Cosmology in one dimension: Vlasov dynamics.

PubMed

Manfredi, Giovanni; Rouet, Jean-Louis; Miller, Bruce; Shiozawa, Yui

2016-04-01

Numerical simulations of self-gravitating systems are generally based on N-body codes, which solve the equations of motion of a large number of interacting particles. This approach suffers from poor statistical sampling in regions of low density. In contrast, Vlasov codes, by meshing the entire phase space, can reach higher accuracy irrespective of the density. Here, we perform one-dimensional Vlasov simulations of a long-standing cosmological problem, namely, the fractal properties of an expanding Einstein-de Sitter universe in Newtonian gravity. The N-body results are confirmed for high-density regions and extended to regions of low matter density, where the N-body approach usually fails.

Micro-bias and macro-performance.

PubMed

Seaver, S M D; Moreira, A A; Sales-Pardo, M; Malmgren, R D; Diermeier, D; Amaral, L A N

2009-02-01

We use agent-based modeling to investigate the effect of conservatism and partisanship on the efficiency with which large populations solve the density classification task - a paradigmatic problem for information aggregation and consensus building. We find that conservative agents enhance the populations' ability to efficiently solve the density classification task despite large levels of noise in the system. In contrast, we find that the presence of even a small fraction of partisans holding the minority position will result in deadlock or a consensus on an incorrect answer. Our results provide a possible explanation for the emergence of conservatism and suggest that even low levels of partisanship can lead to significant social costs.

The impact of stellar feedback on the density and velocity structure of the interstellar medium

NASA Astrophysics Data System (ADS)

Grisdale, Kearn; Agertz, Oscar; Romeo, Alessandro B.; Renaud, Florent; Read, Justin I.

2017-04-01

We study the impact of stellar feedback in shaping the density and velocity structure of neutral hydrogen (H I) in disc galaxies. For our analysis, we carry out ˜4.6 pc resolution N-body+adaptive mesh refinement hydrodynamic simulations of isolated galaxies, set up to mimic a Milky Way and a Large and Small Magellanic Cloud. We quantify the density and velocity structure of the interstellar medium using power spectra and compare the simulated galaxies to observed H I in local spiral galaxies from THINGS (The H I Nearby Galaxy Survey). Our models with stellar feedback give an excellent match to the observed THINGS H I density power spectra. We find that kinetic energy power spectra in feedback-regulated galaxies, regardless of galaxy mass and size, show scalings in excellent agreement with supersonic turbulence (E(k) ∝ k-2) on scales below the thickness of the H I layer. We show that feedback influences the gas density field, and drives gas turbulence, up to large (kpc) scales. This is in stark contrast to density fields generated by large-scale gravity-only driven turbulence. We conclude that the neutral gas content of galaxies carries signatures of stellar feedback on all scales.

Assessing the roles of population density and predation risk in the evolution of offspring size in populations of a placental fish

PubMed Central

Schrader, Matthew; Travis, Joseph

2012-01-01

Population density is an ecological variable that is hypothesized to be a major agent of selection on offspring size. In high-density populations, high levels of intraspecific competition are expected to favor the production of larger offspring. In contrast, lower levels of intraspecific competition and selection for large offspring should be weaker and more easily overridden by direct selection for increased fecundity in low-density populations. Some studies have found associations between population density and offspring size consistent with this hypothesis. However, their interpretations are often clouded by a number of issues. Here, we use data from a 10-year study of nine populations of the least killifish, Heterandria formosa, to describe the associations of offspring size with habitat type, population density, and predation risk. We found that females from spring populations generally produced larger offspring than females from ponds; however, the magnitude of this difference varied among years. Across all populations, larger offspring were associated with higher densities and lower risks of predation. Interestingly, the associations between the two ecological variables (density and predation risk) and offspring size were largely independent of one another. Our results suggest that previously described genetic differences in offspring size are due to density-dependent natural selection. PMID:22957156

Salinization in a stratified aquifer induced by heat transfer from well casings

NASA Astrophysics Data System (ADS)

van Lopik, Jan H.; Hartog, Niels; Zaadnoordijk, Willem Jan; Cirkel, D. Gijsbert; Raoof, Amir

2015-12-01

The temperature inside wells used for gas, oil and geothermal energy production, as well as steam injection, is in general significantly higher than the groundwater temperature at shallower depths. While heat loss from these hot wells is known to occur, the extent to which this heat loss may result in density-driven flow and in mixing of surrounding groundwater has not been assessed so far. However, based on the heat and solute effects on density of this arrangement, the induced temperature contrasts in the aquifer due to heat transfer are expected to destabilize the system and result in convection, while existing salt concentration contrasts in an aquifer would act to stabilize the system. To evaluate the degree of impact that may occur under field conditions, free convection in a 50-m-thick aquifer driven by the heat loss from penetrating hot wells was simulated using a 2D axisymmetric SEAWAT model. In particular, the salinization potential of fresh groundwater due to the upward movement of brackish or saline water in a stratified aquifer is studied. To account for a large variety of well applications and configurations, as well as different penetrated aquifer systems, a wide range of well temperatures, from 40 to 100 °C, together with a range of salt concentration (1-35 kg/m3) contrasts were considered. This large temperature difference with the native groundwater (15 °C) required implementation of a non-linear density equation of state in SEAWAT. We show that density-driven groundwater flow results in a considerable salt mass transport (up to 166,000 kg) to the top of the aquifer in the vicinity of the well (radial distance up to 91 m) over a period of 30 years. Sensitivity analysis showed that density-driven groundwater flow and the upward salt transport was particularly enhanced by the increased heat transport from the well into the aquifer by thermal conduction due to increased well casing temperature, thermal conductivity of the soil, as well as decreased porosity values. Enhanced groundwater flow and salt transport was also observed for increased hydraulic conductivity of the aquifer. While advective salt transport was dominant for lower salt concentration contrasts, under higher salt concentration contrasts transport was controlled by dispersive mixing at the fresh-salt water interface between the two separate convection cells in the fresh and salt water layers. The results of this study indicate heat loss from hot well casings can induce density-driven transport and mixing processes in surrounding groundwater. This process should therefore be considered when monitoring for long-term groundwater quality changes near wells through which hot fluids or gases are transported.

Image enhancement of optical images for binary system of melanocytes and keratinocytes

NASA Astrophysics Data System (ADS)

Takanezawa, S.; Baba, A.; Sako, Y.; Ozaki, Y.; Date, A.; Toyama, K.; Morita, S.

2013-05-01

Automatic determination of the cell shapes of large numbers of melanocytes based on optical images of human skin models have been largely unsuccessful (the complexities introduced by dendrites and the melanin pigmentation over the keratinocytes to give unclear outlines). Here, we present an image enhancement procedure for enhancing the contrast of images with removing the non-uniformity of background. The brightness is normalized also for the non-uniform population density of melanocytes.

Experimental evidence for herbivore limitation of the treeline.

PubMed

Speed, James D M; Austrheim, Gunnar; Hester, Alison J; Mysterud, Atle

2010-11-01

The treeline ecotone divides forest from open alpine or arctic vegetation states. Treelines are generally perceived to be temperature limited. The role of herbivores in limiting the treeline is more controversial, as experimental evidence from relevant large scales is lacking. Here we quantify the impact of different experimentally controlled herbivore densities on the recruitment and survival of birch Betula pubescens tortuosa along an altitudinal gradient in the mountains of southern Norway. After eight years of summer grazing in large-scale enclosures at densities of 0, 25, and 80 sheep/km2, birch recruited within the whole altitudinal range of ungrazed enclosures, but recruitment was rarer in enclosures with low-density sheep and was largely limited to within the treeline in enclosures with high-density sheep. In contrast, the distribution of saplings (birch older than the experiment) did not differ between grazing treatments, suggesting that grazing sheep primarily limit the establishment of new tree recruits rather than decrease the survival of existing individuals. This study provides direct experimental evidence that herbivores can limit the treeline below its potential at the landscape scale and even at low herbivore densities in this climatic zone. Land use changes should thus be considered in addition to climatic changes as potential drivers of ecotone shifts.

Estimating large carnivore populations at global scale based on spatial predictions of density and distribution – Application to the jaguar (Panthera onca)

PubMed Central

Robinson, Hugh S.; Abarca, Maria; Zeller, Katherine A.; Velasquez, Grisel; Paemelaere, Evi A. D.; Goldberg, Joshua F.; Payan, Esteban; Hoogesteijn, Rafael; Boede, Ernesto O.; Schmidt, Krzysztof; Lampo, Margarita; Viloria, Ángel L.; Carreño, Rafael; Robinson, Nathaniel; Lukacs, Paul M.; Nowak, J. Joshua; Salom-Pérez, Roberto; Castañeda, Franklin; Boron, Valeria; Quigley, Howard

2018-01-01

Broad scale population estimates of declining species are desired for conservation efforts. However, for many secretive species including large carnivores, such estimates are often difficult. Based on published density estimates obtained through camera trapping, presence/absence data, and globally available predictive variables derived from satellite imagery, we modelled density and occurrence of a large carnivore, the jaguar, across the species’ entire range. We then combined these models in a hierarchical framework to estimate the total population. Our models indicate that potential jaguar density is best predicted by measures of primary productivity, with the highest densities in the most productive tropical habitats and a clear declining gradient with distance from the equator. Jaguar distribution, in contrast, is determined by the combined effects of human impacts and environmental factors: probability of jaguar occurrence increased with forest cover, mean temperature, and annual precipitation and declined with increases in human foot print index and human density. Probability of occurrence was also significantly higher for protected areas than outside of them. We estimated the world’s jaguar population at 173,000 (95% CI: 138,000–208,000) individuals, mostly concentrated in the Amazon Basin; elsewhere, populations tend to be small and fragmented. The high number of jaguars results from the large total area still occupied (almost 9 million km2) and low human densities (< 1 person/km2) coinciding with high primary productivity in the core area of jaguar range. Our results show the importance of protected areas for jaguar persistence. We conclude that combining modelling of density and distribution can reveal ecological patterns and processes at global scales, can provide robust estimates for use in species assessments, and can guide broad-scale conservation actions. PMID:29579129

Photographic Method For Measurement Of Image Intensifier Tube Contrast

NASA Astrophysics Data System (ADS)

Moore, Robert J.

1981-07-01

An important parameter in an image intensifier-based imaging system is the contrast of the image intensifier tube itself. This paper presents a photographic method for the measurement of the large-scale contrast of an image intensifier tube at the system level which can be performed in the clinical setting with equipment normally found in a modern Radiology Department. A strip of Lead is positioned on-center at the bottom of the grid so that a line image of 100% contrast will be presented to the input phosphor of the image intensifier when the x-ray tube is energized at low kilovoltage. The output phosphor is photographed either with an existing fluorographic camera (photospot or cine) on the imaging tower, or with a 35-mm SLR camera loaded with orthochromatic cine film through the collimating lens of the system from the position normally occupied by the television camera, during fluoroscopy, if no other camera is present on the imaging tower. The resultant on-frame optical density is measured with a densitometer in the central part of the developed frame adjacent to and behind the image of the Lead strip. These optical density readings are converted into a ratio of light intensities from the corresponding regions on the output phosphor using the characteristic curve for the type of film employed, which is obtained by means of light sensitometry. The percent contrast is then calculated from (ratio of intensities - 1)/(ratio of intensities + 1)) X 100. Using data for a variety of CsI image intensifiers used for both gastrointestinal and vascular studies, the method is shown to give measured percent contrasts with a reproducibility of no worse than-2%, independent of type of camera used or type of sensitometer used. Standards of acceptable performance based on the author's experience with this technique over the past five years are presented for systems designed for Barium studies and for systems designed for Iodine studies. The relationship between the percent contrast as defined here, the veiling glare as defined by Siedband, and the contrast ratio as normally defined is discussed, as well as the relevance of large-scale contrast of an image intensifier tube.

EMBEDDED LENSING TIME DELAYS, THE FERMAT POTENTIAL, AND THE INTEGRATED SACHS–WOLFE EFFECT

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

Chen, Bin; Kantowski, Ronald; Dai, Xinyu, E-mail: bchen3@fsu.edu

2015-05-01

We derive the Fermat potential for a spherically symmetric lens embedded in a Friedman–Lemaître–Robertson–Walker cosmology and use it to investigate the late-time integrated Sachs–Wolfe (ISW) effect, i.e., secondary temperature fluctuations in the cosmic microwave background (CMB) caused by individual large-scale clusters and voids. We present a simple analytical expression for the temperature fluctuation in the CMB across such a lens as a derivative of the lens’ Fermat potential. This formalism is applicable to both linear and nonlinear density evolution scenarios, to arbitrarily large density contrasts, and to all open and closed background cosmologies. It is much simpler to use andmore » makes the same predictions as conventional approaches. In this approach the total temperature fluctuation can be split into a time-delay part and an evolutionary part. Both parts must be included for cosmic structures that evolve and both can be equally important. We present very simple ISW models for cosmic voids and galaxy clusters to illustrate the ease of use of our formalism. We use the Fermat potentials of simple cosmic void models to compare predicted ISW effects with those recently extracted from WMAP and Planck data by stacking large cosmic voids using the aperture photometry method. If voids in the local universe with large density contrasts are no longer evolving we find that the time delay contribution alone predicts values consistent with the measurements. However, we find that for voids still evolving linearly, the evolutionary contribution cancels a significant part of the time delay contribution and results in predicted signals that are much smaller than recently observed.« less

The relation between invertebrate drift and two primary controls, discharge and benthic densities, in a large regulated river

USGS Publications Warehouse

Kennedy, Theodore A.; Yackulic, Charles B.; Cross, Wyatt F.; Grams, Paul E.; Yard, Michael D.; Copp, Adam J.

2014-01-01

1. Invertebrate drift is a fundamental process in streams and rivers. Studies from laboratory experiments and small streams have identified numerous extrinsic (e.g. discharge, light intensity, water quality) and intrinsic factors (invertebrate life stage, benthic density, behaviour) that govern invertebrate drift concentrations (# m−3), but the factors that govern invertebrate drift in larger rivers remain poorly understood. For example, while large increases or decreases in discharge can lead to large increases in invertebrate drift, the role of smaller, incremental changes in discharge is poorly described. In addition, while we might expect invertebrate drift concentrations to be proportional to benthic densities (# m−2), the benthic–drift relation has not been rigorously evaluated. 2. Here, we develop a framework for modelling invertebrate drift that is derived from sediment transport studies. We use this framework to guide the analysis of high-resolution data sets of benthic density and drift concentration for four important invertebrate taxa from the Colorado River downstream of Glen Canyon Dam (mean daily discharge 325 m3 s−1) that were collected over 18 months and include multiple observations within days. Ramping of regulated flows on this river segment provides an experimental treatment that is repeated daily and allowed us to describe the functional relations between invertebrate drift and two primary controls, discharge and benthic densities. 3. Twofold daily variation in discharge resulted in a >10-fold increase in drift concentrations of benthic invertebrates associated with pools and detritus (i.e. Gammarus lacustris and Potamopyrgus antipodarum). In contrast, drift concentrations of sessile blackfly larvae (Simuliium arcticum), which are associated with high-velocity cobble microhabitats, decreased by over 80% as discharge doubled. Drift concentrations of Chironomidae increased proportional to discharge. 4. Drift of all four taxa was positively related to benthic density. Drift concentrations of Gammarus, Potamopyrgus and Chironomidae were proportional to benthic density. Drift concentrations of Simulium were positively related to benthic density, but the benthic–drift relation was less than proportional (i.e. a doubling of benthic density only led to a 40% increase in drift concentrations). 5. Our study demonstrates that invertebrate drift concentrations in the Colorado River are jointly controlled by discharge and benthic densities, but these controls operate at different timescales. Twofold daily variation in discharge associated with hydropeaking was the primary control on within-day variation in invertebrate drift concentrations. In contrast, benthic density, which varied 10- to 1000-fold among sampling dates, depending on the taxa, was the primary control on invertebrate drift concentrations over longer timescales (weeks to months).

Influence of geographical scale on the detection of density dependence in the host-parasite system, Arvicola terrestris and Taenia taeniaeformis.

PubMed

Deter, J; Berthier, K; Chaval, Y; Cosson, J F; Morand, S; Charbonnel, N

2006-04-01

Infection by the cestode Taenia taeniaeformis was investigated within numerous cyclic populations of the fossorial water vole Arvicola terrestris sampled during 4 years in Franche-Comté (France). The relative influence of different rodent demographic parameters on the presence of this cestode was assessed by considering (1) the demographic phase of the cycle; (2) density at the local geographical scale (<0.1 km2); (3) mean density at a larger scale (>10 km2). The local scale corresponded to the rodent population (intermediate host), while the large scale corresponded to the definitive host population (wild and feral cats). General linear models based on analyses of 1804 voles revealed the importance of local density but also of year, rodent age, season and interactions between year and season and between age and season. Prevalence was significantly higher in low vole densities than during local outbreaks. By contrast, the large geographical scale density and the demographic phase had less influence on infection by the cestode. The potential impacts of the cestode on the fitness of the host were assessed and infection had no effect on the host body mass, litter size or sexual activity of voles.

Numerical investigation of split flows by gravity currents into two-layered stratified water bodies

NASA Astrophysics Data System (ADS)

Cortés, A.; Wells, M. G.; Fringer, O. B.; Arthur, R. S.; Rueda, F. J.

2015-07-01

The behavior of a two-dimensional (2-D) gravity current impinging upon a density step in a two-layered stratified basin is analyzed using a high-resolution Reynolds-Averaged Navier-Stokes model. The gravity current splits at the density step, and the portion of the buoyancy flux becoming an interflow is largely controlled by the vertical distribution of velocity and density within the gravity current and the magnitude of the density step between the two ambient layers. This is in agreement with recent laboratory observations. The strongest changes in the ambient density profiles occur as a result of the impingement of supercritical currents with strong density contrasts, for which a large portion of the gravity current detaches from the bottom and becomes an interflow. We characterize the current partition process in the simulated experiments using the densimetric Froude number of the current (Fr) across the density step (upstream and downstream). When underflows are formed, more supercritical currents are observed downstream of the density step compared to upstream (Fru < Frd), and thus, stronger mixing of the current with the ambient water downstream. However, when split flows and interflows are formed, smaller Fr values are identified after the current crosses the density step (Fru > Frd), which indicates lower mixing between the current and ambient water after the impingement due to the significant stripping of interfacial material at the density step.

Non-local bias in the halo bispectrum with primordial non-Gaussianity

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

Tellarini, Matteo; Ross, Ashley J.; Wands, David

2015-07-01

Primordial non-Gaussianity can lead to a scale-dependent bias in the density of collapsed halos relative to the underlying matter density. The galaxy power spectrum already provides constraints on local-type primordial non-Gaussianity complementary those from the cosmic microwave background (CMB), while the bispectrum contains additional shape information and has the potential to outperform CMB constraints in future. We develop the bias model for the halo density contrast in the presence of local-type primordial non-Gaussianity, deriving a bivariate expansion up to second order in terms of the local linear matter density contrast and the local gravitational potential in Lagrangian coordinates. Nonlinear evolutionmore » of the matter density introduces a non-local tidal term in the halo model. Furthermore, the presence of local-type non-Gaussianity in the Lagrangian frame leads to a novel non-local convective term in the Eulerian frame, that is proportional to the displacement field when going beyond the spherical collapse approximation. We use an extended Press-Schechter approach to evaluate the halo mass function and thus the halo bispectrum. We show that including these non-local terms in the halo bispectra can lead to corrections of up to 25% for some configurations, on large scales or at high redshift.« less

What sets the central structure of dark matter haloes?

NASA Astrophysics Data System (ADS)

Ogiya, Go; Hahn, Oliver

2018-02-01

Dark matter (DM) haloes forming near the thermal cut-off scale of the density perturbations are unique, since they are the smallest objects and form through monolithic gravitational collapse, while larger haloes contrastingly have experienced mergers. While standard cold dark matter (CDM) simulations readily produce haloes that follow the universal Navarro-Frenk-White (NFW) density profile with an inner slope, ρ ∝ r-α, with α = 1, recent simulations have found that when the free-streaming cut-off expected for the CDM model is resolved, the resulting haloes follow nearly power-law density profiles of α ∼ 1.5. In this paper, we study the formation of density cusps in haloes using idealized N-body simulations of the collapse of proto-haloes. When the proto-halo profile is initially cored due to particle free-streaming at high redshift, we universally find ∼r-1.5 profiles irrespective of the proto-halo profile slope outside the core and large-scale non-spherical perturbations. Quite in contrast, when the proto-halo has a power-law profile, then we obtain profiles compatible with the NFW shape when the density slope of the proto-halo patch is shallower than a critical value, αini ∼ 0.3, while the final slope can be steeper for αini ≳ 0.3. We further demonstrate that the r-1.5 profiles are sensitive to small-scale noise, which gradually drives them towards an inner slope of -1, where they become resilient to such perturbations. We demonstrate that the r-1.5 solutions are in hydrostatic equilibrium, largely consistent with a simple analytic model, and provide arguments that angular momentum appears to determine the inner slope.

T1 weighted brain images at 7 Tesla unbiased for Proton Density, T2* contrast and RF coil receive B1 sensitivity with simultaneous vessel visualization.

PubMed

Van de Moortele, Pierre-François; Auerbach, Edwards J; Olman, Cheryl; Yacoub, Essa; Uğurbil, Kâmil; Moeller, Steen

2009-06-01

At high magnetic field, MR images exhibit large, undesirable signal intensity variations commonly referred to as "intensity field bias". Such inhomogeneities mostly originate from heterogeneous RF coil B(1) profiles and, with no appropriate correction, are further pronounced when utilizing rooted sum of square reconstruction with receive coil arrays. These artifacts can significantly alter whole brain high resolution T(1)-weighted (T(1)w) images that are extensively utilized for clinical diagnosis, for gray/white matter segmentation as well as for coregistration with functional time series. In T(1) weighted 3D-MPRAGE sequences, it is possible to preserve a bulk amount of T(1) contrast through space by using adiabatic inversion RF pulses that are insensitive to transmit B(1) variations above a minimum threshold. However, large intensity variations persist in the images, which are significantly more difficult to address at very high field where RF coil B(1) profiles become more heterogeneous. Another characteristic of T(1)w MPRAGE sequences is their intrinsic sensitivity to Proton Density and T(2)(*) contrast, which cannot be removed with post-processing algorithms utilized to correct for receive coil sensitivity. In this paper, we demonstrate a simple technique capable of producing normalized, high resolution T(1)w 3D-MPRAGE images that are devoid of receive coil sensitivity, Proton Density and T(2)(*) contrast. These images, which are suitable for routinely obtaining whole brain tissue segmentation at 7 T, provide higher T(1) contrast specificity than standard MPRAGE acquisitions. Our results show that removing the Proton Density component can help in identifying small brain structures and that T(2)(*) induced artifacts can be removed from the images. The resulting unbiased T(1)w images can also be used to generate Maximum Intensity Projection angiograms, without additional data acquisition, that are inherently registered with T(1)w structural images. In addition, we introduce a simple technique to reduce residual signal intensity variations induced by transmit B(1) heterogeneity. Because this approach requires two 3D images, one divided with the other, head motion could create serious problems, especially at high spatial resolution. To alleviate such inter-scan motion problems, we developed a new sequence where the two contrast acquisitions are interleaved within a single scan. This interleaved approach however comes with greater risk of intra-scan motion issues because of a longer single scan time. Users can choose between these two trade offs depending on specific protocols and patient populations. We believe that the simplicity and the robustness of this double contrast based approach to address intensity field bias at high field and improve T(1) contrast specificity, together with the capability of simultaneously obtaining angiography maps, advantageously counter balance the potential drawbacks of the technique, mainly a longer acquisition time and a moderate reduction in signal to noise ratio.

T1 weighted Brain Images at 7 Tesla Unbiased for Proton Density, T2* contrast and RF Coil Receive B1 Sensitivity with Simultaneous Vessel Visualization

PubMed Central

Van de Moortele, Pierre-François; Auerbach, Edwards J.; Olman, Cheryl; Yacoub, Essa; Uğurbil, Kâmil; Moeller, Steen

2009-01-01

At high magnetic field, MR images exhibit large, undesirable signal intensity variations commonly referred to as “intensity field bias”. Such inhomogeneities mostly originate from heterogeneous RF coil B1 profiles and, with no appropriate correction, are further pronounced when utilizing rooted sum of square reconstruction with receive coil arrays. These artifacts can significantly alter whole brain high resolution T1-weighted (T1w) images that are extensively utilized for clinical diagnosis, for gray/white matter segmentation as well as for coregistration with functional time series. In T1 weighted 3D-MPRAGE sequences, it is possible to preserve a bulk amount of T1 contrast through space by using adiabatic inversion RF pulses that are insensitive to transmit B1 variations above a minimum threshold. However, large intensity variations persist in the images, which are significantly more difficult to address at very high field where RF coil B1 profiles become more heterogeneous. Another characteristic of T1w MPRAGE sequences is their intrinsic sensitivity to Proton Density and T2* contrast, which cannot be removed with post-processing algorithms utilized to correct for receive coil sensitivity. In this paper, we demonstrate a simple technique capable of producing normalized, high resolution T1w 3D-MPRAGE images that are devoid of receive coil sensitivity, Proton Density and T2* contrast. These images, which are suitable for routinely obtaining whole brain tissue segmentation at 7 Tesla, provide higher T1 contrast specificity than standard MPRAGE acquisitions. Our results show that removing the Proton Density component can help identifying small brain structures and that T2* induced artifacts can be removed from the images. The resulting unbiased T1w images can also be used to generate Maximum Intensity Projection angiograms, without additional data acquisition, that are inherently registered with T1w structural images. In addition, we introduce a simple technique to reduce residual signal intensity variations induced by Transmit B1 heterogeneity. Because this approach requires two 3D images, one divided with the other, head motion could create serious problems, especially at high spatial resolution. To alleviate such inter-scan motion problems, we developed a new sequence where the two contrast acquisitions are interleaved within a single scan. This interleaved approach however comes with greater risk of intra-scan motion issues because of a longer single scan time. Users can choose between these two trade offs depending on specific protocols and patient populations. We believe that the simplicity and the robustness of this double contrast based approach to address intensity field bias at high field and improve T1 contrast specificity, together with the capability of simultaneously obtaining angiography maps, advantageously counter balance the potential drawbacks of the technique, mainly a longer acquisition time and a moderate reduction in signal to noise ratio. PMID:19233292

Material properties of zooplankton and nekton from the California current

NASA Astrophysics Data System (ADS)

Becker, Kaylyn

This study measured the material properties of zooplankton, Pacific hake (Merluccius productus), Humboldt squid (Dosidicus gigas), and two species of myctophids (Symbolophorus californiensis and Diaphus theta) collected from the California Current ecosystem. The density contrast (g) was measured for euphausiids, decapods (Sergestes similis), amphipods (Primno macropa, Phronima sp., and Hyperiid spp.), siphonophore bracts, chaetognaths, larval fish, crab megalopae, larval squid, and medusae. Morphometric data (length, width, and height) were collected for these taxa. Density contrasts varied within and between zooplankton taxa. The mean and standard deviation for euphausiid density contrast were 1.059 +/- 0.009. Relationships between zooplankton density contrast and morphometric measurements, geographic location, and environmental conditions were investigated. Site had a significant effect on euphausiid density contrast. Density contrasts of euphausiids collected in the same geographic area approximately 4-10 days apart were significantly higher (p < 0.001). Sound speed contrast (h) was measured for euphausiids and pelagic decapods (S. similis) and it varied between taxa. The mean and standard deviation for euphausiid sound speed were 1.019 +/- 0.009. Euphausiid mass was calculated from density measurements and volume, and a relationship between euphausiid mass and length was produced. We determined that euphausiid from volumes could be accurately estimated two dimensional measurements of animal body shape, and that biomass (or biovolume) could be accurately calculated from digital photographs of animals. Density contrast (g) was measured for zooplankton, pieces of hake flesh, myctophid flesh, and of the following Humboldt squid body parts: mantle, arms, tentacle, braincase, eyes, pen, and beak. The density contrasts varied within and between fish taxa, as well as among squid body parts. Effects of animal length and environmental conditions on nekton density contrast were investigated. The sound speed contrast (h) was measured for Pacific hake flesh, myctophid flesh, Humboldt squid mantle, and Humboldt squid braincase. Sound speed varied within and between nekton taxa. The material properties reported in this study can be used to improve target strength estimates from acoustic scattering models which would increase the accuracy of biomass estimates from acoustic surveys for these zooplankton and nekton.

Density of Key-Species Determines Efficiency of Macroalgae Detritus Uptake by Intertidal Benthic Communities

PubMed Central

Karlson, Agnes M. L.; Niemand, Clarisse; Savage, Candida; Pilditch, Conrad A

2016-01-01

Accumulating evidence shows that increased biodiversity has a positive effect on ecosystem functioning, but the mechanisms that underpin this positive relationship are contentious. Complete extinctions of regional species pools are comparatively rare whereas compositional changes and reductions in abundance and biomass are common, although seldom the focus of biodiversity-ecosystem functioning studies. We use natural, small-scale patchiness in the density of two species of large bivalves with contrasting feeding modes (the suspension-feeding Austrovenus stutchburyi and deposit-feeding Macomona liliana) to examine their influence on the uptake of nitrogen from macroalgae detritus (i.e. measure of ecosystem function and food web efficiency) by other infauna in a 10-d laboratory isotope-tracer experiment. We predicted that densities of these key bivalve species and functional group diversity (calculated as Shannons H, a density-independent measure of community composition) of the intact infaunal community will be critical factors explaining variance in macroalgal per capita uptake rates by the community members and hence determine total uptake by the community. Results show that only two species, M. liliana and a large orbiniid polychaete (Scoloplos cylindrifer) dominated macroalgal nitrogen taken up by the whole community due to their large biomass. However, their densities were mostly not important or negatively influenced per capita uptake by other species. Instead, the density of a head-down deposit-feeder (the capitellid Heteromastus filiformis), scavengers (mainly nemertines and nereids) and species and functional group diversity, best explained per capita uptake rates in community members. Our results demonstrate the importance of species identity, density and large body size for ecosystem functioning and highlight the complex interactions underlying loss of ecological functions with declining biodiversity and compositional changes. PMID:27414032

The calculations of small molecular conformation energy differences by density functional method

NASA Astrophysics Data System (ADS)

Topol, I. A.; Burt, S. K.

1993-03-01

The differences in the conformational energies for the gauche (G) and trans(T) conformers of 1,2-difluoroethane and for myo-and scyllo-conformer of inositol have been calculated by local density functional method (LDF approximation) with geometry optimization using different sets of calculation parameters. It is shown that in the contrast to Hartree—Fock methods, density functional calculations reproduce the correct sign and value of the gauche effect for 1,2-difluoroethane and energy difference for both conformers of inositol. The results of normal vibrational analysis for1,2-difluoroethane showed that harmonic frequencies calculated in LDF approximation agree with experimental data with the accuracy typical for scaled large basis set Hartree—Fock calculations.

Gravity evidence for a shallow intrusion under Medicine Lake volcano, California.

USGS Publications Warehouse

Finn, C.; Williams, D.L.

1982-01-01

A positive gravity anomaly is associated with Medicine Lake volcano, California. Trials with different Bouguer reduction densities indicate that this positive anomaly cannot be explained by an inappropriate choice of Bouguer reduction density but must be caused by a subvolcanic body. After separating the Medicine Lake gravity high from the regional field, we were able to fit the 27mgal positive residual anomaly with a large, shallow body of high density contrast (+0.41g/cm3) and a thickness of 2.5km. We interpret this body to be an intrusion of dense material emplaced within the several-kilometres-thick older volcanic layer that probably underlies Medicine Lake volcano.-Authors

Divergence of perturbation theory in large scale structures

NASA Astrophysics Data System (ADS)

Pajer, Enrico; van der Woude, Drian

2018-05-01

We make progress towards an analytical understanding of the regime of validity of perturbation theory for large scale structures and the nature of some non-perturbative corrections. We restrict ourselves to 1D gravitational collapse, for which exact solutions before shell crossing are known. We review the convergence of perturbation theory for the power spectrum, recently proven by McQuinn and White [1], and extend it to non-Gaussian initial conditions and the bispectrum. In contrast, we prove that perturbation theory diverges for the real space two-point correlation function and for the probability density function (PDF) of the density averaged in cells and all the cumulants derived from it. We attribute these divergences to the statistical averaging intrinsic to cosmological observables, which, even on very large and "perturbative" scales, gives non-vanishing weight to all extreme fluctuations. Finally, we discuss some general properties of non-perturbative effects in real space and Fourier space.

Critical temperature of noninteracting bosonic gases in cubic optical lattices at arbitrary integer fillings.

PubMed

Rakhimov, Abdulla; Askerzade, Iman N

2014-09-01

We have shown that the critical temperature of a Bose-Einstein condensate to a normal phase transition of noninteracting bosons in cubic optical lattices has a linear dependence on the filling factor, especially at large densities. The condensed fraction exhibits a linear power law dependence on temperature in contrast to the case of ideal homogeneous Bose gases.

On optical imaging through aircraft turbulent boundary layers

NASA Technical Reports Server (NTRS)

Sutton, G. W.

1980-01-01

Optical resolution quality as affected by aircraft turbulent boundary layers is analyzed. Wind-tunnel data was analyzed to obtained the variation of boundary layer turbulence scale length and mass density rms fluctuations with Mach number. The data gave good agreement with a mass density fluctuation turbulence spectrum that is either isotropic of orthogonally anisotropic. The data did not match an isotropic turbulence velocity spectrum which causes an anisotropic non-orthogonal mass density fluctuation spectrum. The results indicate that the average mass density rms fluctuation is about 10% of the maximum mass density across the boundary layer and that the transverse turbulence scale size is about 10% of the boundary layer thickness. The results indicate that the effect of the turbulent boundary layer is large angle scattering which decreases contrast but not resolution. Using extinction as a criteria the range of acceptable aircraft operating conditions are given.

An atomic orbital based real-time time-dependent density functional theory for computing electronic circular dichroism band spectra

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

Goings, Joshua J.; Li, Xiaosong, E-mail: xsli@uw.edu

2016-06-21

One of the challenges of interpreting electronic circular dichroism (ECD) band spectra is that different states may have different rotatory strength signs, determined by their absolute configuration. If the states are closely spaced and opposite in sign, observed transitions may be washed out by nearby states, unlike absorption spectra where transitions are always positive additive. To accurately compute ECD bands, it is necessary to compute a large number of excited states, which may be prohibitively costly if one uses the linear-response time-dependent density functional theory (TDDFT) framework. Here we implement a real-time, atomic-orbital based TDDFT method for computing the entiremore » ECD spectrum simultaneously. The method is advantageous for large systems with a high density of states. In contrast to previous implementations based on real-space grids, the method is variational, independent of nuclear orientation, and does not rely on pseudopotential approximations, making it suitable for computation of chiroptical properties well into the X-ray regime.« less

Simulating rotating fluid bodies: When is vorticity generation via density-stratification important?

NASA Astrophysics Data System (ADS)

Evonuk, M.; Samuel, H.

2012-04-01

Differential rotation is one of the key components needed to maintain a magnetic dynamo, therefore it is important to understand the processes that generate differential rotation in rotating bodies. In a rotating density-stratified fluid, local vorticity generation occurs as fluid parcels move radially, expanding or contracting with respect to the background density stratification. The convergence of this vorticity forms zonal flow structures as a function of the radius and the slope of the background density profile. While this effect is thought to be of importance in bodies that are quickly rotating and highly turbulent with large density stratifications such as Jupiter, it is generally neglected in bodies such as the Earth's outer core, where the density change is small. Simulations of thermal convection in the 2D rotating equatorial plane are conducted to determine the parameter regime where local vorticity generation plays a significant role in organizing the fluid flow. Three regimes are found: a dipolar flow regime, where the flow is not organized by the rotation, a transitional flow regime, and a differential flow regime, where the flow is strongly organized into differential rotation with multiple jets. A scaling law is determined based on the convective Rossby number and the density contrast across the equatorial plane, providing a simple way to determine in which regime a given body lies. While a giant planet such as Jupiter lies firmly in the differential flow regime as expected, the Earth's outer core is also found to lie in the differential flow regime indicating that, even in the Earth's outer core, where the density contrast is small, vorticity contributions via fluid movement through the density stratification may be non-negligible.

Simulating rotating fluid bodies: When is vorticity generation via density-stratification important?

NASA Astrophysics Data System (ADS)

Evonuk, M.; Samuel, H.

2012-12-01

Differential rotation is one of the key components needed to maintain a magnetic dynamo, therefore it is important to understand the processes that generate differential rotation in rotating bodies. In a rotating density-stratified fluid, local vorticity generation occurs as fluid parcels move radially, expanding or contracting with respect to the background density stratification. The convergence of this vorticity forms zonal flow structures as a function of the radius and the slope of the background density profile. While this effect is thought to be of importance in bodies that are quickly rotating and highly turbulent with large density stratifications such as Jupiter, it is generally neglected in bodies such as the Earth's outer core, where the density change is small. Simulations of thermal convection in the 2D rotating equatorial plane are conducted to determine the parameter regime where local vorticity generation plays a significant role in organizing the fluid flow. Three regimes are found: a dipolar flow regime, where the flow is not organized by the rotation, a transitional flow regime, and a differential flow regime, where the flow is strongly organized into differential rotation with multiple jets. A scaling law is determined based on the convective Rossby number and the density contrast across the equatorial plane, providing a simple way to determine in which regime a given body lies. While a giant planet such as Jupiter lies firmly in the differential flow regime as expected, the Earth's outer core is also found to lie in the differential flow regime indicating that, even in the Earth's outer core, where the density contrast is small, vorticity contributions via fluid movement through the density stratification may be non-negligible.

Simulating rotating fluid bodies: When is vorticity generation via density-stratification important?

NASA Astrophysics Data System (ADS)

Evonuk, M.; Samuel, H.

2012-02-01

Differential rotation is one of the key components needed to maintain a magnetic dynamo, therefore it is important to understand the processes that generate differential rotation in rotating bodies. In a rotating density-stratified fluid, local vorticity generation occurs as fluid parcels move radially, expanding or contracting with respect to the background density stratification. The convergence of this vorticity forms zonal flow structures as a function of the radius and the slope of the background density profile. While this effect is thought to be of importance in bodies that are quickly rotating and highly turbulent with large density stratifications such as Jupiter, it is generally neglected in bodies such as the Earth's outer core, where the density change is small. Simulations of thermal convection in the 2D rotating equatorial plane are conducted to determine the parameter regime where local vorticity generation plays a significant role in organizing the fluid flow. Three regimes are found: a dipolar flow regime, where the flow is not organized by the rotation, a transitional flow regime, and a differential flow regime, where the flow is strongly organized into differential rotation with multiple jets. A scaling law is determined based on the convective Rossby number and the density contrast across the equatorial plane, providing a simple way to determine in which regime a given body lies. While a giant planet such as Jupiter lies firmly in the differential flow regime as expected, the Earth's outer core is also found to lie in the differential flow regime indicating that, even in the Earth's outer core, where the density contrast is small, vorticity contributions via fluid movement through the density stratificationmay be non-negligible.

Feedback control of an interacting Bose-Einstein condensate using phase-contrast imaging

NASA Astrophysics Data System (ADS)

Szigeti, S. S.; Hush, M. R.; Carvalho, A. R. R.; Hope, J. J.

