E.; Bass, Eric M.; Heidbrink, William W.; ...

2015-10-30

Recent experiments with the DIII-D tilted neutral beam injection (NBI) varying the beam energetic particle (EP) source profiles have provided strong evidence that unstable Alfven eigenmodes (AE) drive stiff EP transport at a critical EP density gradient. Here the critical gradient is identified by the local AE growth rate being equal to the local ITG/TEM growth rate at the same low toroidal mode number. The growth rates are taken from the gyrokinetic code GYRO. Simulation show that the slowing down beam-like EP distribution has a slightly lower critical gradient than the Maxwellian. The ALPHA EP density transport code, used tomore » validate the model, combines the low-n stiff EP critical density gradient AE mid-core transport with the energy independent high-n ITG/TEM density transport model controling the central core EP density profile. For the on-axis NBI heated DIII-D shot 146102, while the net loss to the edge is small, about half the birth fast ions are transported from the central core r/a < 0.5 and the central density is about half the slowing down density. Lastly, these results are in good agreement with experimental fast ion pressure profiles inferred from MSE constrained EFIT equilibria.« less

People detection in crowded scenes using active contour models

NASA Astrophysics Data System (ADS)

Sidla, Oliver

2009-01-01

The detection of pedestrians in real-world scenes is a daunting task, especially in crowded situations. Our experience over the last years has shown that active shape models (ASM) can contribute significantly to a robust pedestrian detection system. The paper starts with an overview of shape model approaches, it then explains our approach which builds on top of Eigenshape models which have been trained using real-world data. These models are placed over candidate regions and matched to image gradients using a scoring function which integrates i) point distribution, ii) local gradient orientations iii) local image gradient strengths. A matching and shape model update process is iteratively applied in order to fit the flexible models to the local image content. The weights of the scoring function have a significant impact on the ASM performance. We analyze different settings of scoring weights for gradient magnitude, relative orientation differences, distance between model and gradient in an experiment which uses real-world data. Although for only one pedestrian model in an image computation time is low, the number of necessary processing cycles which is needed to track many people in crowded scenes can become the bottleneck in a real-time application. We describe the measures which have been taken in order to improve the speed of the ASM implementation and make it real-time capable.

On the vanishing of the t-term in the short-time expansion of the diffusion coefficient for oscillating gradients in diffusion NMR

NASA Astrophysics Data System (ADS)

Laun, Frederik B.; Demberg, Kerstin; Nagel, Armin M.; Uder, Micheal; Kuder, Tristan A.

2017-11-01

Nuclear magnetic resonance (NMR) diffusion measurements can be used to probe porous structures or biological tissues by means of the random motion of water molecules. The short-time expansion of the diffusion coefficient in powers of sqrt(t), where t is the diffusion time related to the duration of the diffusion-weighting magnetic field gradient profile, is universally connected to structural parameters of the boundaries restricting the diffusive motion. The sqrt(t)-term is proportional to the surface to volume ratio. The t-term is related to permeability and curvature. The short time expansion can be measured with two approaches in NMR-based diffusion experiments: First, by the use of diffusion encodings of short total duration and, second, by application of oscillating gradients of long total duration. For oscillating gradients, the inverse of the oscillation frequency becomes the relevant time scale. The purpose of this manuscript is to show that the oscillating gradient approach is blind to the t-term. On the one hand, this prevents fitting of permeability and curvature measures from this term. On the other hand, the t-term does not bias the determination of the sqrt(t)-term in experiments.

Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

NASA Astrophysics Data System (ADS)

Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

2002-11-01

An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined. Specific goals for the investigation are: 1. To develop an understanding of convection control in diamagnetic fluids with concentration gradients through experimentation and numerical modeling. Specifically solutal buoyancy driven convection due to crystal growth will be considered. 2. To develop predictive measures for successful crystallization in a magnetic field using analyses and numerical modeling for use in future protein crystal growth experiments. This will establish criteria that can be used to estimate the efficacy of magnetic field flow damping on crystallization of candidate proteins. 3. To demonstrate the understanding of convection damping by high magnetic fields to a class of proteins that is of interest and whose structure is as yet not determined. 4. To compare quantitatively, the quality of the grown crystals with and without a magnetic field. X-ray diffraction techniques will be used for the comparative studies. In a preliminary set of experiments, we studied crystal dissolution effects in a 5 Tesla magnet available at NASA Marshall Space Flight Center (MSFC). Using a Schlieren setup, a 1mm crystal of Alum (Aluminum-Potassium Sulfate) was introduced in a 75% saturated solution and the resulting dissolution plume was observed. The experiment was conducted both in the presence and absence of a magnetic field gradient. The magnet produces a gradient field of approx. 1 Tesla2/cm. Image analysis of the recorded images indicated an enhanced plume velocity that was of the order of the measurement limit. For this experiment, both the gradient and gravity fields are in the same direction resulting in an enhanced effective gravity that tends to accelerate the observed plume velocity. While the results are not conclusive, pending further tests, it clearly points out the inadequacy of the MSFC magnet for conducting protein crystallization experiments and the need for a stronger magnet. In spacebased experiments, however, where the gravitational effects are small, only a weak magnetic field will be required to control or mitigate the effects of convective contamination.

Study of Fluid Flow Control in Protein Crystallization using Strong Magnetic Fields

NASA Technical Reports Server (NTRS)

Ramachandran, Narayanan; Leslie, Fred; Ciszak, Ewa

2002-01-01

An important component in biotechnology, particularly in the area of protein engineering and rational drug design is the knowledge of the precise three-dimensional molecular structure of proteins. The quality of structural information obtained from X-ray diffraction methods is directly dependent on the degree of perfection of the protein crystals. As a consequence, the growth of high quality macromolecular crystals for diffraction analyses has been the central focus for biochemists, biologists, and bioengineers. Macromolecular crystals are obtained from solutions that contain the crystallizing species in equilibrium with higher aggregates, ions, precipitants, other possible phases of the protein, foreign particles, the walls of the container, and a likely host of other impurities. By changing transport modes in general, i.e., reduction of convection and sedimentation, as is achieved in "microgravity", researchers have been able to dramatically affect the movement and distribution of macromolecules in the fluid, and thus their transport, formation of crystal nuclei, and adsorption to the crystal surface. While a limited number of high quality crystals from space flights have been obtained, as the recent National Research Council (NRC) review of the NASA microgravity crystallization program pointed out, the scientific approach and research in crystallization of proteins has been mainly empirical yielding inconclusive results. We postulate that we can reduce convection in ground-based experiments and we can understand the different aspects of convection control through the use of strong magnetic fields and field gradients. Whether this limited convection in a magnetic field will provide the environment for the growth of high quality crystals is still a matter of conjecture that our research will address. The approach exploits the variation of fluid magnetic susceptibility with concentration for this purpose and the convective damping is realized by appropriately positioning the crystal growth cell so that the magnetic susceptibility force counteracts terrestrial gravity. The general objective is to test the hypothesis of convective control using a strong magnetic field and magnetic field gradient and to understand the nature of the various forces that come into play. Specifically we aim to delineate causative factors and to quantify them through experiments, analysis and numerical modeling. Once the basic understanding is obtained, the study will focus on testing the hypothesis on proteins of pyruvate dehydrogenase complex (PDC), proteins E1 and E3. Obtaining high crystal quality of these proteins is of great importance to structural biologists since their structures need to be determined. Specific goals for the investigation are: 1. To develop an understanding of convection control in diamagnetic fluids with concentration gradients through experimentation and numerical modeling. Specifically solutal buoyancy driven convection due to crystal growth will be considered. 2. To develop predictive measures for successful crystallization in a magnetic field using analyses and numerical modeling for use in future protein crystal growth experiments. This will establish criteria that can be used to estimate the efficacy of magnetic field flow damping on crystallization of candidate proteins. 3. To demonstrate the understanding of convection damping by high magnetic fields to a class of proteins that is of interest and whose structure is as yet not determined. 4. To compare quantitatively, the quality of the grown crystals with and without a magnetic field. X-ray diffraction techniques will be used for the comparative studies. In a preliminary set of experiments, we studied crystal dissolution effects in a 5 Tesla magnet available at NASA Marshall Space Flight Center (MSFC). Using a Schlieren setup, a 1mm crystal of Alum (Aluminum-Potassium Sulfate) was introduced in a 75% saturated solution and the resulting dissolution plume was observed. The experiment was conducted both in the presence and absence of a magnetic field gradient. The magnet produces a gradient field of approx. 1 Tesla2/cm. Image analysis of the recorded images indicated an enhanced plume velocity that was of the order of the measurement limit. For this experiment, both the gradient and gravity fields are in the same direction resulting in an enhanced effective gravity that tends to accelerate the observed plume velocity. While the results are not conclusive, pending further tests, it clearly points out the inadequacy of the MSFC magnet for conducting protein crystallization experiments and the need for a stronger magnet. In spacebased experiments, however, where the gravitational effects are small, only a weak magnetic field will be required to control or mitigate the effects of convective contamination.

Evidence for Helical Magnetic fields in Kiloparsec-Scale AGN Jets and the Action of a Cosmic Battery

NASA Technical Reports Server (NTRS)

Gabuzda, D. C.; Christodoulou, D. M.; Contopulos, I.; Kazanas, D.

2012-01-01

A search for transverse kiloparsec-scale gradients in Faraday rotation-measure (RM) maps of extragalactic radio sources in the literature has yielded 6 AGNs displaying continuous, monotonic RM gradients across their jets, oriented roughly orthogonal to the local jet direction. The most natural interpretation of such transverse RM gradients is that they are caused by the systematic change in the line-of-sight components of helical magnetic fields associated with these jets. All the identified transverse RM gradients increase in the counterclockwise (CCW) direction on the sky relative to the centers of these AGNs. Taken together with the results of Contopoulos et al. who found evidence for a predominance of clockwise (CW) transverse RM gradients across parsec-scale (VLBI) jets, this provides new evidence for preferred orientations of RM gradients due to helical jet magnetic fields, with a reversal from CW in the inner jets to CCW farther from the centers of activity. This can be explained by the "Poynting-Robertson cosmic-battery" mechanism, which can generate helical magnetic fields with a. characteristic "twist," which are expelled with the jet outflows. If the Poynting-Robertson battery mechanism is not operating, an alternative mechanism must be identified, which is able to explain the 'predominance of CW /CCW RM gradients on parsec/kiloparsec scales.

Arbitrary magnetic field gradient waveform correction using an impulse response based pre-equalization technique.

PubMed

Goora, Frédéric G; Colpitts, Bruce G; Balcom, Bruce J

2014-01-01

The time-varying magnetic fields used in magnetic resonance applications result in the induction of eddy currents on conductive structures in the vicinity of both the sample under investigation and the gradient coils. These eddy currents typically result in undesired degradations of image quality for MRI applications. Their ubiquitous nature has resulted in the development of various approaches to characterize and minimize their impact on image quality. This paper outlines a method that utilizes the magnetic field gradient waveform monitor method to directly measure the temporal evolution of the magnetic field gradient from a step-like input function and extracts the system impulse response. With the basic assumption that the gradient system is sufficiently linear and time invariant to permit system theory analysis, the impulse response is used to determine a pre-equalized (optimized) input waveform that provides a desired gradient response at the output of the system. An algorithm has been developed that calculates a pre-equalized waveform that may be accurately reproduced by the amplifier (is physically realizable) and accounts for system limitations including system bandwidth, amplifier slew rate capabilities, and noise inherent in the initial measurement. Significant improvements in magnetic field gradient waveform fidelity after pre-equalization have been realized and are summarized. Copyright © 2013 Elsevier Inc. All rights reserved.