2010-10-01

The linewidth of an atom laser is limited by density fluctuations in the Bose-Einstein condensate (BEC) from which the atom laser beam is outcoupled. In this paper we show that a stable spatial mode for an interacting BEC can be generated using a realistic control scheme that includes the effects of the measurement backaction. This model extends the feedback theory, based on a phase-contrast imaging setup, presented by Szigeti, Hush, Carvalho, and Hope [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.80.013614 80, 013614 (2009)]. In particular, it is applicable to a BEC with large interatomic interactions and solves the problem of inadequacy of the mean-field (coherent state) approximation by utilizing a fixed number state approximation. Our numerical analysis shows the control to be more effective for a condensate with a large nonlinearity.

Feedback control of an interacting Bose-Einstein condensate using phase-contrast imaging

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

Szigeti, S. S.; Hush, M. R.; Carvalho, A. R. R.

2010-10-15

The linewidth of an atom laser is limited by density fluctuations in the Bose-Einstein condensate (BEC) from which the atom laser beam is outcoupled. In this paper we show that a stable spatial mode for an interacting BEC can be generated using a realistic control scheme that includes the effects of the measurement backaction. This model extends the feedback theory, based on a phase-contrast imaging setup, presented by Szigeti, Hush, Carvalho, and Hope [Phys. Rev. A 80, 013614 (2009)]. In particular, it is applicable to a BEC with large interatomic interactions and solves the problem of inadequacy of the mean-fieldmore » (coherent state) approximation by utilizing a fixed number state approximation. Our numerical analysis shows the control to be more effective for a condensate with a large nonlinearity.« less

Influences on Bythotrephes longimanus life-history characteristics in the Great Lakes

USGS Publications Warehouse

Pothoven, Steven A.; Vanderploeg, Henry A.; Warner, David M.; Schaeffer, Jeffrey S.; Ludsin, Stuart A.; Claramunt, Randall M.; Nalepa, Thomas F.

2012-01-01

We compared Bythotrephes population demographics and dynamics to predator (planktivorous fish) and prey (small-bodied crustacean zooplankton) densities at a site sampled through the growing season in Lakes Michigan, Huron, and Erie. Although seasonal average densities of Bythotrephes were similar across lakes (222/m2 Erie, 247/m2 Huron, 162/m2 Michigan), temporal trends in abundance differed among lakes. In central Lake Erie where Bythotrephes' prey assemblage was dominated by small individuals (60%), where planktivorous fish densities were high (14,317/ha), and where a shallow water column limited availability of a deepwater refuge, the Bythotrephes population was characterized by a small mean body size, large broods with small neonates, allocation of length increases mainly to the spine rather than to the body, and a late summer population decline. By contrast, in Lake Michigan where Bythotrephes' prey assemblage was dominated by large individuals (72%) and planktivorous fish densities were lower (5052/ha), the Bythotrephes population was characterized by a large mean body size (i.e., 37–55% higher than in Erie), small broods with large neonates, nearly all growth in body length occurring between instars 1 and 2, and population persistence into fall. Life-history characteristics in Lake Huron tended to be intermediate to those found in Lakes Michigan and Erie, reflecting lower overall prey and predator densities (1224/ha) relative to the other lakes. Because plasticity in life history can affect interactions with other species, our findings point to the need to understand life-history variation among Great Lakes populations to improve our ability to model the dynamics of these ecosystems.

Effect of Microstructural Parameters on the Relative Densities of Metal Foams

NASA Technical Reports Server (NTRS)

Raj, S. V.; Kerr, Jacob A.

2010-01-01

A detailed quantitative microstructural analyses of primarily open cell FeCrAlY and 314 stainless steel metal foams with different relative densities and pores per inch (p.p.i.) were undertaken in the present investigation to determine the effect of microstructural parameters on the relative densities of metal foams. Several elements of the microstructure, such as longitudinal and transverse cell sizes, cell areas and perimeters, ligament dimensions, cell shapes and volume fractions of closed and open cells, were measured. The cross-sections of the foam ligaments showed a large number of shrinkage cavities, and their circularity factors and average sizes were determined. The volume fractions of closed cells increased linearly with increasing relative density. In contrast, the volume fractions of the open cells and ligaments decreased with increasing relative density. The relative densities and p.p.i. were not significantly dependent on cell size, cell perimeter and ligament dimensions within the limits of experimental scatter. A phenomenological model is proposed to rationalize the present microstructural observations.

Indirect interactions among tropical tree species through shared rodent seed predators: a novel mechanism of tree species coexistence.

PubMed

Garzon-Lopez, Carol X; Ballesteros-Mejia, Liliana; Ordoñez, Alejandro; Bohlman, Stephanie A; Olff, Han; Jansen, Patrick A

2015-08-01

The coexistence of numerous tree species in tropical forests is commonly explained by negative dependence of recruitment on the conspecific seed and tree density due to specialist natural enemies that attack seeds and seedlings ('Janzen-Connell' effects). Less known is whether guilds of shared seed predators can induce a negative dependence of recruitment on the density of different species of the same plant functional group. We studied 54 plots in tropical forest on Barro Colorado Island, Panama, with contrasting mature tree densities of three coexisting large seeded tree species with shared seed predators. Levels of seed predation were far better explained by incorporating seed densities of all three focal species than by conspecific seed density alone. Both positive and negative density dependencies were observed for different species combinations. Thus, indirect interactions via shared seed predators can either promote or reduce the coexistence of different plant functional groups in tropical forest. © 2015 John Wiley & Sons Ltd/CNRS.

Number and density discrimination rely on a common metric: Similar psychophysical effects of size, contrast, and divided attention.

PubMed

Tibber, Marc S; Greenwood, John A; Dakin, Steven C

2012-06-04

While observers are adept at judging the density of elements (e.g., in a random-dot image), it has recently been proposed that they also have an independent visual sense of number. To test the independence of number and density discrimination, we examined the effects of manipulating stimulus structure (patch size, element size, contrast, and contrast-polarity) and available attentional resources on both judgments. Five observers made a series of two-alternative, forced-choice discriminations based on the relative numerosity/density of two simultaneously presented patches containing 16-1,024 Gaussian blobs. Mismatches of patch size and element size (across reference and test) led to bias and reduced sensitivity in both tasks, whereas manipulations of contrast and contrast-polarity had varied effects on observers, implying differing strategies. Nonetheless, the effects reported were consistent across density and number judgments, the only exception being when luminance cues were made available. Finally, density and number judgment were similarly impaired by attentional load in a dual-task experiment. These results are consistent with a common underlying metric to density and number judgments, with the caveat that additional cues may be exploited when they are available.

Comparison of amyloid plaque contrast generated by T2-, T2*-, and susceptibility-weighted imaging methods in transgenic mouse models of Alzheimer’s disease

PubMed Central

Chamberlain, Ryan; Reyes, Denise; Curran, Geoffrey L.; Marjanska, Malgorzata; Wengenack, Thomas M.; Poduslo, Joseph F.; Garwood, Michael; Jack, Clifford R.

2009-01-01

One of the hallmark pathologies of Alzheimer’s disease (AD) is amyloid plaque deposition. Plaques appear hypointense on T2- and T2*-weighted MR images probably due to the presence of endogenous iron, but no quantitative comparison of various imaging techniques has been reported. We estimated the T1, T2, T2*, and proton density values of cortical plaques and normal cortical tissue and analyzed the plaque contrast generated by a collection of T2-, T2*-, and susceptibility-weighted imaging (SWI) methods in ex vivo transgenic mouse specimens. The proton density and T1 values were similar for both cortical plaques and normal cortical tissue. The T2 and T2* values were similar in cortical plaques, which indicates that the iron content of cortical plaques may not be as large as previously thought. Ex vivo plaque contrast was increased compared to a previously reported spin echo sequence by summing multiple echoes and by performing SWI; however, gradient echo and susceptibility weighted imaging was found to be impractical for in vivo imaging due to susceptibility interface-related signal loss in the cortex. PMID:19253386

Uncertainty estimation of Intensity-Duration-Frequency relationships: A regional analysis

NASA Astrophysics Data System (ADS)

Mélèse, Victor; Blanchet, Juliette; Molinié, Gilles

2018-03-01

We propose in this article a regional study of uncertainties in IDF curves derived from point-rainfall maxima. We develop two generalized extreme value models based on the simple scaling assumption, first in the frequentist framework and second in the Bayesian framework. Within the frequentist framework, uncertainties are obtained i) from the Gaussian density stemming from the asymptotic normality theorem of the maximum likelihood and ii) with a bootstrap procedure. Within the Bayesian framework, uncertainties are obtained from the posterior densities. We confront these two frameworks on the same database covering a large region of 100, 000 km2 in southern France with contrasted rainfall regime, in order to be able to draw conclusion that are not specific to the data. The two frameworks are applied to 405 hourly stations with data back to the 1980's, accumulated in the range 3 h-120 h. We show that i) the Bayesian framework is more robust than the frequentist one to the starting point of the estimation procedure, ii) the posterior and the bootstrap densities are able to better adjust uncertainty estimation to the data than the Gaussian density, and iii) the bootstrap density give unreasonable confidence intervals, in particular for return levels associated to large return period. Therefore our recommendation goes towards the use of the Bayesian framework to compute uncertainty.

Novel analysis technique for measuring edge density fluctuation profiles with reflectometry in the Large Helical Device.

PubMed

Creely, A J; Ida, K; Yoshinuma, M; Tokuzawa, T; Tsujimura, T; Akiyama, T; Sakamoto, R; Emoto, M; Tanaka, K; Michael, C A

2017-07-01

A new method for measuring density fluctuation profiles near the edge of plasmas in the Large Helical Device (LHD) has been developed utilizing reflectometry combined with pellet-induced fast density scans. Reflectometer cutoff location was calculated by proportionally scaling the cutoff location calculated with fast far infrared laser interferometer (FIR) density profiles to match the slower time resolution results of the ray-tracing code LHD-GAUSS. Plasma velocity profile peaks generated with this reflectometer mapping were checked against velocity measurements made with charge exchange spectroscopy (CXS) and were found to agree within experimental uncertainty once diagnostic differences were accounted for. Measured density fluctuation profiles were found to peak strongly near the edge of the plasma, as is the case in most tokamaks. These measurements can be used in the future to inform inversion methods of phase contrast imaging (PCI) measurements. This result was confirmed with both a fixed frequency reflectometer and calibrated data from a multi-frequency comb reflectometer, and this method was applied successfully to a series of discharges. The full width at half maximum of the turbulence layer near the edge of the plasma was found to be only 1.5-3 cm on a series of LHD discharges, less than 5% of the normalized minor radius.

Novel analysis technique for measuring edge density fluctuation profiles with reflectometry in the Large Helical Device

NASA Astrophysics Data System (ADS)

Creely, A. J.; Ida, K.; Yoshinuma, M.; Tokuzawa, T.; Tsujimura, T.; Akiyama, T.; Sakamoto, R.; Emoto, M.; Tanaka, K.; Michael, C. A.

2017-07-01

A new method for measuring density fluctuation profiles near the edge of plasmas in the Large Helical Device (LHD) has been developed utilizing reflectometry combined with pellet-induced fast density scans. Reflectometer cutoff location was calculated by proportionally scaling the cutoff location calculated with fast far infrared laser interferometer (FIR) density profiles to match the slower time resolution results of the ray-tracing code LHD-GAUSS. Plasma velocity profile peaks generated with this reflectometer mapping were checked against velocity measurements made with charge exchange spectroscopy (CXS) and were found to agree within experimental uncertainty once diagnostic differences were accounted for. Measured density fluctuation profiles were found to peak strongly near the edge of the plasma, as is the case in most tokamaks. These measurements can be used in the future to inform inversion methods of phase contrast imaging (PCI) measurements. This result was confirmed with both a fixed frequency reflectometer and calibrated data from a multi-frequency comb reflectometer, and this method was applied successfully to a series of discharges. The full width at half maximum of the turbulence layer near the edge of the plasma was found to be only 1.5-3 cm on a series of LHD discharges, less than 5% of the normalized minor radius.

Temperature Dependence of Electric Transport in Few-layer Graphene under Large Charge Doping Induced by Electrochemical Gating

PubMed Central

Gonnelli, R. S.; Paolucci, F.; Piatti, E.; Sharda, Kanudha; Sola, A.; Tortello, M.; Nair, Jijeesh R.; Gerbaldi, C.; Bruna, M.; Borini, S.

2015-01-01

The temperature dependence of electric transport properties of single-layer and few-layer graphene at large charge doping is of great interest both for the study of the scattering processes dominating the conductivity at different temperatures and in view of the theoretically predicted possibility to reach the superconducting state in such extreme conditions. Here we present the results obtained in 3-, 4- and 5-layer graphene devices down to 3.5 K, where a large surface charge density up to about 6.8·1014 cm−2 has been reached by employing a novel polymer electrolyte solution for the electrochemical gating. In contrast with recent results obtained in single-layer graphene, the temperature dependence of the sheet resistance between 20 K and 280 K shows a low-temperature dominance of a T2 component – that can be associated with electron-electron scattering – and, at about 100 K, a crossover to the classic electron-phonon regime. Unexpectedly, this crossover does not show any dependence on the induced charge density, i.e. on the large tuning of the Fermi energy. PMID:25906088

Redshifts of groups and clusters in the rich superclusters 1451+22 and 1615+43

NASA Technical Reports Server (NTRS)

Ciardullo, R.; Ford, H.; Bartko, F.; Harms, R.

1983-01-01

Redshift measurements and finding charts are presented for galaxy clusters in the field of two rich, distant superclusters. Both systems are shown to have morphological and dynamical properties similar to the nearby superclusters, including small internal velocity dispersions and high density contrasts in redshift space. This data is consistent with two interpretations: either both superclusters are highly flattened systems with major axes close to the plane of the sky, or the observed velocity dispersions do not arise from unperturbed Hubble flow. If the latter explanation is correct, these radial velocity data are a powerful probe of the large scale matter density in the universe.

Analysis of defect structure in silicon. Characterization of SEMIX material. Silicon sheet growth development for the large area silicon sheet task of the low-cost solar array project

NASA Technical Reports Server (NTRS)

Natesh, R.; Stringfellow, G. B.; Virkar, A. V.; Dunn, J.; Guyer, T.

1983-01-01

Statistically significant quantitative structural imperfection measurements were made on samples from ubiquitous crystalline process (UCP) Ingot 5848 - 13C. Important correlation was obtained between defect densities, cell efficiency, and diffusion length. Grain boundary substructure displayed a strong influence on the conversion efficiency of solar cells from Semix material. Quantitative microscopy measurements gave statistically significant information compared to other microanalytical techniques. A surface preparation technique to obtain proper contrast of structural defects suitable for quantimet quantitative image analyzer (QTM) analysis was perfected and is used routinely. The relationships between hole mobility and grain boundary density was determined. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density.

Ice nucleation in the upper troposphere: Sensitivity to aerosol number density, temperature, and cooling rate

NASA Technical Reports Server (NTRS)

Jensen, E. J.; Toon, O. B.

1994-01-01

We have investigated the processes that control ice crystal nucleation in the upper troposphere using a numerical model. Nucleation of ice resulting from cooling was simulated for a range of aerosol number densities, initial temperatures, and cooling rates. In contrast to observations of stratus clouds, we find that the number of ice crystals that nucleate in cirrus is relatively insensitive to the number of aerosols present. The ice crystal size distribution at the end of the nucleation process is unaffected by the assumed initial aerosol number density. Essentially, nucleation continues until enough ice crystals are present such that their deposition growth rapidly depletes the vapor and shuts off any further nucleation. However, the number of ice crystals nucleated increases rapidly with decreasing initial temperature and increasing cooling rate. This temperature dependence alone could explain the large ice crystal number density observed in very cold tropical cirrus.

Characterizing Bonding Patterns in Diradicals and Triradicals by Density-Based Wave Function Analysis: A Uniform Approach.

PubMed

Orms, Natalie; Rehn, Dirk R; Dreuw, Andreas; Krylov, Anna I

2018-02-13

Density-based wave function analysis enables unambiguous comparisons of the electronic structure computed by different methods and removes ambiguity of orbital choices. We use this tool to investigate the performance of different spin-flip methods for several prototypical diradicals and triradicals. In contrast to previous calibration studies that focused on energy gaps between high- and low spin-states, we focus on the properties of the underlying wave functions, such as the number of effectively unpaired electrons. Comparison of different density functional and wave function theory results provides insight into the performance of the different methods when applied to strongly correlated systems such as polyradicals. We show that canonical molecular orbitals for species like large copper-containing diradicals fail to correctly represent the underlying electronic structure due to highly non-Koopmans character, while density-based analysis of the same wave function delivers a clear picture of the bonding pattern.

Synchrotron radiation x-ray topography and defect selective etching analysis of threading dislocations in GaN

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

Sintonen, Sakari, E-mail: sakari.sintonen@aalto.fi; Suihkonen, Sami; Jussila, Henri

2014-08-28

The crystal quality of bulk GaN crystals is continuously improving due to advances in GaN growth techniques. Defect characterization of the GaN substrates by conventional methods is impeded by the very low dislocation density and a large scale defect analysis method is needed. White beam synchrotron radiation x-ray topography (SR-XRT) is a rapid and non-destructive technique for dislocation analysis on a large scale. In this study, the defect structure of an ammonothermal c-plane GaN substrate was recorded using SR-XRT and the image contrast caused by the dislocation induced microstrain was simulated. The simulations and experimental observations agree excellently and themore » SR-XRT image contrasts of mixed and screw dislocations were determined. Apart from a few exceptions, defect selective etching measurements were shown to correspond one to one with the SR-XRT results.« less

The role of the large scale convection electric field in erosion of the plasmasphere during moderate and strong storms

NASA Astrophysics Data System (ADS)

Thaller, S. A.; Wygant, J. R.; Cattell, C. A.; Breneman, A. W.; Bonnell, J. W.; Kletzing, C.; De Pascuale, S.; Kurth, W. S.; Hospodarsky, G. B.; Bounds, S. R.

2015-12-01

The Van Allen Probes offer the first opportunity to investigate the response of the plasmasphere to the enhancement and penetration of the large scale duskward convection electric field in different magnetic local time (MLT) sectors. Using electric field measurements and estimates of the cold plasma density from the Van Allen Probes' Electric Fields and Waves (EFW) instrument, we study erosion of the plasmasphere during moderate and strong geomagnetic storms. We present the electric field and density data both on an orbit by orbit basis and synoptically, showing the behavior of the convection electric field and plasmasphere over a period of months. The data indicate that the large scale duskward electric field penetrates deep (L shell < 3) into the inner magnetosphere on both the dusk and dawn sides, but that the plasmasphere response on the dusk and dawn sides differ. In particular, significant (~2 orders of magnitude) decreases in the cold plasma density occur on the dawn side within hours of the onset of enhanced duskward electric field. In contrast, on the dusk side, the plasmapause is located at higher L shell than it is on the dawn side. In some cases, in the post-noon sector, cold plasma density enhancements accompany duskward electric field enhancements for the first orbit after the electric field enchantment, consistent with a duskside, sunward flowing, drainage plume.

Ecologies of ideologies: Explaining party entry and exit in West-European parliaments, 1945-2013.

PubMed

van de Wardt, Marc; Berkhout, Joost; Vermeulen, Floris

2017-06-01

This study introduces a population-ecological approach to the entry and exit of political parties. A primary proposition of population ecology is that organizational entry and exit depends on the number of organizations already present: that is, density. We propose that political parties mainly experience competition from parties in the same ideological niche (left, centre, right). Pooled time-series analyses of 410 parties, 263 elections and 18 West-European countries largely support our expectations. We find that political parties are more likely to exit when density within their niche increases. Also there is competition between adjacent ideological niches, i.e. between centrist and right-wing niches. In contrast to our expectations, neither density nor institutional rules impact party entry. This raises important questions about the rationale of prospective entrants.

Testing the gravitational instability hypothesis?

NASA Technical Reports Server (NTRS)

Babul, Arif; Weinberg, David H.; Dekel, Avishai; Ostriker, Jeremiah P.

1994-01-01

We challenge a widely accepted assumption of observational cosmology: that successful reconstruction of observed galaxy density fields from measured galaxy velocity fields (or vice versa), using the methods of gravitational instability theory, implies that the observed large-scale structures and large-scale flows were produced by the action of gravity. This assumption is false, in that there exist nongravitational theories that pass the reconstruction tests and gravitational theories with certain forms of biased galaxy formation that fail them. Gravitational instability theory predicts specific correlations between large-scale velocity and mass density fields, but the same correlations arise in any model where (a) structures in the galaxy distribution grow from homogeneous initial conditions in a way that satisfies the continuity equation, and (b) the present-day velocity field is irrotational and proportional to the time-averaged velocity field. We demonstrate these assertions using analytical arguments and N-body simulations. If large-scale structure is formed by gravitational instability, then the ratio of the galaxy density contrast to the divergence of the velocity field yields an estimate of the density parameter Omega (or, more generally, an estimate of beta identically equal to Omega(exp 0.6)/b, where b is an assumed constant of proportionality between galaxy and mass density fluctuations. In nongravitational scenarios, the values of Omega or beta estimated in this way may fail to represent the true cosmological values. However, even if nongravitational forces initiate and shape the growth of structure, gravitationally induced accelerations can dominate the velocity field at late times, long after the action of any nongravitational impulses. The estimated beta approaches the true value in such cases, and in our numerical simulations the estimated beta values are reasonably accurate for both gravitational and nongravitational models. Reconstruction tests that show correlations between galaxy density and velocity fields can rule out some physically interesting models of large-scale structure. In particular, successful reconstructions constrain the nature of any bias between the galaxy and mass distributions, since processes that modulate the efficiency of galaxy formation on large scales in a way that violates the continuity equation also produce a mismatch between the observed galaxy density and the density inferred from the peculiar velocity field. We obtain successful reconstructions for a gravitational model with peaks biasing, but we also show examples of gravitational and nongravitational models that fail reconstruction tests because of more complicated modulations of galaxy formation.

Increased x-ray conversion efficiency from ultra high contrast, relativistic laser pulse irradiation of large aspect ratio, vertically aligned nanowires

NASA Astrophysics Data System (ADS)

Hollinger, R. C.; Bargsten, C.; Shlyaptsev, V. N.; Kaymak, V.; Pukhov, A.; Capeluto, M. G.; Wang, Y.; Wang, S.; Rockwood, A.; Curtis, A.; Rocca, J. J.

2016-10-01

Recent experiments at Colorado State University have shown that the effective trapping of clean, Joule-level fs laser pulses of relativistic intensity in arrays of high aspect ratio aligned nanowire creates multi-kev, near solid density, large scale (>4um deep) plasmas. The drastically decreased radiative life time and increased hydrodynamic cooling time from these plasmas increases the x-ray conversion efficiency. We measured a record conversion efficiency of 10% into hv>1KeV photons (2pi steradians), and of 0.3% for hv>6KeV. The experiments used Au and Ni nanowires of 55nm, 80nm and 100nm in diameter with 12% of solid density irradiated by high contrast (>1012) pulses of 60fs FWHM duration from a frequency doubled Ti:Sa laser at intensities of I =5x1019Wcm-2. We also present preliminary results on x-ray emission from Rhodium nanowires in the 19-22KeV range and demonstrate the potential of this picosecond X-ray source in flash radiography. This work was supported by the Fusion Energy Program, Office of Science of the U.S Department of Energy, and by the Defense Threat Reduction Agency Grant HDTRA-1-10-1-0079.

Combined synchrotron X-ray tomography and X-ray powder diffraction using a fluorescing metal foil.

PubMed

Kappen, P; Arhatari, B D; Luu, M B; Balaur, E; Caradoc-Davies, T

2013-06-01

This study realizes the concept of simultaneous micro-X-ray computed tomography and X-ray powder diffraction using a synchrotron beamline. A thin zinc metal foil was placed in the primary, monochromatic synchrotron beam to generate a divergent wave to propagate through the samples of interest onto a CCD detector for tomographic imaging, thus removing the need for large beam illumination and high spatial resolution detection. Both low density materials (kapton tubing and a piece of plant) and higher density materials (Egyptian faience) were investigated, and elemental contrast was explored for the example of Cu and Ni meshes. The viability of parallel powder diffraction using the direct beam transmitted through the foil was demonstrated. The outcomes of this study enable further development of the technique towards in situ tomography∕diffraction studies combining micrometer and crystallographic length scales, and towards elemental contrast imaging and reconstruction methods using well defined fluorescence outputs from combinations of known fluorescence targets (elements).

Multiverse understanding of cosmological coincidences

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

Bousso, Raphael; Hall, Lawrence J.; Nomura, Yasunori

2009-09-15

There is a deep cosmological mystery: although dependent on very different underlying physics, the time scales of structure formation, of galaxy cooling (both radiatively and against the CMB), and of vacuum domination do not differ by many orders of magnitude, but are all comparable to the present age of the universe. By scanning four landscape parameters simultaneously, we show that this quadruple coincidence is resolved. We assume only that the statistical distribution of parameter values in the multiverse grows towards certain catastrophic boundaries we identify, across which there are drastic regime changes. We find order-of-magnitude predictions for the cosmological constant,more » the primordial density contrast, the temperature at matter-radiation equality, the typical galaxy mass, and the age of the universe, in terms of the fine structure constant and the electron, proton and Planck masses. Our approach permits a systematic evaluation of measure proposals; with the causal patch measure, we find no runaway of the primordial density contrast and the cosmological constant to large values.« less

Study of diffusion and local structure of sodium-silicate liquid: the molecular dynamic simulation

NASA Astrophysics Data System (ADS)

Hung, Pham Khac; Noritake, Fumiya; San, Luyen Thi; Van, To Ba; Vinh, Le The

2017-10-01

A systematic analysis on sodium-silicate melt with various silica contents was carried out. The simulation revealed two diffusion mechanisms occurred in the melt: the bond-breaking and hopping between sites. The local structure was analyzed through T-simplexes. It was revealed that T-clusters have a non-spherical shape and represent the diffusion channel, in which Na atoms are dominant, but no any O atoms are located. The SiO2-poor melt acquires a long channel. In contrast, the SiO2-rich melt consists of unconnected short channels. The simulation also revealed the immobile and mobile regions which differ in local structure and constituent composition. We propose a new CL-function to characterizing the spatial distribution of different atom component. The spatial distribution of mobile and immobile atoms is found quite different. In particular, the immobile atoms are concentrated in high-density regions possessing very large density of immobile atoms. The spatial distribution of mobile atoms in contrast is more homogeneous.

High-contrast germanium-doped silica-on-silicon waveguides

NASA Astrophysics Data System (ADS)

Dumais, Patrick; Callender, Claire; Blanchetière, Chantal; Ledderhof, Chris

2012-10-01

Silica-on-silicon planar lightwave circuits have a number of advantages including stability and low insertion loss to optical fiber networks. Standard GeO2 doping levels in the waveguide cores lead to a refractive index contrast, n/n, of 0.75%-2%. This range of index contrast requires relatively large bend radii in order to minimize bend losses. This limits the density scaling of these circuits. By using high dopant levels for a Δn/n of 4%, the bend radius can be decreased to less than 1 mm, from which significant gains in optical circuit density can be obtained. In addition, low-loss ring resonators with free spectral ranges of a few tens of gigahertz can be realized, enabling some additional optical signal processing and filtering on that scale. Optical devices with such high dopant levels have been reported by Bellman et al. in 2004 [1] but to the authors' knowledge, no other experimental work on high-delta GeO2-doped waveguides has been reported since. In this paper, we present experimental measurements on high-delta devices including directional couplers, MMI couplers, Mach-Zehnder interferometers, and ring resonators. Device performance, including propagation loss, bend loss, interferometer contrast ratio and birefringence will be presented. We demonstrate that ring resonators with 40 GHz free spectral range can be fabricated for optical signal processing.

Developmental Environment Effects on Sexual Selection in Male and Female Drosophila melanogaster

PubMed Central

Morimoto, Juliano; Pizzari, Tommaso; Wigby, Stuart

2016-01-01

The developmental environment can potentially alter the adult social environment and influence traits targeted by sexual selection such as body size. In this study, we manipulated larval density in male and female Drosophila melanogaster, which results in distinct adult size phenotypes–high (low) densities for small (large) adults–and measured sexual selection in experimental groups consisting of adult males and females from high, low, or a mixture of low and high larval densities. Overall, large adult females (those reared at low larval density) had more matings, more mates and produced more offspring than small females (those reared at high larval density). The number of offspring produced by females was positively associated with their number of mates (i.e. there was a positive female Bateman gradient) in social groups where female size was experimentally varied, likely due to the covariance between female productivity and mating rate. For males, we found evidence that the larval environment affected the relative importance of sexual selection via mate number (Bateman gradients), mate productivity, paternity share, and their covariances. Mate number and mate productivity were significantly reduced for small males in social environments where males were of mixed sizes, versus social environments where all males were small, suggesting that social heterogeneity altered selection on this subset of males. Males are commonly assumed to benefit from mating with large females, but in contrast to expectations we found that in groups where both the male and female size varied, males did not gain more offspring per mating with large females. Collectively, our results indicate sex-specific effects of the developmental environment on the operation of sexual selection, via both the phenotype of individuals, and the phenotype of their competitors and mates. PMID:27167120

Hydrological disturbance diminishes predator control in wetlands.

PubMed

Dorn, Nathan J; Cook, Mark I

2015-11-01

Effects of predators on prey populations can be especially strong in aquatic ecosystems, but disturbances may mediate the strength of predator limitation and even allow outbreaks of some prey populations. In a two-year study we investigated the numerical responses of crayfish (Procambarus fallax) and small fishes (Poeciliidae and Fundulidae) to a brief hydrological disturbance in replicated freshwater wetlands with an experimental drying and large predatory fish reduction. The experiment and an in situ predation assay tested the component of the consumer stress model positing that disturbances release prey from predator limitation. In the disturbed wetlands, abundances of large predatory fish were seasonally reduced, similar to dynamics in the Everglades (southern Florida). Densities of small fish were unaffected by the disturbance, but crayfish densities, which were similar across all wetlands before drying, increased almost threefold in the year after the disturbance. Upon re-flooding, juvenile crayfish survival was inversely related to the abundance of large fish across wetlands, but we found no evidence for enhanced algal food quality. At a larger landscape scale (500 km2 of the Everglades), crayfish densities over eight years were positively correlated with the severity of local dry disturbances (up to 99 days dry) during the preceding dry season. In contrast, densities of small-bodied fishes in the same wetlands were seasonally depressed by dry disturbances. The results from our experimental wetland drought and the observations of crayfish densities in the Everglades represent a large-scale example of prey population release following a hydrological disturbance in a freshwater ecosystem. The conditions producing crayfish pulses in the Everglades appear consistent with the mechanics of the consumer stress model, and we suggest crayfish pulses may influence the number of nesting wading birds in the Everglades.

Cheetahs and wild dogs show contrasting patterns of suppression by lions.

PubMed

Swanson, Alexandra; Caro, Tim; Davies-Mostert, Harriet; Mills, Michael G L; Macdonald, David W; Borner, Markus; Masenga, Emmanuel; Packer, Craig

2014-11-01

Top predators can dramatically suppress populations of smaller predators, with cascading effects throughout communities, and this pressure is often unquestioningly accepted as a constraint on mesopredator populations. In this study, we reassess whether African lions suppress populations of cheetahs and African wild dogs and examine possible mechanisms for coexistence between these species. Using long-term records from Serengeti National Park, we tested 30 years of population data for evidence of mesopredator suppression, and we examined six years of concurrent radio-telemetry data for evidence of large-scale spatial displacement. The Serengeti lion population nearly tripled between 1966 and 1998; during this time, wild dogs declined but cheetah numbers remained largely unchanged. Prior to their local extinction, wild dogs primarily occupied low lion density areas and apparently abandoned the long-term study area as the lion population 'saturated' the region. In contrast, cheetahs mostly utilized areas of high lion density, and the stability of the cheetah population indicates that neither high levels of lion-inflicted mortality nor behavioural avoidance inflict sufficient demographic consequences to translate into population-level effects. Population data from fenced reserves in southern Africa revealed a similar contrast between wild dogs and cheetahs in their ability to coexist with lions. These findings demonstrate differential responses of subordinate species within the same guild and challenge a widespread perception that lions undermine cheetah conservation efforts. Paired with several recent studies that document fine-scale lion-avoidance by cheetahs, this study further highlights fine-scale spatial avoidance as a possible mechanism for mitigating mesopredator suppression. © 2014 The Authors. Journal of Animal Ecology © 2014 British Ecological Society.

Density-associated recruitment mediates coral population dynamics on a coral reef

NASA Astrophysics Data System (ADS)

Bramanti, Lorenzo; Edmunds, Peter J.

2016-06-01

Theory suggests that density-associated processes can modulate community resilience following declines in population size. Here, we demonstrate density-associated processes in two scleractinian populations on the outer reef of Moorea, French Polynesia, that are rapidly increasing in size following the effects of two catastrophic disturbances. Between 2006 and 2010, predation by the corallivorous crown-of-thorns sea star reduced coral cover by 93 %; in 2010, the dead coral skeletons were removed by a cyclone, and in 2011 and 2012, high coral recruitment initiated population recovery. Coral recruitment was associated with coral cover, but the relationship differed between two coral genera that are almost exclusively broadcast spawners in Moorea. Acroporids recruited at low densities, and the density of recruits was positively associated with cover of Acropora, whereas pocilloporids recruited at high densities, and densities of their recruits were negatively associated with cover of Pocillopora. Together, our results suggest that associations between adult cover and density of both juveniles and recruits can mediate rapid coral community recovery after large disturbances. The difference between taxa in sign of the relationships between recruit density and coral cover indicate that they reflect contrasting mechanisms with the potential to mediate temporal shifts in taxonomic composition of coral communities.

Evaluation of Density Corrections to Methane Fluxes Measured by Open-Path Eddy Covariance over Contrasting Landscapes

NASA Astrophysics Data System (ADS)

Chamberlain, Samuel D.; Verfaillie, Joseph; Eichelmann, Elke; Hemes, Kyle S.; Baldocchi, Dennis D.

2017-11-01

Corrections accounting for air density fluctuations due to heat and water vapour fluxes must be applied to the measurement of eddy-covariance fluxes when using open-path sensors. Experimental tests and ecosystem observations have demonstrated the important role density corrections play in accurately quantifying carbon dioxide (CO2) fluxes, but less attention has been paid to evaluating these corrections for methane (CH4) fluxes. We measured CH4 fluxes with open-path sensors over a suite of sites with contrasting CH4 emissions and energy partitioning, including a pavement airfield, two negligible-flux ecosystems (drained alfalfa and pasture), and two high-flux ecosystems (flooded wetland and rice). We found that density corrections successfully re-zeroed fluxes in negligible-flux sites; however, slight overcorrection was observed above pavement. The primary impact of density corrections varied over negligible- and high-flux ecosystems. For negligible-flux sites, corrections led to greater than 100% adjustment in daily budgets, while these adjustments were only 3-10% in high-flux ecosystems. The primary impact to high-flux ecosystems was a change in flux diel patterns, which may affect the evaluation of relationships between biophysical drivers and fluxes if correction bias exists. Additionally, accounting for density effects to high-frequency CH4 fluctuations led to large differences in observed CH4 flux cospectra above negligible-flux sites, demonstrating that similar adjustments should be made before interpreting CH4 cospectra for comparable ecosystems. These results give us confidence in CH4 fluxes measured by open-path sensors, and demonstrate that density corrections play an important role in adjusting flux budgets and diel patterns across a range of ecosystems.

Facilitating atmosphere oxidation through mantle convection

NASA Astrophysics Data System (ADS)

Lee, K. K. M.; Gu, T.; Creasy, N.; Li, M.; McCammon, C. A.; Girard, J.

2017-12-01

Earth's mantle connects the surface with the deep interior through convection, and the evolution of its redox state will affect the distribution of siderophile elements, recycling of refractory isotopes, and the oxidation state of the atmosphere through volcanic outgassing. While the rise of oxygen in the atmosphere, i.e., the Great Oxidation Event (GOE) occurred 2.4 billion years ago (Ga), multiple lines of evidence point to oxygen production in the atmosphere well before 2.4 Ga. In contrast to the fluctuations of atmospheric oxygen, vanadium in Archean mantle lithosphere suggests that the mantle redox state has been constant for 3.5 Ga. Indeed, the connection between the redox state of the deep Earth and the atmosphere is enigmatic as is the effect of redox state on mantle dynamics. Here we show a redox-induced density contrast affects mantle convection and may potentially cause the oxidation of the upper mantle. We compressed two synthetic enstatite chondritic samples with identical bulk compositions but formed under different oxygen fugacities (fO2) to lower mantle pressures and temperatures and find Al2O3 forms its own phase separate from the dominant bridgmanite phase in the more reduced composition, in contrast to a more Al-rich, bridgmanite-dominated assemblage for a more oxidized starting composition. As a result, the reduced material is 1-1.5% denser than the oxidized material. Subsequent experiments on other plausible mantle compositions, which differ only in redox state of the starting glass materials, show similar results: distinct mineral assemblages and density contrasts up to 4%. Our geodynamic simulations suggest that such a density contrast causes a rapid ascent and accumulation of oxidized material in the upper mantle, with descent of the denser reduced material to the core-mantle boundary. The resulting heterogeneous redox conditions in Earth's interior may have contributed to the large low-shear velocity provinces in the lower mantle and the rise of oxygen in Earth's atmosphere.

Change-in-ratio density estimator for feral pigs is less biased than closed mark-recapture estimates

USGS Publications Warehouse

Hanson, L.B.; Grand, J.B.; Mitchell, M.S.; Jolley, D.B.; Sparklin, B.D.; Ditchkoff, S.S.

2008-01-01

Closed-population capture-mark-recapture (CMR) methods can produce biased density estimates for species with low or heterogeneous detection probabilities. In an attempt to address such biases, we developed a density-estimation method based on the change in ratio (CIR) of survival between two populations where survival, calculated using an open-population CMR model, is known to differ. We used our method to estimate density for a feral pig (Sus scrofa) population on Fort Benning, Georgia, USA. To assess its validity, we compared it to an estimate of the minimum density of pigs known to be alive and two estimates based on closed-population CMR models. Comparison of the density estimates revealed that the CIR estimator produced a density estimate with low precision that was reasonable with respect to minimum known density. By contrast, density point estimates using the closed-population CMR models were less than the minimum known density, consistent with biases created by low and heterogeneous capture probabilities for species like feral pigs that may occur in low density or are difficult to capture. Our CIR density estimator may be useful for tracking broad-scale, long-term changes in species, such as large cats, for which closed CMR models are unlikely to work. ?? CSIRO 2008.

Experimental evidence for short-pulse laser heating of solid-density target to high bulk temperatures.

PubMed

Soloviev, A; Burdonov, K; Chen, S N; Eremeev, A; Korzhimanov, A; Pokrovskiy, G V; Pikuz, T A; Revet, G; Sladkov, A; Ginzburg, V; Khazanov, E; Kuzmin, A; Osmanov, R; Shaikin, I; Shaykin, A; Yakovlev, I; Pikuz, S; Starodubtsev, M; Fuchs, J

2017-09-22

Heating efficiently solid-density, or even compressed, matter has been a long-sought goal in order to allow investigation of the properties of such state of matter of interest for various domains, e.g. astrophysics. High-power lasers, pinches, and more recently Free-Electron-Lasers (FELs) have been used in this respect. Here we show that by using the high-power, high-contrast "PEARL" laser (Institute of Applied Physics-Russian Academy of Science, Nizhny Novgorod, Russia) delivering 7.5 J in a 60 fs laser pulse, such coupling can be efficiently obtained, resulting in heating of a slab of solid-density Al of 0.8 µm thickness at a temperature of 300 eV, and with minimal density gradients. The characterization of the target heating is achieved combining X-ray spectrometry and measurement of the protons accelerated from the Al slab. The measured heating conditions are consistent with a three-temperatures model that simulates resistive and collisional heating of the bulk induced by the hot electrons. Such effective laser energy deposition is achieved owing to the intrinsic high contrast of the laser which results from the Optical Parametric Chirped Pulse Amplification technology it is based on, allowing to attain high target temperatures in a very compact manner, e.g. in comparison with large-scale FEL facilities.

Usefulness of high-density barium for detection of leaks after esophagogastrectomy, total gastrectomy, and total laryngectomy.

PubMed

Swanson, Jonathan O; Levine, Marc S; Redfern, Regina O; Rubesin, Stephen E

2003-08-01

The purpose of this study was to determine the usefulness of a high-density (250% weight/volume) barium compared with a water-soluble contrast agent for the detection of esophageal leaks in patients who had undergone esophagogastrectomy, total gastrectomy, or total laryngectomy. A search of our radiology database from 1998 to 2001 revealed 46 eligible radiographic studies performed using a water-soluble contrast agent alone or a water-soluble contrast agent followed by barium that showed leaks in patients who had undergone esophagogastrectomy, total gastrectomy, or total laryngectomy. The images were reviewed to determine the morphology of the leaks (i.e., blind-ending tracks, sealed-off collections, or free extravasation of contrast material). Medical records were also reviewed to determine whether detection of the leaks seen on the radiographic studies affected patient management. Of the 46 leaks seen on radiographic studies, 23 (50%) were detected with a water-soluble contrast agent and 23 (50%) were detected only with high-density barium. Of the 23 leaks visualized with water-soluble contrast media, six (26%) were characterized by blind-ending tracks, 14 (61%) by sealed-off collections, and three (13%) by free extravasation of contrast material into the mediastinum or neck. Of the 23 leaks visualized only with high-density barium, 19 (83%) were characterized by blind-ending tracks and four (17%) by sealed-off collections. Thus, leaks detected only on images obtained with high-density barium were significantly more likely to be characterized by blind-ending tracks than those detected on images obtained with a water-soluble contrast agent (p = 0.0007). Of the 33 patients with clinical follow-up, the findings seen on these imaging studies affected management in 12 (86%) of 14 patients with leaks depicted by water-soluble contrast media and in 10 (53%) of 19 with leaks depicted only by high-density barium. Our findings support the use of high-density barium as part of the routine postoperative radiographic examination when no leaks are detected on images obtained with a water-soluble contrast agent.

How ions affect the structure of water.

PubMed

Hribar, Barbara; Southall, Noel T; Vlachy, Vojko; Dill, Ken A

2002-10-16

We model ion solvation in water. We use the MB model of water, a simple two-dimensional statistical mechanical model in which waters are represented as Lennard-Jones disks having Gaussian hydrogen-bonding arms. We introduce a charge dipole into MB waters. We perform (NPT) Monte Carlo simulations to explore how water molecules are organized around ions and around nonpolar solutes in salt solutions. The model gives good qualitative agreement with experiments, including Jones-Dole viscosity B coefficients, Samoilov and Hirata ion hydration activation energies, ion solvation thermodynamics, and Setschenow coefficients for Hofmeister series ions, which describe the salt concentration dependence of the solubilities of hydrophobic solutes. The two main ideas captured here are (1) that charge densities govern the interactions of ions with water, and (2) that a balance of forces determines water structure: electrostatics (water's dipole interacting with ions) and hydrogen bonding (water interacting with neighboring waters). Small ions (kosmotropes) have high charge densities so they cause strong electrostatic ordering of nearby waters, breaking hydrogen bonds. In contrast, large ions (chaotropes) have low charge densities, and surrounding water molecules are largely hydrogen bonded.

Understanding spatial connectivity of individuals with non-uniform population density.

PubMed

Wang, Pu; González, Marta C

2009-08-28

We construct a two-dimensional geometric graph connecting individuals placed in space within a given contact distance. The individuals are distributed using a measured country's density of population. We observe that while large clusters (group of individuals connected) emerge within some regions, they are trapped in detached urban areas owing to the low population density of the regions bordering them. To understand the emergence of a giant cluster that connects the entire population, we compare the empirical geometric graph with the one generated by placing the same number of individuals randomly in space. We find that, for small contact distances, the empirical distribution of population dominates the growth of connected components, but no critical percolation transition is observed in contrast to the graph generated by a random distribution of population. Our results show that contact distances from real-world situations as for WIFI and Bluetooth connections drop in a zone where a fully connected cluster is not observed, hinting that human mobility must play a crucial role in contact-based diseases and wireless viruses' large-scale spreading.

On the linearity of tracer bias around voids

NASA Astrophysics Data System (ADS)

Pollina, Giorgia; Hamaus, Nico; Dolag, Klaus; Weller, Jochen; Baldi, Marco; Moscardini, Lauro

2017-07-01

The large-scale structure of the Universe can be observed only via luminous tracers of the dark matter. However, the clustering statistics of tracers are biased and depend on various properties, such as their host-halo mass and assembly history. On very large scales, this tracer bias results in a constant offset in the clustering amplitude, known as linear bias. Towards smaller non-linear scales, this is no longer the case and tracer bias becomes a complicated function of scale and time. We focus on tracer bias centred on cosmic voids, I.e. depressions of the density field that spatially dominate the Universe. We consider three types of tracers: galaxies, galaxy clusters and active galactic nuclei, extracted from the hydrodynamical simulation Magneticum Pathfinder. In contrast to common clustering statistics that focus on auto-correlations of tracers, we find that void-tracer cross-correlations are successfully described by a linear bias relation. The tracer-density profile of voids can thus be related to their matter-density profile by a single number. We show that it coincides with the linear tracer bias extracted from the large-scale auto-correlation function and expectations from theory, if sufficiently large voids are considered. For smaller voids we observe a shift towards higher values. This has important consequences on cosmological parameter inference, as the problem of unknown tracer bias is alleviated up to a constant number. The smallest scales in existing data sets become accessible to simpler models, providing numerous modes of the density field that have been disregarded so far, but may help to further reduce statistical errors in constraining cosmology.

Geophysical study of the San Juan Mountains batholith complex, southwestern Colorado

USGS Publications Warehouse

Drenth, Benjamin J.; Keller, G. Randy; Thompson, Ren A.

2012-01-01

One of the largest and most pronounced gravity lows over North America is over the rugged San Juan Mountains of southwestern Colorado (USA). The mountain range is coincident with the San Juan volcanic field (SJVF), the largest erosional remnant of a widespread mid-Cenozoic volcanic field that spanned much of the southern Rocky Mountains. A buried, low-density silicic batholith complex related to the volcanic field has been the accepted interpretation of the source of the gravity low since the 1970s. However, this interpretation was based on gravity data processed with standard techniques that are problematic in the SJVF region. The combination of high-relief topography, topography with low densities, and the use of a common reduction density of 2670 kg/m3produces spurious large-amplitude gravity lows that may distort the geophysical signature of deeper features such as a batholith complex. We applied an unconventional processing procedure that uses geologically appropriate densities for the uppermost crust and digital topography to mostly remove the effect of the low-density units that underlie the topography associated with the SJVF. This approach resulted in a gravity map that provides an improved representation of deeper sources, including reducing the amplitude of the anomaly attributed to a batholith complex. We also reinterpreted vintage seismic refraction data that indicate the presence of low-velocity zones under the SJVF. Assuming that the source of the gravity low on the improved gravity anomaly map is the same as the source of the low seismic velocities, integrated modeling corroborates the interpretation of a batholith complex and then defines the dimensions and overall density contrast of the complex. Models show that the thickness of the batholith complex varies laterally to a significant degree, with the greatest thickness (∼20 km) under the western SJVF, and lesser thicknesses (<10 km) under the eastern SJVF. The largest group of nested calderas on the surface of the SJVF, the central caldera cluster, is not correlated with the thickest part of the batholith complex. This result is consistent with petrologic interpretations from recent studies that the batholith complex continued to be modified after cessation of volcanism and therefore is not necessarily representative of synvolcanic magma chambers. The total volume of the batholith complex is estimated to be 82,000–130,000 km3. The formation of such a large felsic batholith complex would inevitably involve production of a considerably greater volume of residuum, which could be present in the lower crust or uppermost mantle. The interpreted vertically averaged density contrast (–60 to –110 kg/m3), density (2590–2640 kg/m3), and seismic expression of the batholith complex are consistent with results of geophysical studies of other large batholiths in the western United States.

Interstellar C2, CH, and CN in translucent molecular clouds

NASA Technical Reports Server (NTRS)

Black, John H.; Van Dishoeck, Ewine F.

1989-01-01

Optical absorption-line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A 2Pi-X 2Sigma(+) (1,O) and (2,O) bands of the red system are reported and compared with observations of the violet system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photoprocesses still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models.

Multiple browsers structure tree recruitment in logged temperate forests

USGS Publications Warehouse

Faison, Edward K.; DeStefano, Stephen; Foster, David R.; Rapp, Joshua M.; Compton, Justin A.

2016-01-01

Historical extirpations have resulted in depauperate large herbivore assemblages in many northern forests. In eastern North America, most forests are inhabited by a single wild ungulate species, white-tailed deer (Odocoileus virginianus), and relationships between deer densities and impacts on forest regeneration are correspondingly well documented. Recent recolonizations by moose (Alces americanus) in northeastern regions complicate established deer density thresholds and predictions of browsing impacts on forest dynamics because size and foraging differences between the two animals suggest a lack of functional redundancy. We asked to what extent low densities of deer + moose would structure forest communities differently from that of low densities of deer in recently logged patch cuts of Massachusetts, USA. In each site, a randomized block with three treatment levels of large herbivores–no-ungulates (full exclosure), deer (partial exclosure), and deer + moose (control) was established. After 6–7 years, deer + moose reduced stem densities and basal area by 2-3-fold, Prunus pensylvanica and Quercus spp. recruitment by 3–6 fold, and species richness by 1.7 species (19%). In contrast, in the partial exclosures, deer had non-significant effects on stem density, basal area, and species composition, but significantly reduced species richness by 2.5 species on average (28%). Deer browsing in the partial exclosure was more selective than deer + moose browsing together, perhaps contributing to the decline in species richness in the former treatment and the lack of additional decline in the latter. Moose used the control plots at roughly the same frequency as deer (as determined by remote camera traps), suggesting that the much larger moose was the dominant browser species in terms of animal biomass in these cuts. A lack of functional redundancy with respect to foraging behavior between sympatric large herbivores may explain combined browsing effects that were both large and complex.

Diffraction enhance x-ray imaging for quantitative phase contrast studies

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

Agrawal, A. K.; Singh, B., E-mail: balwants@rrcat.gov.in; Kashyap, Y. S.

2016-05-23

Conventional X-ray imaging based on absorption contrast permits limited visibility of feature having small density and thickness variations. For imaging of weakly absorbing material or materials possessing similar densities, a novel phase contrast imaging techniques called diffraction enhanced imaging has been designed and developed at imaging beamline Indus-2 RRCAT Indore. The technique provides improved visibility of the interfaces and show high contrast in the image forsmall density or thickness gradients in the bulk. This paper presents basic principle, instrumentation and analysis methods for this technique. Initial results of quantitative phase retrieval carried out on various samples have also been presented.

Ecologies of ideologies: Explaining party entry and exit in West-European parliaments, 1945–2013

PubMed Central

Berkhout, Joost; Vermeulen, Floris

2016-01-01

This study introduces a population-ecological approach to the entry and exit of political parties. A primary proposition of population ecology is that organizational entry and exit depends on the number of organizations already present: that is, density. We propose that political parties mainly experience competition from parties in the same ideological niche (left, centre, right). Pooled time-series analyses of 410 parties, 263 elections and 18 West-European countries largely support our expectations. We find that political parties are more likely to exit when density within their niche increases. Also there is competition between adjacent ideological niches, i.e. between centrist and right-wing niches. In contrast to our expectations, neither density nor institutional rules impact party entry. This raises important questions about the rationale of prospective entrants. PMID:29046613

Characteristic density contrasts in the evolution of superclusters. The case of A2142 supercluster

NASA Astrophysics Data System (ADS)

Gramann, Mirt; Einasto, Maret; Heinämäki, Pekka; Teerikorpi, Pekka; Saar, Enn; Nurmi, Pasi; Einasto, Jaan

2015-09-01

Context. The formation and evolution of the cosmic web in which galaxy superclusters are the largest relatively isolated objects is governed by a gravitational attraction of dark matter and antigravity of dark energy (cosmological constant). Aims: We study the characteristic density contrasts in the spherical collapse model for several epochs in the supercluster evolution and their dynamical state. Methods: We analysed the density contrasts for the turnaround, future collapse, and zero gravity in different ΛCDM models and applied them to study the dynamical state of the supercluster A2142 with an almost spherical main body, making it a suitable test object to apply a model that assumes sphericity. Results: We present characteristic density contrasts in the spherical collapse model for different cosmological parameters. The analysis of the supercluster A2142 shows that its high-density core has already started to collapse. The zero-gravity line outlines the outer region of the main body of the supercluster. In the course of future evolution, the supercluster may split into several collapsing systems. Conclusions: The various density contrasts presented in our study and applied to the supercluster A2142 offer a promising way to characterise the dynamical state and expected future evolution of galaxy superclusters.

Compact or spread? A quantitative spatial model of urban areas in Europe since 1990

PubMed Central

Haase, Dagmar; Haase, Annegret

2018-01-01

Changes in urban residential density represent an important issue in terms of land consumption, the conservation of ecosystems, air quality and related human health problems, as well as the consequential challenges for urban and regional planning. It is the decline of residential densities, in particular, that has often been used as the very definition of sprawl, describing a phenomenon that has been extensively studied in the United States and in Western Europe. Whilst these studies provide valuable insights into urbanization processes, only a handful of them have reflected the uneven dynamics of simultaneous urban growth and shrinkage, using residential density changes as a key indicator to uncover the underlying dynamics. This paper introduces a contrasting analysis of recent developments in both de- and re-concentration, defined as decreasing or increasing residential densities, respectively. Using a large sample of European cities, it detects differences in density changes between successional population growth/decline. The paper shows that dedensification, found in some large cities globally, is not a universal phenomenon in growing urban areas; neither the increasing disproportion between a declining demand for and an increasing supply of residential areas nor actual concentration processes in cities were found. Thus, the paper provides a new, very detailed perspective on (de)densification in both shrinking and growing cities and how they specifically contribute to current land take in Europe. PMID:29489851

Compact or spread? A quantitative spatial model of urban areas in Europe since 1990.

PubMed

Wolff, Manuel; Haase, Dagmar; Haase, Annegret

2018-01-01

Changes in urban residential density represent an important issue in terms of land consumption, the conservation of ecosystems, air quality and related human health problems, as well as the consequential challenges for urban and regional planning. It is the decline of residential densities, in particular, that has often been used as the very definition of sprawl, describing a phenomenon that has been extensively studied in the United States and in Western Europe. Whilst these studies provide valuable insights into urbanization processes, only a handful of them have reflected the uneven dynamics of simultaneous urban growth and shrinkage, using residential density changes as a key indicator to uncover the underlying dynamics. This paper introduces a contrasting analysis of recent developments in both de- and re-concentration, defined as decreasing or increasing residential densities, respectively. Using a large sample of European cities, it detects differences in density changes between successional population growth/decline. The paper shows that dedensification, found in some large cities globally, is not a universal phenomenon in growing urban areas; neither the increasing disproportion between a declining demand for and an increasing supply of residential areas nor actual concentration processes in cities were found. Thus, the paper provides a new, very detailed perspective on (de)densification in both shrinking and growing cities and how they specifically contribute to current land take in Europe.

Buoyancy-driven melt segregation in the earth's moon. I - Numerical results

NASA Technical Reports Server (NTRS)

Delano, J. W.

1990-01-01

The densities of lunar mare magmas have been estimated at liquidus temperatures for pressures from 0 to 47 kbar (0.4 GPa; center of the moon) using a third-order Birch-Murnaghan equation and compositionally dependent parameters from Large and Carmichael (1987). Results on primary magmatic compositions represented by pristine volcanic glasses suggest that the density contrast between very-high-Ti melts and their liquidus olivines may approach zero at pressures of about 25 kbar (2.5 GPa). Since this is the pressure regime of the mantle source regions for these magmas, a compositional limit of eruptability for mare liquids may exist that is similar to the highest Ti melt yet observed among the lunar samples. Although the moon may have generated magmas having greater than 16.4 wt pct TiO2, those melts would probably not have reached the lunar surface due to their high densities, and may have even sunk deeper into the moon's interior as negatively buoyant diapirs. This process may have been important for assimilative interactions in the lunar mantle. The phenomenon of melt/solid density crossover may therefore occur not only in large terrestrial-type objects but also in small objects where, despite low pressures, the range of melt compositions is extreme.

Extra-metabolic energy use and the rise in human hyper-density

NASA Astrophysics Data System (ADS)

Burger, Joseph R.; Weinberger, Vanessa P.; Marquet, Pablo A.

2017-03-01

Humans, like all organisms, are subject to fundamental biophysical laws. Van Valen predicted that, because of zero-sum dynamics, all populations of all species in a given environment flux the same amount of energy on average. Damuth’s ’energetic equivalence rule’ supported Van Valen´s conjecture by showing a tradeoff between few big animals per area with high individual metabolic rates compared to abundant small species with low energy requirements. We use metabolic scaling theory to compare variation in densities and individual energy use in human societies to other land mammals. We show that hunter-gatherers occurred at densities lower than the average for a mammal of our size. Most modern humans, in contrast, concentrate in large cities at densities up to four orders of magnitude greater than hunter-gatherers, yet consume up to two orders of magnitude more energy per capita. Today, cities across the globe flux greater energy than net primary productivity on a per area basis. This is possible by importing enormous amounts of energy and materials required to sustain hyper-dense, modern humans. The metabolic rift with nature created by modern cities fueled largely by fossil energy poses formidable challenges for establishing a sustainable relationship on a rapidly urbanizing, yet finite planet.

Extra-metabolic energy use and the rise in human hyper-density.

PubMed

Burger, Joseph R; Weinberger, Vanessa P; Marquet, Pablo A

2017-03-02

Humans, like all organisms, are subject to fundamental biophysical laws. Van Valen predicted that, because of zero-sum dynamics, all populations of all species in a given environment flux the same amount of energy on average. Damuth's 'energetic equivalence rule' supported Van Valen´s conjecture by showing a tradeoff between few big animals per area with high individual metabolic rates compared to abundant small species with low energy requirements. We use metabolic scaling theory to compare variation in densities and individual energy use in human societies to other land mammals. We show that hunter-gatherers occurred at densities lower than the average for a mammal of our size. Most modern humans, in contrast, concentrate in large cities at densities up to four orders of magnitude greater than hunter-gatherers, yet consume up to two orders of magnitude more energy per capita. Today, cities across the globe flux greater energy than net primary productivity on a per area basis. This is possible by importing enormous amounts of energy and materials required to sustain hyper-dense, modern humans. The metabolic rift with nature created by modern cities fueled largely by fossil energy poses formidable challenges for establishing a sustainable relationship on a rapidly urbanizing, yet finite planet.

Geologic and geophysical investigations of the Zuni-Bandera volcanic field, New Mexico

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

Ander, M.E.; Heiken, G.; Eichelberger, J.

1981-05-01

A positive, northeast-trending gravity anomaly, 90 km long and 30 km wide, extends southwest from the Zuni uplift, New Mexico. The Zuni-Bandera volcanic field, an alignment of 74 basaltic vents, is parallel to the eastern edge of the anomaly. Lavas display a bimodal distribution of tholeiitic and alkalic compositions, and were erupted over a period from 4 Myr to present. A residual gravity profile taken perpendicular to the major axis of the anomaly was analyzed using linear programming and ideal body theory to obtain bounds on the density contrast, depth, and minimum thickness of the gravity body. Two-dimensionality was assumed.more » The limiting case where the anomalous body reaches the surface gives 0.1 g/cm/sup 3/ as the greatest lower bound on the maximum density contrast. If 0.4 g/cm/sup 3/ is taken as the geologically reasonable upper limit on the maximum density contrast, the least upper bound on the depth of burial is 3.5 km and minimum thickness is 2 km. A shallow mafic intrusion, emplaced sometime before Laramide deformation, is proposed to account for the positive gravity anomaly. Analysis of a magnetotelluric survey suggests that the intrusion is not due to recent basaltic magma associated with the Zuni-Bandera volcanic field. This large basement structure has controlled the development of the volcanic field; vent orientations have changed somewhat through time, but the trend of the volcanic chain followed the edge of the basement structure. It has also exhibited some control on deformation of the sedimentary section.« less

A comparison of shock-cloud and wind-cloud interactions: effect of increased cloud density contrast on cloud evolution

NASA Astrophysics Data System (ADS)

Goldsmith, K. J. A.; Pittard, J. M.

2018-05-01

The similarities, or otherwise, of a shock or wind interacting with a cloud of density contrast χ = 10 were explored in a previous paper. Here, we investigate such interactions with clouds of higher density contrast. We compare the adiabatic hydrodynamic interaction of a Mach 10 shock with a spherical cloud of χ = 103 with that of a cloud embedded in a wind with identical parameters to the post-shock flow. We find that initially there are only minor morphological differences between the shock-cloud and wind-cloud interactions, compared to when χ = 10. However, once the transmitted shock exits the cloud, the development of a turbulent wake and fragmentation of the cloud differs between the two simulations. On increasing the wind Mach number, we note the development of a thin, smooth tail of cloud material, which is then disrupted by the fragmentation of the cloud core and subsequent `mass-loading' of the flow. We find that the normalized cloud mixing time (tmix) is shorter at higher χ. However, a strong Mach number dependence on tmix and the normalized cloud drag time, t_{drag}^' }, is not observed. Mach-number-dependent values of tmix and t_{drag}^' } from comparable shock-cloud interactions converge towards the Mach-number-independent time-scales of the wind-cloud simulations. We find that high χ clouds can be accelerated up to 80-90 per cent of the wind velocity and travel large distances before being significantly mixed. However, complete mixing is not achieved in our simulations and at late times the flow remains perturbed.

Observations of highly sheared turbulence in the H-mode pedestal using Phase Contrast Imaging on DIII-D

NASA Astrophysics Data System (ADS)

Rost, J. C.; Marinoni, A.; Davis, E. M.; Porkolab, M.; Burrell, K. H.

2017-10-01

Highly sheared turbulence with short radial correlation lengths has been measured near the top of the H-mode pedestal, in addition to the previously measured highly-sheared turbulence measured in the Er well. Turbulence in regions of large velocity shear is characterized by radial correlation lengths shorter than the poloidal wavelength (L < λ 2 cm) and large Doppler-shifted frequencies (f > 200 kHz). The phase contrast imaging (PCI) diagnostic on DIII-D is ideally suited to measuring this density turbulence due to the measurement geometry and high frequency bandwidth. Radial localization is achieved by optical filtering, varying the ExB profile, and shifting the plasma position. Reconfiguration of the Er well, such as at the L-H transition or the transition to wide pedestal QH-mode, shows a near-instantaneous change (t < 1 ms) to the sheared turbulence in the Er well ( 1 cm inside the separatrix). In contrast, the sheared turbulence near the top of the pedestal ( 2 cm inside the separatrix) varies over times scales of tens of ms, consistent with pedestal evolution. Work supported by the US Department of Energy under DE-FG02-94ER54235 and DE-FC02-04ER54698.

Origin of the cosmic network in ΛCDM: Nature vs nurture

NASA Astrophysics Data System (ADS)

Shandarin, Sergei; Habib, Salman; Heitmann, Katrin

2010-05-01

The large-scale structure of the Universe, as traced by the distribution of galaxies, is now being revealed by large-volume cosmological surveys. The structure is characterized by galaxies distributed along filaments, the filaments connecting in turn to form a percolating network. Our objective here is to quantitatively specify the underlying mechanisms that drive the formation of the cosmic network: By combining percolation-based analyses with N-body simulations of gravitational structure formation, we elucidate how the network has its origin in the properties of the initial density field (nature) and how its contrast is then amplified by the nonlinear mapping induced by the gravitational instability (nurture).

Quantitative electron density characterization of soft tissue substitute plastic materials using grating-based x-ray phase-contrast imaging

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

Sarapata, A.; Chabior, M.; Zanette, I.

2014-10-15

Many scientific research areas rely on accurate electron density characterization of various materials. For instance in X-ray optics and radiation therapy, there is a need for a fast and reliable technique to quantitatively characterize samples for electron density. We present how a precise measurement of electron density can be performed using an X-ray phase-contrast grating interferometer in a radiographic mode of a homogenous sample in a controlled geometry. A batch of various plastic materials was characterized quantitatively and compared with calculated results. We found that the measured electron densities closely match theoretical values. The technique yields comparable results between amore » monochromatic and a polychromatic X-ray source. Measured electron densities can be further used to design dedicated X-ray phase contrast phantoms and the additional information on small angle scattering should be taken into account in order to exclude unsuitable materials.« less

Characterizing bonding patterns in diradicals and triradicals by density-based wave function analysis: A uniform approach

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

Orms, Natalie; Rehn, Dirk; Dreuw, Andreas

Density-based wave function analysis enables unambiguous comparisons of electronic structure computed by different methods and removes ambiguity of orbital choices. Here, we use this tool to investigate the performance of different spin-flip methods for several prototypical diradicals and triradicals. In contrast to previous calibration studies that focused on energy gaps between high and low spin-states, we focus on the properties of the underlying wave functions, such as the number of effectively unpaired electrons. Comparison of different density functional and wave function theory results provides insight into the performance of the different methods when applied to strongly correlated systems such asmore » polyradicals. We also show that canonical molecular orbitals for species like large copper-containing diradicals fail to correctly represent the underlying electronic structure due to highly non-Koopmans character, while density-based analysis of the same wave function delivers a clear picture of bonding pattern.« less

Characterizing bonding patterns in diradicals and triradicals by density-based wave function analysis: A uniform approach

DOE PAGES

Orms, Natalie; Rehn, Dirk; Dreuw, Andreas; ...

2017-12-21

Density-based wave function analysis enables unambiguous comparisons of electronic structure computed by different methods and removes ambiguity of orbital choices. Here, we use this tool to investigate the performance of different spin-flip methods for several prototypical diradicals and triradicals. In contrast to previous calibration studies that focused on energy gaps between high and low spin-states, we focus on the properties of the underlying wave functions, such as the number of effectively unpaired electrons. Comparison of different density functional and wave function theory results provides insight into the performance of the different methods when applied to strongly correlated systems such asmore » polyradicals. We also show that canonical molecular orbitals for species like large copper-containing diradicals fail to correctly represent the underlying electronic structure due to highly non-Koopmans character, while density-based analysis of the same wave function delivers a clear picture of bonding pattern.« less

Porosity and test ultrastructure of costate and non-costate Bulimina species

NASA Astrophysics Data System (ADS)

Grunert, Patrick; Piller, Werner E.

2017-04-01

SEM-based investigations of porosity and test wall ultrastructure of Recent costate and non-costate Bulimina species reveal significant differences in pore diameter, pore density and ultrastructural architecture between these two groups. Costate tests of B. inflata and B. mexicana display low pore density, a large pore diameter, and test walls built by a single type of columnar ultrastructural elements. In contrast, non-costate tests of B. aculeata and B. marginata are characterized by significantly higher pore density, smaller pore diameter, and an additional type of ultrastructural elements formed by oblique, tabular crystallite units which encase the pore channels. We interpret the observed combination of traits in B. aculeata and B. marginata as a set of adaptations to poorly oxygenated, intermediate to deep infaunal microhabitats which they typically occupy today. The evolutionary trend towards increased pore density in this group seemingly involved a major modification of the biomineralisation process resulting in the lining of pore channels with a specific type of ultrastructural element to ensure stability of the densely perforated test.

Are lemmings prey or predators?

NASA Astrophysics Data System (ADS)

Turchin, P.; Oksanen, L.; Ekerholm, P.; Oksanen, T.; Henttonen, H.

2000-06-01

Large oscillations in the populations of Norwegian lemmings have mystified both professional ecologists and lay public. Ecologists suspect that these oscillations are driven by a trophic mechanism: either an interaction between lemmings and their food supply, or an interaction between lemmings and their predators. If lemming cycles are indeed driven by a trophic interaction, can we tell whether lemmings act as the resource (`prey') or the consumer (`predator')? In trophic interaction models, peaks of resource density generally have a blunt, rounded shape, whereas peaks of consumer density are sharp and angular. Here we have applied several statistical tests to three lemming datasets and contrasted them with comparable data for cyclic voles. We find that vole peaks are blunt, consistent with their cycles being driven by the interaction with predators. In contrast, the shape of lemming peaks is consistent with the hypothesis that lemmings are functional predators, that is, their cycles are driven by their interaction with food plants. Our findings suggest that a single mechanism, such as interaction between rodents and predators, is unlikely to provide the `universal' explanation of all cyclic rodent dynamics.

Strong wave/mean-flow coupling in baroclinic acoustic streaming

NASA Astrophysics Data System (ADS)

Chini, Greg; Michel, Guillaume

2017-11-01

Recently, Chini et al. demonstrated the potential for large-amplitude acoustic streaming in compressible channel flows subjected to strong background cross-channel density variations. In contrast with classic Rayleigh streaming, standing acoustic waves of O (ɛ) amplitude acquire vorticity owing to baroclinic torques acting throughout the domain rather than via viscous torques acting in Stokes boundary layers. More significantly, these baroclinically-driven streaming flows have a magnitude that also is O (ɛ) , i.e. comparable to that of the sound waves. In the present study, the consequent potential for fully two-way coupling between the waves and streaming flows is investigated using a novel WKBJ analysis. The analysis confirms that the wave-driven streaming flows are sufficiently strong to modify the background density gradient, thereby modifying the leading-order acoustic wave structure. Simulations of the wave/mean-flow system enabled by the WKBJ analysis are performed to illustrate the nature of the two-way coupling, which contrasts sharply with classic Rayleigh streaming, for which the waves can first be determined and the streaming flows subsequently computed.

Kurtosis, skewness, and non-Gaussian cosmological density perturbations

NASA Technical Reports Server (NTRS)

Luo, Xiaochun; Schramm, David N.

1993-01-01

Cosmological topological defects as well as some nonstandard inflation models can give rise to non-Gaussian density perturbations. Skewness and kurtosis are the third and fourth moments that measure the deviation of a distribution from a Gaussian. Measurement of these moments for the cosmological density field and for the microwave background temperature anisotropy can provide a test of the Gaussian nature of the primordial fluctuation spectrum. In the case of the density field, the importance of measuring the kurtosis is stressed since it will be preserved through the weakly nonlinear gravitational evolution epoch. Current constraints on skewness and kurtosis of primeval perturbations are obtained from the observed density contrast on small scales and from recent COBE observations of temperature anisotropies on large scales. It is also shown how, in principle, future microwave anisotropy experiments might be able to reveal the initial skewness and kurtosis. It is shown that present data argue that if the initial spectrum is adiabatic, then it is probably Gaussian, but non-Gaussian isocurvature fluctuations are still allowed, and these are what topological defects provide.

Spin dynamics of possible density wave states in the pseudogap phase of high-temperature superconductors

NASA Astrophysics Data System (ADS)

Hsu, Chen-Hsuan; Wang, Zhiqiang; Chakravarty, Sudip

2012-12-01

In a recent inelastic neutron scattering experiment in the pseudogap state of the high-temperature superconductor YBa2Cu3O6.6, an unusual “vertical” dispersion of the spin excitations with a large in-plane anisotropy was observed. In this paper, we discuss in detail the spin susceptibility of the singlet d-density wave, the triplet d-density wave as well as the more common spin density wave orders with hopping anisotropies. From numerical calculations within the framework of random phase approximation, we find nearly vertical dispersion relations for spin excitations with anisotropic incommensurability at low energy ω≤90meV, which are reminiscent of the experiments. At very high energy ω≥165meV, we also find energy-dependent incommensurability. Although there are some important differences between the three cases, unpolarized neutron measurements cannot discriminate between these alternate possibilities; the vertical dispersion, however, is a distinct feature of all three density wave states in contrast to the superconducting state, which shows an hour-glass shape dispersion.

Predicting Large-scale Effects During Cookoff of Plastic-Bonded Explosives (PBX 9501 PBX 9502 and LX-14)

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

Hobbs, Michael L.; Kaneshige, Michael J.; Erikson, William W.

In this study, we have made reasonable cookoff predictions of large-scale explosive systems by using pressure-dependent kinetics determined from small-scale experiments. Scale-up is determined by properly accounting for pressure generated from gaseous decomposition products and the volume that these reactive gases occupy, e.g. trapped within the explosive, the system, or vented. The pressure effect on the decomposition rates has been determined for different explosives by using both vented and sealed experiments at low densities. Low-density explosives are usually permeable to decomposition gases and can be used in both vented and sealed configurations to determine pressure-dependent reaction rates. In contrast, explosivesmore » that are near the theoretical maximum density (TMD) are not as permeable to decomposition gases, and pressure-dependent kinetics are difficult to determine. Ignition in explosives at high densities can be predicted by using pressure-dependent rates determined from the low-density experiments as long as gas volume changes associated with bulk thermal expansion are also considered. In the current work, cookoff of the plastic-bonded explosives PBX 9501 and PBX 9502 is reviewed and new experimental work on LX-14 is presented. Reactive gases are formed inside these heated explosives causing large internal pressures. The pressure is released differently for each of these explosives. For PBX 9501, permeability is increased and internal pressure is relieved as the nitroplasticizer melts and decomposes. Internal pressure in PBX 9502 is relieved as the material is damaged by cracks and spalling. For LX-14, internal pressure is not relieved until the explosive thermally ignites. The current paper is an extension of work presented at the 26th ICDERS symposium [1].« less

Optimization of Norbornadiene Compounds for Solar Thermal Storage by First-Principles Calculations.

PubMed

Kuisma, Mikael; Lundin, Angelica; Moth-Poulsen, Kasper; Hyldgaard, Per; Erhart, Paul

2016-07-21

Molecular photoswitches capable of storing solar energy are interesting candidates for future renewable energy applications. Here, using quantum mechanical calculations, we carry out a systematic screening of crucial optical (solar spectrum match) and thermal (storage energy density) properties of 64 such compounds based on the norbornadiene-quadricyclane system. Whereas a substantial number of these molecules reach the theoretical maximum solar power conversion efficiency, this requires a strong red-shift of the absorption spectrum, which causes undesirable absorption by the photoisomer as well as reduced thermal stability. These compounds typically also have a large molecular mass, leading to low storage densities. By contrast, single-substituted systems achieve a good compromise between efficiency and storage density, while avoiding competing absorption by the photo-isomer. This establishes guiding principles for the future development of molecular solar thermal storage systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

How the 410-km Discontinuity Reflects Mantle Water Content: Constraints from High-Pressure Experiments on Wadsleyite Single-Crystal Elasticity

NASA Astrophysics Data System (ADS)

Buchen, J.; Marquardt, H.; Boffa Ballaran, T.; Kawazoe, T.; Speziale, S.; Kurnosov, A.

2017-12-01

The olivine-wadsleyite phase transition gives rise to a seismic discontinuity at 410 km depth. By incorporating hydroxyl groups in its crystal structure, wadsleyite can store large amounts of water in the shallow transition zone. The velocity contrast across the 410-km seismic discontinuity has been widely used to deduce mantle mineralogy including estimates of the water content at depth. To interpret seismic observations in terms of mantle mineralogy and deep water cycling, the elastic properties of wadsleyite need to be determined at relevant pressures and temperatures. We performed simultaneous sound wave velocity and density measurements on iron-bearing wadsleyite single crystals at high pressures and first experiments at combined high pressures and high temperatures. When compared with previous work on hydrous iron-bearing wadsleyite with identical Fe/(Mg+Fe) ratio of 0.11, our results show that hydration of iron-bearing wadsleyite reduces the sound wave velocities at low pressures. At high pressures, in contrast, P-wave and S-wave velocities of hydrous and anhydrous iron-bearing wadsleyite cross over and become seismically indistinguishable at conditions of the transition zone. As a consequence, hydrated regions in the shallow transition zone cannot be detected by seismic tomography. Motivated by our experimental results, we modeled velocity, density, and acoustic impedance contrasts across the 410-km seismic discontinuity and found velocity contrasts to vary only slightly with hydration. Instead, we show that the impedance contrast caused by the olivine-wadsleyite phase transition and hence the reflectivity of the 410-km seismic discontinuity are more sensitive to hydration. Our findings give important constraints on the interpretation of seismic observations aiming to trace Earth's deep water cycle.

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

Abolhasani, Ali Akbar; School of Physics, Institute for Research in Fundamental Sciences; Mirbabayi, Mehrdad

A perturbative description of Large Scale Structure is a cornerstone of our understanding of the observed distribution of matter in the universe. Renormalization is an essential and defining step to make this description physical and predictive. Here we introduce a systematic renormalization procedure, which neatly associates counterterms to the UV-sensitive diagrams order by order, as it is commonly done in quantum field theory. As a concrete example, we renormalize the one-loop power spectrum and bispectrum of both density and velocity. In addition, we present a series of results that are valid to all orders in perturbation theory. First, we showmore » that while systematic renormalization requires temporally non-local counterterms, in practice one can use an equivalent basis made of local operators. We give an explicit prescription to generate all counterterms allowed by the symmetries. Second, we present a formal proof of the well-known general argument that the contribution of short distance perturbations to large scale density contrast δ and momentum density π(k) scale as k{sup 2} and k, respectively. Third, we demonstrate that the common practice of introducing counterterms only in the Euler equation when one is interested in correlators of δ is indeed valid to all orders.« less

Superradiance in a Large and Dilute Cloud of Cold Atoms in the Linear-Optics Regime.

PubMed

Araújo, Michelle O; Krešić, Ivor; Kaiser, Robin; Guerin, William

2016-08-12

Superradiance has been extensively studied in the 1970s and 1980s in the regime of superfluorescence, where a large number of atoms are initially excited. Cooperative scattering in the linear-optics regime, or "single-photon superradiance," has been investigated much more recently, and superradiant decay has also been predicted, even for a spherical sample of large extent and low density, where the distance between atoms is much larger than the wavelength. Here, we demonstrate this effect experimentally by directly measuring the decay rate of the off-axis fluorescence of a large and dilute cloud of cold rubidium atoms after the sudden switch off of a low-intensity laser driving the atomic transition. We show that, at large detuning, the decay rate increases with the on-resonance optical depth. In contrast to forward scattering, the superradiant decay of off-axis fluorescence is suppressed near resonance due to attenuation and multiple-scattering effects.