Capillary-Physics Mechanism of Elastic-Wave Mobilization of Residual Oil

NASA Astrophysics Data System (ADS)

Beresnev, I. A.; Pennington, W. D.; Turpening, R. M.

2003-12-01

Much attention has been given to the possibility of vibratory mobilization of residual oil as a method of enhanced recovery. The common features of the relevant applications have nonetheless been inconsistency in the results of field tests and the lack of understanding of a physical mechanism that would explain variable experiences. Such a mechanism can be found in the physics of capillary trapping of oil ganglia, driven through the pore channels by an external pressure gradient. Entrapping of ganglia occurs due to the capillary pressure building on the downstream meniscus entering a narrow pore throat. The resulting internal-pressure imbalance acts against the external gradient, which needs to exceed a certain threshold to carry the ganglion through. The ganglion flow thus exhibits the properties of the Bingham (yield-stress) flow, not the Darcy flow. The application of vibrations is equivalent to the addition of an oscillatory forcing to the constant gradient. When this extra forcing acts along the gradient, an instant "unplugging" occurs, while, when the vibration reverses direction, the flow is plugged. This asymmetry results in an average non-zero flow over one period of vibration, which explains the mobilization effect. The minimum-amplitude and maximum-frequency thresholds apply for the mobilization to occur. When the vibration amplitude exceeds a certain "saturation" level, the flow returns to the Darcy regime. The criterion of the mobilization of a particular ganglion involves the parameters of both the medium (pore geometry, interfacial and wetting properties, fluid viscosity) and the oscillatory field (amplitude and frequency). The medium parameters vary widely under natural conditions. It follows that an elastic wave with a given amplitude and frequency will always produce a certain mobilization effect, mobilizing some ganglia and leaving others intact. The exact macroscopic effect is hard to predict, as it will represent a response of the populations of ganglia with unknown parameter distributions. The variability of responses to vibratory stimulation should thus be expected.

Neutrophil migration under spatially-varying chemoattractant gradient profiles.

PubMed

Halilovic, Iris; Wu, Jiandong; Alexander, Murray; Lin, Francis

2015-01-01

Chemotaxis plays an important role in biological processes such as cancer metastasis, embryogenesis, wound healing, and immune response. Neutrophils are the frontline defenders against invasion of foreign microorganisms into our bodies. To achieve this important immune function, a neutrophil can sense minute chemoattractant concentration differences across its cell body and effectively migrate toward the chemoattractant source. Furthermore, it has been demonstrated in various studies that neutrophils are highly sensitive to changes in the surrounding chemoattractant environments, suggesting the role of a chemotactic memory for processing the complex spatiotemporal chemical guiding signals. Using a microfluidic device, in the present study we characterized neutrophil migration under spatially varying profiles of interleukine-8 gradients, which consist of three spatially ordered regions of a shallow gradient, a steep gradient and a nearly saturated gradient. This design allowed us to examine how neutrophils migrate under different chemoattractant gradient profiles, and how the migratory response is affected when the cell moves from one gradient profile to another in a single experiment. Our results show robust neutrophil chemotaxis in the shallow and steep gradient, but not the saturated gradient. Furthermore, neutrophils display a transition from chemotaxis to flowtaxis when they migrate across the steep gradient interface, and the relative efficiency of this transition depends on the cell's chemotaxis history. Finally, some neutrophils were observed to adjust their morphology to different gradient profiles.

Gint2D-T2 correlation NMR of porous media

NASA Astrophysics Data System (ADS)

Zhang, Yan; Blümich, Bernhard

2015-03-01

The internal magnetic field gradient induced in porous media by magnetic susceptibility differences at material interfaces impacts diffusion measurements in particular at high magnetic field and can be used to probe the pore structure. Insight about the relationship between pore space and internal gradient Gint can be obtained from 2D Laplace NMR experiments. When measuring distributions of transverse relaxation times T2 in fluid filled porous media, relaxation and diffusion in internal gradients arise simultaneously and data are often interpreted with the assumption that one or the other parameter be constant throughout the sample. To examine this assumption we measure correlations of the distributions of Gint2D and T2 by 2D Laplace NMR for three different kinds of samples, glass beads with different bead diameters saturated with water, glass beads filled with oil and water, and a wet mortar sample. For the first two samples the cases where either the internal gradient or diffusion dominates were examined separately in order to better understand the relationship between Gint and D. These results are useful for assessing the impact of internal gradients and diffusion in unknown samples, such as the mortar sample. The experiments were performed at different magnetic field strengths corresponding to 300 MHz and 700 MHz 1H Larmor frequency to identify the impact of the magnetic field on the internal gradient. Subsequently, spatially resolved Gint2D-T2 maps were obtained to study the sample heterogeneity.

[Quantitative experiment and analysis of gradient-induced eddy currents on magnetic resonance imaging].

PubMed

He, Wenjing; Zhu, Yuanzhong; Wang, Wenzhou; Zou, Kai; Zhang, Kai; He, Chao

2017-04-01

Pulsed magnetic field gradients generated by gradient coils are widely used in signal location in magnetic resonance imaging (MRI). However, gradient coils can also induce eddy currents in final magnetic field in the nearby conducting structures which lead to distortion and artifact in images, misguiding clinical diagnosis. We tried in our laboratory to measure the magnetic field of gradient-induced eddy current in 1.5 T superconducting magnetic resonance imaging device; and extracted key parameters including amplitude and time constant of exponential terms according to inductance-resistance series mathematical module. These parameters of both self-induced component and crossing component are useful to design digital filters to implement pulse pre-emphasize to reshape the waveform. A measure device that is a basement equipped with phantoms and receiving coils was designed and placed in the isocenter of the magnetic field. By applying testing sequence, contrast experiments were carried out in a superconducting magnet before and after eddy current compensation. Sets of one dimension signal were obtained as raw data to calculate gradient-induced eddy currents. Curve fitting by least squares method was also done to match inductance-resistance series module. The results also illustrated that pulse pre-emphasize measurement with digital filter was correct and effective in reducing eddy current effect. Pre-emphasize waveform was developed based on system function. The usefulness of pre-emphasize measurement in reducing eddy current was confirmed and the improvement was also presented. All these are valuable for reducing artifact in magnetic resonance imaging device.

Centrifuge in space fluid flow visualization experiment

NASA Technical Reports Server (NTRS)

Arnold, William A.; Wilcox, William R.; Regel, Liya L.; Dunbar, Bonnie J.

1993-01-01

A prototype flow visualization system is constructed to examine buoyancy driven flows during centrifugation in space. An axial density gradient is formed by imposing a thermal gradient between the two ends of the test cell. Numerical computations for this geometry showed that the Prandtl number plays a limited part in determining the flow.

Phenotypic plasticity of invasive Spartina densiflora (Poaceae) along a broad latitudinal gradient on the Pacific Coast of North America

USDA-ARS?s Scientific Manuscript database

We examined morphological and physiological leaf traits of Spartina densiflora plants in populations from invaded estuarine sites across broad latitudinal and climate gradients along the Pacific west coast of North America, and in favourable conditions in a common garden experiment. We hypothesized ...

Entanglement-Gradient Routing for Quantum Networks.

PubMed

Gyongyosi, Laszlo; Imre, Sandor

2017-10-27

We define the entanglement-gradient routing scheme for quantum repeater networks. The routing framework fuses the fundamentals of swarm intelligence and quantum Shannon theory. Swarm intelligence provides nature-inspired solutions for problem solving. Motivated by models of social insect behavior, the routing is performed using parallel threads to determine the shortest path via the entanglement gradient coefficient, which describes the feasibility of the entangled links and paths of the network. The routing metrics are derived from the characteristics of entanglement transmission and relevant measures of entanglement distribution in quantum networks. The method allows a moderate complexity decentralized routing in quantum repeater networks. The results can be applied in experimental quantum networking, future quantum Internet, and long-distance quantum communications.

The Influence of Wavelength-Dependent Absorption and Temperature Gradients on Temperature Determination in Laser-Heated Diamond-Anvil Cells

NASA Astrophysics Data System (ADS)

Deng, J.; Lee, K. K. M.; Du, Z.; Benedetti, L. R.

2016-12-01

In situ temperature measurements in the laser-heated diamond-anvil cell (LHDAC) are among the most fundamental experiments undertaken in high-pressure science. Despite its importance, few efforts have been made to examine the alteration of thermal radiation spectra of hot samples by wavelength-dependent absorption of the sample itself together with temperature gradients within samples while laser heating and their influence on temperature measurement. For example, iron-bearing minerals show strong wavelength dependent absorption in the wavelength range used to determine temperature, which, together with temperature gradients can account for largely aliased apparent temperatures (e.g., 1200 K deviation for a 4000 K melting temperature) in some experiments obtained by fitting of detected thermal radiation intensities. As such, conclusions of melting temperatures, phase diagrams and partitioning behavior, may be grossly incorrect for these materials. In general, wavelength-dependent absorption and temperature gradients of samples are two key factors to consider in order to rigorously constrain temperatures, which have been largely ignored in previous LHDAC studies. A reevaluation of temperatures measured in recent high-profile papers will be reviewed.

Experimental Study of a Three-Dimensional Shear-Driven Turbulent Boundary Layer with Streamwise Adverse Pressure Gradient

NASA Technical Reports Server (NTRS)

Driver, David M.; Johnston, James P.

1990-01-01

The effects of a strong adverse pressure gradient on a three-dimensional turbulent boundary layer are studied in an axisymmetric spinning cylinder geometry. Velocity measurements made with a three-component laser Doppler velocimeter include all three mean flow components, all six Reynolds stress components, and all ten triple-product correlations. Reynolds stress diminishes as the flow becomes three-dimensional. Lower levels of shear stress were seen to persist under adverse pressure gradient conditions. This low level of stress was seen to roughly correlate with the magnitude of cross-flow (relative to free stream flow) for this experiment as well as most of the other experiments in the literature. Variations in pressure gradient do not appear to alter this correlation. For this reason, it is hypothesized that a three-dimensional boundary layer is more prone to separate than a two-dimensional boundary layer, although it could not be directly shown here. None of the computations performed with either a Prandtl mixing length, k-epsilon, or a Launder-Reece-Rodi full Reynolds-stress model were able to predict the reduction in Reynolds stress.

Chemotaxis and auto-chemotaxis of self-propelling artificial droplet swimmers

NASA Astrophysics Data System (ADS)

Jin, Chenyu; Krueger, Carsten; Maass, Corinna

Chemotaxis and auto-chemotaxis are key mechanisms in the dynamics of micro-organisms, e.g. in the acquisition of nutrients and in the communication between individuals, influencing the collective behavior. However, chemical signalling and the natural environment of biological swimmers are generally complex, making them hard to access analytically. Simple experimental systems showing similar features could provide vital insights. We present such a swimmer system, as well as controlled assays to study chemotactic effects quantitatively and reproducibly. In our experiments, we let auto-chemotactic droplet swimmers pass through bifurcating microfluidic channels and record anticorrelations between the branch choices of consecutive droplets. We present an analytical model based on balancing stochastic forces versus a diffusing chemical gradient matching the experimental data. supported by the DFG SPP 1726 ''Microswimmers'' and the MaxSynBio network.