Cosmological perturbations during the Bose-Einstein condensation of dark matter

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

Freitas, R.C.; Gonçalves, S.V.B., E-mail: rodolfo.camargo@pq.cnpq.br, E-mail: sergio.vitorino@pq.cnpq.br

In the present work, we analyze the evolution of the scalar and tensorial perturbations and the quantities relevant for the physical description of the Universe, as the density contrast of the scalar perturbations and the gravitational waves energy density during the Bose-Einstein condensation of dark matter. The behavior of these parameters during the Bose-Einstein phase transition of dark matter is analyzed in details. To study the cosmological dynamics and evolution of scalar and tensorial perturbations in a Universe with and without cosmological constant we use both analytical and numerical methods. The Bose-Einstein phase transition modifies the evolution of gravitational wavesmore » of cosmological origin, as well as the process of large-scale structure formation.« less

Diffuse interface modeling of three-phase contact line dynamics on curved boundaries: A lattice Boltzmann model for large density and viscosity ratios

NASA Astrophysics Data System (ADS)

Fakhari, Abbas; Bolster, Diogo

2017-04-01

We introduce a simple and efficient lattice Boltzmann method for immiscible multiphase flows, capable of handling large density and viscosity contrasts. The model is based on a diffuse-interface phase-field approach. Within this context we propose a new algorithm for specifying the three-phase contact angle on curved boundaries within the framework of structured Cartesian grids. The proposed method has superior computational accuracy compared with the common approach of approximating curved boundaries with stair cases. We test the model by applying it to four benchmark problems: (i) wetting and dewetting of a droplet on a flat surface and (ii) on a cylindrical surface, (iii) multiphase flow past a circular cylinder at an intermediate Reynolds number, and (iv) a droplet falling on hydrophilic and superhydrophobic circular cylinders under differing conditions. Where available, our results show good agreement with analytical solutions and/or existing experimental data, highlighting strengths of this new approach.

Turbulence and transport in high density, increased β LAPD plasmas

NASA Astrophysics Data System (ADS)

Rossi, Giovanni; Carter, Troy; Guice, Danny

2014-10-01

A new LaB6 cathode plasma source has recently been deployed on the Large Plasma Device (LAPD), allowing for the production of significantly higher plasma density (ne ~ 3 ×1013 cm-3) and temperature (Te ~ 12 eV and Ti ~ 6 eV). This source produces a smaller core plasma (~20cm diameter) that can be embedded in the lower temperature, lower density standard LAPD plasma (60 cm diameter, 1012 cm-3, Te ~ 5 eV, Ti ~ 1 eV). We will present first results from experiments exploring the nature of turbulence and transport produced by this high density core plasma. In contrast to the edge of the standard LAPD plasma, coherent fluctuations are observed in the edge of the high density core plasma. These coherent modes are dominant at low field (~400 G) with a transition to a more broadband spectrum at higher fields (~1 kG). The combination of increased density and temperature with lowered field in LAPD leads to significant increases in plasma β (in fact β ~ 1 can be achieved for B ~ 100 G). As the field is lowered, the strength of correlated magnetic fluctuations increases substantially.

Referenceless perceptual fog density prediction model

NASA Astrophysics Data System (ADS)

Choi, Lark Kwon; You, Jaehee; Bovik, Alan C.

2014-02-01

We propose a perceptual fog density prediction model based on natural scene statistics (NSS) and "fog aware" statistical features, which can predict the visibility in a foggy scene from a single image without reference to a corresponding fogless image, without side geographical camera information, without training on human-rated judgments, and without dependency on salient objects such as lane markings or traffic signs. The proposed fog density predictor only makes use of measurable deviations from statistical regularities observed in natural foggy and fog-free images. A fog aware collection of statistical features is derived from a corpus of foggy and fog-free images by using a space domain NSS model and observed characteristics of foggy images such as low contrast, faint color, and shifted intensity. The proposed model not only predicts perceptual fog density for the entire image but also provides a local fog density index for each patch. The predicted fog density of the model correlates well with the measured visibility in a foggy scene as measured by judgments taken in a human subjective study on a large foggy image database. As one application, the proposed model accurately evaluates the performance of defog algorithms designed to enhance the visibility of foggy images.

Phase-field-based lattice Boltzmann modeling of large-density-ratio two-phase flows

NASA Astrophysics Data System (ADS)

Liang, Hong; Xu, Jiangrong; Chen, Jiangxing; Wang, Huili; Chai, Zhenhua; Shi, Baochang

2018-03-01

In this paper, we present a simple and accurate lattice Boltzmann (LB) model for immiscible two-phase flows, which is able to deal with large density contrasts. This model utilizes two LB equations, one of which is used to solve the conservative Allen-Cahn equation, and the other is adopted to solve the incompressible Navier-Stokes equations. A forcing distribution function is elaborately designed in the LB equation for the Navier-Stokes equations, which make it much simpler than the existing LB models. In addition, the proposed model can achieve superior numerical accuracy compared with previous Allen-Cahn type of LB models. Several benchmark two-phase problems, including static droplet, layered Poiseuille flow, and spinodal decomposition are simulated to validate the present LB model. It is found that the present model can achieve relatively small spurious velocity in the LB community, and the obtained numerical results also show good agreement with the analytical solutions or some available results. Lastly, we use the present model to investigate the droplet impact on a thin liquid film with a large density ratio of 1000 and the Reynolds number ranging from 20 to 500. The fascinating phenomena of droplet splashing is successfully reproduced by the present model and the numerically predicted spreading radius exhibits to obey the power law reported in the literature.

Boosting the Recoverable Energy Density of Lead-Free Ferroelectric Ceramic Thick Films through Artificially Induced Quasi-Relaxor Behavior.

PubMed

Peddigari, Mahesh; Palneedi, Haribabu; Hwang, Geon-Tae; Lim, Kyung Won; Kim, Ga-Yeon; Jeong, Dae-Yong; Ryu, Jungho

2018-06-20

Dielectric ceramic film capacitors, which store energy in the form of electric polarization, are promising for miniature pulsed power electronic device applications. For a superior energy storage performance of the capacitors, large recoverable energy density, along with high efficiency, high power density, fast charge/discharge rate, and good thermal/fatigue stability, is desired. Herein, we present highly dense lead-free 0.942[Na 0.535 K 0.480 NbO 3 ]-0.058LiNbO 3 (KNNLN) ferroelectric ceramic thick films (∼5 μm) demonstrating remarkable energy storage performance. The nanocrystalline KNNLN thick film fabricated by aerosol deposition (AD) process and annealed at 600 °C displayed a quasi-relaxor ferroelectric behavior, which is in contrast to the typical ferroelectric nature of the KNNLN ceramic in its bulk form. The AD film exhibited a large recoverable energy density of 23.4 J/cm 3 , with an efficiency of over 70% under the electric field of 1400 kV/cm. Besides, an ultrahigh power density of 38.8 MW/cm 3 together with a fast discharge speed of 0.45 μs, good fatigue endurance (up to 10 6 cycles), and thermal stability in a wide temperature range of 20-160 °C was also observed. Using the AD process, we could make a highly dense microstructure of the film containing nano-sized grains, which gave rise to the quasi-relaxor ferroelectric characteristics and the remarkable energy storage properties.

Free-energy-based lattice Boltzmann model for the simulation of multiphase flows with density contrast.

PubMed

Shao, J Y; Shu, C; Huang, H B; Chew, Y T

2014-03-01

A free-energy-based phase-field lattice Boltzmann method is proposed in this work to simulate multiphase flows with density contrast. The present method is to improve the Zheng-Shu-Chew (ZSC) model [Zheng, Shu, and Chew, J. Comput. Phys. 218, 353 (2006)] for correct consideration of density contrast in the momentum equation. The original ZSC model uses the particle distribution function in the lattice Boltzmann equation (LBE) for the mean density and momentum, which cannot properly consider the effect of local density variation in the momentum equation. To correctly consider it, the particle distribution function in the LBE must be for the local density and momentum. However, when the LBE of such distribution function is solved, it will encounter a severe numerical instability. To overcome this difficulty, a transformation, which is similar to the one used in the Lee-Lin (LL) model [Lee and Lin, J. Comput. Phys. 206, 16 (2005)] is introduced in this work to change the particle distribution function for the local density and momentum into that for the mean density and momentum. As a result, the present model still uses the particle distribution function for the mean density and momentum, and in the meantime, considers the effect of local density variation in the LBE as a forcing term. Numerical examples demonstrate that both the present model and the LL model can correctly simulate multiphase flows with density contrast, and the present model has an obvious improvement over the ZSC model in terms of solution accuracy. In terms of computational time, the present model is less efficient than the ZSC model, but is much more efficient than the LL model.

Ecological correlates of group-size variation in a resource-defense ungulate, the sedentary guanaco.

PubMed

Marino, Andrea; Baldi, Ricardo

2014-01-01

For large herbivores, predation-risk, habitat structure and population density are often reported as major determinants of group size variation within and between species. However, whether the underlying causes of these relationships imply an ecological adaptation or are the result of a purely mechanistic process in which fusion and fragmentation events only depend on the rate of group meeting, is still under debate. The aim of this study was to model guanaco family and bachelor group sizes in contrasting ecological settings in order to test hypotheses regarding the adaptive significance of group-size variation. We surveyed guanaco group sizes within three wildlife reserves located in eastern Patagonia where guanacos occupy a mosaic of grasslands and shrublands. Two of these reserves have been free from predators for decades while in the third, pumas often prey on guanacos. All locations have experienced important changes in guanaco abundance throughout the study offering the opportunity to test for density effects. We found that bachelor group size increased with increasing density, as expected by the mechanistic approach, but was independent of habitat structure or predation risk. In contrast, the smaller and territorial family groups were larger in the predator-exposed than in the predator-free locations, and were larger in open grasslands than in shrublands. However, the influence of population density on these social units was very weak. Therefore, family group data supported the adaptive significance of group-size variation but did not support the mechanistic idea. Yet, the magnitude of the effects was small and between-population variation in family group size after controlling for habitat and predation was negligible, suggesting that plasticity of these social units is considerably low. Our results showed that different social units might respond differentially to local ecological conditions, supporting two contrasting hypotheses in a single species, and highlight the importance of taking into account the proximate interests and constraints to which group members may be exposed to when deriving predictions about group-size variation.

Advanced UVOIR Mirror Technology Development for Very Large Space Telescopes

NASA Technical Reports Server (NTRS)

Stahl, H. Philip

2011-01-01

Objective of this work is to define and initiate a long-term program to mature six inter-linked critical technologies for future UVOIR space telescope mirrors to TRL6 by 2018 so that a viable flight mission can be proposed to the 2020 Decadal Review. (1) Large-Aperture, Low Areal Density, High Stiffness Mirrors: 4 to 8 m monolithic & 8 to 16 m segmented primary mirrors require larger, thicker, stiffer substrates. (2) Support System:Large-aperture mirrors require large support systems to ensure that they survive launch and deploy on orbit in a stress-free and undistorted shape. (3) Mid/High Spatial Frequency Figure Error:A very smooth mirror is critical for producing a high-quality point spread function (PSF) for high-contrast imaging. (4) Segment Edges:Edges impact PSF for high-contrast imaging applications, contributes to stray light noise, and affects the total collecting aperture. (5) Segment-to-Segment Gap Phasing:Segment phasing is critical for producing a high-quality temporally stable PSF. (6) Integrated Model Validation:On-orbit performance is determined by mechanical and thermal stability. Future systems require validated performance models. We are pursuing multiple design paths give the science community the option to enable either a future monolithic or segmented space telescope.

Ionic fluids with r-6 pair interactions have power-law electrostatic screening

NASA Astrophysics Data System (ADS)

Kjellander, Roland; Forsberg, Björn

2005-06-01

The decay behaviour of radial distribution functions for large distances r is investigated for classical Coulomb fluids where the ions interact with an r-6 potential (e.g. a dispersion interaction) in addition to the Coulombic and the short-range repulsive potentials (e.g. a hard core). The pair distributions and the density-density (NN), charge-density (QN) and charge-charge (QQ) correlation functions are investigated analytically and by Monte Carlo simulations. It is found that the NN correlation function ultimately decays like r-6 for large r, just as it does for fluids of electroneutral particles interacting with an r-6 potential. The prefactor is proportional to the squared compressibility in both cases. The QN correlations decay in general like r-8 and the QQ correlations like r-10 in the ionic fluid. The average charge density around an ion decays generally like r-8 and the average electrostatic potential like r-6. This behaviour is in stark contrast to the decay behaviour for classical Coulomb fluids in the absence of the r-6 potential, where all these functions decay exponentially for large r. The power-law decays are, however, the same as for quantum Coulomb fluids. This indicates that the inclusion of the dispersion interaction as an effective r-6 interaction potential in classical systems yields the same decay behaviour for the pair correlations as in quantum ionic systems. An exceptional case is the completely symmetric binary electrolyte for which only the NN correlation has a power-law decay but not the QQ correlations. These features are shown by an analysis of the bridge function.

Spatial variation in reproductive effort of a southern Australian seagrass.

PubMed

Smith, Timothy M; York, Paul H; Macreadie, Peter I; Keough, Michael J; Ross, D Jeff; Sherman, Craig D H

2016-09-01

In marine environments characterised by habitat-forming plants, the relative allocation of resources into vegetative growth and flowering is an important indicator of plant condition and hence ecosystem health. In addition, the production and abundance of seeds can give clues to local resilience. Flowering density, seed bank, biomass and epiphyte levels were recorded for the temperate seagrass Zostera nigricaulis in Port Phillip Bay, south east Australia at 14 sites chosen to represent several regions with different physicochemical conditions. Strong regional differences were found within the large bay. Spathe and seed density were very low in the north of the bay (3 sites), low in the centre of the bay (2 sites) intermediate in the Outer Geelong Arm (2 sites), high in Swan Bay (2 sites) and very high in the Inner Geelong Arm (3 sites). In the south (2 sites) seed density was low and spathe density was high. These regional patterns were largely consistent for the 5 sites sampled over the three year period. Timing of flowering was consistent across sites, occurring from August until December with peak production in October, except during the third year of monitoring when overall densities were lower and peaked in November. Seagrass biomass, epiphyte load, canopy height and stem density showed few consistent spatial and temporal patterns. Variation in spathe and seed density and morphology across Port Phillip Bay reflects varying environmental conditions and suggests that northern sites may be restricted in their ability to recover from disturbance through sexual reproduction. In contrast, sites in the west and south of the bay have greater potential to recover from disturbances due to a larger seed bank and these sites could act as source populations for sites where seed production is low. Copyright © 2016 Elsevier Ltd. All rights reserved.

Correlation between clot density and recanalization success or stroke etiology in acute ischemic stroke patients

PubMed Central

Kallmes, David F; Brinjikji, Waleed

2017-01-01

Background Predicting recanalization success for patients undergoing endovascular treatment for acute ischemic stroke is of significant interest. Studies have previously correlated the success of recanalization with the density of the clot. We evaluated clot density and its relationship to revascularization success and stroke etiology. Methods We conducted a retrospective review of 118 patients undergoing intra-arterial therapy for acute ischemic stroke. Mean and maximum thrombus density was measured by drawing a circular region of interest on an axial slice of a non-contrast computed tomography scan. T-tests were used to compare clot density to recanalization success or to stroke etiology, namely large artery atherosclerosis and cardioembolism. Recanalization success was compared in four device groups: aspiration, stent retriever, aspiration and stent retriever, and all other. Results There was no significant difference in the mean clot density in patients with successful (n = 80) versus unsuccessful recanalization (n = 38, 50.1 ± 7.4 Hounsfield unit (HU) vs. 53 ± 12.7 HU; P = 0.17). Comparing the large artery thromboembolism (n = 35) to the cardioembolic etiology group (n = 56), there was no significant difference in mean clot density (51.5 ± 7.7 HU vs. 49.7 ± 8.5 HU; P = 0.31). A subgroup analysis of middle cerebral artery occlusions (n = 65) showed similar, non-statistically significant differences between groups. There was no difference in the rate of recanalization success in patients with a mean clot density greater than 50 HU or less than 50 HU in each of the four device groups. Conclusions There was no relationship between clot density and revascularization success or stroke etiology in our study. More research is needed to determine if clot density can predict recanalization rates or indicate etiology. PMID:28604188

Theoretical Analysis of Thermal Transport in Graphene Supported on Hexagonal Boron Nitride: The Importance of Strong Adhesion Due to π -Bond Polarization

NASA Astrophysics Data System (ADS)

Pak, Alexander J.; Hwang, Gyeong S.

2016-09-01

One important attribute of graphene that makes it attractive for high-performance electronics is its inherently large thermal conductivity (κ ) for the purposes of thermal management. Using a combined density-functional theory and classical molecular-dynamics approach, we predict that the κ of graphene supported on hexagonal boron nitride (h -BN) can be as large as 90% of the κ of suspended graphene, in contrast to the significant suppression of κ (more than 70% reduction) on amorphous silica. Interestingly, we find that this enhanced thermal transport is largely attributed to increased lifetimes of the in-plane acoustic phonon modes, which is a notable contrast from the dominant contribution of out-of-plane acoustic modes in suspended graphene. This behavior is possible due to the charge polarization throughout graphene that induces strong interlayer adhesion between graphene and h -BN. These findings highlight the potential benefit of layered dielectric substrates such as h -BN for graphene-based thermal management, in addition to their electronic advantages. Furthermore, our study brings attention to the importance of understanding the interlayer interactions of graphene with layered dielectric materials which may offer an alternative technological platform for substrates in electronics.

Incipient microphase separation in short chain perfluoropolyether-block-poly(ethylene oxide) copolymers.

PubMed

Chintapalli, Mahati; Timachova, Ksenia; Olson, Kevin R; Banaszak, Michał; Thelen, Jacob L; Mecham, Sue J; DeSimone, Joseph M; Balsara, Nitash P

2017-06-07

Incipient microphase separation is observed by wide angle X-ray scattering (WAXS) in short chain multiblock copolymers consisting of perfluoropolyether (PFPE) and poly(ethylene oxide) (PEO) segments. Two PFPE-PEO block copolymers were studied; one with dihydroxyl end groups and one with dimethyl carbonate end groups. Despite having a low degree of polymerization (N ∼ 10), these materials exhibited significant scattering intensity, due to disordered concentration fluctuations between their PFPE-rich and PEO-rich domains. The disordered scattering intensity was fit to a model based on a multicomponent random phase approximation to determine the value of the interaction parameter, χ, and the radius of gyration, R g . Over the temperature range 30-90 °C, the values of χ were determined to be very large (∼2-2.5), indicating a high degree of immiscibility between the PFPE and PEO blocks. In PFPE-PEO, due to the large electron density contrast between the fluorinated and non-fluorinated block and the high value of χ, disordered scattering was detected at intermediate scattering angles, (q ∼ 2 nm -1 ) for relatively small polymer chains. Our ability to detect concentration fluctuations was enabled by both a relatively large value of χ and significant scattering contrast.

Mass density images from the diffraction enhanced imaging technique.

PubMed

Hasnah, M O; Parham, C; Pisano, E D; Zhong, Z; Oltulu, O; Chapman, D

2005-02-01

Conventional x-ray radiography measures the projected x-ray attenuation of an object. It requires attenuation differences to obtain contrast of embedded features. In general, the best absorption contrast is obtained at x-ray energies where the absorption is high, meaning a high absorbed dose. Diffraction-enhanced imaging (DEI) derives contrast from absorption, refraction, and extinction. The refraction angle image of DEI visualizes the spatial gradient of the projected electron density of the object. The projected electron density often correlates well with the projected mass density and projected absorption in soft-tissue imaging, yet the mass density is not an "energy"-dependent property of the object, as is the case of absorption. This simple difference can lead to imaging with less x-ray exposure or dose. In addition, the mass density image can be directly compared (i.e., a signal-to-noise comparison) with conventional radiography. We present the method of obtaining the mass density image, the results of experiments in which comparisons are made with radiography, and an application of the method to breast cancer imaging.

Origin of the cosmic network in {Lambda}CDM: Nature vs nurture

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

Shandarin, Sergei; Habib, Salman; Heitmann, Katrin

The large-scale structure of the Universe, as traced by the distribution of galaxies, is now being revealed by large-volume cosmological surveys. The structure is characterized by galaxies distributed along filaments, the filaments connecting in turn to form a percolating network. Our objective here is to quantitatively specify the underlying mechanisms that drive the formation of the cosmic network: By combining percolation-based analyses with N-body simulations of gravitational structure formation, we elucidate how the network has its origin in the properties of the initial density field (nature) and how its contrast is then amplified by the nonlinear mapping induced by themore » gravitational instability (nurture).« less

Preliminary research on dual-energy X-ray phase-contrast imaging

NASA Astrophysics Data System (ADS)

Han, Hua-Jie; Wang, Sheng-Hao; Gao, Kun; Wang, Zhi-Li; Zhang, Can; Yang, Meng; Zhang, Kai; Zhu, Pei-Ping

2016-04-01

Dual-energy X-ray absorptiometry (DEXA) has been widely applied to measure the bone mineral density (BMD) and soft-tissue composition of the human body. However, the use of DEXA is greatly limited for low-Z materials such as soft tissues due to their weak absorption, while X-ray phase-contrast imaging (XPCI) shows significantly improved contrast in comparison with the conventional standard absorption-based X-ray imaging for soft tissues. In this paper, we propose a novel X-ray phase-contrast method to measure the area density of low-Z materials, including a single-energy method and a dual-energy method. The single-energy method is for the area density calculation of one low-Z material, while the dual-energy method aims to calculate the area densities of two low-Z materials simultaneously. Comparing the experimental and simulation results with the theoretical ones, the new method proves to have the potential to replace DEXA in area density measurement. The new method sets the prerequisites for a future precise and low-dose area density calculation method for low-Z materials. Supported by Major State Basic Research Development Program (2012CB825800), Science Fund for Creative Research Groups (11321503) and National Natural Science Foundation of China (11179004, 10979055, 11205189, 11205157)

Ion distributions, exclusion coefficients, and separation factors of electrolytes in a charged cylindrical nanopore: a partially perturbative density functional theory study.

PubMed

Peng, Bo; Yu, Yang-Xin

2009-10-07

The structural and thermodynamic properties for charge symmetric and asymmetric electrolytes as well as mixed electrolyte system inside a charged cylindrical nanopore are investigated using a partially perturbative density functional theory. The electrolytes are treated in the restricted primitive model and the internal surface of the cylindrical nanopore is considered to have a uniform charge density. The proposed theory is directly applicable to the arbitrary mixed electrolyte solution containing ions with the equal diameter and different valences. Large amount of simulation data for ion density distributions, separation factors, and exclusion coefficients are used to determine the range of validity of the partially perturbative density functional theory for monovalent and multivalent counterion systems. The proposed theory is found to be in good agreement with the simulations for both mono- and multivalent counterion systems. In contrast, the classical Poisson-Boltzmann equation only provides reasonable descriptions of monovalent counterion system at low bulk density, and is qualitatively and quantitatively wrong in the prediction for the multivalent counterion systems due to its neglect of the strong interionic correlations in these systems. The proposed density functional theory has also been applied to an electrolyte absorbed into a pore that is a model of the filter of a physiological calcium channel.

Enhanced discharge energy density of rGO/PVDF nanocomposites: The role of the heterointerface

NASA Astrophysics Data System (ADS)

Zhang, Ye; Wang, Yaqiong; Qi, Shaojun; Dunn, Steve; Dong, Hanshan; Button, Tim

2018-05-01

Recent reports of conductive-filler/polymer composites with large dielectric permittivity (K) make them potential candidates for flexible capacitors. Hence, an interesting question is how these high K composites behave under a strong electric field strength. In this letter, we use in-situ-reduced graphite oxide (rGO)/poly(vinylidene fluoride) (PVDF) nanocomposites as an example to study the energy storage behaviour of high K materials. We show the dielectric behaviour contrasts between weak and strong fields. High K materials inevitably become more lossy with increasing field strength. Simultaneously, we reveal that the in-situ reduction temperature can affect the energy storage performance. Improved energy storage performance is achieved for a nanocomposite reduced at a moderate temperature. When reduced at 160 °C, a device with an rGO volume fraction of 1.5 vol. % displayed a discharge energy density of 0.67 J/cm3 at 50 MV/m. This was 2.9 times greater than pure PVDF. We develop a model to explain this behaviour that proposes a reduced electrical contrast of the rGO/PVDF heterointerface minimising the recombination of localized charge carriers. Our results indicate, simultaneously, the potential and limitation of high K nanocomposites and shed light on the optimisation of the design and fabrication of high discharge energy density flexible capacitors for microelectronic devices.

Gravity in extensional regimes: A case study in the Central Volcanic Region, New Zealand

NASA Astrophysics Data System (ADS)

Greve, A.; Stern, T. A.

2017-12-01

Using the interpretation of a large crustal seismic experiment conducted in 2009 as boundary model, we produced a sequence of new 2D gravity models for the central North Island in New Zealand. The Bouguer gravity field in the region ranges from -100 to 60 mGal and is dominated by the long wavelength signals of the subduction of the Pacific beneath the Australian plate along the Hikurangi margin and the transition from continental to oceanic lithosphere about the Bay of Plenty coast (NE New Zealand). Removal of these broad regional trends reveals the presence of a triangular shaped area, within the lines Taranaki-Coromandel and Taranaki - White Island, with negative anomalies between -30 and 60 mGal and positive anomalies around 10 mGal along the margins. This area, commonly referred to as the Central Volcanic Region (CVR) represents the continental continuation of the Lau-Havre, oceanic, back-arc rift basin. The Taupo Volcanic Zone forms the active eastern half of the CVR, where anomalously high heat output, geothermal activity and active volcanism occur. The new gravity model includes the presence of a 90km wide, ca. 10 km thick rift pillow of new underplated, lower crust between the depths of 15 and 25 km. A positive density contrast of 300 kg/m3 for this body is consistent with the observed seismic velocities (6.8 ≤ Vp ≤ 7.1 km/s). A ca. 2.5 km deep basin dominates the upper crustal structure and is about 50 km wide, infilled by low density volcaniclastics, with adopted average negative densities of -425 kg/m3. In the mid-crustal region, between 2.5 and 15 km depth, isostatic compensation requires a small density contrast of -110 kg/m3. This density contrast, with respect to a standard crustal model, can be ascribed to the presence of low density intrusives, within the old and now stretched crust. On the basis of this new crustal structure model we estimate a stretching factor (ß) for the old crust of 2-2.4. The intruded mid crust and the underplated new crust are most likely the primary sources of the impressive 4 GW heat output of the CVR.

Population density of red langurs in Sabangau tropical peat-swamp forest, Central Kalimantan, Indonesia.

PubMed

Ehlers Smith, David A; Ehlers Smith, Yvette C

2013-08-01

Because of the large-scale destruction of Borneo's rainforests on mineral soils, tropical peat-swamp forests (TPSFs) are increasingly essential for conserving remnant biodiversity, particularly in the lowlands where the majority of habitat conversion has occurred. Consequently, effective strategies for biodiversity conservation are required, which rely on accurate population density and distribution estimates as a baseline. We sought to establish the first population density estimates of the endemic red langur (Presbytis rubicunda) in Sabangau TPSF, the largest remaining contiguous lowland forest-block on Borneo. Using Distance sampling principles, we conducted line transect surveys in two of Sabangau's three principle habitat sub-classes and calculated group density at 2.52 groups km⁻² (95% CI 1.56-4.08) in the mixed-swamp forest sub-class. Based on an average recorded group size of 6.95 individuals, population density was 17.51 ind km⁻², the second highest density recorded in this species. The accessible area of the tall-interior forest, however, was too disturbed to yield density estimates representative of the entire sub-class, and P. rubicunda was absent from the low-pole forest, likely as a result of the low availability of the species' preferred foods. This absence in 30% of Sabangau's total area indicates the importance of in situ population surveys at the habitat-specific level for accurately informing conservation strategies. We highlight the conservation value of TPSFs for P. rubicunda given the high population density and large areas remaining, and recommend 1) quantifying the response of P. rubicunda to the logging and burning of its habitats; 2) surveying degraded TPSFs for viable populations, and 3) effectively delineating TPSF sub-class boundaries from remote imagery to facilitate population estimates across the wider peat landscape, given the stark contrast in densities found across the habitat sub-classes of Sabangau. © 2013 Wiley Periodicals, Inc.

Origin of the Two Scales of Wind Ripples on Mars

NASA Technical Reports Server (NTRS)

Lapotre, Mathieu G. A.; Ewing, Ryan C.; Lamb, Michael P.; Fischer, Woodward W.; Grotzinger, John P.; Rubin, David M.; Lewis, Kevin W.; Day, Mackenzie; Gupta, Sanjeev; Banham, Steeve G.;

Origin of the two scales of wind ripples on Mars

NASA Astrophysics Data System (ADS)

Lapotre, M. G. A.; Ewing, R. C.; Lamb, M. P.; Fischer, W. W.; Grotzinger, J. P.; Rubin, D. M.; Lewis, K. W.; Ballard, M.; Day, M. D.; Gupta, S.; Banham, S.; Bridges, N.; Des Marais, D. J.; Fraeman, A. A.; Grant, J. A., III; Ming, D. W.; Mischna, M.; Rice, M. S.; Sumner, D. Y.; Vasavada, A. R.; Yingst, R. A.

2016-12-01

Earth's sandy deserts host two main types of bedforms - decimeter-scale ripples and larger dunes. Years of orbital observations on Mars also confirmed the existence of two modes of active eolian bedforms - meter-scale ripples, and dunes. By analogy to terrestrial ripples, which are thought to form from a grain mechanism, it was hypothesized that large martian ripples also formed from grain impacts, but spaced further apart due to elongated saltation trajectories from the lower martian gravity and different atmospheric properties. However, the Curiosity rover recently documented the coexistence of three scales of bedforms in Gale crater. Because a grain impact mechanism cannot readily explain two distinct and coeval ripple modes in similar sand sizes, a new mechanism seems to be required to explain one of the scales of ripples. Small ripples are most similar to Earth's impact ripples, with straight crests and subdued profiles. In contrast, large martian ripples are sinuous and asymmetric, with lee slopes dominated by grain flows and grainfall deposits. Thus, large martian ripples resemble current ripples formed underwater on Earth, suggesting that they may form from a fluid-drag mechanism. To test this hypothesis, we develop a scaling relation to predict the spacing of fluid-drag ripples from an extensive flume data compilation. The size of large martian ripples is predicted by our scaling relation when adjusted for martian atmospheric properties. Specifically, we propose that the wavelength of martian wind-drag ripples arises from the high kinematic viscosity of the low-density atmosphere. Because fluid density controls drag-ripple size, our scaling relation can help constrain paleoatmospheric density from wind-drag ripple stratification.

Investigation of Physical Processes Limiting Plasma Density in DIII--D

NASA Astrophysics Data System (ADS)

Maingi, R.

1996-11-01

Understanding the physical processes which limit operating density is crucial in achieving peak performance in confined plasmas. Studies from many of the world's tokamaks have indicated the existence(M. Greenwald, et al., Nucl. Fusion 28) (1988) 2199 of an operational density limit (Greenwald limit, n^GW_max) which is proportional to the plasma current and independent of heating power. Several theories have reproduced the current dependence, but the lack of a heating power dependence in the data has presented an enigma. This limit impacts the International Thermonuclear Experimental Reactor (ITER) because the nominal operating density for ITER is 1.5 × n^GW_max. In DIII-D, experiments are being conducted to understand the physical processes which limit operating density in H-mode discharges; these processes include X-point MARFE formation, high core recycling and neutral pressure, resistive MHD stability, and core radiative collapse. These processes affect plasma properties, i.e. edge/scrape-off layer conduction and radiation, edge pressure gradient and plasma current density profile, and core radiation, which in turn restrict the accessible density regime. With divertor pumping and D2 pellet fueling, core neutral pressure is reduced and X-point MARFE formation is effectively eliminated. Injection of the largest-sized pellets does cause transient formation of divertor MARFEs which occasionally migrate to the X-point, but these are rapidly extinguished in pumped discharges in the time between pellets. In contrast to Greenwald et al., it is found that the density relaxation time after pellets is largely independent of the density relative to the Greenwald limit. Fourier analysis of Mirnov oscillations indicates the de-stabilization and growth of rotating, tearing-type modes (m/n= 2/1) when the injected pellets cause large density perturbations, and these modes often reduce energy confinement back to L-mode levels. We are examining the mechanisms for de-stabilization of the mode, the primary ones being neo-classical pressure gradient drivers. Discharges with a gradual density increase are often free of large amplitude tearing modes, allowing access to the highest density regimes in which off-axis beam deposition can lead to core radiative collapse, i.e. a central power balance limit. The highest achieved barne was 1.5 × n^GW_max with τ_E/τ_E^JET-DIII-D >= 0.9. The highest density obtained in L-mode discharges was 3 × n^GW_max. Implications of these results for ITER will be discussed.

Experimental study on the interspecific interactions between the two bloom-forming algal species and the rotifer Brachionus plicatilis

NASA Astrophysics Data System (ADS)

Xie, Zhihao; Xiao, Hui; Tang, Xuexi; Cai, Hengjiang

2009-06-01

The interspecific interactions between the rotifer Brachionus plicatilis and two harmful algal blooms (HAB) species were investigated experimentally by single culture method. B. plicatilis population and the growth of the two algae were compared at different algal cell densities. The results demonstrated that the B. plicatilis obtained sufficient nutrition from Prorocentrum donghaiense to support net population increase. With exposure to 2.5×104 cells mL-1 of P. donghaiense, the number of B. plicatilis increased faster than it did when exposed to other four algal densities (5, 10, 15 and 20 ×104 cells mL-1), and the increase rate of B. plicatilis population ( r) at this algal density was 0.104 ± 0.015 rd-1. Cell densities of P. donghaiense decreased due to the grazing of B. plicatilis. In contrast, Heterosigma akashiwo had an adverse effect on B. plicatilis population and its growth was largely unaffected by rotifer grazing. In this case, B. plicatilis population decreased and H. akashiwo grew at a rate similar to that of the control.

The effect of aging on the density of the sensory nerve fiber innervation of bone and acute skeletal pain.

PubMed

Jimenez-Andrade, Juan M; Mantyh, William G; Bloom, Aaron P; Freeman, Katie T; Ghilardi, Joseph R; Kuskowski, Michael A; Mantyh, Patrick W

2012-05-01

As humans age there is a decline in most sensory systems including vision, hearing, taste, smell, and tactile acuity. In contrast, the frequency and severity of musculoskeletal pain generally increases with age. To determine whether the density of sensory nerve fibers that transduce skeletal pain changes with age, calcitonin gene related peptide (CGRP) and neurofilament 200 kDa (NF200) sensory nerve fibers that innervate the femur were examined in the femurs of young (4-month-old), middle-aged (13-month-old) and old (36-month-old) male F344/BNF1 rats. Whereas the bone quality showed a significant age-related decline, the density of CGRP(+) and NF200(+) nerve fibers that innervate the bone remained remarkably unchanged as did the severity of acute skeletal fracture pain. Thus, while bone mass, quality, and strength undergo a significant decline with age, the density of sensory nerve fibers that transduce noxious stimuli remain largely intact. These data may in part explain why musculoskeletal pain increases with age. Copyright © 2012 Elsevier Inc. All rights reserved.

Vulnerability of reactive skin to electric current perception--a pilot study implicating mast cells and the lymphatic microvasculature.

PubMed

Quatresooz, Pascale; Piérard-Franchimont, Claudine; Piérard, Gérald E

2009-09-01

Sensitive/reactive skin is regarded as a manifestation of sensory irritation. This susceptibility condition to various exogenous factors suggests the intervention of some neuropeptides and other neurobiological mediators. Mast cells are among the putative implicated cells. The present immunohistochemical and morphometric study was performed on two groups of 36 gender- and age-matched subjects complaining or not from reactive skin as determined by electric current perception. In the mid upper part of the dermis, the numerical density in mast cells and the size of the microvasculature were assessed distinguishing the blood and lymphatic vessels. Globally, the distributions of data were large in reactive skin. This condition was characterized by a prominent increase in both the numerical density in mast cells and the overall size of the lymphatics. By contrast, no difference was found in the size of cutaneous blood vessels. More precisely, it appeared that a subgroup of people with reactive skin exhibited these changes contrasting with some other individuals whose data remained close to the normal range. Mast cells and lymphatics are probably involved in the process of sensory irritation affecting a subgroup of the population.

Effect of water temperature and population density on the population dynamics of Schistosoma mansoni intermediate host snails.

PubMed

McCreesh, Nicky; Arinaitwe, Moses; Arineitwe, Wilber; Tukahebwa, Edridah M; Booth, Mark

2014-11-12

Mathematical models can be used to identify areas at risk of increased or new schistosomiasis transmission as a result of climate change. The results of these models can be very different when parameterised to different species of host snail, which have varying temperature preferences. Currently, the experimental data needed by these models are available for only a few species of snail. The choice of density-dependent functions can also affect model results, but the effects of increasing densities on Biomphalaria populations have only previously been investigated in artificial aquariums. Laboratory experiments were conducted to estimate Biomphalaria sudanica mortality, fecundity and growth rates at ten different constant water temperatures, ranging from 13-32°C. Snail cages were used to determine the effects of snail densities on B. sudanica and B. stanleyi mortality and fecundity rates in semi-natural conditions in Lake Albert. B. sudanica survival and fecundity were highest at 20°C and 22°C respectively. Growth in shell diameter was estimated to be highest at 23°C in small and medium sized snails, but the relationship between temperature and growth was not clear. The fecundity of both B. sudanica and B. stanleyi decreased by 72-75% with a four-fold increase in population density. Increasing densities four-fold also doubled B. stanleyi mortality rates, but had no effect on the survival of B. sudanica. The optimum temperature for fecundity was lower for B. sudanica than for previously studied species of Biomphalaria. In contrast to other Biomphalaria species, B. sudanica have a distinct peak temperature for survival, as opposed to a plateau of highly suitable temperatures. For both B. stanleyi and B. sudanica, fecundity decreased with increasing population densities. This means that snail populations may experience large fluctuations in numbers, even in the absence of any external factors such as seasonal temperature changes. Survival also decreased with increasing density for B. stanleyi, in contrast to B. sudanica and other studied Biomphalaria species where only fecundity has been shown to decrease.

Melt segregation from partially molten source regions - The importance of melt density and source region size

NASA Technical Reports Server (NTRS)

Stolper, E.; Hager, B. H.; Walker, D.; Hays, J. F.

1981-01-01

An investigation is conducted regarding the changes expected in the density contrast between basic melts and peridotites with increasing pressure using the limited data available on the compressibilities of silicate melts and data on the densities of mantle minerals. It is concluded that since compressibilities of silicate melts are about an order of magnitude greater than those of mantle minerals, the density contrast between basic melts and mantle minerals must diminish significantly with increasing pressure. An earlier analysis regarding the migration of liquid in partially molten source regions conducted by Walker et al. (1978) is extended, giving particular attention to the influence of the diminished density contrast between melt and residual crystals with increasing source region depth and to the influence of source region size. This analysis leads to several generalizations concerning the factors influencing the depths at which magmas will segregate from their source regions and the degrees of partial melting that can be achieved in these source regions before melt segregation occurs.

Quantitative breast MRI radiomics for cancer risk assessment and the monitoring of high-risk populations

NASA Astrophysics Data System (ADS)

Mendel, Kayla R.; Li, Hui; Giger, Maryellen L.

2016-03-01

Breast density is routinely assessed qualitatively in screening mammography. However, it is challenging to quantitatively determine a 3D density from a 2D image such as a mammogram. Furthermore, dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) is used more frequently in the screening of high-risk populations. The purpose of our study is to segment parenchyma and to quantitatively determine volumetric breast density on pre-contrast axial DCE-MRI images (i.e., non-contrast) using a semi-automated quantitative approach. In this study, we retroactively examined 3D DCE-MRI images taken for breast cancer screening of a high-risk population. We analyzed 66 cases with ages between 28 and 76 (mean 48.8, standard deviation 10.8). DCE-MRIs were obtained on a Philips 3.0 T scanner. Our semi-automated DCE-MRI algorithm includes: (a) segmentation of breast tissue from non-breast tissue using fuzzy cmeans clustering (b) separation of dense and fatty tissues using Otsu's method, and (c) calculation of volumetric density as the ratio of dense voxels to total breast voxels. We examined the relationship between pre-contrast DCE-MRI density and clinical BI-RADS density obtained from radiology reports, and obtained a statistically significant correlation [Spearman ρ-value of 0.66 (p < 0.0001)]. Our method within precision medicine may be useful for monitoring high-risk populations.

Anomalously large isotope effect in the glass transition of water

DOE PAGES

Gainaru, Catalin; Agapov, Alexander L.; Fuentes-Landete, Violeta; ...

2014-11-24

Here we present the discovery of an unusually large isotope effect in the structural relaxation and the glass transition temperature T g of water. Dielectric relaxation spectroscopy of low-density as well as of vapor deposited amorphous water reveal T g differences of 10±2K between H 2O and D 2O, sharply contrasting with other hydrogen bonded liquids for which H/D exchange increases T g by typically less than 1K. We show that the large isotope effect and the unusual variation of relaxation times in water at low temperatures can be explained in terms of quantum effects. Thus, our findings shed newmore » light on water's peculiar low-temperature dynamics and the possible role of quantum effects in its structural relaxation, and possibly in dynamics of other low molecular weight liquids.« less

Genetically targeted 3D visualisation of Drosophila neurons under Electron Microscopy and X-Ray Microscopy using miniSOG

PubMed Central

Ng, Julian; Browning, Alyssa; Lechner, Lorenz; Terada, Masako; Howard, Gillian; Jefferis, Gregory S. X. E.

2016-01-01

Large dimension, high-resolution imaging is important for neural circuit visualisation as neurons have both long- and short-range patterns: from axons and dendrites to the numerous synapses at terminal endings. Electron Microscopy (EM) is the favoured approach for synaptic resolution imaging but how such structures can be segmented from high-density images within large volume datasets remains challenging. Fluorescent probes are widely used to localise synapses, identify cell-types and in tracing studies. The equivalent EM approach would benefit visualising such labelled structures from within sub-cellular, cellular, tissue and neuroanatomical contexts. Here we developed genetically-encoded, electron-dense markers using miniSOG. We demonstrate their ability in 1) labelling cellular sub-compartments of genetically-targeted neurons, 2) generating contrast under different EM modalities, and 3) segmenting labelled structures from EM volumes using computer-assisted strategies. We also tested non-destructive X-ray imaging on whole Drosophila brains to evaluate contrast staining. This enabled us to target specific regions for EM volume acquisition. PMID:27958322

Critical behavior of subcellular density organization during neutrophil activation and migration.

PubMed

Baker-Groberg, Sandra M; Phillips, Kevin G; Healy, Laura D; Itakura, Asako; Porter, Juliana E; Newton, Paul K; Nan, Xiaolin; McCarty, Owen J T

2015-12-01

Physical theories of active matter continue to provide a quantitative understanding of dynamic cellular phenomena, including cell locomotion. Although various investigations of the rheology of cells have identified important viscoelastic and traction force parameters for use in these theoretical approaches, a key variable has remained elusive both in theoretical and experimental approaches: the spatiotemporal behavior of the subcellular density. The evolution of the subcellular density has been qualitatively observed for decades as it provides the source of image contrast in label-free imaging modalities (e.g., differential interference contrast, phase contrast) used to investigate cellular specimens. While these modalities directly visualize cell structure, they do not provide quantitative access to the structures being visualized. We present an established quantitative imaging approach, non-interferometric quantitative phase microscopy, to elucidate the subcellular density dynamics in neutrophils undergoing chemokinesis following uniform bacterial peptide stimulation. Through this approach, we identify a power law dependence of the neutrophil mean density on time with a critical point, suggesting a critical density is required for motility on 2D substrates. Next we elucidate a continuum law relating mean cell density, area, and total mass that is conserved during neutrophil polarization and migration. Together, our approach and quantitative findings will enable investigators to define the physics coupling cytoskeletal dynamics with subcellular density dynamics during cell migration.

Critical behavior of subcellular density organization during neutrophil activation and migration

PubMed Central

Baker-Groberg, Sandra M.; Phillips, Kevin G.; Healy, Laura D.; Itakura, Asako; Porter, Juliana E.; Newton, Paul K.; Nan, Xiaolin; McCarty, Owen J.T.

2015-01-01

Physical theories of active matter continue to provide a quantitative understanding of dynamic cellular phenomena, including cell locomotion. Although various investigations of the rheology of cells have identified important viscoelastic and traction force parameters for use in these theoretical approaches, a key variable has remained elusive both in theoretical and experimental approaches: the spatiotemporal behavior of the subcellular density. The evolution of the subcellular density has been qualitatively observed for decades as it provides the source of image contrast in label-free imaging modalities (e.g., differential interference contrast, phase contrast) used to investigate cellular specimens. While these modalities directly visualize cell structure, they do not provide quantitative access to the structures being visualized. We present an established quantitative imaging approach, non-interferometric quantitative phase microscopy, to elucidate the subcellular density dynamics in neutrophils undergoing chemokinesis following uniform bacterial peptide stimulation. Through this approach, we identify a power law dependence of the neutrophil mean density on time with a critical point, suggesting a critical density is required for motility on 2D substrates. Next we elucidate a continuum law relating mean cell density, area, and total mass that is conserved during neutrophil polarization and migration. Together, our approach and quantitative findings will enable investigators to define the physics coupling cytoskeletal dynamics with subcellular density dynamics during cell migration. PMID:26640599

The density of dark matter in the Galactic bulge and implications for indirect detection

DOE PAGES

Hooper, Dan

2016-11-29

A recent study, making use of the number of horizontal branch stars observed in infrared photometric surveys and kinematic measurements of M-giant stars from the BRAVA survey, combined with N-body simulations of stellar populations, has presented a new determination of the dark matter mass within the bulge-bar region of the Milky Way. That study constrains the total mass within themore » $$\\pm 2.2 \\times \\pm 1.4 \\times \\pm 1.2$$ kpc volume of the bulge-bar region to be ($$1.84 \\pm 0.07) \\times 10^{10} \\, M_{\\odot}$$, of which 9-30% is made up of dark matter. Here, we use this result to constrain the the Milky Way's dark matter density profile, and discuss the implications for indirect dark matter searches. Furthermore uncertainties remain significant, these results favor dark matter distributions with a cusped density profile. For example, for a scale radius of 20 kpc and a local dark matter density of 0.4 GeV/cm$^3$, density profiles with an inner slope of 0.69 to 1.40 are favored, approximately centered around the standard NFW value. In contrast, profiles with large flat-density cores are disfavored by this information.« less

Regional distribution of T-tubule density in left and right atria in dogs.

PubMed

Arora, Rishi; Aistrup, Gary L; Supple, Stephen; Frank, Caleb; Singh, Jasleen; Tai, Shannon; Zhao, Anne; Chicos, Laura; Marszalec, William; Guo, Ang; Song, Long-Sheng; Wasserstrom, J Andrew

2017-02-01

The peculiarities of transverse tubule (T-tubule) morphology and distribution in the atrium-and how they contribute to excitation-contraction coupling-are just beginning to be understood. The objectives of this study were to determine T-tubule density in the intact, live right and left atria in a large animal and to determine intraregional differences in T-tubule organization within each atrium. Using confocal microscopy, T-tubules were imaged in both atria in intact, Langendorf-perfused normal dog hearts loaded with di-4-ANEPPS. T-tubules were imaged in large populations of myocytes from the endocardial surface of each atrium. Computerized data analysis was performed using a new MatLab (Mathworks, Natick, MA) routine, AutoTT. There was a large percentage of myocytes that had no T-tubules in both atria with a higher percentage in the right atrium (25.1%) than in the left atrium (12.5%) (P < .02). The density of transverse and longitudinal T-tubule elements was low in cells that did contain T-tubules, but there were no significant differences in density between the left atrial appendage, the pulmonary vein-posterior left atrium, the right atrial appendage, and the right atrial free wall. In contrast, there were significant differences in sarcomere spacing and cell width between different regions of the atria. There is a sparse T-tubule network in atrial myocytes throughout both dog atria, with significant numbers of myocytes in both atria-the right atrium more so than the left atrium-having no T-tubules at all. These regional differences in T-tubule distribution, along with differences in cell width and sarcomere spacing, may have implications for the emergence of substrate for atrial fibrillation. Copyright © 2016 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.

New Type of the Interface Evolution in the Richtmyer-Meshkov Instability

NASA Technical Reports Server (NTRS)

Abarzhi, S. I.; Herrmann, M.

2003-01-01

We performed systematic theoretical and numerical studies of the nonlinear large-scale coherent dynamics in the Richtmyer-Meshkov instability for fluids with contrast densities. Our simulations modeled the interface dynamics for compressible and viscous uids. For a two-fluid system we observed that in the nonlinear regime of the instability the bubble velocity decays and its surface attens, and the attening is accompanied by slight oscillations. We found the theoretical solution for the system of conservation laws, describing the principal influence of the density ratio on the motion of the nonlinear bubble. The solution has no adjustable parameters, and shows that the attening of the bubble front is a distinct property universal for all values of the density ratio. This property follows from the fact that the RM bubbles decelerate. The theoretical and numerical results validate each other, describe the new type of the bubble front evolution in RMI, and identify the bubble curvature as important and sensitive diagnostic parameter.

Spatial heterogeneity in the effects of climate and density-dependence on dispersal in a house sparrow metapopulation

PubMed Central

Pärn, Henrik; Ringsby, Thor Harald; Jensen, Henrik; Sæther, Bernt-Erik

2012-01-01

Dispersal plays a key role in the response of populations to climate change and habitat fragmentation. Here, we use data from a long-term metapopulation study of a non-migratory bird, the house sparrow (Passer domesticus), to examine the influence of increasing spring temperature and density-dependence on natal dispersal rates and how these relationships depend on spatial variation in habitat quality. The effects of spring temperature and population size on dispersal rate depended on the habitat quality. Dispersal rate increased with temperature and population size on poor-quality islands without farms, where house sparrows were more exposed to temporal fluctuations in weather conditions and food availability. By contrast, dispersal rate was independent of spring temperature and population size on high-quality islands with farms, where house sparrows had access to food and shelter all the year around. This illustrates large spatial heterogeneity within the metapopulation in how population density and environmental fluctuations affect the dispersal process. PMID:21613299

Holography and thermalization in optical pump-probe spectroscopy

NASA Astrophysics Data System (ADS)

Bagrov, A.; Craps, B.; Galli, F.; Keränen, V.; Keski-Vakkuri, E.; Zaanen, J.

2018-04-01

Using holography, we model experiments in which a 2 +1 D strange metal is pumped by a laser pulse into a highly excited state, after which the time evolution of the optical conductivity is probed. We consider a finite-density state with mildly broken translation invariance and excite it by oscillating electric field pulses. At zero density, the optical conductivity would assume its thermalized value immediately after the pumping has ended. At finite density, pulses with significant dc components give rise to slow exponential relaxation, governed by a vector quasinormal mode. In contrast, for high-frequency pulses the amplitude of the quasinormal mode is strongly suppressed, so that the optical conductivity assumes its thermalized value effectively instantaneously. This surprising prediction may provide a stimulus for taking up the challenge to realize these experiments in the laboratory. Such experiments would test a crucial open question faced by applied holography: are its predictions artifacts of the large N limit or do they enjoy sufficient UV independence to hold at least qualitatively in real-world systems?

Autofluorescence imaging of macular pigment: influence and correction of ocular media opacities

NASA Astrophysics Data System (ADS)

Sharifzadeh, Mohsen; Obana, Akira; Gohto, Yuko; Seto, Takahiko; Gellermann, Werner

2014-09-01

The healthy adult human retina contains in its macular region a high concentration of blue-light absorbing carotenoid compounds, known as macular pigment (MP). Consisting of the carotenoids lutein, zeaxanthin, and meso-zeaxanthin, the MP is thought to shield the vulnerable tissue layers in the retina from light-induced damage through its function as an optical attenuator and to protect the tissue cells within its immediate vicinity through its function as a potent antioxidant. Autofluorescence imaging (AFI) is emerging as a viable optical method for MP screening of large subject populations, for tracking of MP changes over time, and for monitoring MP uptake in response to dietary supplementation. To investigate the influence of ocular media opacities on AFI-based MP measurements, in particular, the influence of lens cataracts, we conducted a clinical trial with a large subject population (93 subjects) measured before and after cataract surgery. General AFI image contrast, retinal blood vessel contrast, and presurgery lens opacity scores [Lens Opacities Classification System III (LOCS III)] were investigated as potential predictors for image degradation. These clinical results show that lens cataracts can severely degrade the achievable pixel contrasts in the AFI images, which results in nominal MP optical density levels that are artifactually reduced. While LOCS III scores and blood vessel contrast are found to be only a weak predictor for this effect, a strong correlation exists between the reduction factor and the image contrast, which can be quantified via pixel intensity histogram parameters. Choosing the base width of the histogram, the presence or absence of ocular media opacities can be determined and, if needed, the nominal MP levels can be corrected with factors depending on the strength of the opacity.

Assessing Sexual Dicromatism: The Importance of Proper Parameterization in Tetrachromatic Visual Models

PubMed Central

Janisse, Kevyn; Doucet, Stéphanie M.

2017-01-01

Perceptual models of animal vision have greatly contributed to our understanding of animal-animal and plant-animal communication. The receptor-noise model of color contrasts has been central to this research as it quantifies the difference between two colors for any visual system of interest. However, if the properties of the visual system are unknown, assumptions regarding parameter values must be made, generally with unknown consequences. In this study, we conduct a sensitivity analysis of the receptor-noise model using avian visual system parameters to systematically investigate the influence of variation in light environment, photoreceptor sensitivities, photoreceptor densities, and light transmission properties of the ocular media and the oil droplets. We calculated the chromatic contrast of 15 plumage patches to quantify a dichromatism score for 70 species of Galliformes, a group of birds that display a wide range of sexual dimorphism. We found that the photoreceptor densities and the wavelength of maximum sensitivity of the short-wavelength-sensitive photoreceptor 1 (SWS1) can change dichromatism scores by 50% to 100%. In contrast, the light environment, transmission properties of the oil droplets, transmission properties of the ocular media, and the peak sensitivities of the cone photoreceptors had a smaller impact on the scores. By investigating the effect of varying two or more parameters simultaneously, we further demonstrate that improper parameterization could lead to differences between calculated and actual contrasts of more than 650%. Our findings demonstrate that improper parameterization of tetrachromatic visual models can have very large effects on measures of dichromatism scores, potentially leading to erroneous inferences. We urge more complete characterization of avian retinal properties and recommend that researchers either determine whether their species of interest possess an ultraviolet or near-ultraviolet sensitive SWS1 photoreceptor, or present models for both. PMID:28076391

A Mouse Model of Visual Perceptual Learning Reveals Alterations in Neuronal Coding and Dendritic Spine Density in the Visual Cortex.

PubMed

Wang, Yan; Wu, Wei; Zhang, Xian; Hu, Xu; Li, Yue; Lou, Shihao; Ma, Xiao; An, Xu; Liu, Hui; Peng, Jing; Ma, Danyi; Zhou, Yifeng; Yang, Yupeng

2016-01-01

Visual perceptual learning (VPL) can improve spatial vision in normally sighted and visually impaired individuals. Although previous studies of humans and large animals have explored the neural basis of VPL, elucidation of the underlying cellular and molecular mechanisms remains a challenge. Owing to the advantages of molecular genetic and optogenetic manipulations, the mouse is a promising model for providing a mechanistic understanding of VPL. Here, we thoroughly evaluated the effects and properties of VPL on spatial vision in C57BL/6J mice using a two-alternative, forced-choice visual water task. Briefly, the mice underwent prolonged training at near the individual threshold of contrast or spatial frequency (SF) for pattern discrimination or visual detection for 35 consecutive days. Following training, the contrast-threshold trained mice showed an 87% improvement in contrast sensitivity (CS) and a 55% gain in visual acuity (VA). Similarly, the SF-threshold trained mice exhibited comparable and long-lasting improvements in VA and significant gains in CS over a wide range of SFs. Furthermore, learning largely transferred across eyes and stimulus orientations. Interestingly, learning could transfer from a pattern discrimination task to a visual detection task, but not vice versa. We validated that this VPL fully restored VA in adult amblyopic mice and old mice. Taken together, these data indicate that mice, as a species, exhibit reliable VPL. Intrinsic signal optical imaging revealed that mice with perceptual training had higher cut-off SFs in primary visual cortex (V1) than those without perceptual training. Moreover, perceptual training induced an increase in the dendritic spine density in layer 2/3 pyramidal neurons of V1. These results indicated functional and structural alterations in V1 during VPL. Overall, our VPL mouse model will provide a platform for investigating the neurobiological basis of VPL.

Quiet-Sun Connection between the C IV Resonance Lines and the Photospheric Magnetic Field

NASA Astrophysics Data System (ADS)

Brynildsen, Nils; Kjeldseth-Moe, Olav; Maltby, Per

1996-05-01

The quiet-Sun relation between the C iv resonance line parameters and the photospheric magnetic field is studied with a spatial resolution of 1" x 1". The material is ordered into groups according to the magnitude of the magnetic flux density, |B|, and conditional probabilities are calculated. We find that red shifted profiles with either high intensity, large Doppler shift, or large line broadening occupy an increasing fraction of the area when |B| increases. These results are contrasted by blueshifted profiles which indicate a slight decrease with increasing magnetic flux density. The similarity in the results obtained with magneto grams taken several hours before and after the UV data led us to suggest that the tendency for red shifted profiles to outnumber blueshifted profiles in quiet regions originates in the super-granular network. Suggestions regarding the origin of the redshift phenomenon are briefly confronted with the observations. It appears difficult to explain the observations with models based on continuous gas flows. However, a model containing Alfvén wave pulses traveling from the corona toward the transition region promises to be compatible with the observations.

Fundamental characteristics of input waste of small MSW incinerators in Korea.

PubMed

Choi, Ki-In; Lee, Suk-Hui; Lee, Dong-Hoon; Osako, Masahiro

2008-11-01

Waste incineration in a small incinerator is a simple and convenient way of treating waste discharged from small areas or from large facilities and buildings such as business centers, marketplaces, factories, and military units. Despite their ostensible advantages, however, many small incinerators frequently suffer from serious problems, e.g., unsystematic waste feeding, unstable combustion, deficient air pollution control devices, and consequently, environmental pollution. To obtain a better understanding of the characterization of wastes in small incinerators, we investigated a series of fundamental characteristics, i.e., physical composition, bulk density, proximate and ultimate analysis, potential energy content, and so on. The main waste components in small incinerators were identified as paper and plastic; the proportion of food waste was less than that in large incinerators. Especially, a low ratio of food waste had a strong influence on other waste characteristics, e.g., lower moisture content and bulk density, and higher potential energy. On the other hand, in contrast with that of HCl, there was no distinguishable linear relationship between Cl content in waste and PCDD/DF concentration in combustion gas.

The role of cone-beam breast-CT for breast cancer detection relative to breast density.

PubMed

Wienbeck, Susanne; Uhlig, Johannes; Luftner-Nagel, Susanne; Zapf, Antonia; Surov, Alexey; von Fintel, Eva; Stahnke, Vera; Lotz, Joachim; Fischer, Uwe

2017-12-01

To evaluate the impact of breast density on the diagnostic accuracy of non-contrast cone-beam breast computed tomography (CBBCT) in comparison to mammography for the detection of breast masses. A retrospective study was conducted from August 2015 to July 2016. Fifty-nine patients (65 breasts, 112 lesions) with BI-RADS, 5th edition 4 or 5 assessment in mammography and/or ultrasound of the breast received an additional non-contrast CBBCT. Independent double blind reading by two radiologists was performed for mammography and CBBCT imaging. Sensitivity, specificity and AUC were compared between the modalities. Breast lesions were histologically examined in 85 of 112 lesions (76%). The overall sensitivity for CBBCT (reader 1: 91%, reader 2: 88%) was higher than in mammography (both: 68%, p<0.001), and also for the high-density group (p<0.05). The specificity and AUC was higher for mammography in comparison to CBBCT (p<0.05 and p<0.001). The interobserver agreement (ICC) between the readers was 90% (95% CI: 86-93%) for mammography and 87% (95% CI: 82-91%) for CBBCT. Compared with two-view mammography, non-contrast CBBCT has higher sensitivity, lower specificity, and lower AUC for breast mass detection in both high and low density breasts. • Overall sensitivity for non-contrast CBBCT ranged between 88%-91%. • Sensitivity was higher for CBBCT than mammography in both density types (p<0.001). • Specificity was higher for mammography than CBBCT in both density types (p<0.05). • AUC was larger for mammography than CBBCT in both density types (p<0.001).

Statistical Measures of Large-Scale Structure

NASA Astrophysics Data System (ADS)

Vogeley, Michael; Geller, Margaret; Huchra, John; Park, Changbom; Gott, J. Richard

1993-12-01

\\inv Mpc} To quantify clustering in the large-scale distribution of galaxies and to test theories for the formation of structure in the universe, we apply statistical measures to the CfA Redshift Survey. This survey is complete to m_{B(0)}=15.5 over two contiguous regions which cover one-quarter of the sky and include ~ 11,000 galaxies. The salient features of these data are voids with diameter 30-50\\hmpc and coherent dense structures with a scale ~ 100\\hmpc. Comparison with N-body simulations rules out the ``standard" CDM model (Omega =1, b=1.5, sigma_8 =1) at the 99% confidence level because this model has insufficient power on scales lambda >30\\hmpc. An unbiased open universe CDM model (Omega h =0.2) and a biased CDM model with non-zero cosmological constant (Omega h =0.24, lambda_0 =0.6) match the observed power spectrum. The amplitude of the power spectrum depends on the luminosity of galaxies in the sample; bright (L>L(*) ) galaxies are more strongly clustered than faint galaxies. The paucity of bright galaxies in low-density regions may explain this dependence. To measure the topology of large-scale structure, we compute the genus of isodensity surfaces of the smoothed density field. On scales in the ``non-linear" regime, <= 10\\hmpc, the high- and low-density regions are multiply-connected over a broad range of density threshold, as in a filamentary net. On smoothing scales >10\\hmpc, the topology is consistent with statistics of a Gaussian random field. Simulations of CDM models fail to produce the observed coherence of structure on non-linear scales (>95% confidence level). The underdensity probability (the frequency of regions with density contrast delta rho //lineρ=-0.8) depends strongly on the luminosity of galaxies; underdense regions are significantly more common (>2sigma ) in bright (L>L(*) ) galaxy samples than in samples which include fainter galaxies.

Charge Structure and Counterion Distribution in Hexagonal DNA Liquid Crystal

PubMed Central

Dai, Liang; Mu, Yuguang; Nordenskiöld, Lars; Lapp, Alain; van der Maarel, Johan R. C.

2007-01-01

A hexagonal liquid crystal of DNA fragments (double-stranded, 150 basepairs) with tetramethylammonium (TMA) counterions was investigated with small angle neutron scattering (SANS). We obtained the structure factors pertaining to the DNA and counterion density correlations with contrast matching in the water. Molecular dynamics (MD) computer simulation of a hexagonal assembly of nine DNA molecules showed that the inter-DNA distance fluctuates with a correlation time around 2 ns and a standard deviation of 8.5% of the interaxial spacing. The MD simulation also showed a minimal effect of the fluctuations in inter-DNA distance on the radial counterion density profile and significant penetration of the grooves by TMA. The radial density profile of the counterions was also obtained from a Monte Carlo (MC) computer simulation of a hexagonal array of charged rods with fixed interaxial spacing. Strong ordering of the counterions between the DNA molecules and the absence of charge fluctuations at longer wavelengths was shown by the SANS number and charge structure factors. The DNA-counterion and counterion structure factors are interpreted with the correlation functions derived from the Poisson-Boltzmann equation, MD, and MC simulation. Best agreement is observed between the experimental structure factors and the prediction based on the Poisson-Boltzmann equation and/or MC simulation. The SANS results show that TMA is too large to penetrate the grooves to a significant extent, in contrast to what is shown by MD simulation. PMID:17098791

Scanned-probe field-emission studies of vertically aligned carbon nanofibers

NASA Astrophysics Data System (ADS)

Merkulov, Vladimir I.; Lowndes, Douglas H.; Baylor, Larry R.

2001-02-01

Field emission properties of dense and sparse "forests" of randomly placed, vertically aligned carbon nanofibers (VACNFs) were studied using a scanned probe with a small tip diameter of ˜1 μm. The probe was scanned in directions perpendicular and parallel to the sample plane, which allowed for measuring not only the emission turn-on field at fixed locations but also the emission site density over large surface areas. The results show that dense forests of VACNFs are not good field emitters as they require high extracting (turn-on) fields. This is attributed to the screening of the local electric field by the neighboring VACNFs. In contrast, sparse forests of VACNFs exhibit moderate-to-low turn-on fields as well as high emission site and current densities, and long emission lifetime, which makes them very promising for various field emission applications.

Implicit Incompressible SPH.

PubMed

Ihmsen, Markus; Cornelis, Jens; Solenthaler, Barbara; Horvath, Christopher; Teschner, Matthias

2013-07-25

We propose a novel formulation of the projection method for Smoothed Particle Hydrodynamics (SPH). We combine a symmetric SPH pressure force and an SPH discretization of the continuity equation to obtain a discretized form of the pressure Poisson equation (PPE). In contrast to previous projection schemes, our system does consider the actual computation of the pressure force. This incorporation improves the convergence rate of the solver. Furthermore, we propose to compute the density deviation based on velocities instead of positions as this formulation improves the robustness of the time-integration scheme. We show that our novel formulation outperforms previous projection schemes and state-of-the-art SPH methods. Large time steps and small density deviations of down to 0.01% can be handled in typical scenarios. The practical relevance of the approach is illustrated by scenarios with up to 40 million SPH particles.

Implicit incompressible SPH.

PubMed

Ihmsen, Markus; Cornelis, Jens; Solenthaler, Barbara; Horvath, Christopher; Teschner, Matthias

2014-03-01

We propose a novel formulation of the projection method for Smoothed Particle Hydrodynamics (SPH). We combine a symmetric SPH pressure force and an SPH discretization of the continuity equation to obtain a discretized form of the pressure Poisson equation (PPE). In contrast to previous projection schemes, our system does consider the actual computation of the pressure force. This incorporation improves the convergence rate of the solver. Furthermore, we propose to compute the density deviation based on velocities instead of positions as this formulation improves the robustness of the time-integration scheme. We show that our novel formulation outperforms previous projection schemes and state-of-the-art SPH methods. Large time steps and small density deviations of down to 0.01 percent can be handled in typical scenarios. The practical relevance of the approach is illustrated by scenarios with up to 40 million SPH particles.

Developmental morphology of cover crop species exhibit contrasting behaviour to changes in soil bulk density, revealed by X-ray computed tomography

PubMed Central

Burr-Hersey, Jasmine E.; Mooney, Sacha J.; Bengough, A. Glyn; Mairhofer, Stefan

2017-01-01

Plant roots growing through soil typically encounter considerable structural heterogeneity, and local variations in soil dry bulk density. The way the in situ architecture of root systems of different species respond to such heterogeneity is poorly understood due to challenges in visualising roots growing in soil. The objective of this study was to visualise and quantify the impact of abrupt changes in soil bulk density on the roots of three cover crop species with contrasting inherent root morphologies, viz. tillage radish (Raphanus sativus), vetch (Vicia sativa) and black oat (Avena strigosa). The species were grown in soil columns containing a two-layer compaction treatment featuring a 1.2 g cm-3 (uncompacted) zone overlaying a 1.4 g cm-3 (compacted) zone. Three-dimensional visualisations of the root architecture were generated via X-ray computed tomography, and an automated root-segmentation imaging algorithm. Three classes of behaviour were manifest as a result of roots encountering the compacted interface, directly related to the species. For radish, there was switch from a single tap-root to multiple perpendicular roots which penetrated the compacted zone, whilst for vetch primary roots were diverted more horizontally with limited lateral growth at less acute angles. Black oat roots penetrated the compacted zone with no apparent deviation. Smaller root volume, surface area and lateral growth were consistently observed in the compacted zone in comparison to the uncompacted zone across all species. The rapid transition in soil bulk density had a large effect on root morphology that differed greatly between species, with major implications for how these cover crops will modify and interact with soil structure. PMID:28753645

Developmental morphology of cover crop species exhibit contrasting behaviour to changes in soil bulk density, revealed by X-ray computed tomography.

PubMed

Burr-Hersey, Jasmine E; Mooney, Sacha J; Bengough, A Glyn; Mairhofer, Stefan; Ritz, Karl

2017-01-01

Plant roots growing through soil typically encounter considerable structural heterogeneity, and local variations in soil dry bulk density. The way the in situ architecture of root systems of different species respond to such heterogeneity is poorly understood due to challenges in visualising roots growing in soil. The objective of this study was to visualise and quantify the impact of abrupt changes in soil bulk density on the roots of three cover crop species with contrasting inherent root morphologies, viz. tillage radish (Raphanus sativus), vetch (Vicia sativa) and black oat (Avena strigosa). The species were grown in soil columns containing a two-layer compaction treatment featuring a 1.2 g cm-3 (uncompacted) zone overlaying a 1.4 g cm-3 (compacted) zone. Three-dimensional visualisations of the root architecture were generated via X-ray computed tomography, and an automated root-segmentation imaging algorithm. Three classes of behaviour were manifest as a result of roots encountering the compacted interface, directly related to the species. For radish, there was switch from a single tap-root to multiple perpendicular roots which penetrated the compacted zone, whilst for vetch primary roots were diverted more horizontally with limited lateral growth at less acute angles. Black oat roots penetrated the compacted zone with no apparent deviation. Smaller root volume, surface area and lateral growth were consistently observed in the compacted zone in comparison to the uncompacted zone across all species. The rapid transition in soil bulk density had a large effect on root morphology that differed greatly between species, with major implications for how these cover crops will modify and interact with soil structure.

Discovery of a Protocluster Associated with a Lyα Blob Pair at z = 2.3

NASA Astrophysics Data System (ADS)

Bădescu, Toma; Yang, Yujin; Bertoldi, Frank; Zabludoff, Ann; Karim, Alexander; Magnelli, Benjamin

2017-08-01

Bright Lyα blobs (LABs)—extended nebulae with sizes of ˜100 kpc and Lyα luminosities of ˜1044 erg s-1—often reside in overdensities of compact Lyα emitters (LAEs) that may be galaxy protoclusters. The number density, variance, and internal kinematics of LABs suggest that they themselves trace group-like halos. Here, we test this hierarchical picture, presenting deep, wide-field Lyα narrowband imaging of a 1° × 0.°5 region around a LAB pair at z = 2.3 discovered previously by a blind survey. We find 183 Lyα emitters, including the original LAB pair and three new LABs with Lyα luminosities of (0.9{--}1.3)× {10}43 erg s-1 and isophotal areas of 16-24 arcsec2. Using the LAEs as tracers and a new kernel density estimation method, we discover a large-scale overdensity (Boötes J1430+3522) with a surface density contrast of {δ }{{Σ }}=2.7, a volume density contrast of δ ˜10.4, and a projected diameter of ≈20 comoving Mpc. Comparing with cosmological simulations, we conclude that this LAE overdensity will evolve into a present-day Coma-like cluster with {log}(M/{M}⊙ ) ˜ 15.1 ± 0.2. In this and three other wide-field LAE surveys re-analyzed here, the extents and peak amplitudes of the largest LAE overdensities are similar, not increasing with survey size, and implying that they were indeed the largest structures then and today evolve into rich clusters. Intriguingly, LABs favor the outskirts of the densest LAE concentrations, I.e., intermediate LAE overdensities of {δ }{{Σ }}=1{--}2. We speculate that these LABs mark infalling protogroups being accreted by the more massive protocluster.

Fine scale bio-physical oceanographic characteristics predict the foraging occurrence of contrasting seabird species; Gannet (Morus bassanus) and storm petrel (Hydrobates pelagicus)

NASA Astrophysics Data System (ADS)

Scott, B. E.; Webb, A.; Palmer, M. R.; Embling, C. B.; Sharples, J.

2013-10-01

As we begin to manage our oceans in much more spatial detail we must understand a great deal more about oceanographic habitat preferences of marine mobile top predators. In this unique field study we test a hypothesis on the mechanisms defining mobile predator foraging habitat characteristics by comparing temporally and spatially detailed bio-physical oceanographic data from contrasting topographical locations. We contrast the foraging locations of two very different seabird species, gannets and storm petrels, by repeatedly sampling a bank and a nearby flat area over daily tidal cycles during spring and neap tides. The results suggest that storm petrels are linked to foraging in specific locations where internal waves are produced, which is mainly on banks. These locations can also include the presence of high biomass of chlorophyll. In contrast, the location where more gannets are foraging is significantly influenced by temporal variables with higher densities of foraging birds much more likely during the neap tide than times of spring tide. The foraging times of both species was influenced by differences between the vertical layers of the water column above and below the thermocline; via either vertical shear of horizontal currents or absolute differences in speed between layers. Higher densities of foraging gannets were significantly more likely to be found at ebb tides in both bank and flat regions however over the bank, the density of foraging gannets was higher when the differences in speed between the layers were at a maximum. Both gannets and storm petrels appear to be more likely to forage when wind direction is opposed to tidal direction. This detailed understanding links foraging behaviour to predictable spatial and temporal bio-physical vertical characteristics and thus can be immediately used to explain variance and increase certainty in past abundance and distributional surveys. These results also illuminate the types of variables that should be considered when assessing potential changes to the distribution and characteristics of habitats from increased anthropogenic disturbances such as large scale offshore wind, wave and tidal renewable deployments.

Current-induced changes of migration energy barriers in graphene and carbon nanotubes

NASA Astrophysics Data System (ADS)

Obodo, J. T.; Rungger, I.; Sanvito, S.; Schwingenschlögl, U.

2016-05-01

An electron current can move atoms in a nanoscale device with important consequences for the device operation and breakdown. We perform first principles calculations aimed at evaluating the possibility of changing the energy barriers for atom migration in carbon-based systems. In particular, we consider the migration of adatoms and defects in graphene and carbon nanotubes. Although the current-induced forces are large for both the systems, in graphene the force component along the migration path is small and therefore the barrier height is little affected by the current flow. In contrast, the same barrier is significantly reduced in carbon nanotubes as the current increases. Our work also provides a real-system numerical demonstration that current-induced forces within density functional theory are non-conservative.An electron current can move atoms in a nanoscale device with important consequences for the device operation and breakdown. We perform first principles calculations aimed at evaluating the possibility of changing the energy barriers for atom migration in carbon-based systems. In particular, we consider the migration of adatoms and defects in graphene and carbon nanotubes. Although the current-induced forces are large for both the systems, in graphene the force component along the migration path is small and therefore the barrier height is little affected by the current flow. In contrast, the same barrier is significantly reduced in carbon nanotubes as the current increases. Our work also provides a real-system numerical demonstration that current-induced forces within density functional theory are non-conservative. Electronic supplementary information (ESI) available. See DOI: 10.1039/C6NR00534A

THE ROLE OF CORE MASS IN CONTROLLING EVAPORATION: THE KEPLER RADIUS DISTRIBUTION AND THE KEPLER-36 DENSITY DICHOTOMY

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

Lopez, Eric D.; Fortney, Jonathan J.

2013-10-10

We use models of coupled thermal evolution and photo-evaporative mass loss to understand the formation and evolution of the Kepler-36 system. We show that the large contrast in mean planetary density observed by Carter et al. can be explained as a natural consequence of photo-evaporation from planets that formed with similar initial compositions. However, rather than being due to differences in XUV irradiation between the planets, we find that this contrast is due to the difference in the masses of the planets' rock/iron cores and the impact that this has on mass-loss evolution. We explore in detail how our coupledmore » models depend on irradiation, mass, age, composition, and the efficiency of mass loss. Based on fits to large numbers of coupled evolution and mass-loss runs, we provide analytic fits to understand threshold XUV fluxes for significant atmospheric loss, as a function of core mass and mass-loss efficiency. Finally we discuss these results in the context of recent studies of the radius distribution of Kepler candidates. Using our parameter study, we make testable predictions for the frequency of sub-Neptune-sized planets. We show that 1.8-4.0 R{sub ⊕} planets should become significantly less common on orbits within 10 days and discuss the possibility of a narrow 'occurrence valley' in the radius-flux distribution. Moreover, we describe how photo-evaporation provides a natural explanation for the recent observations of Ciardi et al. that inner planets are preferentially smaller within the systems.« less

Mixing in heterogeneous internally-heated convection

NASA Astrophysics Data System (ADS)

Limare, A.; Kaminski, E. C.; Jaupart, C. P.; Farnetani, C. G.; Fourel, L.; Froment, M.

2017-12-01

Past laboratory experiments of thermo chemical convection have dealt with systems involving fluids with different intrinsic densities and viscosities in a Rayleigh-Bénard setup. Although these experiments have greatly improved our understanding of the Earth's mantle dynamics, they neglect a fundamental component of planetary convection: internal heat sources. We have developed a microwave-based method in order to study convection and mixing in systems involving two layers of fluid with different densities, viscosities, and internal heat production rates. Our innovative laboratory experiments are appropriate for the early Earth, when the lowermost mantle was likely enriched in incompatible and heat producing elements and when the heat flux from the core probably accounted for a small fraction of the mantle heat budget. They are also relevant to the present-day mantle if one considers that radioactive decay and secular cooling contribute both to internal heating. Our goal is to quantify how two fluid layers mix, which is still very difficult to resolve accurately in 3-D numerical calculations. Viscosities and microwave absorptions are tuned to achieve high values of the Rayleigh-Roberts and Prandtl numbers relevant for planetary convection. We start from a stably stratified system where the lower layer has higher internal heat production and density than the upper layer. Due to mixing, the amount of enriched material gradually decreases to zero over a finite time called the lifetime. Based on more than 30 experiments, we have derived a scaling law that relates the lifetime of an enriched reservoir to the layer thickness ratio, a, to the density and viscosity contrasts between the two layers, and to their two different internal heating rates in the form of an enrichment factor beta=1+2*a*H1/H, where H1 is the heating rate of the lower fluid and H is the average heating rate. We find that the lifetime of the lower enriched reservoir varies as beta**(-7/3) in the low viscosity contrast limit, and as beta**(-4/3) in the large viscosity contrast limit. Our state-of-the-art experimental technique thus provides insights on chemical differentiation processes and on the evolution of mantle heterogeneities on both short and long time-scales.

A Feature-based Approach to Big Data Analysis of Medical Images

PubMed Central

Toews, Matthew; Wachinger, Christian; Estepar, Raul San Jose; Wells, William M.