Viral capsid mobility: a dynamic conduit for inactivation.

PubMed

Broo, K; Wei, J; Marshall, D; Brown, F; Smith, T J; Johnson, J E; Schneemann, A; Siuzdak, G

2001-02-27

Mass spectrometry and fluorescent probes have provided direct evidence that alkylating agents permeate the protein capsid of naked viruses and chemically inactivate the nucleic acid. N-acetyl-aziridine and a fluorescent alkylating agent, dansyl sulfonate aziridine, inactivated three different viruses, flock house virus, human rhinovirus-14, and foot and mouth disease virus. Mass spectral studies as well as fluorescent probes showed that alkylation of the genome was the mechanism of inactivation. Because particle integrity was not affected by selective alkylation (as shown by electron microscopy and sucrose gradient experiments), it was reasoned that the dynamic nature of the viral capsid acts as a conduit to the interior of the particle. Potential applications include fluorescent labeling for imaging viral genomes in living cells, the sterilization of blood products, vaccine development, and viral inactivation in vivo.

How does pedogenesis drive plant diversity?

PubMed

Laliberté, Etienne; Grace, James B; Huston, Michael A; Lambers, Hans; Teste, François P; Turner, Benjamin L; Wardle, David A

2013-06-01

Some of the most species-rich plant communities occur on ancient, strongly weathered soils, whereas those on recently developed soils tend to be less diverse. Mechanisms underlying this well-known pattern, however, remain unresolved. Here, we present a conceptual model describing alternative mechanisms by which pedogenesis (the process of soil formation) might drive plant diversity. We suggest that long-term soil chronosequences offer great, yet largely untapped, potential as 'natural experiments' to determine edaphic controls over plant diversity. Finally, we discuss how our conceptual model can be evaluated quantitatively using structural equation modeling to advance multivariate theories about the determinants of local plant diversity. This should help us to understand broader-scale diversity patterns, such as the latitudinal gradient of plant diversity. Copyright © 2013 Elsevier Ltd. All rights reserved.

Relationships of field habitat measurements, visual habitat indices, and land cover to benthic macroinvertebrates in urbanized streams of the Santa Clara Valley, California

USGS Publications Warehouse

Fend, S.V.; Carter, J.L.; Kearns, F.R.

2005-01-01

We evaluated several approaches for measuring natural and anthropogenic habitat characteristics to predict benthic macroinvertebrate assemblages over a range of urban intensity at 85 stream sites in the Santa Clara Valley, California. Land cover was summarized as percentage urban land cover and impervious area within upstream buffers and the upstream subwatersheds. Field measurements characterized water chemistry, channel slope, sediment, and riparian canopy. In . addition to applying the visual-based habitat assessment in U.S. Environmental Protection Agency's rapid bioassessment protocol, we developed a simplified urban habitat assessment index based on turbidity, fine sediment deposition, riparian condition, and channel modification. Natural and anthropogenic habitat variables covaried along longitudinal stream gradients and were highly correlated with elevation. At the scale of the entire watershed, benthic macroinvertebrate measures were equally correlated with variables expressing natural gradients and urbanization effects. When natural gradients were reduced by partitioning sites into ecoregion subsection groupings, habitat variables most highly correlated with macroinvertebrate measures differed between upland and valley floor site groups. Among the valley floor sites, channel slope and physical modification of channel and riparian habitats appeared more important than upstream land cover or water quality in determining macroinvertebrate richness and ordination scores. Among upland sites, effects of upstream reservoir releases on habitat quality appeared important. Rapid habitat evaluation methods appeared to be an effective method for describing habitat features important to benthic macroinvertebrates when adapted for the region and the disturbance of interest. ?? 2005 by the American Fisheries Society.

Velocity Gradient Power Functional for Brownian Dynamics.

PubMed

de Las Heras, Daniel; Schmidt, Matthias

2018-01-12

We present an explicit and simple approximation for the superadiabatic excess (over ideal gas) free power functional, admitting the study of the nonequilibrium dynamics of overdamped Brownian many-body systems. The functional depends on the local velocity gradient and is systematically obtained from treating the microscopic stress distribution as a conjugate field. The resulting superadiabatic forces are beyond dynamical density functional theory and are of a viscous nature. Their high accuracy is demonstrated by comparison to simulation results.

Implementation of a Balance Operator in NCOM

DTIC Science & Technology

2016-04-07

the background temperature Tb and salinity Sb fields do), f is the Coriolis parameter, k is the vertical unit vector, ∇ is the horizontal gradient, p... effectively used as a natural metric in the space of cost function gradients. The associated geometry inhibits descent in the unbalanced directions and...28) where f is the local Coriolis parameter, ∆yv is the local grid spacing in the y direction at a v point, and the overbars indicates horizontal

Velocity Gradient Power Functional for Brownian Dynamics

NASA Astrophysics Data System (ADS)

de las Heras, Daniel; Schmidt, Matthias

2018-01-01

We present an explicit and simple approximation for the superadiabatic excess (over ideal gas) free power functional, admitting the study of the nonequilibrium dynamics of overdamped Brownian many-body systems. The functional depends on the local velocity gradient and is systematically obtained from treating the microscopic stress distribution as a conjugate field. The resulting superadiabatic forces are beyond dynamical density functional theory and are of a viscous nature. Their high accuracy is demonstrated by comparison to simulation results.

The Role of Three-Dimensional Boundary Stresses in Limiting the Occurrence and Size of Experimental Landslides

NASA Astrophysics Data System (ADS)

Prancevic, Jeffrey P.; Lamb, Michael P.; Palucis, Marisa C.; Venditti, Jeremy G.

2018-01-01

The occurrence of seepage-induced shallow landslides on hillslopes and steep channel beds is important for landscape evolution and natural hazards. Infinite-slope stability models have been applied for seven decades, but sediment beds generally require higher water saturation levels than predicted for failure, and controlled experiments are needed to test models. We initiated 90 landslides in a 5 m long laboratory flume with a range in sediment sizes (D = 0.7, 2, 5, and 15 mm) and hillslope angles (θ = 20° to 43°), resulting in subsurface flow that spanned the Darcian and turbulent regimes, and failures that occurred with subsaturated and supersaturated sediment beds. Near complete saturation was required for failure in most experiments, with water levels far greater than predicted by infinite-slope stability models. Although 3-D force balance models predict that larger landslides are less stable, observed downslope landslide lengths were typically only several decimeters, not the entire flume length. Boundary stresses associated with short landslides can explain the increased water levels required for failure, and we suggest that short failures are tied to heterogeneities in granular properties. Boundary stresses also limited landslide thicknesses, and landslides progressively thinned on lower gradient hillslopes until they were one grain diameter thick, corresponding to a change from near-saturated to supersaturated sediment beds. Thus, landslides are expected to be thick on steep hillslopes with large frictional stresses acting on the boundaries, whereas landslides should be thin on low-gradient hillslopes or in channel beds with a critical saturation level that is determined by sediment size.

Analysis of bacterial migration. 2: Studies with multiple attractant gradients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strauss, I.; Frymier, P.D.; Hahn, C.M.

1995-02-01

Many motile bacteria exhibit chemotaxis, the ability to bias their random motion toward or away from increasing concentrations of chemical substances which benefit or inhibit their survival, respectively. Since bacteria encounter numerous chemical concentration gradients simultaneously in natural surroundings, it is necessary to know quantitatively how a bacterial population responds in the presence of more than one chemical stimulus to develop predictive mathematical models describing bacterial migration in natural systems. This work evaluates three hypothetical models describing the integration of chemical signals from multiple stimuli: high sensitivity, maximum signal, and simple additivity. An expression for the tumbling probability for individualmore » stimuli is modified according to the proposed models and incorporated into the cell balance equation for a 1-D attractant gradient. Random motility and chemotactic sensitivity coefficients, required input parameters for the model, are measured for single stimulus responses. Theoretical predictions with the three signal integration models are compared to the net chemotactic response of Escherichia coli to co- and antidirectional gradients of D-fucose and [alpha]-methylaspartate in the stopped-flow diffusion chamber assay. Results eliminate the high-sensitivity model and favor the simple additivity over the maximum signal. None of the simple models, however, accurately predict the observed behavior, suggesting a more complex model with more steps in the signal processing mechanism is required to predict responses to multiple stimuli.« less

Gradient x Isocratic Elution CCC on the Isolation of Verbascoside and Other Phenylethanoids: Influence of the Complexity of the Matrix.

PubMed

Leitão, Gilda Guimarães; Pinto, Shaft Correa; de Oliveira, Danilo Ribeiro; Timoteo, Patrícia; Guimarães, Michelle Guedes; Cordova, Wilmer H Perera; Leitão, Suzana Guimarães

2015-11-01

Verbascoside is a phenylethanoid glycoside widely distributed in nature, especially among the order Lamiales, occurring in numerous plants that are constituents of folk medicine preparations. This natural compound, previously isolated by our group from the ethyl acetate extract of Lantana trifolia using the gradient approach in countercurrent chromatography, was now isolated from the butanol extract of the same plant and from Lippia alba f. intermedia (Verbenaceae) using countercurrent chromatography in either gradient or isocratic elution modes. The ethyl acetate extract of L. alba, rich in phenylethanoids and flavonoids, was fractionated using countercurrent chromatography in the step-gradient elution approach. The four-step solvent system was composed of n-hexane-ethyl acetate-n-butanol-water (4 : 10 : X : 10), where X = 1 (solvent system A), 3 (solvent system B), 5 (solvent system C), and 7 (solvent system D), and allowed for the isolation of verbascoside along with other phenylethanoids and flavonoids from both plants. Verbascoside and 2'-O-β-apiosylverbascoside were further isolated from the n-butanol extract of L. trifolia using the solvent system ethyl acetate-n-butanol-water 10 : 2 : 10 on an isocratic run. The difference in the complexity of the two plant extracts demanded different purification steps, which included a second high-speed countercurrent chromatography purification using the isocratic elution mode. Georg Thieme Verlag KG Stuttgart · New York.

The Influence of Lithology on the Formation of Reaction Infiltration Instabilities in Mantle Rocks

NASA Astrophysics Data System (ADS)

Pec, M.; Holtzman, B. K.; Zimmerman, M. E.; Kohlstedt, D. L.