2015-01-01

This paper proposes an inference method well-suited to large sets of medical images. The method is based upon a framework where distinctive 3D scale-invariant features are indexed efficiently to identify approximate nearest-neighbor (NN) feature matches in O(log N) computational complexity in the number of images N. It thus scales well to large data sets, in contrast to methods based on pair-wise image registration or feature matching requiring O(N) complexity. Our theoretical contribution is a density estimator based on a generative model that generalizes kernel density estimation and K-nearest neighbor (KNN) methods. The estimator can be used for on-the-fly queries, without requiring explicit parametric models or an off-line training phase. The method is validated on a large multi-site data set of 95,000,000 features extracted from 19,000 lung CT scans. Subject-level classification identifies all images of the same subjects across the entire data set despite deformation due to breathing state, including unintentional duplicate scans. State-of-the-art performance is achieved in predicting chronic pulmonary obstructive disorder (COPD) severity across the 5-category GOLD clinical rating, with an accuracy of 89% if both exact and one-off predictions are considered correct. PMID:26221685

A Feature-Based Approach to Big Data Analysis of Medical Images.

PubMed

Toews, Matthew; Wachinger, Christian; Estepar, Raul San Jose; Wells, William M

2015-01-01

This paper proposes an inference method well-suited to large sets of medical images. The method is based upon a framework where distinctive 3D scale-invariant features are indexed efficiently to identify approximate nearest-neighbor (NN) feature matches-in O (log N) computational complexity in the number of images N. It thus scales well to large data sets, in contrast to methods based on pair-wise image registration or feature matching requiring O(N) complexity. Our theoretical contribution is a density estimator based on a generative model that generalizes kernel density estimation and K-nearest neighbor (KNN) methods.. The estimator can be used for on-the-fly queries, without requiring explicit parametric models or an off-line training phase. The method is validated on a large multi-site data set of 95,000,000 features extracted from 19,000 lung CT scans. Subject-level classification identifies all images of the same subjects across the entire data set despite deformation due to breathing state, including unintentional duplicate scans. State-of-the-art performance is achieved in predicting chronic pulmonary obstructive disorder (COPD) severity across the 5-category GOLD clinical rating, with an accuracy of 89% if both exact and one-off predictions are considered correct.

On the shape of giant soap bubbles.

PubMed

Cohen, Caroline; Darbois Texier, Baptiste; Reyssat, Etienne; Snoeijer, Jacco H; Quéré, David; Clanet, Christophe

2017-03-07

We study the effect of gravity on giant soap bubbles and show that it becomes dominant above the critical size [Formula: see text], where [Formula: see text] is the mean thickness of the soap film and [Formula: see text] is the capillary length ([Formula: see text] stands for vapor-liquid surface tension, and [Formula: see text] stands for the liquid density). We first show experimentally that large soap bubbles do not retain a spherical shape but flatten when increasing their size. A theoretical model is then developed to account for this effect, predicting the shape based on mechanical equilibrium. In stark contrast to liquid drops, we show that there is no mechanical limit of the height of giant bubble shapes. In practice, the physicochemical constraints imposed by surfactant molecules limit the access to this large asymptotic domain. However, by an exact analogy, it is shown how the giant bubble shapes can be realized by large inflatable structures.

Automated assessment of breast tissue density in non-contrast 3D CT images without image segmentation based on a deep CNN

NASA Astrophysics Data System (ADS)

Zhou, Xiangrong; Kano, Takuya; Koyasu, Hiromi; Li, Shuo; Zhou, Xinxin; Hara, Takeshi; Matsuo, Masayuki; Fujita, Hiroshi

2017-03-01

This paper describes a novel approach for the automatic assessment of breast density in non-contrast three-dimensional computed tomography (3D CT) images. The proposed approach trains and uses a deep convolutional neural network (CNN) from scratch to classify breast tissue density directly from CT images without segmenting the anatomical structures, which creates a bottleneck in conventional approaches. Our scheme determines breast density in a 3D breast region by decomposing the 3D region into several radial 2D-sections from the nipple, and measuring the distribution of breast tissue densities on each 2D section from different orientations. The whole scheme is designed as a compact network without the need for post-processing and provides high robustness and computational efficiency in clinical settings. We applied this scheme to a dataset of 463 non-contrast CT scans obtained from 30- to 45-year-old-women in Japan. The density of breast tissue in each CT scan was assigned to one of four categories (glandular tissue within the breast <25%, 25%-50%, 50%-75%, and >75%) by a radiologist as ground truth. We used 405 CT scans for training a deep CNN and the remaining 58 CT scans for testing the performance. The experimental results demonstrated that the findings of the proposed approach and those of the radiologist were the same in 72% of the CT scans among the training samples and 76% among the testing samples. These results demonstrate the potential use of deep CNN for assessing breast tissue density in non-contrast 3D CT images.

The role of propagule pressure, genetic diversity and microsite availability for Senecio vernalis invasion.

PubMed

Erfmeier, Alexandra; Hantsch, Lydia; Bruelheide, Helge

2013-01-01

Genetic diversity is supposed to support the colonization success of expanding species, in particular in situations where microsite availability is constrained. Addressing the role of genetic diversity in plant invasion experimentally requires its manipulation independent of propagule pressure. To assess the relative importance of these components for the invasion of Senecio vernalis, we created propagule mixtures of four levels of genotype diversity by combining seeds across remote populations, across proximate populations, within single populations and within seed families. In a first container experiment with constant Festuca rupicola density as matrix, genotype diversity was crossed with three levels of seed density. In a second experiment, we tested for effects of establishment limitation and genotype diversity by manipulating Festuca densities. Increasing genetic diversity had no effects on abundance and biomass of S. vernalis but positively affected the proportion of large individuals to small individuals. Mixtures composed from proximate populations had a significantly higher proportion of large individuals than mixtures composed from within seed families only. High propagule pressure increased emergence and establishment of S. vernalis but had no effect on individual growth performance. Establishment was favoured in containers with Festuca, but performance of surviving seedlings was higher in open soil treatments. For S. vernalis invasion, we found a shift in driving factors from density dependence to effects of genetic diversity across life stages. While initial abundance was mostly linked to the amount of seed input, genetic diversity, in contrast, affected later stages of colonization probably via sampling effects and seemed to contribute to filtering the genotypes that finally grew up. In consequence, when disentangling the mechanistic relationships of genetic diversity, seed density and microsite limitation in colonization of invasive plants, a clear differentiation between initial emergence and subsequent survival to juvenile and adult stages is required.

Density, ages, and growth rates in old-growth and young-growth forests in coastal Oregon

USGS Publications Warehouse

Tappeiner, J. C.; Huffman, D.; Spies, T.; Bailey, John D.

1997-01-01

We studied the ages and diameter growth rates of trees in former Douglas-fir (Pseudotsuga menziesii (Mirb.)Franco) old-growth stands on 10 sites and compared them with young-growth stands (50-70 years old, regenerated after timber harvest) in the Coast Range of western Oregon. The diameters and diameter growth rates for the first 100 years of trees in the old-growth stands were significantly greater than those in the young-growth stands. Growth rates in the old stands were comparable with those from long-term studies of young stands in which density is about 100-120 trees/ha; often young-growth stand density is well over 500 trees/ha. Ages of large trees in the old stands ranged from 100 to 420 years; ages in young stands varied by only about 5 to 10 years. Apparently, regeneration of old-growth stands on these sites occurred over a prolonged period, and trees grew at low density with little self-thinning; in contrast, after timber harvest, young stands may develop with high density of trees with similar ages and considerable self-thinning. The results suggest that thinning may be needed in dense young stands where the management objective is to speed development of old-growth characteristics.

Factors leading to different viability predictions for a grizzly bear data set

USGS Publications Warehouse

Mills, L.S.; Hayes, S.G.; Wisdom, M.J.; Citta, J.; Mattson, D.J.; Murphy, K.

1996-01-01

Population viability analysis programs are being used increasingly in research and management applications, but there has not been a systematic study of the congruence of different program predictions based on a single data set. We performed such an analysis using four population viability analysis computer programs: GAPPS, INMAT, RAMAS/AGE, and VORTEX. The standardized demographic rates used in all programs were generalized from hypothetical increasing and decreasing grizzly bear (Ursus arctos horribilis) populations. Idiosyncracies of input format for each program led to minor differences in intrinsic growth rates that translated into striking differences in estimates of extinction rates and expected population size. In contrast, the addition of demographic stochasticity, environmental stochasticity, and inbreeding costs caused only a small divergence in viability predictions. But, the addition of density dependence caused large deviations between the programs despite our best attempts to use the same density-dependent functions. Population viability programs differ in how density dependence is incorporated, and the necessary functions are difficult to parameterize accurately. Thus, we recommend that unless data clearly suggest a particular density-dependent model, predictions based on population viability analysis should include at least one scenario without density dependence. Further, we describe output metrics that may differ between programs; development of future software could benefit from standardized input and output formats across different programs.

The shadow of Saturn's icy satellites in the E ring

NASA Astrophysics Data System (ADS)

Schmidt, J.; Sremcevic, M.

2008-09-01

We analyze shadows that Saturnian satellites cast in the E ring, a faint, broad dust ring composed of icy grains. The brightness contrast of a moon's shadow relative to the surrounding ring allows to infer local properties of the size distribution of ring particles. We derive the shadow contrast from a large number of Cassini images of Enceladus taken in various filters in a range of phase angles 144 to 164 degrees. For Tethys and Dione we identify a clear shadow in images with phase angles larger than 160 degrees. From the data we obtain the number density of E ring grains at the orbits of Tethys and Dione relative to the one near Enceladus. The latter we constrain from the variation of the shadow contrast with color and phase angle. From the Enceladus data we construct the phase curve of the E ring dust between 144 and 164 degrees. We compare to data obtained from Earth-bound observations by de Pater et al 2004 and in situ measurements by the Cosmic Dust Analyzer onboard Cassini.

Mechanism Of Long Term Change In Electrochrcmism Of LixWO3 Films

NASA Astrophysics Data System (ADS)

Nagai, Junichi; Kamimori, Tadatoshi; Mizuhashi, Mamoru

1984-11-01

The degradation mechanism of gradual decrease of the contrast between colored and bleached states of Lix'. WO3 films with switching cycles was investigated. We made electro-chemical and quantitative chemical analyses to clarify this phenomenon. It was found that the decrease in contrast was mostly attributed to the parallel cathodic shift of emf(x), passibly caused by ion exchange reaction expressed by: WOH + Li+ WOLi + H. Fully ion-exchanged WO3 films showed no appreciable change in spite of the presence of a large amount of Li in them. These films were capable of accepting as much Li as the fresh films did on coloration and reached to the same optical densities. It is concluded that there are two kinds of active sites available for accepting lithium ions in the WO3 structure, one for ion exchange and the other for coloration.

Cytoskeletal Components Define Protein Location to Membrane Microdomains*

PubMed Central

Szymanski, Witold G.; Zauber, Henrik; Erban, Alexander; Gorka, Michal; Wu, Xu Na; Schulze, Waltraud X.

2015-01-01

The plasma membrane is an important compartment that undergoes dynamic changes in composition upon external or internal stimuli. The dynamic subcompartmentation of proteins in ordered low-density (DRM) and disordered high-density (DSM) membrane phases is hypothesized to require interactions with cytoskeletal components. Here, we systematically analyzed the effects of actin or tubulin disruption on the distribution of proteins between membrane density phases. We used a proteomic screen to identify candidate proteins with altered submembrane location, followed by biochemical or cell biological characterization in Arabidopsis thaliana. We found that several proteins, such as plasma membrane ATPases, receptor kinases, or remorins resulted in a differential distribution between membrane density phases upon cytoskeletal disruption. Moreover, in most cases, contrasting effects were observed: Disruption of actin filaments largely led to a redistribution of proteins from DRM to DSM membrane fractions while disruption of tubulins resulted in general depletion of proteins from the membranes. We conclude that actin filaments are necessary for dynamic movement of proteins between different membrane phases and that microtubules are not necessarily important for formation of microdomains as such, but rather they may control the protein amount present in the membrane phases. PMID:26091700

Visualization and simulation of density driven convection in porous media using magnetic resonance imaging

NASA Astrophysics Data System (ADS)

Montague, James A.; Pinder, George F.; Gonyea, Jay V.; Hipko, Scott; Watts, Richard

2018-05-01

Magnetic resonance imaging is used to observe solute transport in a 40 cm long, 26 cm diameter sand column that contained a central core of low permeability silica surrounded by higher permeability well-sorted sand. Low concentrations (2.9 g/L) of Magnevist, a gadolinium based contrast agent, produce density driven convection within the column when it starts in an unstable state. The unstable state, for this experiment, exists when higher density contrast agent is present above the lower density water. We implement a numerical model in OpenFOAM to reproduce the observed fluid flow and transport from a density difference of 0.3%. The experimental results demonstrate the usefulness of magnetic resonance imaging in observing three-dimensional gravity-driven convective-dispersive transport behaviors in medium scale experiments.

A multi-wavelength, high-contrast contact radiography system for the study of low-density aerogel foams

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

Opachich, Y. P., E-mail: opachiyp@nv.doe.gov; Koch, J. A.; Haugh, M. J.

2016-07-15

A multi-wavelength, high contrast contact radiography system has been developed to characterize density variations in ultra-low density aerogel foams. These foams are used to generate a ramped pressure drive in materials strength experiments at the National Ignition Facility and require precision characterization in order to reduce errors in measurements. The system was used to characterize density variations in carbon and silicon based aerogels to ∼10.3% accuracy with ∼30 μm spatial resolution. The system description, performance, and measurement results collected using a 17.8 mg/cc carbon based JX–6 (C{sub 20}H{sub 30}) aerogel are discussed in this manuscript.

A multi-wavelength, high-contrast contact radiography system for the study of low density aerogel foams

DOE PAGES

Opachich, Y.P.; Koch, J.A.; Haugh, M. J.; ...

2017-07-01

A multi wavelength, high contrast contact radiography system has been developed to characterize density variations in ultra-low density aerogel foams. These foams are used to generate a ramped pressure drive in materials strength experiments at the National Ignition Facility (NIF) and require precision characterization in order to reduce errors in measurements. The system was used to characterize density variations in carbon and silicon based aerogels to ~10.3% accuracy with ~30 μm spatial resolution. The system description, performance and measurement results collected using a 17.8 mg/cc carbon based JX–6 (C 20H 30) aerogel are discussed in this manuscript.

Landslide processes in saprolitic soils of a tropical rain forest, Puerto Rico

USGS Publications Warehouse

Larsen, Matthew C.; Simon, Andrew; Larue, D.K.; Draper, G.

1990-01-01

Slickensides are present in the saprolite along relict fractures and joints derived from the parent rock; they are common in quartz-diorite bedrock, and less so in marine-deposited volcaniclastic bedrock. The failure planes of many landslides have exposed these relict fractures and joints as slickensides, and landslides appear to move on these pre-existing planes of weakness in the saprolite. The larges landslides (areas greater than 20,000 m2, however, are those that fail along saprolite-bedrock boundaries, which are zones of contrasting density and permeability within or at the base of the weathered profile.

Spherical collapse in chameleon models

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

Brax, Ph.; Rosenfeld, R.; Steer, D.A., E-mail: brax@spht.saclay.cea.fr, E-mail: rosenfel@ift.unesp.br, E-mail: daniele.steer@apc.univ-paris7.fr

2010-08-01

We study the gravitational collapse of an overdensity of nonrelativistic matter under the action of gravity and a chameleon scalar field. We show that the spherical collapse model is modified by the presence of a chameleon field. In particular, we find that even though the chameleon effects can be potentially large at small scales, for a large enough initial size of the inhomogeneity the collapsing region possesses a thin shell that shields the modification of gravity induced by the chameleon field, recovering the standard gravity results. We analyse the behaviour of a collapsing shell in a cosmological setting in themore » presence of a thin shell and find that, in contrast to the usual case, the critical density for collapse in principle depends on the initial comoving size of the inhomogeneity.« less

Xylem anatomy correlates with gas exchange, water-use efficiency and growth performance under contrasting water regimes: evidence from Populus deltoides x Populus nigra hybrids.

PubMed

Fichot, Régis; Laurans, Françoise; Monclus, Romain; Moreau, Alain; Pilate, Gilles; Brignolas, Franck

2009-12-01

Six Populus deltoides Bartr. ex Marsh. x P. nigra L. genotypes were selected to investigate whether stem xylem anatomy correlated with gas exchange rates, water-use efficiency (WUE) and growth performance. Clonal copies of the genotypes were grown in a two-plot common garden test under contrasting water regimes, with one plot maintained irrigated and the other one subjected to moderate summer water deficit. The six genotypes displayed a large range of xylem anatomy, mean vessel and fibre diameter varying from about 40 to 60 microm and from 7.5 to 10.5 microm, respectively. Decreased water availability resulted in a reduced cell size and an important rise in vessel density, but the extent of xylem plasticity was both genotype and trait dependent. Vessel diameter and theoretical xylem-specific hydraulic conductivity correlated positively with stomatal conductance, carbon isotope discrimination and growth performance-related traits and negatively with intrinsic WUE, especially under water deficit conditions. Vessel diameter and vessel density measured under water deficit conditions correlated with the relative losses in biomass production in response to water deprivation; this resulted from the fact that a more plastic xylem structure was generally accompanied by a larger loss in biomass production.

Common low-density lipoprotein receptor p.G116S variant has a large effect on plasma low-density lipoprotein cholesterol in circumpolar inuit populations.

PubMed

Dubé, Joseph B; Wang, Jian; Cao, Henian; McIntyre, Adam D; Johansen, Christopher T; Hopkins, Scarlett E; Stringer, Randa; Hosseinzadeh, Siyavash; Kennedy, Brooke A; Ban, Matthew R; Young, T Kue; Connelly, Philip W; Dewailly, Eric; Bjerregaard, Peter; Boyer, Bert B; Hegele, Robert A

2015-02-01

Inuit are considered to be vulnerable to cardiovascular disease because their lifestyles are becoming more Westernized. During sequence analysis of Inuit individuals at extremes of lipid traits, we identified 2 nonsynonymous variants in low-density lipoprotein receptor (LDLR), namely p.G116S and p.R730W. Genotyping these variants in 3324 Inuit from Alaska, Canada, and Greenland showed they were common, with allele frequencies 10% to 15%. Only p.G116S was associated with dyslipidemia: the increase in LDL cholesterol was 0.54 mmol/L (20.9 mg/dL) per allele (P=5.6×10(-49)), which was >3× larger than the largest effect sizes seen with other common variants in other populations. Carriers of p.G116S had a 3.02-fold increased risk of hypercholesterolemia (95% confidence interval, 2.34-3.90; P=1.7×10(-17)), but did not have classical familial hypercholesterolemia. In vitro, p.G116S showed 60% reduced ligand-binding activity compared with wild-type receptor. In contrast, p.R730W was associated with neither LDL cholesterol level nor altered in vitro activity. LDLR p.G116S is thus unique: a common dysfunctional variant in Inuit whose large effect on LDL cholesterol may have public health implications. © 2014 American Heart Association, Inc.

Liquid fractionation. Part I: Basic principles and experimental simulations

NASA Astrophysics Data System (ADS)

McBirney, Alexander R.; Baker, Brian H.; Nilson, Robert H.

1985-03-01

A possible explanation for the closely associated magmas of contrasting compositions erupted from many mature volcanic centers can be found in the large differences of density produced by relatively small compositional variations in liquids that evolve by crystallization or melting at the walls of shallow magma chambers. A mechanism of liquid fractionation in which differentiated liquids segragate gravitationally to form compositionally graded columns of magma may surmount the long-standing problem of explaining large volumes of highly evolved liquids that reach advanced degrees of differentiation in times that are too short to be consistent with conventional models of crystal fractionation based on crystal settling. In those types of magmas that decrease in density as they differentiate, a fractionated liquid next to a wall may form a buoyant compositional boundary layer that flows up the wall and accumulates as a separate zone in the upper levels of the reservoir. Magmas that increase in density as they differentiate will have the opposite behavior; they descend along the wall and pond on the floor. Both types of systems can be modeled using simple aqueous solutions and techniques similar to those developed by Chen and Turner (1980). The insights gained through experiments of this kind suggest a number of processes that may be responsible for common types of volcanic behavior and patterns of differentiation in shallow plutons.

Ocean acidification induces biochemical and morphological changes in the calcification process of large benthic foraminifera.

PubMed

Prazeres, Martina; Uthicke, Sven; Pandolfi, John M

2015-03-22

Large benthic foraminifera are significant contributors to sediment formation on coral reefs, yet they are vulnerable to ocean acidification. Here, we assessed the biochemical and morphological impacts of acidification on the calcification of Amphistegina lessonii and Marginopora vertebralis exposed to different pH conditions. We measured growth rates (surface area and buoyant weight) and Ca-ATPase and Mg-ATPase activities and calculated shell density using micro-computer tomography images. In A. lessonii, we detected a significant decrease in buoyant weight, a reduction in the density of inner skeletal chambers, and an increase of Ca-ATPase and Mg-ATPase activities at pH 7.6 when compared with ambient conditions of pH 8.1. By contrast, M. vertebralis showed an inhibition in Mg-ATPase activity under lowered pH, with growth rate and skeletal density remaining constant. While M. vertebralis is considered to be more sensitive than A. lessonii owing to its high-Mg-calcite skeleton, it appears to be less affected by changes in pH, based on the parameters assessed in this study. We suggest difference in biochemical pathways of calcification as the main factor influencing response to changes in pH levels, and that A. lessonii and M. vertebralis have the ability to regulate biochemical functions to cope with short-term increases in acidity. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Dependence of high density nitrogen-vacancy center ensemble coherence on electron irradiation doses and annealing time

NASA Astrophysics Data System (ADS)

Zhang, C.; Yuan, H.; Zhang, N.; Xu, L. X.; Li, B.; Cheng, G. D.; Wang, Y.; Gui, Q.; Fang, J. C.

2017-12-01

Negatively charged nitrogen-vacancy (NV-) center ensembles in diamond have proved to have great potential for use in highly sensitive, small-package solid-state quantum sensors. One way to improve sensitivity is to produce a high-density NV- center ensemble on a large scale with a long coherence lifetime. In this work, the NV- center ensemble is prepared in type-Ib diamond using high energy electron irradiation and annealing, and the transverse relaxation time of the ensemble—T 2—was systematically investigated as a function of the irradiation electron dose and annealing time. Dynamical decoupling sequences were used to characterize T 2. To overcome the problem of low signal-to-noise ratio in T 2 measurement, a coupled strip lines waveguide was used to synchronously manipulate NV- centers along three directions to improve fluorescence signal contrast. Finally, NV- center ensembles with a high concentration of roughly 1015 mm-3 were manipulated within a ~10 µs coherence time. By applying a multi-coupled strip-lines waveguide to improve the effective volume of the diamond, a sub-femtotesla sensitivity for AC field magnetometry can be achieved. The long-coherence high-density large-scale NV- center ensemble in diamond means that types of room-temperature micro-sized solid-state quantum sensors with ultra-high sensitivity can be further developed in the near future.

Putting density back into the habitat-quality equation: case study of an open-nesting forest bird.

PubMed

Pérot, Aurore; Villard, Marc-André

2009-12-01

Ecological traps and other cases of apparently maladaptive habitat selection cast doubt on the relevance of density as an indicator of habitat quality. Nevertheless, the prevalence of these phenomena remains poorly known, and density may still reflect habitat quality in most systems. We examined the relationship between density and two other parameters of habitat quality in an open-nesting passerine species: the Ovenbird (Seiurus aurocapilla). We hypothesized that the average individual bird makes a good decision when selecting its breeding territory and that territory spacing reflects site productivity or predation risk. Therefore, we predicted that density would be positively correlated with productivity (number of young fledged per unit area). Because individual performance is sensitive to events partly determined by chance, such as nest predation, we further predicted density would be weakly correlated or uncorrelated with the proportion of territories fledging young. We collected data in 23 study sites (25 ha each), 16 of which were located in untreated mature northern hardwood forest and seven in stands partially harvested (treated) 1-7 years prior to the survey. Density explained most of the variability in productivity (R(2)= 0.73), and there was no apparent decoupling between density and productivity in treated plots. In contrast, there was no significant relationship between density and the proportion of territories fledging >or=1 young over the entire breeding season. These results suggest that density reflects habitat quality at the plot scale in this study system. To our knowledge this is one of the few studies testing the value of territory density as an indicator of habitat quality in an open-nesting bird species on the basis of a relatively large number of sizeable study plots.

Properties and spatial distribution of galaxy superclusters

NASA Astrophysics Data System (ADS)

Liivamägi, Lauri Juhan

2017-01-01

Astronomy is a science that can offer plenty of unforgettable imagery, and the large-scale distribution of galaxies is no exception. Among the first features the viewer's eye is likely to be drawn to, are large concentrations of galaxies - galaxy superclusters, contrasting to the seemingly empty regions beside them. Superclusters can extend from tens to over hundred megaparsecs, they contain from hundreds to thousands of galaxies, and many galaxy groups and clusters. Unlike galaxy clusters, superclusters are clearly unrelaxed systems, not gravitationally bound as crossing times exceed the age of the universe, and show little to no radial symmetry. Superclusters, as part of the large-scale structure, are sensitive to the initial power spectrum and the following evolution. They are massive enough to leave an imprint on the cosmic microwave background radiation. Superclusters can also provide an unique environment for their constituent galaxies and galaxy clusters. In this study we used two different observational and one simulated galaxy samples to create several catalogues of structures that, we think, correspond to what are generally considered galaxy superclusters. Superclusters were delineated as continuous over-dense regions in galaxy luminosity density fields. When calculating density fields several corrections were applied to remove small-scale redshift distortions and distance-dependent selection effects. Resulting catalogues of objects display robust statistical properties, showing that flux-limited galaxy samples can be used to create nearly volume-limited catalogues of superstructures. Generally, large superclusters can be regarded as massive, often branching filamentary structures, that are mainly characterised by their length. Smaller superclusters, on the other hand, can display a variety of shapes. Spatial distribution of superclusters shows large-scale variations, with high-density concentrations often found in semi-regularly spaced groups. Future studies are needed to quantify the relations between superclusters and finer details of the galaxy distribution. Supercluster catalogues from this thesis have already been used in numerous other studies.

Imaging the Chicxulub central crater zone from large scale seismic acoustic wave propagation and gravity modeling

NASA Astrophysics Data System (ADS)

Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.

2017-12-01

Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments

Gravity Gradient Tensor of Arbitrary 3D Polyhedral Bodies with up to Third-Order Polynomial Horizontal and Vertical Mass Contrasts

NASA Astrophysics Data System (ADS)

Ren, Zhengyong; Zhong, Yiyuan; Chen, Chaojian; Tang, Jingtian; Kalscheuer, Thomas; Maurer, Hansruedi; Li, Yang

2018-03-01

During the last 20 years, geophysicists have developed great interest in using gravity gradient tensor signals to study bodies of anomalous density in the Earth. Deriving exact solutions of the gravity gradient tensor signals has become a dominating task in exploration geophysics or geodetic fields. In this study, we developed a compact and simple framework to derive exact solutions of gravity gradient tensor measurements for polyhedral bodies, in which the density contrast is represented by a general polynomial function. The polynomial mass contrast can continuously vary in both horizontal and vertical directions. In our framework, the original three-dimensional volume integral of gravity gradient tensor signals is transformed into a set of one-dimensional line integrals along edges of the polyhedral body by sequentially invoking the volume and surface gradient (divergence) theorems. In terms of an orthogonal local coordinate system defined on these edges, exact solutions are derived for these line integrals. We successfully derived a set of unified exact solutions of gravity gradient tensors for constant, linear, quadratic and cubic polynomial orders. The exact solutions for constant and linear cases cover all previously published vertex-type exact solutions of the gravity gradient tensor for a polygonal body, though the associated algorithms may differ in numerical stability. In addition, to our best knowledge, it is the first time that exact solutions of gravity gradient tensor signals are derived for a polyhedral body with a polynomial mass contrast of order higher than one (that is quadratic and cubic orders). Three synthetic models (a prismatic body with depth-dependent density contrasts, an irregular polyhedron with linear density contrast and a tetrahedral body with horizontally and vertically varying density contrasts) are used to verify the correctness and the efficiency of our newly developed closed-form solutions. Excellent agreements are obtained between our solutions and other published exact solutions. In addition, stability tests are performed to demonstrate that our exact solutions can safely be used to detect shallow subsurface targets.

THE STRUCTURE OF SPIRAL SHOCKS EXCITED BY PLANETARY-MASS COMPANIONS

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

Zhu, Zhaohuan; Stone, James M.; Rafikov, Roman R.

2015-11-10

Direct imaging observations have revealed spiral structures in protoplanetary disks. Previous studies have suggested that planet-induced spiral arms cannot explain some of these spiral patterns, due to the large pitch angle and high contrast of the spiral arms in observations. We have carried out three-dimensional (3D) hydrodynamical simulations to study spiral wakes/shocks excited by young planets. We find that, in contrast with linear theory, the pitch angle of spiral arms does depend on the planet mass, which can be explained by the nonlinear density wave theory. A secondary (or even a tertiary) spiral arm, especially for inner arms, is alsomore » excited by a massive planet. With a more massive planet in the disk, the excited spiral arms have larger pitch angle and the separation between the primary and secondary arms in the azimuthal direction is also larger. We also find that although the arms in the outer disk do not exhibit much vertical motion, the inner arms have significant vertical motion, which boosts the density perturbation at the disk atmosphere. Combining hydrodynamical models with Monte-Carlo radiative transfer calculations, we find that the inner spiral arms are considerably more prominent in synthetic near-IR images using full 3D hydrodynamical models than images based on two-dimensional models assuming vertical hydrostatic equilibrium, indicating the need to model observations with full 3D hydrodynamics. Overall, companion-induced spiral arms not only pinpoint the companion’s position but also provide three independent ways (pitch angle, separation between two arms, and contrast of arms) to constrain the companion’s mass.« less

Pulsed laser deposited GeTe-rich GeTe-Sb2Te3 thin films

PubMed Central

Bouška, M.; Pechev, S.; Simon, Q.; Boidin, R.; Nazabal, V.; Gutwirth, J.; Baudet, E.; Němec, P.

2016-01-01

Pulsed laser deposition technique was used for the fabrication of Ge-Te rich GeTe-Sb2Te3 (Ge6Sb2Te9, Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15) amorphous thin films. To evaluate the influence of GeTe content in the deposited films on physico-chemical properties of the GST materials, scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffraction and reflectometry, atomic force microscopy, Raman scattering spectroscopy, optical reflectivity, and sheet resistance temperature dependences as well as variable angle spectroscopic ellipsometry measurements were used to characterize as-deposited (amorphous) and annealed (crystalline) layers. Upon crystallization, optical functions and electrical resistance of the films change drastically, leading to large optical and electrical contrast between amorphous and crystalline phases. Large changes of optical/electrical properties are accompanied by the variations of thickness, density, and roughness of the films due to crystallization. Reflectivity contrast as high as ~0.21 at 405 nm was calculated for Ge8Sb2Te11, Ge10Sb2Te13, and Ge12Sb2Te15 layers. PMID:27199107

Molecular dynamics simulation of the plastic behavior anisotropy of shock-compressed monocrystal nickel

NASA Astrophysics Data System (ADS)

Chen, Ya-Zhou; Zhou, Liu-Cheng; He, Wei-Feng; Sun, Yu; Li, Ying-Hong; Jiao, Yang; Luo, Si-Hai

2017-01-01

Molecular dynamics simulations were used to study the plastic behavior of monocrystalline nickel under shock compression along the [100] and [110] orientations. The shock Hugoniot relation, local stress curve, and process of microstructure development were determined. Results showed the apparent anisotropic behavior of monocrystalline nickel under shock compression. The separation of elastic and plastic waves was also obvious. Plastic deformation was more severely altered along the [110] direction than the [100] direction. The main microstructure phase transformed from face-centered cubic to body-centered cubic and generated a large-scale and low-density stacking fault along the family of { 111 } crystal planes under shock compression along the [100] direction. By contrast, the main mechanism of plastic deformation in the [110] direction was the nucleation of the hexagonal, close-packed phase, which generated a high density of stacking faults along the [110] and [1̅10] directions.

Large-Scale Structure Studies with the REFLEX Cluster Survey

NASA Astrophysics Data System (ADS)

Schuecker, P.; Bohringer, H.; Guzzo, L.; Collins, C.; Neumann, D. M.; Schindler, S.; Voges, W.

1998-12-01

First preliminary results of the ROSAT ESO Flux-Limited X-Ray (REFLEX) Cluster Survey are described. The survey covers 13,924 square degrees of the southern hemisphere. The present sample consists of about 470 rich clusters (1/3 non Abell/ACO clusters) with X-ray fluxes S >= 3.0 times 10^{-12} erg s^{-1} cm^{-2} (0.1-2.4 keV) and redshifts z <= 0.3. In contrast to other low-redshift surveys, the cumulative flux-number counts have an almost Euclidean slope. Comoving cluster number densities are found to be almost redshift-independent throughout the total survey volume. The X-ray luminosity function is well described by a Schechter function. The power spectrum of the number density fluctuations could be measured on scales up to 400 h^{-1} Mpc. A deeper survey with about 800 galaxy clusters in the same area is in progress.

Dynamical transition, hydrophobic interface, and the temperature dependence of electrostatic fluctuations in proteins.

PubMed

Lebard, David N; Matyushov, Dmitry V

2008-12-01

Molecular dynamics simulations have revealed a dramatic increase, with increasing temperature, of the amplitude of electrostatic fluctuations caused by water at the active site of metalloprotein plastocyanin. The increased breadth of electrostatic fluctuations, expressed in terms of the reorganization energy of changing the redox state of the protein, is related to the formation of the hydrophobic protein-water interface, allowing large-amplitude collective fluctuations of the water density in the protein's first solvation shell. On top of the monotonic increase of the reorganization energy with increasing temperature, we have observed a spike at approximately 220 K also accompanied by a significant slowing of the exponential collective Stokes shift dynamics. In contrast to the local density fluctuations of the hydration-shell waters, these spikes might be related to the global property of the water solvent crossing the Widom line or undergoing a weak first-order transition.

Statistical time-dependent model for the interstellar gas

NASA Technical Reports Server (NTRS)

Gerola, H.; Kafatos, M.; Mccray, R.

1974-01-01

We present models for temperature and ionization structure of low, uniform-density (approximately 0.3 per cu cm) interstellar gas in a galactic disk which is exposed to soft X rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction, temperature, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas that agrees with various observations. Cold regions in the low-density gas may have the appearance of clouds in 21-cm absorption. The time-dependent model, in contrast to the steady-state model, predicts large fluctuations in ionization rate and the existence of cold (approximately 30 K), ionized (ionized fraction equal to about 0.1) regions.

Extreme fluctuations in stochastic network coordination with time delays

NASA Astrophysics Data System (ADS)

Hunt, D.; Molnár, F.; Szymanski, B. K.; Korniss, G.

2015-12-01

We study the effects of uniform time delays on the extreme fluctuations in stochastic synchronization and coordination problems with linear couplings in complex networks. We obtain the average size of the fluctuations at the nodes from the behavior of the underlying modes of the network. We then obtain the scaling behavior of the extreme fluctuations with system size, as well as the distribution of the extremes on complex networks, and compare them to those on regular one-dimensional lattices. For large complex networks, when the delay is not too close to the critical one, fluctuations at the nodes effectively decouple, and the limit distributions converge to the Fisher-Tippett-Gumbel density. In contrast, fluctuations in low-dimensional spatial graphs are strongly correlated, and the limit distribution of the extremes is the Airy density. Finally, we also explore the effects of nonlinear couplings on the stability and on the extremes of the synchronization landscapes.

A method for vibrational assessment of cortical bone

NASA Astrophysics Data System (ADS)

Song, Yan; Gunaratne, Gemunu H.

2006-09-01

Large bones from many anatomical locations of the human skeleton consist of an outer shaft (cortex) surrounding a highly porous internal region (trabecular bone) whose structure is reminiscent of a disordered cubic network. Age related degradation of cortical and trabecular bone takes different forms. Trabecular bone weakens primarily by loss of connectivity of the porous network, and recent studies have shown that vibrational response can be used to obtain reliable estimates for loss of its strength. In contrast, cortical bone degrades via the accumulation of long fractures and changes in the level of mineralization of the bone tissue. In this paper, we model cortical bone by an initially solid specimen with uniform density to which long fractures are introduced; we find that, as in the case of trabecular bone, vibrational assessment provides more reliable estimates of residual strength in cortical bone than is possible using measurements of density or porosity.

Vulnerability of age-0 pallid sturgeon Scaphirhynchus albus to predation; effects of predator type, turbidity, body size, and prey density

USGS Publications Warehouse

French, William E.; Graeb, Brian D. S.; Chipps, Steven R.; Klumb, Robert A.

2014-01-01

Predation can play an important role in the recruitment dynamics of fishes with intensity regulated by behavioral (i.e., prey selectivity) and/or environmental conditions that may be especially important for rare or endangered fishes. We conducted laboratory experiments to quantify prey selection and capture efficiency by three predators employing distinct foraging strategies: pelagic piscivore (walleye Sander vitreus); benthic piscivore (flathead catfish Pylodictis olivaris) and generalist predator (smallmouth bass Micropterus dolomieu) foraging on two size classes of age-0 pallid sturgeon: large (75–100 mm fork length [FL]) and small (40–50 mm FL). Experiments at high (> 70 nephalometric turbidity units [NTU]) and low (< 5 NTU) turbidity for each predator were conducted with high and low densities of pallid sturgeon and contrasting densities of an alternative prey, fathead minnow Pimephales promelas. Predator behaviors (strikes, captures, and consumed prey) were also quantified for each prey type. Walleye and smallmouth bass negatively selected pallid sturgeon (Chesson’s α = 0.04–0.1) across all treatments, indicating low relative vulnerability to predation. Relative vulnerability to predation by flathead catfish was moderate for small pallid sturgeon (α = 0.44, neutral selection), but low for large pallid sturgeon (α = 0.11, negative selection). Turbidity (up to 100 NTU) did not affect pallid sturgeon vulnerability, even at low density of alternative prey. Age-0 pallid sturgeon were easily captured by all predators, but were rarely consumed, suggesting mechanisms other than predator capture efficiency govern sturgeon predation vulnerability.

Phase contrast in high resolution electron microscopy

DOEpatents

Rose, H.H.

1975-09-23

This patent relates to a device for developing a phase contrast signal for a scanning transmission electron microscope. The lens system of the microscope is operated in a condition of defocus so that predictable alternate concentric regions of high and low electron density exist in the cone of illumination. Two phase detectors are placed beneath the object inside the cone of illumination, with the first detector having the form of a zone plate, each of its rings covering alternate regions of either higher or lower electron density. The second detector is so configured that it covers the regions of electron density not covered by the first detector. Each detector measures the number of electrons incident thereon and the signal developed by the first detector is subtracted from the signal developed by the record detector to provide a phase contrast signal. (auth)

Modeling 3-D density distribution in the mantle from inversion of geoid anomalies: Application to the Yellowstone Province

NASA Astrophysics Data System (ADS)

Chaves, Carlos Alberto Moreno; Ussami, Naomi

2013-12-01

developed a three-dimensional scheme to invert geoid anomalies aiming to map density variations in the mantle. Using an ellipsoidal-Earth approximation, the model space is represented by tesseroids. To assess the quality of the density models, the resolution and covariance matrices were computed. From a synthetic geoid anomaly caused by a plume tail with Gaussian noise added, the inversion code was able to recover a plausible solution about the density contrast and geometry when it is compared to the synthetic model. To test the inversion algorithm in a natural case study, geoid anomalies from the Yellowstone Province (YP) were inverted. From the Earth Gravitational Model 2008 expanded up to degree 2160, lower crust- and mantle-related negative geoid anomalies with amplitude of approximately 70 m were obtained after removing long-wavelength components (>5400 km) and crustal effects. We estimated three density models for the YP. The first model, the EDM-1 (estimated density model), uses a starting model with density contrast equal to 0. The other two models, the EDM-2 and EDM-3, use an initial density derived from two S-velocity models for the western United States, the Dynamic North America Models of S Waves by Obrebsky et al. (2011) and the Northwestern United States Teleseismic Tomography of S Waves (NWUS11-S) by James et al. (2011). In these three models, a lower and an upper bound for the density solution was also imposed as a priori information. Regardless of the initial constraints, the inversion of the residual geoid indicates that the lower crust and the upper mantle of the YP have a predominantly negative density contrast ( -50 kg/m3) relative to the surrounding mantle. This solution reveals that the density contrast extends at least to 660 km depth. Regional correlation analysis between the EDM-1 and NWUS11-S indicates an anticorrelation (coefficient of -0.7) at 400 km depth. Our study suggests that the mantle density derived from the inversion of geoid could be integrated with seismic velocity models to image mantle anomalous features beyond the depth limit of investigation achieved combining gravity and seismic tomography. ©2013. American Geophysical Union. All Rights Reserved.

Implications of the observed Pluto-Charon density contrast

NASA Astrophysics Data System (ADS)

Bierson, C. J.; Nimmo, F.; McKinnon, W. B.

2018-07-01

Observations by the New Horizons spacecraft have determined that Pluto has a larger bulk density than Charon by 153 ± 44 kg m-3 (2σ uncertainty). We use a thermal model of Pluto and Charon to determine if this density contrast could be due to porosity variations alone, with Pluto and Charon having the same bulk composition. We find that Charon can preserve a larger porous ice layer than Pluto due to its lower gravity and lower heat flux but that the density contrast can only be explained if the initial ice porosity is ≳ 30%, extends to ≳100 km depth and Pluto retains a subsurface ocean today. We also find that other processes such as a modern ocean on Pluto, self-compression, water-rock interactions, and volatile (e.g., CO) loss cannot, even in combination, explain this difference in density. Although an initially high porosity cannot be completely ruled out, we conclude that it is more probable that Pluto and Charon have different bulk compositions. This difference could arise either from forming Charon via a giant impact, or via preferential loss of H2O on Pluto due to heating during rapid accretion.

Study of phenomena related to the sintering process of silicon nitride at atmospheric pressure

NASA Technical Reports Server (NTRS)

Bertani, A.

1982-01-01

A procedure was perfected for the production of components used in engineering applications of silicon nitride. Particles of complex geometry that combine remarkable mechanical properties with a high density are obtained. The process developed, in contrast to the "hot pressing" method, does not use external pressures, and in contrast to the reaction bonding method, final densities close to the theoretical value are obtained.

Plasmon dispersion and Coulomb drag in low-density electron bi-layers

NASA Astrophysics Data System (ADS)

Badalyan, S. M.; Kim, C. S.; Vignale, G.; Senatore, G.

2007-03-01

We investigate the effect of exchange and correlation (xc) on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a new approach, which employs dynamic xc kernels in the calculation of the bi-layer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. We observe that both optical and acoustical plasmon modes are strongly affected by xc corrections and shift in opposite directions with decreasing density. This is in stark contrast with the tendency observed within the random phase approximation (RPA). We find that the introduction of xc corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the RPA is found to disappear when the xc corrections are included. Our numerical results are in good agreement with the results of recent experiments by M. Kellogg et al., Solid State Commun. 123, 515 (2002).

Spin-orbit coupling and transport in strongly correlated two-dimensional systems

NASA Astrophysics Data System (ADS)

Huang, Jian; Pfeiffer, L. N.; West, K. W.

2017-05-01

Measuring the magnetoresistance (MR) of ultraclean GaAs two-dimensional holes for a large rs range of 20-50, two striking behaviors in relation to the spin-orbit coupling (SOC) emerge in response to strong electron-electron interaction. First, in exact correspondence to the zero-field metal-to-insulator transition (MIT), the sign of the MR switches from being positive in the metallic regime to being negative in the insulating regime when the carrier density crosses the critical density pc of MIT (rs˜39 ). Second, as the SOC-driven correction Δ ρ to the MR decreases with reducing carrier density (or the in-plane wave vector), it exhibits an upturn in the close proximity just above pc where rs is beyond 30, indicating a substantially enhanced SOC effect. This peculiar behavior echoes with a trend of delocalization long suspected for the SOC-interaction interplay. Meanwhile, for p 40 , in contrast to the common belief that a magnet field enhances Wigner crystallization, the negative MR is likely linked to enhanced interaction.

Satellite Gravity Drilling the Earth

NASA Technical Reports Server (NTRS)

vonFrese, R. R. B.; Potts, L. V.; Leftwich, T. E.; Kim, H. R.; Han, S.-H.; Taylor, P. T.; Ashgharzadeh, M. F.

2005-01-01

Analysis of satellite-measured gravity and topography can provide crust-to-core mass variation models for new insi@t on the geologic evolution of the Earth. The internal structure of the Earth is mostly constrained by seismic observations and geochemical considerations. We suggest that these constraints may be augmented by gravity drilling that interprets satellite altitude free-air gravity observations for boundary undulations of the internal density layers related to mass flow. The approach involves separating the free-air anomalies into terrain-correlated and -decorrelated components based on the correlation spectrum between the anomalies and the gravity effects of the terrain. The terrain-decorrelated gravity anomalies are largely devoid of the long wavelength interfering effects of the terrain gravity and thus provide enhanced constraints for modeling mass variations of the mantle and core. For the Earth, subcrustal interpretations of the terrain-decorrelated anomalies are constrained by radially stratified densities inferred from seismic observations. These anomalies, with frequencies that clearly decrease as the density contrasts deepen, facilitate mapping mass flow patterns related to the thermodynamic state and evolution of the Earth's interior.

Near Critical Preferential Attachment Networks have Small Giant Components

NASA Astrophysics Data System (ADS)

Eckhoff, Maren; Mörters, Peter; Ortgiese, Marcel

2018-05-01

Preferential attachment networks with power law exponent τ >3 are known to exhibit a phase transition. There is a value ρ c>0 such that, for small edge densities ρ ≤ ρ c every component of the graph comprises an asymptotically vanishing proportion of vertices, while for large edge densities ρ >ρ c there is a unique giant component comprising an asymptotically positive proportion of vertices. In this paper we study the decay in the size of the giant component as the critical edge density is approached from above. We show that the size decays very rapidly, like \\exp (-c/ √{ρ -ρ c}) for an explicit constant c>0 depending on the model implementation. This result is in contrast to the behaviour of the class of rank-one models of scale-free networks, including the configuration model, where the decay is polynomial. Our proofs rely on the local neighbourhood approximations of Dereich and Mörters (Ann Probab 41(1):329-384, 2013) and recent progress in the theory of branching random walks (Gantert et al. in Ann Inst Henri Poincaré Probab Stat 47(1):111-129, 2011).

Indicators of fishing mortality on reef-shark populations in the world's first shark sanctuary: the need for surveillance and enforcement

NASA Astrophysics Data System (ADS)

Vianna, Gabriel M. S.; Meekan, Mark G.; Ruppert, Jonathan L. W.; Bornovski, Tova H.; Meeuwig, Jessica J.

2016-09-01

Shark sanctuaries are promoted as a management tool to achieve conservation goals following global declines of shark populations. We assessed the status of reef-shark populations and indicators of fishing pressure across the world's first shark sanctuary in Palau. Using underwater surveys and stereophotogrammetry, we documented large differences in abundance and size structure of shark populations across the sanctuary, with a strong negative relationship between shark densities and derelict fishing gear on reefs. Densities of 10.9 ± 4.7 (mean ± SE) sharks ha-1 occurred on reefs adjacent to the most populated islands of Palau, contrasting with lower densities of 1.6 ± 0.8 sharks ha-1 on remote uninhabited reefs, where surveillance and enforcement was limited. Our observations suggest that fishing still remains a major factor structuring shark populations in Palau, demonstrating that there is an urgent need for better enforcement and surveillance that targets both illegal and licensed commercial fisheries to provide effective protection for sharks within the sanctuary.

Visualization and simulation of density driven convection in porous media using magnetic resonance imaging.

PubMed

Montague, James A; Pinder, George F; Gonyea, Jay V; Hipko, Scott; Watts, Richard

2018-05-01

Magnetic resonance imaging is used to observe solute transport in a 40cm long, 26cm diameter sand column that contained a central core of low permeability silica surrounded by higher permeability well-sorted sand. Low concentrations (2.9g/L) of Magnevist, a gadolinium based contrast agent, produce density driven convection within the column when it starts in an unstable state. The unstable state, for this experiment, exists when higher density contrast agent is present above the lower density water. We implement a numerical model in OpenFOAM to reproduce the observed fluid flow and transport from a density difference of 0.3%. The experimental results demonstrate the usefulness of magnetic resonance imaging in observing three-dimensional gravity-driven convective-dispersive transport behaviors in medium scale experiments. Copyright © 2017 Elsevier B.V. All rights reserved.

Advanced UVOIR Mirror Technology Development (AMTD) for Very Large Space Telescopes

NASA Technical Reports Server (NTRS)

Postman, Marc; Soummer, Remi; Sivramakrishnan, Annand; Macintosh, Bruce; Guyon, Olivier; Krist, John; Stahl, H. Philip; Smith, W. Scott; Mosier, Gary; Kirk, Charles;

Cause of different local time distribution in the postsunset equatorial ionospheric irregularity occurrences between June and December solstices

NASA Astrophysics Data System (ADS)

Su, S.-Y.; Chao, C. K.; Liu, C. H.

2009-04-01

Global averaged postsunset equatorial ionospheric density irregularity occurrences observed by ROCSAT during the moderate to high solar activity years of 1999 to 2004 indicate a different local time distribution between June and December solstices. The irregularity occurrences during the December solstice show a faster increase rate to peak at 2100-2200 local time, while the irregularity occurrences during the June solstice have a slower increase rate and peak one hour later in local time than that in the December solstice. The cause of such different local time distributions is attributed to a large contrast in the time of zonal drift reversal and the magnitude of postsunset vertical drift observed by ROCSAT at longitudes of large magnetic declination in the two solstices. That is, a delay in the zonal drift reversal in association with a smaller postsunset vertical drift observed at longitudes of positive magnetic declination has greatly inhibited the irregularity occurrences during the June solstice in contrast to an earlier zonal drift reversal together with a large vertical drift occurring at longitudes of negative magnetic declination to accelerate the irregularity occurrences during the December solstice. We think that the different geomagnetic field strengths that existed between the longitudes of positive and negative magnetic declinations have played a crucial role in determining the different local time distributions of irregularity occurrences for the two solstices.

MEK-ERK inhibition corrects the defect in VLDL assembly in HepG2 cells: potential role of ERK in VLDL-ApoB100 particle assembly.

PubMed

Tsai, Julie; Qiu, Wei; Kohen-Avramoglu, Rita; Adeli, Khosrow

2007-01-01

Hepatic VLDL assembly is defective in HepG2 cells, resulting in the secretion of immature triglyceride-poor LDL-sized apoB particles. We investigated the mechanisms underlying defective VLDL assembly in HepG2 and have obtained evidence implicating the MEK-ERK pathway. HepG2 cells exhibited considerably higher levels of the ERK1/2 mass and activity compared with primary hepatocytes. Inhibition of ERK1/2 using the MEK1/MEK2 inhibitor, U0126 (but not the inactive analogue) led to a significant increase in apoB secretion. In the presence of oleic acid, ERK1/2 inhibition caused a major shift in the lipoprotein distribution with a majority of particles secreted as VLDL, an effect independent of insulin. In contrast, overexpression of constitutively active MEK1 decreased apoB and large VLDL secretion. MEK1/2 inhibition significantly increased both cellular and microsomal TG mass, and mRNA levels for DGAT-1 and DGAT-2. In contrast to ERK, modulation of the PI3-K pathway or inhibition of the p38 MAP kinase, had no effect on lipoprotein density profile. Modulation of the MEK-ERK pathway in primary hamster hepatocytes led to changes in apoB secretion and altered the density profile of apoB-containing lipoproteins. Inhibition of the overactive ras-MEK-ERK pathway in HepG2 cells can correct the defect in VLDL assembly leading to the secretion of large, VLDL-sized particles, similar to primary hepatocytes, implicating the MEK-ERK cascade in VLDL assembly in the HepG2 model. Modulation of this pathway in primary hepatocytes also regulates apoB secretion and appears to alter the formation of VLDL-1 sized particles.

Silicon impacts on structure, stability and aromaticity of C20-nSin heterofullerenes (n = 1-10): A density functional perspective

NASA Astrophysics Data System (ADS)

Koohi, M.; Soleimani Amiri, S.; Shariati, M.

2017-01-01

Density functional theory (DFT) calculations are applied to compare and contrast silicon atom substitution doped C20-nSin heterofullerene analogous with n = 1-10, at B3LYP/AUG-cc-pVTZ. Vibrational frequency analysis confirms that all studied systems are true minima. Isolating the dopants is an applicable strategy for obtaining highly doped stable heterofullerenes, since it avoids weak silicon―silicon single bonds. Comparing and contrasting the optimized geometries shows that except C11Si9 and C10Si10 species (with deformed cages of segregated analogous), all eight fullerenic cages are the complete isolated-pentagon analogous. Hence, the dopants must be completely isolated from each other by means of strong Cdbnd C double bonds. Isolable or extractable fullerene isomers must be not only thermodynamically but also stable against electronic excitations. We then predicted that these isomers must have not only relatively large heats of atomization per carbon as a criterion of thermodynamic stability but also relatively large HOMO-LUMO energy separation against electronic excitations. The calculated the highest binding energy (6.52 eV/atom), heat of atomization per carbon (3193.2 kcal mol-1), band gap (2.86 eV) and nucleus independent chemical shift at the cage center (-50.00 ppm) for C18Si2 reveals it as the most stable heterofullerene. It has Ci symmetry and contains two silicon atoms in equatorial. High charge transfer on the surfaces of our scrutinized heterofullerenes provokes further investigations on their possible application for hydrogen storage. We hope that the present study will stimulate new experiments.

Fully automated corneal endothelial morphometry of images captured by clinical specular microscopy

NASA Astrophysics Data System (ADS)

Bucht, Curry; Söderberg, Per; Manneberg, Göran

2010-02-01

The corneal endothelium serves as the posterior barrier of the cornea. Factors such as clarity and refractive properties of the cornea are in direct relationship to the quality of the endothelium. The endothelial cell density is considered the most important morphological factor of the corneal endothelium. Pathological conditions and physical trauma may threaten the endothelial cell density to such an extent that the optical property of the cornea and thus clear eyesight is threatened. Diagnosis of the corneal endothelium through morphometry is an important part of several clinical applications. Morphometry of the corneal endothelium is presently carried out by semi automated analysis of pictures captured by a Clinical Specular Microscope (CSM). Because of the occasional need of operator involvement, this process can be tedious, having a negative impact on sampling size. This study was dedicated to the development and use of fully automated analysis of a very large range of images of the corneal endothelium, captured by CSM, using Fourier analysis. Software was developed in the mathematical programming language Matlab. Pictures of the corneal endothelium, captured by CSM, were read into the analysis software. The software automatically performed digital enhancement of the images, normalizing lights and contrasts. The digitally enhanced images of the corneal endothelium were Fourier transformed, using the fast Fourier transform (FFT) and stored as new images. Tools were developed and applied for identification and analysis of relevant characteristics of the Fourier transformed images. The data obtained from each Fourier transformed image was used to calculate the mean cell density of its corresponding corneal endothelium. The calculation was based on well known diffraction theory. Results in form of estimated cell density of the corneal endothelium were obtained, using fully automated analysis software on 292 images captured by CSM. The cell density obtained by the fully automated analysis was compared to the cell density obtained from classical, semi-automated analysis and a relatively large correlation was found.

Surface density mapping of natural tissue by a scanning haptic microscope (SHM).

PubMed

Moriwaki, Takeshi; Oie, Tomonori; Takamizawa, Keiichi; Murayama, Yoshinobu; Fukuda, Toru; Omata, Sadao; Nakayama, Yasuhide

2013-02-01

To expand the performance capacity of the scanning haptic microscope (SHM) beyond surface mapping microscopy of elastic modulus or topography, surface density mapping of a natural tissue was performed by applying a measurement theory of SHM, in which a frequency change occurs upon contact of the sample surface with the SHM sensor - a microtactile sensor (MTS) that vibrates at a pre-determined constant oscillation frequency. This change was mainly stiffness-dependent at a low oscillation frequency and density-dependent at a high oscillation frequency. Two paragon examples with extremely different densities but similar macroscopic elastic moduli in the range of natural soft tissues were selected: one was agar hydrogels and the other silicon organogels with extremely low (less than 25 mg/cm(3)) and high densities (ca. 1300 mg/cm(3)), respectively. Measurements were performed in saline solution near the second-order resonance frequency, which led to the elastic modulus, and near the third-order resonance frequency. There was little difference in the frequency changes between the two resonance frequencies in agar gels. In contrast, in silicone gels, a large frequency change by MTS contact was observed near the third-order resonance frequency, indicating that the frequency change near the third-order resonance frequency reflected changes in both density and elastic modulus. Therefore, a density image of the canine aortic wall was subsequently obtained by subtracting the image observed near the second-order resonance frequency from that near the third-order resonance frequency. The elastin-rich region had a higher density than the collagen-rich region.

Water circulation and global mantle dynamics: Insight from numerical modeling

NASA Astrophysics Data System (ADS)

Nakagawa, Takashi; Nakakuki, Tomoeki; Iwamori, Hikaru

2015-05-01

We investigate water circulation and its dynamical effects on global-scale mantle dynamics in numerical thermochemical mantle convection simulations. Both dehydration-hydration processes and dehydration melting are included. We also assume the rheological properties of hydrous minerals and density reduction caused by hydrous minerals. Heat transfer due to mantle convection seems to be enhanced more effectively than water cycling in the mantle convection system when reasonable water dependence of viscosity is assumed, due to effective slab dehydration at shallow depths. Water still affects significantly the global dynamics by weakening the near-surface oceanic crust and lithosphere, enhancing the activity of surface plate motion compared to dry mantle case. As a result, including hydrous minerals, the more viscous mantle is expected with several orders of magnitude compared to the dry mantle. The average water content in the whole mantle is regulated by the dehydration-hydration process. The large-scale thermochemical anomalies, as is observed in the deep mantle, is found when a large density contrast between basaltic material and ambient mantle is assumed (4-5%), comparable to mineral physics measurements. Through this study, the effects of hydrous minerals in mantle dynamics are very important for interpreting the observational constraints on mantle convection.

Time-resolved cathodoluminescence microscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states.

PubMed

Moerland, Robert J; Weppelman, I Gerward C; Garming, Mathijs W H; Kruit, Pieter; Hoogenboom, Jacob P

2016-10-17

We show cathodoluminescence-based time-resolved electron beam spectroscopy in order to directly probe the spontaneous emission decay rate that is modified by the local density of states in a nanoscale environment. In contrast to dedicated laser-triggered electron-microscopy setups, we use commercial hardware in a standard SEM, which allows us to easily switch from pulsed to continuous operation of the SEM. Electron pulses of 80-90 ps duration are generated by conjugate blanking of a high-brightness electron beam, which allows probing emitters within a large range of decay rates. Moreover, we simultaneously attain a resolution better than λ/10, which ensures details at deep-subwavelength scales can be retrieved. As a proof-of-principle, we employ the pulsed electron beam to spatially measure excited-state lifetime modifications in a phosphor material across the edge of an aluminum half-plane, coated on top of the phosphor. The measured emission dynamics can be directly related to the structure of the sample by recording photon arrival histograms together with the secondary-electron signal. Our results show that time-resolved electron cathodoluminescence spectroscopy is a powerful tool of choice for nanophotonics, within reach of a large audience.

Properties of medium-density fiberboard produced in an oil-heated laboratory press

Treesearch

O. Suchsland; G.E. Woodson

1976-01-01

Medium-density fiberboards from pressurized double-disk refined fibers have a close correlation between layer density and layer dynamic modulus of elasticity. Density distribution over the thickness was readily controlled by manipulating platen temperature and applied pressure. Thus, overall modulus of elasticity could be adjusted. In contrast to modulus of elasticity...

Buoyant miscible displacement flow of shear-thinning fluids: Experiments and Simulations

NASA Astrophysics Data System (ADS)

Ale Etrati Khosroshahi, Seyed Ali; Frigaard, Ian

2017-11-01

We study displacement flow of two miscible fluids with density and viscosity contrast in an inclined pipe. Our focus is mainly on displacements where transverse mixing is not significant and thus a two-layer, stratified flow develops. Our experiments are carried out in a long pipe, covering a wide range of flow-rates, inclination angles and viscosity ratios. Density and viscosity contrasts are achieved by adding Glycerol and Xanthan gum to water, respectively. At each angle, flow rate and viscosity ratio are varied and density contrast is fixed. We identify and map different flow regimes, instabilities and front dynamics based on Fr , Re / Frcosβ and viscosity ratio m. The problem is also studied numerically to get a better insight into the flow structure and shear-thinning effects. Numerical simulations are completed using OpenFOAM in both pipe and channel geometries and are compared against the experiments. Schlumberger, NSERC.

Correlation of Tumor Immunohistochemistry with Dynamic Contrast-Enhanced and DSC-MRI Parameters in Patients with Gliomas.

PubMed

Nguyen, T B; Cron, G O; Bezzina, K; Perdrizet, K; Torres, C H; Chakraborty, S; Woulfe, J; Jansen, G H; Thornhill, R E; Zanette, B; Cameron, I G

2016-12-01

Tumor CBV is a prognostic and predictive marker for patients with gliomas. Tumor CBV can be measured noninvasively with different MR imaging techniques; however, it is not clear which of these techniques most closely reflects histologically-measured tumor CBV. Our aim was to investigate the correlations between dynamic contrast-enhanced and DSC-MR imaging parameters and immunohistochemistry in patients with gliomas. Forty-three patients with a new diagnosis of glioma underwent a preoperative MR imaging examination with dynamic contrast-enhanced and DSC sequences. Unnormalized and normalized cerebral blood volume was obtained from DSC MR imaging. Two sets of plasma volume and volume transfer constant maps were obtained from dynamic contrast-enhanced MR imaging. Plasma volume obtained from the phase-derived vascular input function and bookend T1 mapping (Vp_Φ) and volume transfer constant obtained from phase-derived vascular input function and bookend T1 mapping (K trans _Φ) were determined. Plasma volume obtained from magnitude-derived vascular input function (Vp_SI) and volume transfer constant obtained from magnitude-derived vascular input function (K trans _SI) were acquired, without T1 mapping. Using CD34 staining, we measured microvessel density and microvessel area within 3 representative areas of the resected tumor specimen. The Mann-Whitney U test was used to test for differences according to grade and degree of enhancement. The Spearman correlation was performed to determine the relationship between dynamic contrast-enhanced and DSC parameters and histopathologic measurements. Microvessel area, microvessel density, dynamic contrast-enhanced, and DSC-MR imaging parameters varied according to the grade and degree of enhancement (P < .05). A strong correlation was found between microvessel area and Vp_Φ and between microvessel area and unnormalized blood volume (r s ≥ 0.61). A moderate correlation was found between microvessel area and normalized blood volume, microvessel area and Vp_SI, microvessel area and K trans _Φ, microvessel area and K trans _SI, microvessel density and Vp_Φ, microvessel density and unnormalized blood volume, and microvessel density and normalized blood volume (0.44 ≤ r s ≤ 0.57). A weaker correlation was found between microvessel density and K trans _Φ and between microvessel density and K trans _SI (r s ≤ 0.41). With dynamic contrast-enhanced MR imaging, use of a phase-derived vascular input function and bookend T1 mapping improves the correlation between immunohistochemistry and plasma volume, but not between immunohistochemistry and the volume transfer constant. With DSC-MR imaging, normalization of tumor CBV could decrease the correlation with microvessel area. © 2016 by American Journal of Neuroradiology.

Development of Cell Analysis Software for Cultivated Corneal Endothelial Cells.

PubMed

Okumura, Naoki; Ishida, Naoya; Kakutani, Kazuya; Hongo, Akane; Hiwa, Satoru; Hiroyasu, Tomoyuki; Koizumi, Noriko

2017-11-01

To develop analysis software for cultured human corneal endothelial cells (HCECs). Software was designed to recognize cell borders and to provide parameters such as cell density, coefficient of variation, and polygonality of cultured HCECs based on phase contrast images. Cultured HCECs with high or low cell density were incubated with Ca-free and Mg-free phosphate-buffered saline for 10 minutes to reveal the cell borders and were then analyzed with software (n = 50). Phase contrast images showed that cell borders were not distinctly outlined, but these borders became more distinctly outlined after phosphate-buffered saline treatment and were recognized by cell analysis software. The cell density value provided by software was similar to that obtained using manual cell counting by an experienced researcher. Morphometric parameters, such as the coefficient of variation and polygonality, were also produced by software, and these values were significantly correlated with cell density (Pearson correlation coefficients -0.62 and 0.63, respectively). The software described here provides morphometric information from phase contrast images, and it enables subjective and noninvasive quality assessment for tissue engineering therapy of the corneal endothelium.

In-Line Phase-Contrast X-ray Imaging and Tomography for Materials Science

PubMed Central

Mayo, Sheridan C.; Stevenson, Andrew W.; Wilkins, Stephen W.

2012-01-01

X-ray phase-contrast imaging and tomography make use of the refraction of X-rays by the sample in image formation. This provides considerable additional information in the image compared to conventional X-ray imaging methods, which rely solely on X-ray absorption by the sample. Phase-contrast imaging highlights edges and internal boundaries of a sample and is thus complementary to absorption contrast, which is more sensitive to the bulk of the sample. Phase-contrast can also be used to image low-density materials, which do not absorb X-rays sufficiently to form a conventional X-ray image. In the context of materials science, X-ray phase-contrast imaging and tomography have particular value in the 2D and 3D characterization of low-density materials, the detection of cracks and voids and the analysis of composites and multiphase materials where the different components have similar X-ray attenuation coefficients. Here we review the use of phase-contrast imaging and tomography for a wide variety of materials science characterization problems using both synchrotron and laboratory sources and further demonstrate the particular benefits of phase contrast in the laboratory setting with a series of case studies. PMID:28817018

In-Line Phase-Contrast X-ray Imaging and Tomography for Materials Science.

PubMed

Mayo, Sheridan C; Stevenson, Andrew W; Wilkins, Stephen W

2012-05-24

X-ray phase-contrast imaging and tomography make use of the refraction of X-rays by the sample in image formation. This provides considerable additional information in the image compared to conventional X-ray imaging methods, which rely solely on X-ray absorption by the sample. Phase-contrast imaging highlights edges and internal boundaries of a sample and is thus complementary to absorption contrast, which is more sensitive to the bulk of the sample. Phase-contrast can also be used to image low-density materials, which do not absorb X-rays sufficiently to form a conventional X-ray image. In the context of materials science, X-ray phase-contrast imaging and tomography have particular value in the 2D and 3D characterization of low-density materials, the detection of cracks and voids and the analysis of composites and multiphase materials where the different components have similar X-ray attenuation coefficients. Here we review the use of phase-contrast imaging and tomography for a wide variety of materials science characterization problems using both synchrotron and laboratory sources and further demonstrate the particular benefits of phase contrast in the laboratory setting with a series of case studies.

Grid-texture mechanisms in human vision: Contrast detection of regular sparse micro-patterns requires specialist templates.

PubMed

Baker, Daniel H; Meese, Tim S

2016-07-27

Previous work has shown that human vision performs spatial integration of luminance contrast energy, where signals are squared and summed (with internal noise) over area at detection threshold. We tested that model here in an experiment using arrays of micro-pattern textures that varied in overall stimulus area and sparseness of their target elements, where the contrast of each element was normalised for sensitivity across the visual field. We found a power-law improvement in performance with stimulus area, and a decrease in sensitivity with sparseness. While the contrast integrator model performed well when target elements constituted 50-100% of the target area (replicating previous results), observers outperformed the model when texture elements were sparser than this. This result required the inclusion of further templates in our model, selective for grids of various regular texture densities. By assuming a MAX operation across these noisy mechanisms the model also accounted for the increase in the slope of the psychometric function that occurred as texture density decreased. Thus, for the first time, mechanisms that are selective for texture density have been revealed at contrast detection threshold. We suggest that these mechanisms have a role to play in the perception of visual textures.

Grid-texture mechanisms in human vision: Contrast detection of regular sparse micro-patterns requires specialist templates

PubMed Central

Baker, Daniel H.; Meese, Tim S.

2016-01-01

Previous work has shown that human vision performs spatial integration of luminance contrast energy, where signals are squared and summed (with internal noise) over area at detection threshold. We tested that model here in an experiment using arrays of micro-pattern textures that varied in overall stimulus area and sparseness of their target elements, where the contrast of each element was normalised for sensitivity across the visual field. We found a power-law improvement in performance with stimulus area, and a decrease in sensitivity with sparseness. While the contrast integrator model performed well when target elements constituted 50–100% of the target area (replicating previous results), observers outperformed the model when texture elements were sparser than this. This result required the inclusion of further templates in our model, selective for grids of various regular texture densities. By assuming a MAX operation across these noisy mechanisms the model also accounted for the increase in the slope of the psychometric function that occurred as texture density decreased. Thus, for the first time, mechanisms that are selective for texture density have been revealed at contrast detection threshold. We suggest that these mechanisms have a role to play in the perception of visual textures. PMID:27460430

Climatic variation modulates the indirect effects of large herbivores on small-mammal habitat use.

PubMed

Long, Ryan A; Wambua, Alois; Goheen, Jacob R; Palmer, Todd M; Pringle, Robert M

2017-07-01

Large mammalian herbivores (LMH) strongly shape the composition and architecture of plant communities. A growing literature shows that negative direct effects of LMH on vegetation frequently propagate to suppress the abundance of smaller consumers. Indirect effects of LMH on the behaviour of these consumers, however, have received comparatively little attention despite their potential ecological significance. We sought to understand (i) how LMH indirectly shape small-mammal habitat use by altering the density and distribution of understorey plants; (ii) how these effects vary with climatic context (here, seasonality in rainfall); and (iii) the extent to which behavioural responses of small mammals are contingent upon small-mammal density. We tested the effects of a diverse LMH community on small-mammal habitat use using 4 years of spatially explicit small-mammal trapping and vegetation data from the UHURU Experiment, a replicated set of LMH exclosures in semi-arid Kenyan savanna. Small-mammal habitat use was positively associated with tree density and negatively associated with bare (unvegetated) patches in all plots and seasons. In the presence of LMH, and especially during the dry season, small mammals consistently selected tree cover and avoided bare patches. In contrast, when LMH were excluded, small mammals were weakly associated with tree cover and did not avoid bare patches as strongly. These behavioural responses of small mammals were largely unaffected by changes in small-mammal density associated with LMH exclusion. Our results show that LMH indirectly affect small-mammal behaviour, and that these effects are influenced by climate and can arise via density-independent mechanisms. This raises the possibility that anthropogenic LMH declines might interact with changing patterns of rainfall to alter small-mammal distribution and behaviour, independent of numerical responses by small mammals to these perturbations. For example, increased rainfall in East Africa (as predicted in many recent climate-model simulations) may relax constraints on small-mammal distribution where LMH are rare or absent, whereas increased aridity and/or drought frequency may tighten them. © 2017 The Authors. Journal of Animal Ecology © 2017 British Ecological Society.

Inside pyroclastic density currents - uncovering the enigmatic flow structure and transport behaviour in large-scale experiments

NASA Astrophysics Data System (ADS)

Breard, Eric C. P.; Lube, Gert

2017-01-01

Pyroclastic density currents (PDCs) are the most lethal threat from volcanoes. While there are two main types of PDCs (fully turbulent, fully dilute pyroclastic surges and more concentrated pyroclastic flows encompassing non-turbulent to turbulent transport) pyroclastic flows, which are the subject of the present study, are far more complex than dilute pyroclastic surges and remain the least understood type despite their far greater hazard, greater runout length and ability to transport vast quantities of material across the Earth's surface. Here we present large-scale experiments of natural volcanic material and gas in order to provide the missing quantitative view of the internal structure and gas-particle transport mechanisms in pyroclastic flows. We show that the outer flow structure with head, body and wake regions broadly resembles current PDC analogues of dilute gravity currents. However, the internal structure, in which lower levels consist of a concentrated granular fluid and upper levels are more dilute, contrasts significantly with the internal structure of fully dilute gravity currents. This bipartite vertical structure shows strong analogy to current conceptual models of high-density turbidity currents, which are responsible for the distribution of coarse sediment in marine basins and of great interest to the hydrocarbon industry. The lower concentrated and non-turbulent levels of the PDC (granular-fluid basal flow) act as a fast-flowing carrier for the more dilute and turbulent upper levels of the current (ash-cloud surge). Strong kinematic coupling between these flow parts reduces viscous dissipation and entrainment of ambient air into the lower part of the ash-cloud surge. This leads to a state of forced super-criticality whereby fast and destructive PDCs can endure even at large distances from volcanoes. Importantly, the basal flow/ash-cloud surge coupling yields a characteristically smooth rheological boundary across the non-turbulent/turbulent interface, as well as vertical velocity and density profiles in the ash-cloud surge, which strongly differ from current theoretical predictions. Observed generation of successive pulses of high dynamic pressure within the upper dilute levels of the PDC may be important to understand the destructive potential of PDCs. The experiments further show that a wide range in the degree of coupling between particle and gas phases is critical to the vertical and longitudinal segregation of the currents into reaches that have starkly contrasting sediment transport capacities. In particular, the formation of mesoscale turbulence clusters under strong particle-gas feedback controls vertical stratification inside the turbulent upper levels of the current (ash-cloud surge) and triggers significant transfers of mass and momentum from the ash-cloud surge onto the granular-fluid basal flow. These results open up new pathways to advance current computational PDC hazard models and to describe and interpret PDCs as well as other types of high-density gravity currents transported across the surfaces of Earth and other planets and across marine basins.

Crust-mantle density distribution in the eastern Qinghai-Tibet Plateau revealed by satellite-derived gravity gradients

NASA Astrophysics Data System (ADS)

LI, Honglei; Fang, Jian; Braitenberg, Carla; Wang, Xinsheng

2015-04-01

As the highest, largest and most active plateau on Earth, the Qinghai-Tibet Plateau has a complex crust-mantle structure, especially in its eastern part. In response to the subduction of the lithospheric mantle of the Indian plate, large-scale crustal motion occurs in this area. Despite the many previous studies, geodynamic processes at depth remain unclear. Knowledge of crust and upper mantle density distribution allows a better definition of the deeper geological structure and thus provides critically needed information for understanding of the underlying geodynamic processes. With an unprecedented precision of 1-2 mGal and a spatial resolution better than 100 km, GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission products can be used to constrain the crust-mantle density distribution. Here we used GOCE gravitational gradients at an altitude of 10km after reducing the effects of terrain, sediment thickness variations, and Moho undulations to image the density structures of eastern Tibet up to 200 km depths. We inverted the residual satellite gravitational gradients using a least square approach. The initial density model for the inversion is based on seismic velocities from the tomography. The model is composed of rectangular blocks, having a uniform density, with widths of about 100 km and variable thickness and depths. The thickness of the rectangular cells changes from10 to 60km in accordance with the seismic model. Our results reveal some large-scale, structurally controlled density variations at depths. The lithospheric root defined by higher-density contrast features from southwest to northeast, with shallowing in the central part: base of lithosphere reaches a depth of180 km, less than 100km, and 200 km underneath the Lhasa, Songpan-Ganzi, and Ordos crustal blocks, respectively. However, these depth values only represent a first-order parameterization because they depend on model discretization inherited from the original seismic tomography model. For example, the thickness of the uniform density blocks centered at140 km depth is as large as 60 km. Low-density crustal anomalies beneath the southern Lhasa and Songpan-Ganzi blocks in our model support the idea of weak lower crust and possible crustal flow, as a result of the thermal anomalies caused by the upwelling of hot deep materials. The weak lower crust may cause the decoupling of the upper crust and the mantle. These results are consistent with many other geophysical studies, confirming the effectiveness of the GOCE gravitational gradient data. Using these data in combination with other geodynamic constraints (e.g., gravity and seismic structure and preliminary reference Earth model), an improved dynamic model can be derived.

Spatial correlations of Diceroprocta apache and its host plants: Evidence for a negative impact from Tamarix invasion

USGS Publications Warehouse

Ellingson, A.R.; Andersen, D.C.

2002-01-01

1. The hypothesis that the habitat-scale spatial distribution of the, Apache cicada Diceroprocta apache Davis is unaffected by the presence of the invasive exotic saltcedar Tamarix ramosissima was tested using data from 205 1-m2 quadrats placed within the flood-plain of the Bill Williams River, Arizona, U.S.A. Spatial dependencies within and between cicada density and habitat variables were estimated using Moran's I and its bivariate analogue to discern patterns and associations at spatial scales from 1 to 30 m. 2. Apache cicadas were spatially aggregated in high-density clusters averaging 3m in diameter. A positive association between cicada density, estimated by exuvial density, and the per cent canopy cover of a native tree, Goodding's willow Salix gooddingii, was detected in a non-spatial correlation analysis. No non-spatial association between cicada density and saltcedar canopy cover was detected. 3. Tests for spatial cross-correlation using the bivariate IYZ indicated the presence of a broad-scale negative association between cicada density and saltcedar canopy cover. This result suggests that large continuous stands of saltcedar are associated with reduced cicada density. In contrast, positive associations detected at spatial scales larger than individual quadrats suggested a spill-over of high cicada density from areas featuring Goodding's willow canopy into surrounding saltcedar monoculture. 4. Taken together and considered in light of the Apache cicada's polyphagous habits, the observed spatial patterns suggest that broad-scale factors such as canopy heterogeneity affect cicada habitat use more than host plant selection. This has implications for management of lower Colorado River riparian woodlands to promote cicada presence and density through maintenance or creation of stands of native trees as well as manipulation of the characteristically dense and homogeneous saltcedar canopies.

Spatial correlations of Diceroprocta apache and its host plants: Evidence for a negative impact from Tamarix invasion

USGS Publications Warehouse

Ellingson, A.R.; Andersen, D.C.

2002-01-01

1. The hypothesis that the habitat-scale spatial distribution of the Apache cicada Diceroprocta apache Davis is unaffected by the presence of the invasive exotic saltcedar Tamarix ramosissima was tested using data from 205 1-m2 quadrats placed within the flood-plain of the Bill Williams River, Arizona, U.S.A. Spatial dependencies within and between cicada density and habitat variables were estimated using Moran's I and its bivariate analogue to discern patterns and associations at spatial scales from 1 to 30 m.2. Apache cicadas were spatially aggregated in high-density clusters averaging 3 m in diameter. A positive association between cicada density, estimated by exuvial density, and the per cent canopy cover of a native tree, Goodding's willow Salix gooddingii, was detected in a non-spatial correlation analysis. No non-spatial association between cicada density and saltcedar canopy cover was detected.3. Tests for spatial cross-correlation using the bivariate IYZ indicated the presence of a broad-scale negative association between cicada density and saltcedar canopy cover. This result suggests that large continuous stands of saltcedar are associated with reduced cicada density. In contrast, positive associations detected at spatial scales larger than individual quadrats suggested a spill-over of high cicada density from areas featuring Goodding's willow canopy into surrounding saltcedar monoculture.4. Taken together and considered in light of the Apache cicada's polyphagous habits, the observed spatial patterns suggest that broad-scale factors such as canopy heterogeneity affect cicada habitat use more than host plant selection. This has implications for management of lower Colorado River riparian woodlands to promote cicada presence and density through maintenance or creation of stands of native trees as well as manipulation of the characteristically dense and homogeneous saltcedar canopies.