2017-12-01

The formation of oceanic plates requires extraction of large volumes of melt from the mantle. Several lines of evidence suggest that melt extraction is rapid and, therefore, necessitates high-permeability pathways. Such pathways may form as a result of melt-rock reactions. We report the results of a series of Darcy-type experiments designed to study the development of channels due to melt-solid reactions in mantle lithologies. We sandwiched a partially molten rock between a melt source and a porous sink and annealed it at high pressure (P = 300 MPa) and high temperatures (T = 1200° or 1250°C) with a controlled pressure gradient (∂P/∂z = 0-100 MPa/mm). To study the influence of lithology on the channel formation, we synthesized partially molten rocks of harzburgitic (40:40:20 Ol - Opx - basalt), wehrlitic (40:40:20 Ol - Cpx - basalt) and lherzolitic (65:25:10 Ol - Opx - Cpx) composition. The melt source was a disk of alkali basalt. In all experiments, irrespective of the exact mineralogy, melt - undersaturated in silica - from the source dissolved pyroxene in the partially molten rock and precipitated olivine ( Fo82), thereby forming a dunite reaction layer at the interface between the source and the partially molten rock. In samples annealed under a small pressure gradient, the reaction layer was roughly planar. However, if the velocity of melt due to porous flow exceeded 0.1 µm/s, the reaction layer locally protruded into the partially molten rock forming finger-like, melt-rich channels in rocks of wehrlitic and harzburgitic composition. The lherzolitic rocks were generally impermeable to the melt except at highest-pressure gradients where a narrow fracture developed, forming a dyke which drained the melt reservoir. Three-dimensional reconstructions using micro-CT images revealed clear differences between the dyke (a narrow, through-going planar feature) and the channels formed by reactive infiltration (multiple sinuous finger-like features). Apparently, the fraction of soluble minerals together with the melt fraction in the partially molten rock control whether dykes or reactive channels develop. Our experiments demonstrate that melt-rock reactions can lead to channelization in mantle lithologies, and the observed lithological transformations broadly agree with those observed in nature

Lateral shearing optical gradient force in coupled nanobeam photonic crystal cavities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Han; Zhang, Xingwang; Chau, Fook Siong

2016-04-25

We report the experimental observation of lateral shearing optical gradient forces in nanoelectromechanical systems (NEMS) controlled dual-coupled photonic crystal (PhC) nanobeam cavities. With an on-chip integrated NEMS actuator, the coupled cavities can be mechanically reconfigured in the lateral direction while maintaining a constant coupling gap. Shearing optical gradient forces are generated when the two cavity centers are laterally displaced. In our experiments, positive and negative lateral shearing optical forces of 0.42 nN and 0.29 nN are observed with different pumping modes. This study may broaden the potential applications of the optical gradient force in nanophotonic devices and benefit the futuremore » nanooptoelectromechanical systems.« less

A Geophysical Flow Experiment in a Compressible Critical Fluid

NASA Technical Reports Server (NTRS)

Hegseth, John; Garcia, Laudelino

1996-01-01

The first objective of this experiment is to build an experimental system in which, in analogy to a geophysical system, a compressible fluid in a spherical annulus becomes radially stratified in density through an A.C. electric field. When this density gradient is demonstrated, the system will be augmented so that the fluid can be driven by heating and rotation and tested in preparation for a microgravity experiment. This apparatus consists of a spherical capacitor filled with critical fluid in a temperature controlled environment. To make the fluid critical, the apparatus will be operated near the critical pressure, critical density, and critical temperature of the fluid. This will result in a highly compressible fluid because of the properties of the fluid near its critical point. A high voltage A.C. source applied across the capacitor will create a spherically symmetric central force because of the dielectric properties of the fluid in an electric field gradient. This central force will induce a spherically symmetric density gradient that is analogous to a geophysical fluid system. To generate such a density gradient the system must be small (approx. 1 inch diameter). This small cell will also be capable of driving the critical fluid by heating and rotation. Since a spherically symmetric density gradient can only be made in microgravity, another small cell, of the same geometry, will be built that uses incompressible fluid. The driving of the fluid by rotation and heating in these small cells will be developed. The resulting instabilities from the driving in these two systems will then be studied. The second objective is to study the pattern forming instabilities (bifurcations) resulting from the well controlled experimental conditions in the critical fluid cell. This experiment will come close to producing conditions that are geophysically similar and will be studied as the driving parameters are changed.

Can spatial patterns along climatic gradients predict ecosystem responses to climate change? Experimenting with reaction-diffusion simulations.

PubMed

Roitberg, Elena; Shoshany, Maxim

2017-01-01

Following a predicted decline in water resources in the Mediterranean Basin, we used reaction-diffusion equations to gain a better understanding of expected changes in properties of vegetation patterns that evolve along the rainfall transition between semi-arid and arid rainfall regions. Two types of scenarios were investigated: the first, a discrete scenario, where the potential consequences of climate change are represented by patterns evolving at discrete rainfall levels along a rainfall gradient. This scenario concerns space-for-time substitutions characteristic of the rainfall gradient hypothesis. The second, a continuous scenario, represents explicitly the effect of rainfall decline on patterns which evolved at different rainfall levels along the rainfall gradient prior to the climate change. The eccentricity of patterns that emerge through these two scenarios was found to decrease with decreasing rainfall, while their solidity increased. Due to their inverse modes of change, their ratio was found to be a highly sensitive indicator for pattern response to rainfall decline. An eccentricity ratio versus rainfall (ER:R) line was generalized from the results of the discrete experiment, where ERs above this line represent developed (recovered) patterns and ERs below this line represent degraded patterns. For the rainfall range of 1.2 to 0.8 mm/day, the continuous rainfall decline experiment with ERs that lie above the ER:R line, yielded patterns less affected by rainfall decline than would be expected according to the discrete representation of ecosystems' response. Thus, for this range, space-for-time substitution represents an overestimation of the consequences of the expected rainfall decline. For rainfall levels below 0.8 mm/day, eccentricity ratios from the discrete and continuous experiments practically converge to the same trend of pattern change along the ER:R line. Thus, the rainfall gradient hypothesis may be valid for regions characterized by this important rainfall range, which typically include desert fringe ecosystems.

SAGRAD: A Program for Neural Network Training with Simulated Annealing and the Conjugate Gradient Method

PubMed Central

Bernal, Javier; Torres-Jimenez, Jose

2015-01-01

SAGRAD (Simulated Annealing GRADient), a Fortran 77 program for computing neural networks for classification using batch learning, is discussed. Neural network training in SAGRAD is based on a combination of simulated annealing and Møller’s scaled conjugate gradient algorithm, the latter a variation of the traditional conjugate gradient method, better suited for the nonquadratic nature of neural networks. Different aspects of the implementation of the training process in SAGRAD are discussed, such as the efficient computation of gradients and multiplication of vectors by Hessian matrices that are required by Møller’s algorithm; the (re)initialization of weights with simulated annealing required to (re)start Møller’s algorithm the first time and each time thereafter that it shows insufficient progress in reaching a possibly local minimum; and the use of simulated annealing when Møller’s algorithm, after possibly making considerable progress, becomes stuck at a local minimum or flat area of weight space. Outlines of the scaled conjugate gradient algorithm, the simulated annealing procedure and the training process used in SAGRAD are presented together with results from running SAGRAD on two examples of training data. PMID:26958442

Infiltration of chitin by protein coacervates defines the squid beak mechanical gradient.

PubMed

Tan, YerPeng; Hoon, Shawn; Guerette, Paul A; Wei, Wei; Ghadban, Ali; Hao, Cai; Miserez, Ali; Waite, J Herbert

2015-07-01

The beak of the jumbo squid Dosidicus gigas is a fascinating example of how seamlessly nature builds with mechanically mismatched materials. A 200-fold stiffness gradient begins in the hydrated chitin of the soft beak base and gradually increases to maximum stiffness in the dehydrated distal rostrum. Here, we combined RNA-Seq and proteomics to show that the beak contains two protein families. One family consists of chitin-binding proteins (DgCBPs) that physically join chitin chains, whereas the other family comprises highly modular histidine-rich proteins (DgHBPs). We propose that DgHBPs play multiple key roles during beak bioprocessing, first by forming concentrated coacervate solutions that diffuse into the DgCBP-chitin scaffold, and second by inducing crosslinking via an abundant GHG sequence motif. These processes generate spatially controlled desolvation, resulting in the impressive biomechanical gradient. Our findings provide novel molecular-scale strategies for designing functional gradient materials.

Design and fabrication of a chitosan hydrogel with gradient structures via a step-by-step cross-linking process.

PubMed

Xu, Yongxiang; Yuan, Shenpo; Han, Jianmin; Lin, Hong; Zhang, Xuehui

2017-11-15

The development of scaffolds to mimic the gradient structure of natural tissue is an important consideration for effective tissue engineering. In the present study, a physical cross-linking chitosan hydrogel with gradient structures was fabricated via a step-by-step cross-linking process using sodium tripolyphosphate and sodium hydroxide as sequential cross-linkers. Chitosan hydrogels with different structures (single, double, and triple layers) were prepared by modifying the gelling process. The properties of the hydrogels were further adjusted by varying the gelling conditions, such as gelling time, pH, and composition of the crosslinking solution. Slight cytotoxicity was showed in MTT assay for hydrogels with uncross-linking chitosan solution and non-cytotoxicity was showed for other hydrogels. The results suggest that step-by-step cross-linking represents a practicable method to fabricate scaffolds with gradient structures. Copyright © 2017. Published by Elsevier Ltd.

Interpretation of sucrose gradient sedimentation pattern of deoxyribonucleic acid fragments resulting from random breaks.

PubMed

Litwin, S; Shahn, E; Kozinski, A W

1969-07-01

Mass distribution in a sucrose gradient of deoxyribonucleic acid (DNA) fragments arising as a result of random breaks is predicted by analytical means from which computer evaluations are plotted. The analytical results are compared with the results of verifying experiments: (i) a Monte Carlo computer experiment in which simulated molecules of DNA were individuals of unit length subjected to random "breaks" applied by a random number generator, and (ii) an in vitro experiment in which molecules of T4 DNA, highly labeled with (32)P, were stored in liquid nitrogen for variable periods of time during which a precisely known number of (32)P atoms decayed, causing single-stranded breaks. The distribution of sizes of the resulting fragments was measured in an alkaline sucrose gradient. The profiles obtained in this fashion were compared with the mathematical predictions. Both experiments agree with the analytical approach and thus permit the use of the graphs obtained from the latter as a means of determining the average number of random breaks in DNA from distributions obtained experimentally in a sucrose gradient. An example of the application of this procedure to a previously unresolved problem is provided in the case of DNA from ultraviolet-irradiated phage which undergoes a dose-dependent intracellular breakdown. The relationship between the number of lethal hits and the number of single-stranded breaks was not previously established. A comparison of the calculated number of nicks per strand of DNA with the known dose in phage-lethal hits reveals a relationship closely approximating one lethal hit to one single-stranded break.

Effects of air-exposure gradients on spatial infection patterns of Perkinsus marinus in the eastern oyster Crassostrea virginica.

PubMed

Malek, Jennafer C; Breitburg, Denise L

2016-02-25

Spatial distributions of species can be shaped by factors such as parasites, mortality, and reproduction, all of which may be influenced by differences in physical factors along environmental gradients. In nearshore tidal waters, an elevational gradient in aerial exposure during low tide can shape the spatial distributions of benthic marine organisms. The eastern oyster Crassostrea virginica is an ecologically and economically important species that can dominate both subtidal and intertidal habitats along the east coast of the USA. Our goal was to determine whether prevalence and intensity of Perkinsus marinus (the causative agent of Dermo disease) infections vary along intertidal to subtidal gradients during summer. We used (1) field experiments conducted at 4 sites in the Chesapeake Bay and a Virginia coastal bay, (2) a controlled air-exposure experiment, and (3) field surveys from 7 sites ranging from Maine to North Carolina to test for effects of tidal exposure on infection. Results from our field surveys suggested that high intertidal oysters tend to have higher infection prevalence than subtidal oysters, but there was no effect on infection intensity. Field experiments rarely yielded significant effects of tidal exposure on infection prevalence and intensity. Overall, our study shows that exposure to air may not be a strong driver of infection patterns in this host-parasite system.

The electric field gradient in natural iron-doped chrysoberyl Al2BeO4 and sinhalite MgAlBO4 single crystals

NASA Astrophysics Data System (ADS)

Lottermoser, Werner; Redhammer, Günther J.; Weber, Sven-Ulf; Litterst, Fred Jochen; Tippelt, Gerold; Dlugosz, Stephen; Bank, Hermann; Amthauer, Georg; Grodzicki, Michael

2011-12-01

This work reports on the evaluation of the electric field gradient (EFG) in natural chrysoberyl Al2BeO4 and sinhalite MgAlBO4 using two different procedures: (1) experimental, with single crystal Mössbauer spectroscopy (SCMBS) on the three principal sections of each sample and (2) a "fully quantitative" method with cluster molecular orbital calculations based on the density functional theory. Whereas the experimental and theoretical results for the EFG tensor are in quantitative agreement, the calculated isomer shifts and optical d-d-transitions exhibit systematic deviations from the measured values. These deviations indicate that the substitution of Al and Mg with iron should be accompanied by considerable local expansion of the coordination octahedra.

Spatial-mode storage in a gradient-echo memory

NASA Astrophysics Data System (ADS)

Higginbottom, D. B.; Sparkes, B. M.; Rancic, M.; Pinel, O.; Hosseini, M.; Lam, P. K.; Buchler, B. C.

2012-08-01

Three-level atomic gradient echo memory (Λ-GEM) is a proposed candidate for efficient quantum storage and for linear optical quantum computation with time-bin multiplexing [Hosseini , Nature (London)NATUAS0028-083610.1038/nature08325 461, 241 (2009)]. In this paper we investigate the spatial multimode properties of a Λ-GEM system. Using a high-speed triggered CCD, we demonstrate the storage of complex spatial modes and images. We also present an in-principle demonstration of spatial multiplexing by showing selective recall of spatial elements of a stored spin wave. Using our measurements, we consider the effect of diffusion within the atomic vapor and investigate its role in spatial decoherence. Our measurements allow us to quantify the spatial distortion due to both diffusion and inhomogeneous control field scattering and compare these to theoretical models.

The epidemiological transition in Eastern and Western Europe: a historic natural experiment.

PubMed

Karanikolos, Marina; Adany, Roza; McKee, Martin

2017-10-01

The continent of Europe has experienced remarkable changes in the past 25 years, providing scope for natural experiments that offer insight into the complex determinants of health. We analysed trends in life expectancy at birth in three parts of Europe, those countries that were members of the European Union (EU) prior to 2004, countries that joined the European Union since then, and the twelve countries that emerged from the Soviet Union to form the Commonwealth of Independent States (CIS). The contribution of deaths at different ages to these changes was assessed using Arriaga's method of decomposing changes in life expectancy. Europe remains divided geographically, with an East-West gradient. The former Soviet countries experienced a marked initial decline in life expectancy and have only recovered after 2005. However, the situation for those of working ages is little better than in 1990. The pre-2004 EU has seen substantial gains throughout the past 25 years, although there is some evidence that this may be slowing, or even reversing, at older ages. The countries joining the EU in 2004 subsequently began to see some improvements in the early 1990s, but have experienced larger gains since 2000. Europe offers a valuable natural laboratory for understanding the impact of political, economic, and social changes on health. While the historic divisions of Europe are still visible, there is also evidence that individual countries are doing better or worse than their neighbours, providing many lessons that can be learned from. © The Author 2017. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved.

Geographical gradients in selection can reveal genetic constraints for evolutionary responses to ocean acidification

PubMed Central

Gaitán-Espitia, Juan Diego; Marshall, Dustin; Dupont, Sam; Bacigalupe, Leonardo D.; Bodrossy, Levente; Hobday, Alistair J.

2017-01-01

Geographical gradients in selection can shape different genetic architectures in natural populations, reflecting potential genetic constraints for adaptive evolution under climate change. Investigation of natural pH/pCO2 variation in upwelling regions reveals different spatio-temporal patterns of natural selection, generating genetic and phenotypic clines in populations, and potentially leading to local adaptation, relevant to understanding effects of ocean acidification (OA). Strong directional selection, associated with intense and continuous upwellings, may have depleted genetic variation in populations within these upwelling regions, favouring increased tolerances to low pH but with an associated cost in other traits. In contrast, diversifying or weak directional selection in populations with seasonal upwellings or outside major upwelling regions may have resulted in higher genetic variances and the lack of genetic correlations among traits. Testing this hypothesis in geographical regions with similar environmental conditions to those predicted under climate change will build insights into how selection may act in the future and how populations may respond to stressors such as OA. PMID:28148831

Collective gradient sensing and chemotaxis: modeling and recent developments

NASA Astrophysics Data System (ADS)

Camley, Brian A.

2018-06-01

Cells measure a vast variety of signals, from their environment’s stiffness to chemical concentrations and gradients; physical principles strongly limit how accurately they can do this. However, when many cells work together, they can cooperate to exceed the accuracy of any single cell. In this topical review, I will discuss the experimental evidence showing that cells collectively sense gradients of many signal types, and the models and physical principles involved. I also propose new routes by which experiments and theory can expand our understanding of these problems.

Environmental Impact Research Program: Reservoir Bank Erosion and Cultural Resources: Experiments in Mapping and Predicting the Erosion of Archeological Sediments at Reservoirs Along the Middle Missouri River with Sequential Historical Aerial Photographs

DTIC Science & Technology

1989-08-01

points on both the photos and base map. Transects placed at 100-m intervals along the waterline, oriented perpendicular to the gradient or slope just...the identifica- tion of major factors influencing bank erosion, independent variables measured included gradient of the land at the intersection of...have a very steep gradient , approaching vertical in some cases, broken only by intermittent minor drainages which have dissected terrace margins. b

RES: Regularized Stochastic BFGS Algorithm

NASA Astrophysics Data System (ADS)

Mokhtari, Aryan; Ribeiro, Alejandro

2014-12-01

RES, a regularized stochastic version of the Broyden-Fletcher-Goldfarb-Shanno (BFGS) quasi-Newton method is proposed to solve convex optimization problems with stochastic objectives. The use of stochastic gradient descent algorithms is widespread, but the number of iterations required to approximate optimal arguments can be prohibitive in high dimensional problems. Application of second order methods, on the other hand, is impracticable because computation of objective function Hessian inverses incurs excessive computational cost. BFGS modifies gradient descent by introducing a Hessian approximation matrix computed from finite gradient differences. RES utilizes stochastic gradients in lieu of deterministic gradients for both, the determination of descent directions and the approximation of the objective function's curvature. Since stochastic gradients can be computed at manageable computational cost RES is realizable and retains the convergence rate advantages of its deterministic counterparts. Convergence results show that lower and upper bounds on the Hessian egeinvalues of the sample functions are sufficient to guarantee convergence to optimal arguments. Numerical experiments showcase reductions in convergence time relative to stochastic gradient descent algorithms and non-regularized stochastic versions of BFGS. An application of RES to the implementation of support vector machines is developed.

Heating-freezing effects on the orientation of kaolin clay particles

DOE PAGES

Jaradat, Karam A.; Darbari, Zubin; Elbakhshwan, Mohamed; ...

2017-09-29

The effects of temperature changes on the particle orientation of a consolidated kaolin are studied using XRD experiments. Here, two sets of equipment were utilized in this study: a benchtop equipment, and a synchrotron beamline at the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory. The kaolin specimens tested in the benchtop XRD were subjected to elevated and freezing temperatures ex-situ, while those used for the NSLS-II experiment were exposed to the temperature changes in-situ. The temperatures considered in this study range from freezing (-10 °C) to elevated temperature below boiling (90 °C). The thermally-induced reorientation of claymore » mineral particles is highly dependent on the relative orientation of the clay mineral particles with respect to the applied thermal gradient. For example, kaolin samples with kaolinite particles oriented perpendicular to the thermal gradient, and to the expected thermally-induced pore water flow, experience much higher particles reorientations compared to samples with particles initially oriented parallel to the thermal gradient. Lastly, freezing kaolin preserved its microstructure as ice crystals form.« less

Closed-loop Separation Control Using Oscillatory Flow Excitation

NASA Technical Reports Server (NTRS)

Allan, Brian G.; Juang, Jer-Nan; Raney, David L.; Seifert, Avi; Pack, latunia G.; Brown, Donald E.

2000-01-01

Design and implementation of a digital feedback controller for a flow control experiment was performed. The experiment was conducted in a cryogenic pressurized wind tunnel on a generic separated configuration at a chord Reynolds number of 16 million and a Mach number of 0.25. The model simulates the upper surface of a 20% thick airfoil at zero angle-of-attack. A moderate favorable pressure gradient, up to 55% of the chord, is followed by a severe adverse pressure gradient which is relaxed towards the trailing edge. The turbulent separation bubble, behind the adverse pressure gradient, is then reduced by introducing oscillatory flow excitation just upstream of the point of flow separation. The degree of reduction in the separation region can be controlled by the amplitude of the oscillatory excitation. A feedback controller was designed to track a given trajectory for the desired degree of flow reattachment and to improve the transient behavior of the flow system. Closed-loop experiments demonstrated that the feedback controller was able to track step input commands and improve the transient behavior of the open-loop response.

Heating-freezing effects on the orientation of kaolin clay particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaradat, Karam A.; Darbari, Zubin; Elbakhshwan, Mohamed

The effects of temperature changes on the particle orientation of a consolidated kaolin are studied using XRD experiments. Here, two sets of equipment were utilized in this study: a benchtop equipment, and a synchrotron beamline at the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory. The kaolin specimens tested in the benchtop XRD were subjected to elevated and freezing temperatures ex-situ, while those used for the NSLS-II experiment were exposed to the temperature changes in-situ. The temperatures considered in this study range from freezing (-10 °C) to elevated temperature below boiling (90 °C). The thermally-induced reorientation of claymore » mineral particles is highly dependent on the relative orientation of the clay mineral particles with respect to the applied thermal gradient. For example, kaolin samples with kaolinite particles oriented perpendicular to the thermal gradient, and to the expected thermally-induced pore water flow, experience much higher particles reorientations compared to samples with particles initially oriented parallel to the thermal gradient. Lastly, freezing kaolin preserved its microstructure as ice crystals form.« less

Rheological Properties of Quasi-2D Fluids in Microgravity

NASA Technical Reports Server (NTRS)

Trittel, Torsten; Stannarius, Ralf; Eremin, Alexey; Harth, Kirsten; Clark, Noel A.; Maclennan, Joseph; Glaser, Matthew; Park, Cheol; Hall, Nancy; Tin, Padetha

2016-01-01

Freely suspended smectic films of sub-micrometer thickness and lateral extensions of several millimeters are used to study thermally driven convection and diffusion in the film plane. The experiments were performed during a six minute microgravity phase of a TEXUS suborbital rocket flight (Texus 52, launched April 27, 2015). The project served as a preliminary test for a planned ISS Experiment with liquid crystal films (OASIS), and in addition it provided new experimental data on smectic films exposed to in-plane thermal gradients.We find an attraction of the smectic material towards the cold edge of the film in a temperature gradient, similar to a Soret effect. This process is reversed when this edge is heated up again. Thermal convection driven by two thermocontacts in the film is practically absent, even at temperature gradients up to 10 Kmm, thermally driven convection sets in when the hot post reaches the transition temperature to the nematic phase.An additional experiment was performed under microgravity conditions to test the stability of liquid crystal bridges in different smectic phases.

NMR-based diffusion pore imaging.

PubMed

Laun, Frederik Bernd; Kuder, Tristan Anselm; Wetscherek, Andreas; Stieltjes, Bram; Semmler, Wolfhard

2012-08-01

Nuclear magnetic resonance (NMR) diffusion experiments offer a unique opportunity to study boundaries restricting the diffusion process. In a recent Letter [Phys. Rev. Lett. 107, 048102 (2011)], we introduced the idea and concept that such diffusion experiments can be interpreted as NMR imaging experiments. Consequently, images of closed pores, in which the spins diffuse, can be acquired. In the work presented here, an in-depth description of the diffusion pore imaging technique is provided. Image artifacts due to gradient profiles of finite duration, field inhomogeneities, and surface relaxation are considered. Gradients of finite duration lead to image blurring and edge enhancement artifacts. Field inhomogeneities have benign effects on diffusion pore images, and surface relaxation can lead to a shrinkage and shift of the pore image. The relation between boundary structure and the imaginary part of the diffusion weighted signal is analyzed, and it is shown that information on pore coherence can be obtained without the need to measure the phase of the diffusion weighted signal. Moreover, it is shown that quite arbitrary gradient profiles can be used for diffusion pore imaging. The matrices required for numerical calculations are stated and provided as supplemental material.

Slow wave contraction frequency plateaus in the small intestine are composed of discrete waves of interval increase associated with dislocations.

PubMed

Parsons, Sean P; Huizinga, Jan D

2018-06-03

What is the central question of this study? What is the nature of slow wave driven contraction frequency gradients in the small intestine? What is the main finding and its importance? Frequency plateaus are composed of discrete waves of increased interval, each wave associated with a contraction dislocation. Smooth frequency gradients are generated by localised neural modulation of wave frequency, leading to functionally important wave turbulence. Both patterns are emergent properties of a network of coupled oscillators, the interstitial cells of Cajal. A gut-wide network of interstitial cells of Cajal (ICC) generate electrical oscillations (slow waves) that orchestrate waves of muscle contraction. In the small intestine there is a gradient in slow wave frequency from high at the duodenum to low at the terminal ileum. Time-averaged measurements of frequency have suggested either a smooth or stepped (plateaued) gradient. We measured individual contraction intervals from diameter maps of the mouse small intestine to create interval maps (IMaps). IMaps showed that each frequency plateau was composed of discrete waves of increased interval. Each interval wave originated at a terminating contraction wave, a "dislocation", at the plateau's proximal boundary. In a model chain of coupled phase oscillators, interval wave frequency increased as coupling decreased or as the natural frequency gradient or noise increased. Injuring the intestine at a proximal point to destroy coupling, suppressed distal steps which then reappeared with gap junction block by carbenoxolone. This lent further support to our previous hypothesis that lines of dislocations were fixed by points of low coupling strength. Dislocations induced by electrical field pulses in the intestine and by equivalent phase shift in the model, were associated with interval waves. When the enteric nervous system was active, IMaps showed a chaotic, turbulent pattern of interval change with no frequency steps or plateaus. This probably resulted from local, stochastic release of neurotransmitters. Plateaus, dislocations, interval waves and wave turbulence arise from a dynamic interplay between natural frequency and coupling in the ICC network. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

[Application of general retention time formula for gradient liquid chromatography in the studies of ladder-like gradient elution].

PubMed

Sun, Xiaoli; Hao, Weiqiang; Wang, Junde; Di, Bin; Chen, Qiang; Zhuang, Wei; Yu, Qiang; Zhang, Peipei

2013-08-01

By not explicitly specifying the type of solvent strength model, the features of ladder-like gradient elution were studied based on the general retention time formula that was derived in our previous work. For the case where the solute is eluted at like gradient, we derived the expression that connects the mobile phase composition (phiR), at which the solute is eluted from the column, with the gradient slope (B). It was shown that phiR will increase with the increase of B in this case. For the case where the solute is eluted at the last isocratic segment of the ladder-like gradient, it was proven that the retention time (tR) will correlate linearly with the reciprocal of the gradient slope (1/B) when the initial and final mobile phase compositions are set to be constant. In experiments, by taking biphenyl as the sample, the values of retention time in isocratic and gradient elution were measured on a C18 column by using a mixture of methanol and water as the mobile phase. The experimental values were found to be well consistent with the theoretical values that were calculated from the expressions. These expressions will be helpful to understand the features of the ladder-like gradient in practice.

Mathematical modeling of sample stacking methods in microfluidic systems

NASA Astrophysics Data System (ADS)

Horek, Jon

Gradient focusing methods are a general class of experimental techniques used to simultaneously separate and increase the cross-sectionally averaged concentration of charged particle mixtures. In comparison, Field Amplified Sample Stacking (FASS) techniques first concentrate the collection of molecules before separating them. Together, we denote gradient focusing and FASS methods "sample stacking" and study the dynamics of a specific method, Temperature Gradient Focusing (TGF), in which an axial temperature gradient is applied along a channel filled with weak buffer. Gradients in electroosmotic fluid flow and electrophoretic species velocity create the simultaneous separating and concentrating mechanism mentioned above. In this thesis, we begin with the observation that very little has been done to model the dynamics of gradient focusing, and proceed to solve the fundamental equations of fluid mechanics and scalar transport, assuming the existence of slow axial variations and the Taylor-Aris dispersion coefficient. In doing so, asymptotic methods reduce the equations from 3D to 1D, and we arrive at a simple 1D model which can be used to predict the transient evolution of the cross-sectionally averaged analyte concentration. In the second half of this thesis, we run several numerical focusing experiments with a 3D finite volume code. Comparison of the 1D theory and 3D simulations illustrates not only that the asymptotic theory converges as a certain parameter tends to zero, but also that fairly large axial slip velocity gradients lead to quite small errors in predicted steady variance. Additionally, we observe that the axial asymmetry of the electrophoretic velocity model leads to asymmetric peak shapes, a violation of the symmetric Gaussians predicted by the 1D theory. We conclude with some observations on the effect of Peclet number and gradient strength on the performance of focusing experiments, and describe a method for experimental optimization. Such knowledge is useful for design of lab-on-a-chip devices.

Laboratory Layered Latte

NASA Astrophysics Data System (ADS)

Xue, Nan; Khodaparast, Sepideh; Zhu, Lailai; Nunes, Janine; Kim, Hyoungsoo; Stone, Howard

2017-11-01

Layered composite fluids are sometimes observed in confined systems of rather chaotic initial states, for example, layered lattes formed by pouring espresso into a glass of warm milk. In such configurations, pouring forces a lower density liquid (espresso) into a higher density ambient, which is similar to the fountain effects that characterize a wide range of flows driven by injecting a fluid into a second miscible phase. Although the initial state of the mixture is complex and chaotic, there are conditions where the mixture cools at room temperature and exhibits an organized layered pattern. Here we report controlled experiments injecting a fluid into a miscible phase and show that, above a critical injection velocity, layering naturally emerges over the time scale of minutes. We perform experimental and numerical analyses of the time-dependent flows to observe and understand the convective circulation in the layers. We identify critical conditions to produce the layering and relate the results quantitatively to the critical Rayleigh number in double-diffusive convection, which indicates the competition between the horizontal thermal gradient and the vertical density gradient generated by the fluid injection. Based on this understanding, we show how to employ this single-step process to produce layered structures in soft materials, where the local elastic properties as well as the local material concentration vary step-wise along the length of the material.

Paleolatitudinal Gradients in Marine Phytoplankton Composition and Cell Size

NASA Astrophysics Data System (ADS)

Henderiks, J.; Bordiga, M.; Bartol, M.; Šupraha, L.

2014-12-01

Coccolithophores, a prominent group of marine calcifying unicellular algae, are widely studied in context of current and past climate change. We know that marine phytoplankton are sensitive to climatic changes, but the complex interplay of several processes such as warming, changes in nutrient content, and ocean acidification, makes future scenarios difficult to predict. Some taxa may be more susceptible to environmental perturbations than others, as evidenced by significantly different species-specific sensitivities observed in laboratory experiments. However, short-term plastic responses may not translate into longer-term climatic adaptation, nor should we readily extrapolate the behavior of single strains in the laboratory to natural, multi-species assemblages and their interactions in the ocean. The extensive fossil record of coccolithophores (in the form of coccoliths) reveals high morphological and taxonomic diversity and allows reconstructing the cell size of individual taxonomic groups. In a suite of deep-sea drilling sites from the Atlantic Ocean, we document distinct latitudinal gradients in phytoplankton composition and cell size across major climate transitions of the late Eocene - earliest Oligocene, and the middle - late Miocene. With these data we test hypotheses of species migration, phenotypic evolution, as well as the rates of species extinction and speciation in relation to concurrent paleoenvironmental changes during the Cenozoic.

Multifactor analysis and simulation of the surface runoff and soil infiltration at different slope gradients

NASA Astrophysics Data System (ADS)

Huang, J.; Kang, Q.; Yang, J. X.; Jin, P. W.

2017-08-01

The surface runoff and soil infiltration exert significant influence on soil erosion. The effects of slope gradient/length (SG/SL), individual rainfall amount/intensity (IRA/IRI), vegetation cover (VC) and antecedent soil moisture (ASM) on the runoff depth (RD) and soil infiltration (INF) were evaluated in a series of natural rainfall experiments in the South of China. RD is found to correlate positively with IRA, IRI, and ASM factors and negatively with SG and VC. RD decreased followed by its increase with SG and ASM, it increased with a further decrease with SL, exhibited a linear growth with IRA and IRI, and exponential drop with VC. Meanwhile, INF exhibits a positive correlation with SL, IRA and IRI and VC, and a negative one with SG and ASM. INF was going up and then down with SG, linearly rising with SL, IRA and IRI, increasing by a logit function with VC, and linearly falling with ASM. The VC level above 60% can effectively lower the surface runoff and significantly enhance soil infiltration. Two RD and INF prediction models, accounting for the above six factors, were constructed using the multiple nonlinear regression method. The verification of those models disclosed a high Nash-Sutcliffe coefficient and low root-mean-square error, demonstrating good predictability of both models.

Homoepitaxial Boron Doped Diamond Anvils as Heating Elements in a Diamond Anvil Cell

NASA Astrophysics Data System (ADS)

Montgomery, Jeffrey; Samudrala, Gopi; Smith, Spencer; Tsoi, Georgiy; Vohra, Yogesh; Weir, Samuel

2013-03-01

Recent advances in designer-diamond technology have allowed for the use of electrically and thermally conducting homoepitaxially-grown layers of boron-doped diamond (grown at 1200 °C with a 2% mixture of CH4 in H, resulting in extremely high doping levels ~ 1020/cm3) to be used as heating elements in a diamond anvil cell (DAC). These diamonds allow for precise control of the temperature inside of the diamond anvil itself, particularly when coupled with a cryostat. Furthermore, the unmatched thermally conducting nature of diamond ensures that no significant lateral gradient in temperature occurs across the culet area. Since a thermocouple can easily be attached anywhere on the diamond surface, we can also measure diamond temperatures directly. With two such heaters, one can raise sample temperatures uniformly, or with any desired gradient along the pressure axis while preserving optical access. In our continuing set of benchmark experiments, we use two newly created matching heater anvils with 500 μm culets to analyze the various fluorescence emission lines of ruby microspheres, which show more complicated behavior than traditional ruby chips. We also report on the temperature dependence of the high-pressure Raman modes of paracetamol (C8H9NO2) up to 20 GPa.

Reduction of Diffusion-Weighted Imaging Contrast of Acute Ischemic Stroke at Short Diffusion Times.

PubMed

Baron, Corey Allan; Kate, Mahesh; Gioia, Laura; Butcher, Kenneth; Emery, Derek; Budde, Matthew; Beaulieu, Christian

2015-08-01

Diffusion-weighted imaging (DWI) of tissue water is a sensitive and specific indicator of acute brain ischemia, where reductions of the diffusion of tissue water are observed acutely in the stroke lesion core. Although these diffusion changes have been long attributed to cell swelling, the precise nature of the biophysical mechanisms remains uncertain. The potential cause of diffusion reductions after stroke was investigated using an advanced DWI technique, oscillating gradient spin-echo DWI, that enables much shorter diffusion times and can improve specificity for alterations of structure at the micron level. Diffusion measurements in the white matter lesions of patients with acute ischemic stroke were reduced by only 8% using oscillating gradient spin-echo DWI, in contrast to a 37% decrease using standard DWI. Neurite beading has recently been proposed as a mechanism for the diffusion changes after ischemic stroke with some ex vivo evidence. To explore whether beading could cause such differential results, simulations of beaded cylinders and axonal swelling were performed, yielding good agreement with experiment. Short diffusion times result in dramatically reduced diffusion contrast of human stroke. Simulations implicate a combination of neuronal beading and axonal swelling as the key structural changes leading to the reduced apparent diffusion coefficient after stroke. © 2015 American Heart Association, Inc.

Epidermis architecture and material properties of the skin of four snake species

PubMed Central

Klein, Marie-Christin G.; Gorb, Stanislav N.

2012-01-01

On the basis of structural and experimental data, it was previously demonstrated that the snake integument consists of a hard, robust, inflexible outer surface (Oberhäutchen and β-layer) and softer, flexible inner layers (α-layers). It is not clear whether this phenomenon is a general adaptation of snakes to limbless locomotion or only to specific conditions, such as habitat and locomotion. The aim of the present study was to compare the structure and material properties of the outer scale layers (OSLs) and inner scale layers (ISLs) of the exuvium epidermis in four snake species specialized to live in different habitats: Lampropeltis getula californiae (terrestrial), Epicrates cenchria cenchria (generalist), Morelia viridis (arboreal) and Gongylophis colubrinus (sand-burrowing). Scanning electron microscopy (SEM) of skin cross sections revealed a strong variation in the epidermis structure between species. The nanoindentation experiments clearly demonstrated a gradient of material properties along the epidermis in the integument of all the species studied. The presence of such a gradient is a possible adaptation to locomotion and wear minimization on natural substrates. In general, the difference in both the effective elastic modulus and hardness of the OSL and ISL between species was not large compared with the difference in epidermis thickness and architecture. PMID:22896567

SES Gradients Among Mexicans in the United States and in Mexico: A New Twist to the Hispanic Paradox?

PubMed Central

Palloni, Alberto; Riosmena, Fernando; Wong, Rebeca

2016-01-01

Recent empirical findings have suggested the existence of a twist in the Hispanic paradox, in which Mexican and other Hispanic foreign-born migrants living in the United States experience shallower socioeconomic status (SES) health disparities than those in the U.S. population. In this article, we seek to replicate this finding and test conjectures that could explain this new observed phenomenon using objective indicators of adult health by educational attainment in several groups: (1) Mexicanborn individuals living in Mexico and in the United States, (2) U.S.-born Mexican Americans, and (3) non-Hispanic American whites. Our analytical strategy improves upon previous research on three fronts. First, we derive four hypotheses from a general framework that has also been used to explain the standard Hispanic paradox. Second, we study biomarkers rather than self-reported health and related conditions. Third, we use a binational data platform that includes both Mexicans living in Mexico (Mexican National Health and Nutrition Survey 2006) and Mexican migrants to the United States (NHANES 1999–2010). We find steep education gradients among Mexicans living in Mexico’s urban areas in five of six biomarkers of metabolic syndrome (MetS) and in the overall MetS score. Mexican migrants living in the United States experience similar patterns to Mexicans living in Mexico in glucose and obesity biomarkers. These results are inconsistent with previous findings, suggesting that Mexican migrants in the United States experience significantly attenuated health gradients relative to the non-Hispanic white U.S. population. Our empirical evidence also contradicts the idea that SES-health gradients in Mexico are shallower than those in the United States and could be invoked to explain shallower gradients among Mexicans living in the United States. PMID:27655408

SES Gradients Among Mexicans in the United States and in Mexico: A New Twist to the Hispanic Paradox?

PubMed

Beltrán-Sánchez, Hiram; Palloni, Alberto; Riosmena, Fernando; Wong, Rebeca

2016-10-01

Recent empirical findings have suggested the existence of a twist in the Hispanic paradox, in which Mexican and other Hispanic foreign-born migrants living in the United States experience shallower socioeconomic status (SES) health disparities than those in the U.S. In this article, we seek to replicate this finding and test conjectures that could explain this new observed phenomenon using objective indicators of adult health by educational attainment in several groups: (1) Mexican-born individuals living in Mexico and in the United States, (2) U.S.-born Mexican Americans, and (3) non-Hispanic American whites. Our analytical strategy improves upon previous research on three fronts. First, we derive four hypotheses from a general framework that has also been used to explain the standard Hispanic paradox. Second, we study biomarkers rather than self-reported health and related conditions. Third, we use a binational data platform that includes both Mexicans living in Mexico (Mexican National Health and Nutrition Survey 2006) and Mexican migrants to the United States (NHANES 1999-2010). We find steep education gradients among Mexicans living in Mexico's urban areas in five of six biomarkers of metabolic syndrome (MetS) and in the overall MetS score. Mexican migrants living in the United States experience similar patterns to Mexicans living in Mexico in glucose and obesity biomarkers. These results are inconsistent with previous findings, suggesting that Mexican migrants in the United States experience significantly attenuated health gradients relative to the non-Hispanic white U.S. Our empirical evidence also contradicts the idea that SES-health gradients in Mexico are shallower than those in the United States and could be invoked to explain shallower gradients among Mexicans living in the United States.

A CO2 concentration gradient facility for testing CO2 enrichment and soil effects on grassland ecosystem function

USDA-ARS?s Scientific Manuscript database

Continuing increases in atmospheric CO2 concentrations mandate techniques for examining impacts on terrestrial ecosystems. Most experiments examine only two or a few levels of CO2 concentration and a single soil type, but if CO2 can be varied as a gradient from subambient to superambient concentra...

Long-term effects of weed control with picloram along a gradient of spotted knapweed invasion

Treesearch

Yvette K. Ortega; Dean E. Pearson

2011-01-01

Broadleaf herbicides are commonly used in rangelands to suppress exotic weeds and release native communities from negative impacts of invasion. However, few studies have comprehensively evaluated treatment effects on differing community components across a gradient of initial invasion levels.We conducted a 6-yr experiment within grasslands of western Montana to measure...

Generalization Gradients in Human Predictive Learning: Effects of Discrimination Training and within-Subjects Testing

ERIC Educational Resources Information Center

Vervliet, Bram; Iberico, Carlos; Vervoort, Ellen; Baeyens, Frank

2011-01-01

Generalization gradients have been investigated widely in animal conditioning experiments, but much less so in human predictive learning tasks. Here, we apply the experimental design of a recent study on conditioned fear generalization in humans (Lissek et al., 2008) to a predictive learning task, and examine the effects of a number of relevant…

Size exclusion chromatography-gradients, an alternative approach to polymer gradient chromatography: 2. Separation of poly(meth)acrylates using a size exclusion chromatography-solvent/non-solvent gradient.

PubMed

Schollenberger, Martin; Radke, Wolfgang

2011-10-28

A gradient ranging from methanol to tetrahydrofuran (THF) was applied to a series of poly(methyl methacrylate) (PMMA) standards, using the recently developed concept of SEC-gradients. Contrasting to conventional gradients the samples eluted before the solvent, i.e. within the elution range typical for separations by SEC, however, the high molar mass PMMAs were retarded as compared to experiments on the same column using pure THF as the eluent. The molar mass dependence on retention volume showed a complex behaviour with a nearly molar mass independent elution for high molar masses. This molar mass dependence was explained in terms of solubility and size exclusion effects. The solubility based SEC-gradient was proven to be useful to separate PMMA and poly(n-butyl crylate) (PnBuA) from a poly(t-butyl crylate) (PtBuA) sample. These samples could be separated neither by SEC in THF, due to their very similar hydrodynamic volumes, nor by an SEC-gradient at adsorbing conditions, due to a too low selectivity. The example shows that SEC-gradients can be applied not only in adsorption/desorption mode, but also in precipitation/dissolution mode without risking blocking capillaries or breakthrough peaks. Thus, the new approach is a valuable alternative to conventional gradient chromatography. Copyright © 2011 Elsevier B.V. All rights reserved.

$L_{0}$ Gradient Projection.

PubMed

Ono, Shunsuke

2017-04-01

Minimizing L 0 gradient, the number of the non-zero gradients of an image, together with a quadratic data-fidelity to an input image has been recognized as a powerful edge-preserving filtering method. However, the L 0 gradient minimization has an inherent difficulty: a user-given parameter controlling the degree of flatness does not have a physical meaning since the parameter just balances the relative importance of the L 0 gradient term to the quadratic data-fidelity term. As a result, the setting of the parameter is a troublesome work in the L 0 gradient minimization. To circumvent the difficulty, we propose a new edge-preserving filtering method with a novel use of the L 0 gradient. Our method is formulated as the minimization of the quadratic data-fidelity subject to the hard constraint that the L 0 gradient is less than a user-given parameter α . This strategy is much more intuitive than the L 0 gradient minimization because the parameter α has a clear meaning: the L 0 gradient value of the output image itself, so that one can directly impose a desired degree of flatness by α . We also provide an efficient algorithm based on the so-called alternating direction method of multipliers for computing an approximate solution of the nonconvex problem, where we decompose it into two subproblems and derive closed-form solutions to them. The advantages of our method are demonstrated through extensive experiments.

Conjugate gradient method for phase retrieval based on the Wirtinger derivative.

PubMed

Wei, Zhun; Chen, Wen; Qiu, Cheng-Wei; Chen, Xudong

2017-05-01

A conjugate gradient Wirtinger flow (CG-WF) algorithm for phase retrieval is proposed in this paper. It is shown that, compared with recently reported Wirtinger flow and its modified methods, the proposed CG-WF algorithm is able to dramatically accelerate the convergence rate while keeping the dominant computational cost of each iteration unchanged. We numerically illustrate the effectiveness of our method in recovering 1D Gaussian signals and 2D natural color images under both Gaussian and coded diffraction pattern models.

Sea surface temperature of the coastal zones of France

NASA Technical Reports Server (NTRS)

Deschamps, P. Y.; Crepon, M.; Monget, J. M.; Verger, F. (Principal Investigator); Frouin, R.; Cassanet, J.; Wald, L.

1980-01-01

The various thermal gradients in the coastal zones of France were mapped with regard to natural phenomena and man made thermal effluents. The mesoscale thermal features of the English Channel, the Bay of Biscay, and the northwestern Mediterranean Sea were also studied. The evolution of the thermal gradients generated by the main estuaries of the French coastal zones was investigated along with the modeling of diurnal heating of the sea surface and its influence on the oceanic surface layers.

Plant pollinator networks along a gradient of urbanisation.

PubMed

Geslin, Benoît; Gauzens, Benoit; Thébault, Elisa; Dajoz, Isabelle

2013-01-01

Habitat loss is one of the principal causes of the current pollinator decline. With agricultural intensification, increasing urbanisation is among the main drivers of habitat loss. Consequently studies focusing on pollinator community structure along urbanisation gradients have increased in recent years. However, few studies have investigated how urbanisation affects plant-pollinator interaction networks. Here we assessed modifications of plant-pollinator interactions along an urbanisation gradient based on the study of their morphological relationships. Along an urbanisation gradient comprising four types of landscape contexts (semi-natural, agricultural, suburban, urban), we set up experimental plant communities containing two plant functional groups differing in their morphological traits ("open flowers" and "tubular flowers"). Insect visitations on these communities were recorded to build plant-pollinator networks. A total of 17 857 interactions were recorded between experimental plant communities and flower-visitors. The number of interactions performed by flower-visitors was significantly lower in urban landscape context than in semi-natural and agricultural ones. In particular, insects such as Syrphidae and solitary bees that mostly visited the open flower functional group were significantly impacted by urbanisation, which was not the case for bumblebees. Urbanisation also impacted the generalism of flower-visitors and we detected higher interaction evenness in urban landscape context than in agricultural and suburban ones. Finally, in urban context, these modifications lowered the potential reproductive success of the open flowers functional group. Our findings show that open flower plant species and their specific flower-visitors are especially sensitive to increasing urbanisation. These results provide new clues to improve conservation measures within urbanised areas in favour of specialist flower-visitors. To complete this functional approach, studies using networks resolved to the species level along urbanised gradients would be required.

Plant Pollinator Networks along a Gradient of Urbanisation

PubMed Central

Geslin, Benoît; Gauzens, Benoit; Thébault, Elisa; Dajoz, Isabelle

2013-01-01

Background Habitat loss is one of the principal causes of the current pollinator decline. With agricultural intensification, increasing urbanisation is among the main drivers of habitat loss. Consequently studies focusing on pollinator community structure along urbanisation gradients have increased in recent years. However, few studies have investigated how urbanisation affects plant-pollinator interaction networks. Here we assessed modifications of plant-pollinator interactions along an urbanisation gradient based on the study of their morphological relationships. Methodology/Principal Findings Along an urbanisation gradient comprising four types of landscape contexts (semi-natural, agricultural, suburban, urban), we set up experimental plant communities containing two plant functional groups differing in their morphological traits (“open flowers” and “tubular flowers”). Insect visitations on these communities were recorded to build plant-pollinator networks. A total of 17 857 interactions were recorded between experimental plant communities and flower-visitors. The number of interactions performed by flower-visitors was significantly lower in urban landscape context than in semi-natural and agricultural ones. In particular, insects such as Syrphidae and solitary bees that mostly visited the open flower functional group were significantly impacted by urbanisation, which was not the case for bumblebees. Urbanisation also impacted the generalism of flower-visitors and we detected higher interaction evenness in urban landscape context than in agricultural and suburban ones. Finally, in urban context, these modifications lowered the potential reproductive success of the open flowers functional group. Conclusions/Significance Our findings show that open flower plant species and their specific flower-visitors are especially sensitive to increasing urbanisation. These results provide new clues to improve conservation measures within urbanised areas in favour of specialist flower-visitors. To complete this functional approach, studies using networks resolved to the species level along urbanised gradients would be required. PMID:23717421

Mesoscale numerical modeling of meteorological events in a strong topographic gradient in the northeastern part of Mexico

NASA Astrophysics Data System (ADS)

Pineda-Martinez, Luis F.; Carbajal, Noel

2009-08-01

A series of numerical experiments were carried out to study the effect of meteorological events such as warm and cold air masses on climatic features and variability of a understudied region with strong topographic gradients in the northeastern part of Mexico. We applied the mesoscale model MM5. We investigated the influence of soil moisture availability in the performance of the model under two representative events for winter and summer. The results showed that a better resolution in land use cover improved the agreement among observed and calculated data. The topography induces atmospheric circulation patterns that determine the spatial distribution of climate and seasonal behavior. The numerical experiments reveal regions favorable to forced convection on the eastern side of the mountain chains Eastern Sierra Madre and Sierra de Alvarez. These processes affect the vertical and horizontal structure of the meteorological variables along the topographic gradient.

Learning-Related Shifts in Generalization Gradients for Complex Sounds

PubMed Central

Wisniewski, Matthew G.; Church, Barbara A.; Mercado, Eduardo

2010-01-01

Learning to discriminate stimuli can alter how one distinguishes related stimuli. For instance, training an individual to differentiate between two stimuli along a single dimension can alter how that individual generalizes learned responses. In this study, we examined the persistence of shifts in generalization gradients after training with sounds. University students were trained to differentiate two sounds that varied along a complex acoustic dimension. Students subsequently were tested on their ability to recognize a sound they experienced during training when it was presented among several novel sounds varying along this same dimension. Peak shift was observed in Experiment 1 when generalization tests immediately followed training, and in Experiment 2 when tests were delayed by 24 hours. These findings further support the universality of generalization processes across species, modalities, and levels of stimulus complexity. They also raise new questions about the mechanisms underlying learning-related shifts in generalization gradients. PMID:19815929

Modeling digits. Digit patterning is controlled by a Bmp-Sox9-Wnt Turing network modulated by morphogen gradients.

PubMed

Raspopovic, J; Marcon, L; Russo, L; Sharpe, J

2014-08-01

During limb development, digits emerge from the undifferentiated mesenchymal tissue that constitutes the limb bud. It has been proposed that this process is controlled by a self-organizing Turing mechanism, whereby diffusible molecules interact to produce a periodic pattern of digital and interdigital fates. However, the identities of the molecules remain unknown. By combining experiments and modeling, we reveal evidence that a Turing network implemented by Bmp, Sox9, and Wnt drives digit specification. We develop a realistic two-dimensional simulation of digit patterning and show that this network, when modulated by morphogen gradients, recapitulates the expression patterns of Sox9 in the wild type and in perturbation experiments. Our systems biology approach reveals how a combination of growth, morphogen gradients, and a self-organizing Turing network can achieve robust and reproducible pattern formation. Copyright © 2014, American Association for the Advancement of Science.

Spatial transposition gradients in visual working memory.

PubMed

Rerko, Laura; Oberauer, Klaus; Lin, Hsuan-Yu

2014-01-01

In list memory, access to individual items reflects limits of temporal distinctiveness. This is reflected in the finding that neighbouring list items tend to be confused most often. This article investigates the analogous effect of spatial proximity in a visual working-memory task. Items were presented in different locations varying in spatial distance. A retro-cue indicated the location of the item relevant for the subsequent memory test. In two recognition experiments, probes matching spatially close neighbours of the relevant item led to more false alarms than probes matching distant neighbours or non-neighbouring memory items. In two probed-recall experiments, one with simultaneous, the other with sequential memory item presentation, items closer to the cued location were more frequently chosen for recall than more distant items. These results reflect a spatial transposition gradient analogous to the temporal transposition gradient in serial recall and challenge fixed-capacity models of visual working memory (WM).

Flame Synthesis of Single- and Multi-Walled Carbon Nanotubes and Nanofibers

NASA Technical Reports Server (NTRS)

VanderWal, R. L.; Ticich, Thomas M.

2001-01-01

Metal-catalyzed carbon nanotubes are highly sought for a diverse range of applications that include nanoelectronics, battery electrode material, catalysis, hydrogen storage media and reinforcing agents in polymer composites. These latter applications will require vast quantities of nanotubes at competitive prices to be economically feasible. Moreover, reinforcing applications may not require ultrahigh purity nanotubes. Indeed, functionalization of nanotubes to facilitate interfacial bonding within composites will naturally introduce defects into the tube walls, lessening their tensile strength. Current methods of aerosol synthesis of carbon nanotubes include laser ablation of composite targets of carbon and catalyst metal within high temperature furnaces and decomposition of a organometallics in hydrocarbons mixtures within a tube furnace. Common to each approach is the generation of particles in the presence of the reactive hydrocarbon species at elevated temperatures. In the laser-ablation approach, the situation is even more dynamic in that particles and nanotubes are borne during the transient cooling phase of the laser-induced plasma for which the temperature far exceeds that of the surrounding hot gases within the furnace process tube. A shared limitation is that more efficient methods of nanoparticle synthesis are not readily incorporated into these approaches. In contrast, combustion can quite naturally create nanomaterials such as carbon black. Flame synthesis is well known for its commercial scalability and energy efficiency. However, flames do present a complex chemical environment with steep gradients in temperature and species concentrations. Moreover, reaction times are limited within buoyant driven flows to tens of milliseconds. Therein microgravity can greatly lessen temperature and spatial gradients while allowing independent control of flame residence times. In preparation for defining the microgravity experiments, the work presented here focuses on the effect of catalyst particle size and reactant gas in 1g.

In Situ 3D Segmentation of Individual Plant Leaves Using a RGB-D Camera for Agricultural Automation.

PubMed

Xia, Chunlei; Wang, Longtan; Chung, Bu-Keun; Lee, Jang-Myung

2015-08-19

In this paper, we present a challenging task of 3D segmentation of individual plant leaves from occlusions in the complicated natural scene. Depth data of plant leaves is introduced to improve the robustness of plant leaf segmentation. The low cost RGB-D camera is utilized to capture depth and color image in fields. Mean shift clustering is applied to segment plant leaves in depth image. Plant leaves are extracted from the natural background by examining vegetation of the candidate segments produced by mean shift. Subsequently, individual leaves are segmented from occlusions by active contour models. Automatic initialization of the active contour models is implemented by calculating the center of divergence from the gradient vector field of depth image. The proposed segmentation scheme is tested through experiments under greenhouse conditions. The overall segmentation rate is 87.97% while segmentation rates for single and occluded leaves are 92.10% and 86.67%, respectively. Approximately half of the experimental results show segmentation rates of individual leaves higher than 90%. Nevertheless, the proposed method is able to segment individual leaves from heavy occlusions.

Laboratory-Scale Evidence for Lightning-Mediated Gene Transfer in Soil

PubMed Central

Demanèche, Sandrine; Bertolla, Franck; Buret, François; Nalin, Renaud; Sailland, Alain; Auriol, Philippe; Vogel, Timothy M.; Simonet, Pascal

2001-01-01

Electrical fields and current can permeabilize bacterial membranes, allowing for the penetration of naked DNA. Given that the environment is subjected to regular thunderstorms and lightning discharges that induce enormous electrical perturbations, the possibility of natural electrotransformation of bacteria was investigated. We demonstrated with soil microcosm experiments that the transformation of added bacteria could be increased locally via lightning-mediated current injection. The incorporation of three genes coding for antibiotic resistance (plasmid pBR328) into the Escherichia coli strain DH10B recipient previously added to soil was observed only after the soil had been subjected to laboratory-scale lightning. Laboratory-scale lightning had an electrical field gradient (700 versus 600 kV m−1) and current density (2.5 versus 12.6 kA m−2) similar to those of full-scale lightning. Controls handled identically except for not being subjected to lightning produced no detectable antibiotic-resistant clones. In addition, simulated storm cloud electrical fields (in the absence of current) did not produce detectable clones (transformation detection limit, 10−9). Natural electrotransformation might be a mechanism involved in bacterial evolution. PMID:11472916