Spatial variability of shelf sediments in the STRATAFORM natural laboratory, Northern California

USGS Publications Warehouse

Goff, J.A.; Wheatcroft, R.A.; Lee, H.; Drake, D.E.; Swift, D.J.P.; Fan, S.

2002-01-01

The "Correlation Length Experiment", an intensive box coring effort on the Eel River shelf (Northern California) in the summer of 1997, endeavored to characterize the lateral variability of near-surface shelf sediments over scales of meters to kilometers. Coring focused on two sites, K60 and S60, separated by ??? 15 km along the 60 m isobath. The sites are near the sand-to-mud transition, although K60 is sandier owing to its proximity to the Eel River mouth. Nearly 140 cores were collected on dip and strike lines with core intervals from < 10m to 1 km. Measurements on each core included bulk density computed from gamma-ray attenuation, porosity converted from resistivity measurements, and surficial grain size. Grain size was also measured over the full depth range within a select subset of cores. X-radiograph images were also examined. Semi-variograms were computed for strike, dip, and down-hole directions at each site. The sand-to-mud transition exerts a strong influence on all measurements: on average, bulk density increases and porosity decreases with regional increases in mean grain size. Analysis of bulk density measurements indicates very strong contrasts in the sediment variability at K60 and S60. No coherent bedding is seen at K60; in the strike direction, horizontal variability is "white" (fully uncorrelated) from the smallest scales examined (a few meters) to the largest (8 km), with a variance equal to that seen within the cores. In contrast, coherent bedding exists at S60 related to the preservation of the 1995 flood deposit. A correlatable structure is found in the strike direction with a decorrelation distance of ??? 800 m, and can be related to long-wavelength undulations in the topography and/or thickness of the flood layer or overburden. We hypothesize that the high degree of bulk density variability at K60 is a result of more intense physical reworking of the seabed in the sandier environment. Without significant averaging, the resistivity-based porosity measurements are only marginally correlated to gamma-ray-bulk density measurements, and are largely independent of mean grain size. Furthermore, porosity displays a high degree of incoherent variability at both sites. Porosity, with a much smaller sample volume than bulk density, may therefore resolve small-scale biogenic variability which is filtered out in the bulk density measurement. ?? 2002 Elsevier Science Ltd. All rights reserved.

Non-Invasive Imaging of Reactor Cores Using Cosmic Ray Muons

NASA Astrophysics Data System (ADS)

Milner, Edward

2011-10-01

Cosmic ray muons penetrate deeply in material, with some passing completely through very thick objects. This penetrating quality is the basis of two distinct, but related imaging techniques. The first measures the number of cosmic ray muons transmitted through parts of an object. Relatively fewer muons are absorbed along paths in which they encounter less material, compared to higher density paths, so the relative density of material is measured. This technique is called muon transmission imaging, and has been used to infer the density and structure of a variety of large masses, including mine overburden, volcanoes, pyramids, and buildings. In a second, more recently developed technique, the angular deflection of muons is measured by trajectory-tracking detectors placed on two opposing sides of an object. Muons are deflected more strongly by heavy nuclei, since multiple Coulomb scattering angle is approximately proportional to the nuclear charge. Therefore, a map showing regions of large deflection will identify the location of uranium in contrast to lighter nuclei. This technique is termed muon scattering tomography (MST) and has been developed to screen shipping containers for the presence of concealed nuclear material. Both techniques are a good way of non-invasively inspecting objects. A previously unexplored topic was applying MST to imaging large objects. Here we demonstrate extending the MST technique to the task of identifying relatively thick objects inside very thick shielding. We measured cosmic ray muons passing through a physical arrangement of material similar to a nuclear reactor, with thick concrete shielding and a heavy metal core. Newly developed algorithms were used to reconstruct an image of the ``mock reactor core,'' with resolution of approximately 30 cm.

An x-ray backlit Talbot-Lau deflectometer for high-energy-density electron density diagnostics.

PubMed

Valdivia, M P; Stutman, D; Stoeckl, C; Theobald, W; Mileham, C; Begishev, I A; Bromage, J; Regan, S P

2016-02-01

X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on thin Cu foil targets. Grating survival was demonstrated for 30 J, 8 ps laser pulses. The first x-ray deflectometry images obtained under laser backlighting showed up to 25% image contrast and thus enabled detection of electron areal density gradients with a maximum value of 8.1 ± 0.5 × 10(23) cm(-3) in a low-Z millimeter sized sample. An electron density profile was obtained from refraction measurements with an error of <8%. The 50 ± 15 μm spatial resolution achieved across the full field of view was found to be limited by the x-ray source-size, similar to conventional radiography.

INFERRING THE CORONAL DENSITY IRREGULARITY FROM EUV SPECTRA

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

Hahn, M.; Savin, D. W., E-mail: mhahn@astro.columbia.edu

2016-09-20

Understanding the density structure of the solar corona is important for modeling both coronal heating and the solar wind. Direct measurements are difficult because of line-of-sight integration and possible unresolved structures. We present a new method for quantifying such structures using density-sensitive extreme ultraviolet line intensities to derive a density irregularity parameter, a relative measure of the amount of structure along the line of sight. We also present a simple model to relate the inferred irregularities to physical quantities, such as the filling factor and density contrast. For quiet-Sun regions and interplume regions of coronal holes, we find a densitymore » contrast of at least a factor of 3–10 and corresponding filling factors of about 10%–20%. Our results are in rough agreement with other estimates of the density structures in these regions. The irregularity diagnostic provides a useful relative measure of unresolved structure in various regions of the corona.« less

Individual variation in cone photoreceptor density in house sparrows: implications for between-individual differences in visual resolution and chromatic contrast.

PubMed

Ensminger, Amanda L; Fernández-Juricic, Esteban

2014-01-01

Between-individual variation has been documented in a wide variety of taxa, especially for behavioral characteristics; however, intra-population variation in sensory systems has not received similar attention in wild animals. We measured a key trait of the visual system, the density of retinal cone photoreceptors, in a wild population of house sparrows (Passer domesticus). We tested whether individuals differed from each other in cone densities given within-individual variation across the retina and across eyes. We further tested whether the existing variation could lead to individual differences in two aspects of perception: visual resolution and chromatic contrast. We found consistent between-individual variation in the densities of all five types of avian cones, involved in chromatic and achromatic vision. Using perceptual modeling, we found that this degree of variation translated into significant between-individual differences in visual resolution and the chromatic contrast of a plumage signal that has been associated with mate choice and agonistic interactions. However, there was no evidence for a relationship between individual visual resolution and chromatic contrast. The implication is that some birds may have the sensory potential to perform "better" in certain visual tasks, but not necessarily in both resolution and contrast simultaneously. Overall, our findings (a) highlight the need to consider multiple individuals when characterizing sensory traits of a species, and (b) provide some mechanistic basis for between-individual variation in different behaviors (i.e., animal personalities) and for testing the predictions of several widely accepted hypotheses (e.g., honest signaling).

Individual Variation in Cone Photoreceptor Density in House Sparrows: Implications for Between-Individual Differences in Visual Resolution and Chromatic Contrast

PubMed Central

Ensminger, Amanda L.; Fernández-Juricic, Esteban

2014-01-01

Between-individual variation has been documented in a wide variety of taxa, especially for behavioral characteristics; however, intra-population variation in sensory systems has not received similar attention in wild animals. We measured a key trait of the visual system, the density of retinal cone photoreceptors, in a wild population of house sparrows (Passer domesticus). We tested whether individuals differed from each other in cone densities given within-individual variation across the retina and across eyes. We further tested whether the existing variation could lead to individual differences in two aspects of perception: visual resolution and chromatic contrast. We found consistent between-individual variation in the densities of all five types of avian cones, involved in chromatic and achromatic vision. Using perceptual modeling, we found that this degree of variation translated into significant between-individual differences in visual resolution and the chromatic contrast of a plumage signal that has been associated with mate choice and agonistic interactions. However, there was no evidence for a relationship between individual visual resolution and chromatic contrast. The implication is that some birds may have the sensory potential to perform “better” in certain visual tasks, but not necessarily in both resolution and contrast simultaneously. Overall, our findings (a) highlight the need to consider multiple individuals when characterizing sensory traits of a species, and (b) provide some mechanistic basis for between-individual variation in different behaviors (i.e., animal personalities) and for testing the predictions of several widely accepted hypotheses (e.g., honest signaling). PMID:25372039

Population density shapes patterns of survival and reproduction in Eleutheria dichotoma (Hydrozoa: Anthoathecata).

PubMed

Dańko, Aleksandra; Schaible, Ralf; Pijanowska, Joanna; Dańko, Maciej J

2018-01-01

Budding hydromedusae have high reproductive rates due to asexual reproduction and can occur in high population densities along the coasts, specifically in tidal pools. In laboratory experiments, we investigated the effects of population density on the survival and reproductive strategies of a single clone of Eleutheria dichotoma . We found that sexual reproduction occurs with the highest rate at medium population densities. Increased sexual reproduction was associated with lower budding (asexual reproduction) and survival probability. Sexual reproduction results in the production of motile larvae that can, in contrast to medusae, seek to escape unfavorable conditions by actively looking for better environments. The successful settlement of a larva results in starting the polyp stage, which is probably more resistant to environmental conditions. This is the first study that has examined the life-history strategies of the budding hydromedusa E. dichotoma by conducting a long-term experiment with a relatively large sample size that allowed for the examination of age-specific mortality and reproductive rates. We found that most sexual and asexual reproduction occurred at the beginning of life following a very rapid process of maturation. The parametric models fitted to the mortality data showed that population density was associated with an increase in the rate of aging, an increase in the level of late-life mortality plateau, and a decrease in the hidden heterogeneity in individual mortality rates. The effects of population density on life-history traits are discussed in the context of resource allocation and the r/K-strategies' continuum concept.

Changes in reproductive life-history strategies in response to nest density in a shell-brooding cichlid, Telmatochromis vittatus

NASA Astrophysics Data System (ADS)

Ota, Kazutaka; Hori, Michio; Kohda, Masanori

2012-01-01

To determine whether the appearance of a reproductively parasitic tactic varies, and how this variation affects territorial males of the Lake Tanganyika cichlid fish Telmatochromis vittatus, we examined the reproductive ecology of territorial males in Mtondwe and compared it with that of a neighboring Wonzye population, where nest density differs from that at Mtondwe. In Wonzye, with high nest density, male tactics change with their body size from a territorial to a non-territorial parasitic tactic called piracy in which they conquer several nests defended by territorial males and take over the nests while females are spawning. These "pirate" males could decrease the costs incurred by travelling among nests by exclusively targeting aggregations of nests in close proximity while avoiding separate nests. Territorial males in Wonzye sacrifice the potential higher attractiveness offered by large nests and instead compete for nests farther from neighbors on which pirates less frequently intrude. In contrast, the Mtondwe population had lower nest density and piracy was absent. Given that the success of piracy depends on the close proximity of nests, nest density is likely responsible for the observed variation in the occurrence of piracy between the two populations. Furthermore, in Mtondwe, territorial males competed for larger nests and were smaller than the territorial males in Wonzye. Thus, this lower nest density may free territorial males from the selection pressures for increased size caused by both defense against nest piracy and the need to develop into pirates as they grow.

Variation in abundance of Pacific Blue Mussel (Mytilus trossulus) in the Northern Gulf of Alaska, 2006-2015

NASA Astrophysics Data System (ADS)

Bodkin, James L.; Coletti, Heather A.; Ballachey, Brenda E.; Monson, Daniel H.; Esler, Daniel; Dean, Thomas A.

2018-01-01

Mussels are conspicuous and ecologically important components of nearshore marine communities around the globe. Pacific blue mussels (Mytilus trossulus) are common residents of intertidal habitats in protected waters of the North Pacific, serving as a conduit of primary production to a wide range of nearshore consumers including predatory invertebrates, sea ducks, shorebirds, sea otters, humans, and other terrestrial mammals. We monitored seven metrics of intertidal Pacific blue mussel abundance at five sites in each of three regions across the northern Gulf of Alaska: Katmai National Park and Preserve (Katmai) (2006-2015), Kenai Fjords National Park (Kenai Fjords) (2008-2015) and western Prince William Sound (WPWS) (2007-2015). Metrics included estimates of: % cover at two tide heights in randomly selected rocky intertidal habitat; and in selected mussel beds estimates of: the density of large mussels (≥ 20 mm); density of all mussels > 2 mm estimated from cores extracted from those mussel beds; bed size; and total abundance of large and all mussels, i.e. the product of density and bed size. We evaluated whether these measures of mussel abundance differed among sites or regions, whether mussel abundance varied over time, and whether temporal patterns in abundance were site specific, or synchronous at regional or Gulf-wide spatial scales. We found that, for all metrics, mussel abundance varied on a site-by-site basis. After accounting for site differences, we found similar temporal patterns in several measures of abundance (both % cover metrics, large mussel density, large mussel abundance, and mussel abundance estimated from cores), in which abundance was initially high, declined significantly over several years, and subsequently recovered. Averaged across all sites, we documented declines of 84% in large mussel abundance through 2013 with recovery to 41% of initial abundance by 2015. These findings suggest that factors operating across the northern Gulf of Alaska were affecting mussel survival and subsequently abundance. In contrast, density of primarily small mussels obtained from cores (as an index of recruitment), varied markedly by site, but did not show meaningful temporal trends. We interpret this to indicate that settlement was driven by site-specific features rather than Gulf wide factors. By extension, we hypothesize that temporal changes in mussel abundance observed was not a result of temporal variation in larval supply leading to variation in recruitment, but rather suggestive of mortality as a primary demographic factor driving mussel abundance. Our results highlight the need to better understand underlying mechanisms of change in mussels, as well as implications of that change to nearshore consumers.

Variation in abundance of Pacific Blue Mussel (Mytilus trossulus) in the Northern Gulf of Alaska, 2006–2015

USGS Publications Warehouse

Bodkin, James L.; Coletti, Heather A.; Ballachey, Brenda E.; Monson, Daniel; Esler, Daniel N.; Dean, Thomas A.

2017-01-01

Mussels are conspicuous and ecologically important components of nearshore marine communities around the globe. Pacific blue mussels (Mytilus trossulus) are common residents of intertidal habitats in protected waters of the North Pacific, serving as a conduit of primary production to a wide range of nearshore consumers including predatory invertebrates, sea ducks, shorebirds, sea otters, humans, and other terrestrial mammals. We monitored seven metrics of intertidal Pacific blue mussel abundance at five sites in each of three regions across the northern Gulf of Alaska: Katmai National Park and Preserve (Katmai) (2006–2015), Kenai Fjords National Park (Kenai Fjords) (2008–2015) and western Prince William Sound (WPWS) (2007–2015). Metrics included estimates of: % cover at two tide heights in randomly selected rocky intertidal habitat; and in selected mussel beds estimates of: the density of large mussels (≥ 20 mm); density of all mussels > 2 mm estimated from cores extracted from those mussel beds; bed size; and total abundance of large and all mussels, i.e. the product of density and bed size. We evaluated whether these measures of mussel abundance differed among sites or regions, whether mussel abundance varied over time, and whether temporal patterns in abundance were site specific, or synchronous at regional or Gulf-wide spatial scales. We found that, for all metrics, mussel abundance varied on a site-by-site basis. After accounting for site differences, we found similar temporal patterns in several measures of abundance (both % cover metrics, large mussel density, large mussel abundance, and mussel abundance estimated from cores), in which abundance was initially high, declined significantly over several years, and subsequently recovered. Averaged across all sites, we documented declines of 84% in large mussel abundance through 2013 with recovery to 41% of initial abundance by 2015. These findings suggest that factors operating across the northern Gulf of Alaska were affecting mussel survival and subsequently abundance. In contrast, density of primarily small mussels obtained from cores (as an index of recruitment), varied markedly by site, but did not show meaningful temporal trends. We interpret this to indicate that settlement was driven by site-specific features rather than Gulf wide factors. By extension, we hypothesize that temporal changes in mussel abundance observed was not a result of temporal variation in larval supply leading to variation in recruitment, but rather suggestive of mortality as a primary demographic factor driving mussel abundance. Our results highlight the need to better understand underlying mechanisms of change in mussels, as well as implications of that change to nearshore consumers.

Coherent mode decomposition using mixed Wigner functions of Hermite-Gaussian beams.

PubMed

Tanaka, Takashi

2017-04-15

A new method of coherent mode decomposition (CMD) is proposed that is based on a Wigner-function representation of Hermite-Gaussian beams. In contrast to the well-known method using the cross spectral density (CSD), it directly determines the mode functions and their weights without solving the eigenvalue problem. This facilitates the CMD of partially coherent light whose Wigner functions (and thus CSDs) are not separable, in which case the conventional CMD requires solving an eigenvalue problem with a large matrix and thus is numerically formidable. An example is shown regarding the CMD of synchrotron radiation, one of the most important applications of the proposed method.

Role of Defects on Regioselectivity of Nano Pristine Graphene.

PubMed

Kudur Jayaprakash, Gururaj; Casillas, Norberto; Astudillo-Sánchez, Pablo D; Flores-Moreno, Roberto

2016-11-17

Here analytical Fukui functions based on density functional theory are applied to investigate the redox reactivity of pristine and defected graphene lattices. A carbon H-terminated graphene structure (with 96 carbon atoms) and a graphene defected surface with Stone-Wales rearrangement and double vacancy defects are used as models. Pristine sp 2 -hybridized, hexagonal arranged carbon atoms exhibit a symmetric reactivity. In contrast, common carbon atoms at reconstructed polygons in Stone-Wales and double vacancy graphene display large reactivity variations. The improved reactivity and the regioselectivity at defected graphene is correlated to structural changes that caused carbon-carbon bond length variations at defected zones.

Ecoinformatics Can Reveal Yield Gaps Associated with Crop-Pest Interactions: A Proof-of-Concept

PubMed Central

Rosenheim, Jay A.; Meisner, Matthew H.

2013-01-01

Farmers and private consultants execute a vast, decentralized data collection effort with each cropping cycle, as they gather pest density data to make real-time pest management decisions. Here we present a proof of concept for an ecoinformatics approach to pest management research, which attempts to harness these data to answer questions about pest-crop interactions. The impact of herbivory by Lygus hesperus on cotton is explored as a case study. Consultant-derived data satisfied a ‘positive control’ test for data quality by clearly resolving the expected negative relationship between L. hesperus density and retention of flower buds. The enhanced statistical power afforded by the large ecoinformatics dataset revealed an early-season window of crop sensitivity, during which L. hesperus densities as low as 1-2 per sample were associated with yield loss. In contrast, during the mid-season insecticide use by farmers was often unnecessary, as cotton compensated fully for moderate L. hesperus densities. Because the dataset emerged from the commercial production setting, it also revealed the limited degree to which farmers were willing to delay crop harvest to provide opportunities for compensatory fruiting. Observational approaches to pest management research have strengths and weaknesses that complement those of traditional, experimental approaches; combining these methods can contribute to enhanced agricultural productivity. PMID:24260408

In vivo comparison of tantalum, tungsten, and bismuth enteric contrast agents to complement intravenous iodine for double-contrast dual-energy CT of the bowel

PubMed Central

Rathnayake, Samira; Mongan, John; Torres, Andrew S.; Colborn, Robert; Gao, Dong-Wei; Yeh, Benjamin M; Fu, Yanjun

2016-01-01

To assess the ability of dual-energy CT (DECT) to separate intravenous contrast of bowel wall from intraluminal contrast, we scanned 16 rabbits on a clinical DECT scanner: n=3 using only iodinated intravenous contrast; and n=13 double-contrast enhanced scans using iodinated intravenous contrast and experimental enteric non-iodinated contrast agents in the bowel lumen (5 bismuth-, 4 tungsten-, and 4 tantalum-based). Representative image pairs from conventional CT images and DECT iodine density maps of small bowel (116 pairs from 232 images) were viewed by four abdominal imaging attending radiologists to independently score each comparison pair on a visual analog scale (−100 to +100%) for: 1) preference in small bowel wall visualization; and 2) preference in completeness of intraluminal enteric contrast subtraction. Median small bowel wall visualization was scored 39 and 42 percentage points (95% CI: 30–44% and 36–45%, p<0.001 both) higher at double-contrast DECT than at conventional CT with enteric tungsten and tantalum contrast, respectively. Median small bowel wall visualization at double-contrast DECT was scored 29 and 35 percentage points (95% CI: 20–35% and 33–39%, p<0.001 both) higher with enteric tungsten and tantalum, respectively, than with bismuth contrast. Median completeness of intraluminal enteric contrast subtraction in double-contrast DECT iodine density maps was scored 28 and 29 percentage points (95% CI: 15–31% and 28–33%, p<0.001 both) higher with enteric tungsten and tantalum, respectively, than with bismuth contrast. Results suggest that in vivo double-contrast DECT with iodinated intravenous and either tantalum- or tungsten-based enteric contrast provide better visualization of small bowel than conventional CT. PMID:26892945

The gene expression pattern induced by high plating density in cultured bovine and buffalo granulosa cells might be regulated by specific miRNA species

PubMed Central

YENUGANTI, Vengala Rao; BADDELA, Vijay Simha; BAUFELD, Anja; SINGH, Dheer; VANSELOW, Jens

2015-01-01

Precise regulation of cell type-specific gene expression profiles precedes the profound morphological reorganization of somatic cell layers during folliculogenesis, ovulation and luteinization. Cell culture models are essential to the study of corresponding molecular mechanisms of gene regulation. In a recent study, it was shown that an increased cell plating density can largely change gene expression profiles of cultured bovine granulosa cells. In our present study, we comparatively analyzed cell plating density effects on cultured bovine and buffalo granulosa cells. Cells were isolated from small- to medium-sized follicles (2–6 mm) and cultured under serum-free conditions at different plating densities. The abundance of selected marker transcripts and associated miRNA candidates was determined by quantitative real-time RT-PCR. We found in both species that the abundance of CYP19A1, CCNE1 and PCNA transcripts was remarkably lower at a high plating density, whereas VNN2 and RGS2 transcripts significantly increased. In contrast, putative regulators of CYP19A1, miR-378, miR-106a and let-7f were significantly higher in both species or only in buffalo, respectively. Also miR-15a, a regulator of CCNE1, was upregulated in both species. Thus, increased plating density induced similar changes of mRNA and miRNA expression in granulosa cells from buffalo and cattle. From these data, we conclude that specific miRNA species might be involved in the observed density-induced gene regulation. PMID:25740097

Free Radical Metabolism of Methyleugenol and Related Compounds

PubMed Central

2015-01-01

Methyleugenol, the methyl ether of eugenol, both of which are flavorant constituents of spices, has been listed by the National Toxicology Program’s Report on Carcinogens as reasonably anticipated to be a human carcinogen. This finding is based on the observation of increased incidence of malignant tumors at multiple tissue sites in experimental animals of different species. By contrast, eugenol is not listed. In this study, we show that both methyleugenol and eugenol readily undergo peroxidative metabolism in vitro to form free radicals with large hyperfine interactions of the methylene allylic hydrogen atoms. These large hyperfine splittings indicate large electron densities adjacent to those hydrogen atoms. Methyleugenol undergoes autoxidation such that the commercial product contains 10–30 mg/L hydroperoxide and is capable of activating peroxidases without the presence of added hydrogen peroxide. Additionally, the hydroperoxide is not a good substrate for catalase, which demonstrates that these antioxidant defenses will not be effective in protecting against methyleugenol exposure. PMID:24564854

Overview and Summary of Advanced UVOIR Mirror Technology Development (AMTD) Project

NASA Technical Reports Server (NTRS)

Stahl, H. Philip

2014-01-01

ASTRO2010 Decadal Survey stated that an advanced large-aperture ultraviolet, optical, near-infrared (UVOIR) telescope is required to enable the next generation of compelling astrophysics and exoplanet science; and, that present technology is not mature enough to affordably build and launch any potential UVOIR mission concept. AMTD is a multiyear effort to develop, demonstrate and mature critical technologies to TRL-6 by 2018 so that a viable flight mission can be proposed to the 2020 Decadal Review. AMTD builds on the state of art (SOA) defined by over 30 years of monolithic & segmented ground & space-telescope mirror technology to mature six key technologies: center dotLarge-Aperture, Low Areal Density, High Stiffness Mirror Substrates: Both (4 to 8 m) monolithic and (8 to 16 m) segmented telescopes require larger and stiffer mirrors. center dotSupport System: Large-aperture mirrors require large support systems to ensure that they survive launch, deploy on orbit, and maintain a stable, undistorted shape. center dotMid/High Spatial Frequency Figure Error: Very smooth mirror is critical for producing high-quality point spread function (PSF) for high contrast imaging. center dotSegment Edges: The quality of segment edges impacts PSF for high-contrast imaging applications, contributes to stray light noise, and affects total collecting aperture. center dotSegment to Segment Gap Phasing: Segment phasing is critical for producing high-quality temporally-stable PSF. center dotIntegrated Model Validation: On-orbit performance is driven by mechanical & thermal stability. Compliance cannot be 100% tested, but relies on modeling. Because we cannot predict the future, AMTD is pursuing multiple design paths to provide the science community with options to enable either large aperture monolithic or segmented mirrors with clear engineering metrics traceable to science requirements

Analysis of speckle patterns in phase-contrast images of lung tissue

NASA Astrophysics Data System (ADS)

Kitchen, M. J.; Paganin, D.; Lewis, R. A.; Yagi, N.; Uesugi, K.

2005-08-01

Propagation-based phase-contrast images of mice lungs have been obtained at the SPring-8 synchrotron research facility. Such images exhibit a speckled intensity pattern that bears a superficial resemblance to alveolar structures. This speckle results from focussing effects as projected air-filled alveoli form aberrated compound refractive lenses. An appropriate phase-retrieval algorithm has been utilized to reconstruct the approximate projected lung tissue thickness from single-phase-contrast mice chest radiographs. The results show projected density variations across the lung, highlighting regions of low density corresponding to air-filled regions. Potentially, this offers a better method than conventional radiography for detecting lung diseases such as fibrosis, emphysema and cancer, though this has yet to be demonstrated. As such, the approach can assist in continuing studies of lung function utilizing propagation-based phase-contrast imaging.

Nondestructive Evaluation of Advanced Materials with X-ray Phase Mapping

NASA Technical Reports Server (NTRS)

Hu, Zhengwei

2005-01-01

X-ray radiation has been widely used for imaging applications since Rontgen first discovered X-rays over a century ago. Its large penetration depth makes it ideal for the nondestructive visualization of the internal structure and/or defects of materials unobtainable otherwise. Currently used nondestructive evaluation (NDE) tools, X-ray radiography and tomography, are absorption-based, and work well in heavy-element materials where density or composition variations due to internal structure or defects are high enough to produce appreciable absorption contrast. However, in many cases where materials are light-weight and/or composites that have similar mass absorption coefficients, the conventional absorption-based X-ray methods for NDE become less useful. Indeed, the light-weight and ultra-high-strength requirements for the most advanced materials used or developed for current flight mission and future space exploration pose a great challenge to the standard NDE tools in that the absorption contrast arising from the internal structure of these materials is often too weak to be resolved. In this presentation, a solution to the problem, the use of phase information of X-rays for phase contrast X-ray imaging, will be discussed, along with a comparison between the absorption-based and phase-contrast imaging methods. Latest results on phase contrast X-ray imaging of lightweight Space Shuttle foam in 2D and 3D will be presented, demonstrating new opportunities to solve the challenging issues encountered in advanced materials development and processing.

Axisymmetric annular curtain stability

NASA Astrophysics Data System (ADS)

Ahmed, Zahir U.; Khayat, Roger E.; Maissa, Philippe; Mathis, Christian

2012-06-01

A temporal stability analysis was carried out to investigate the stability of an axially moving viscous annular liquid jet subject to axisymmetric disturbances in surrounding co-flowing viscous gas media. We investigated in this study the effects of inertia, surface tension, the gas-to-liquid density ratio, the inner-to-outer radius ratio and the gas-to-liquid viscosity ratio on the stability of the jet. With an increase in inertia, the growth rate of the unstable disturbances is found to increase. The dominant (or most unstable) wavenumber decreases with increasing Reynolds number for larger values of the gas-to-liquid viscosity ratio. However, an opposite tendency for the most unstable wavenumber is predicted for small viscosity ratio in the same inertia range. The surrounding gas density, in the presence of viscosity, always reduces the growth rate, hence stabilizing the flow. There exists a critical value of the density ratio above which the flow becomes stable for very small viscosity ratio, whereas for large viscosity ratio, no stable flow appears in the same range of the density ratio. The curvature has a significant destabilizing effect on the thin annular jet, whereas for a relatively thick jet, the maximum growth rate decreases as the inner radius increases, irrespective of the surrounding gas viscosity. The degree of instability increases with Weber number for a relatively large viscosity ratio. In contrast, for small viscosity ratio, the growth rate exhibits a dramatic dependence on the surface tension. There is a small Weber number range, which depends on the viscosity ratio, where the flow is stable. The viscosity ratio always stabilizes the flow. However, the dominant wavenumber increases with increasing viscosity ratio. The range of unstable wavenumbers is affected only by the curvature effect.

Repeated social stress leads to contrasting patterns of structural plasticity in the amygdala and hippocampus.

PubMed

Patel, D; Anilkumar, S; Chattarji, S; Buwalda, B

2018-03-23

Previous studies have demonstrated that repeated immobilization and restraint stress cause contrasting patterns of dendritic reorganization as well as alterations in spine density in amygdalar and hippocampal neurons. Whether social and ethologically relevant stressors can induce similar patterns of morphological plasticity remains largely unexplored. Hence, we assessed the effects of repeated social defeat stress on neuronal morphology in basolateral amygdala (BLA), hippocampal CA1 and infralimbic medial prefrontal cortex (mPFC). Male Wistar rats experienced social defeat stress on 5 consecutive days during confrontation in the resident-intruder paradigm with larger and aggressive Wild-type Groningen rats. This resulted in clear social avoidance behavior one day after the last confrontation. To assess the morphological consequences of repeated social defeat, 2 weeks after the last defeat, animals were sacrificed and brains were stained using a Golgi-Cox procedure. Morphometric analyses revealed that, compared to controls, defeated Wistar rats showed apical dendritic decrease in spine density on CA1 but not BLA. Sholl analysis demonstrated a significant dendritic atrophy of CA1 basal dendrites in defeated animals. In contrast, basal dendrites of BLA pyramidal neurons exhibited enhanced dendritic arborization in defeated animals. Social stress failed to induce lasting structural changes in mPFC neurons. Our findings demonstrate for the first time that social defeat stress elicits divergent patterns of structural plasticity in the hippocampus versus amygdala, similar to what has previously been reported with repeated physical stressors. Therefore, brain region specific variations may be a universal feature of stress-induced plasticity that is shared by both physical and social stressors. Copyright © 2018 Elsevier B.V. All rights reserved.

Spatially Explicit Modeling Reveals Cephalopod Distributions Match Contrasting Trophic Pathways in the Western Mediterranean Sea

PubMed Central

Puerta, Patricia; Hunsicker, Mary E.; Quetglas, Antoni; Álvarez-Berastegui, Diego; Esteban, Antonio; González, María; Hidalgo, Manuel

2015-01-01

Populations of the same species can experience different responses to the environment throughout their distributional range as a result of spatial and temporal heterogeneity in habitat conditions. This highlights the importance of understanding the processes governing species distribution at local scales. However, research on species distribution often averages environmental covariates across large geographic areas, missing variability in population-environment interactions within geographically distinct regions. We used spatially explicit models to identify interactions between species and environmental, including chlorophyll a (Chla) and sea surface temperature (SST), and trophic (prey density) conditions, along with processes governing the distribution of two cephalopods with contrasting life-histories (octopus and squid) across the western Mediterranean Sea. This approach is relevant for cephalopods, since their population dynamics are especially sensitive to variations in habitat conditions and rarely stable in abundance and location. The regional distributions of the two cephalopod species matched two different trophic pathways present in the western Mediterranean Sea, associated with the Gulf of Lion upwelling and the Ebro river discharges respectively. The effects of the studied environmental and trophic conditions were spatially variant in both species, with usually stronger effects along their distributional boundaries. We identify areas where prey availability limited the abundance of cephalopod populations as well as contrasting effects of temperature in the warmest regions. Despite distributional patterns matching productive areas, a general negative effect of Chla on cephalopod densities suggests that competition pressure is common in the study area. Additionally, results highlight the importance of trophic interactions, beyond other common environmental factors, in shaping the distribution of cephalopod populations. Our study presents a valuable approach for understanding the spatially variant ecology of cephalopod populations, which is important for fisheries and ecosystem management. PMID:26201075

3D depth-to-basement and density contrast estimates using gravity and borehole data

NASA Astrophysics Data System (ADS)

Barbosa, V. C.; Martins, C. M.; Silva, J. B.

2009-05-01

We present a gravity inversion method for simultaneously estimating the 3D basement relief of a sedimentary basin and the parameters defining the parabolic decay of the density contrast with depth in a sedimentary pack assuming the prior knowledge about the basement depth at a few points. The sedimentary pack is approximated by a grid of 3D vertical prisms juxtaposed in both horizontal directions, x and y, of a right-handed coordinate system. The prisms' thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data. To produce stable depth-to-basement estimates we impose smoothness on the basement depths through minimization of the spatial derivatives of the parameters in the x and y directions. To estimate the parameters defining the parabolic decay of the density contrast with depth we mapped a functional containing prior information about the basement depths at a few points. We apply our method to synthetic data from a simulated complex 3D basement relief with two sedimentary sections having distinct parabolic laws describing the density contrast variation with depth. Our method retrieves the true parameters of the parabolic law of density contrast decay with depth and produces good estimates of the basement relief if the number and the distribution of boreholes are sufficient. We also applied our method to real gravity data from the onshore and part of the shallow offshore Almada Basin, on Brazil's northeastern coast. The estimated 3D Almada's basement shows geologic structures that cannot be easily inferred just from the inspection of the gravity anomaly. The estimated Almada relief presents steep borders evidencing the presence of gravity faults. Also, we note the existence of three terraces separating two local subbasins. These geologic features are consistent with Almada's geodynamic origin (the Mesozoic breakup of Gondwana and the opening of the South Atlantic Ocean) and they are important in understanding the basin evolution and in detecting structural oil traps.

The Feedback Between Continents and Compositional Anomalies in the Deep Mantle

NASA Astrophysics Data System (ADS)

Lowman, J. P.; Trim, S. J.

2014-12-01

Findings from global seismic tomography studies suggest that the deep mantle may harbor a pair of broad, steep-sided, relatively dense compositionally anomalous provinces. The longevity and stability of these Large Low Shear-Wave Velocity Provinces (LLSVPs) has received considerable interest but their possible influence on surface motion has drawn lesser attention. Recent work using numerical mantle convection models investigated the feedback between oceanic plate motion and high density compositional anomalies. It was found that surface mobility is affected by the presence of compositional anomalies such that critical density contrasts and volumes of the enriched material produce a transition to stagnant-lid convection. For lesser volumes and density contrast (for example, volumes that are representative of the concentrations in the Earth's mantle) the presence of the compositional anomalies affects mean plate velocity and size when compared to the characteristics of systems in which the enriched material is absent. In addition, numerous studies and lines of evidence in the geologic record suggest that the presence of the density anomalies plays a role in determining the location of mantle upwellings, which in turn influence surface dynamics. In this study, we present the results from a study implementing a two-dimensional mantle convection model featuring an anomalously dense component and distinct continental and oceanic lithosphere. The mass, momentum, and energy conservation equations are solved using a hybrid spectral-finite difference code. Compositional variations are tracked using Lagrangian tracer particles. Mobile tectonic plates are modeled using a force-balance method and plate boundary locations evolve in response to interior stresses, plate velocity, age and lithospheric chemistry (i.e., oceanic versus continental). We examine the influence of continents on compositional anomaly morphology and longevity and the influence of compositional anomalies on continental size, mobility and aggregation. The influence of continents is isolated by comparing our calculations with cases in which continents are absent.

SU-F-207-07: Dual-Energy Computed Tomography Detection Limit of Various Radiopaque Contrast Agents That Can Be Infused Within Absorbable Inferior Vena Cava Filters

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

Melancon, A; Jacobsen, M; Salatan, F

Purpose: Absorbable IVC filters are shown to be safe and efficacious in preventing pulmonary embolism. These absorbable filters disappear from the body after their required duration, alleviating costly removal procedures and downstream complications. Monitoring the positioning and integrity of absorbable devices using dual-energy computed tomography (DECT) would improve treatment efficacy. The purpose of this study is to determine the limit of detection and the energy dependence of DECT for various contrast agents that may be infused within the IVC filters including gold nanoparticles (AuNP) having diameters of 2 and 4 nm. Methods: All imaging studies were performed on a GEmore » Discovery CT750 system in Gemstone Spectral Imaging (GSI) mode. Plastic vials containing the contrast agent solutions of water and blood were placed in a water bath, and images were acquired with the GSI-5 preset. The images were reformatted into the coronal plane and 5mm diameter ROIs were placed within each solution on a GE Advantage Workstation. Monoenergetic reconstructions were generated from 40 – 140 keV. Results: Mass attenuation (contrast per unit density) for AuNPs was greater than iron, but less than barium and iodine. Contrast was 10.2 (± 3.6) HU for 4 nm AuNP at 0.72 mg/ml and 12.1 (± 4.2) for 2 nm AuNP at 0.31 mg/ml at 70 keV suggesting reasonable chance of visualization at these concentrations for 70 keV reconstruction. The contrast as a function of CT energy is similar in both water and blood. Iodine is most dependent, followed closely by barium and iron, and trailed by a large margin by the AuNP. This was unexpected given Au’s large atomic number and the predominance of photoelectric effect at low energy. Conclusion: Infusion of IVC filters with AuNP is feasible. Discrimination of AuNP-infused IVC filters from surrounding anatomy warrants further investigation.« less

Pseudo-hemothorax at computed tomography due to residual contrast media.

PubMed

Romero, Matías; Bächler, Pablo

2014-01-01

Pleural effusion is a clinical problem that has many causes, with hemothorax being one of them. Computed tomography readily characterizes pleural fluid with determination of the attenuation value, helping to distinguish hemothorax from other types of effusion. Herein, we report the case of a 67-year-old man with end-stage renal disease in which a high-density pleural effusion due to residual contrast media was misinterpreted as hemothorax. Radiologists should consider the possibility of contrast media retention when interpreting a high-density pleural effusion in patients with end-stage renal disease. Recognition of this entity is crucial to avoid misdiagnosis, which might lead to unnecessary testing or procedures. Copyright © 2014 Elsevier Inc. All rights reserved.

High population density enhances recruitment and survival of a harvested coral reef fish.

PubMed

Wormald, Clare L; Steele, Mark A; Forrester, Graham E

2013-03-01

A negative relationship between population growth and population density (direct density dependence) is necessary for population regulation and is assumed in most models of harvested populations. Experimental tests for density dependence are lacking for large-bodied, harvested fish because of the difficulty of manipulating population density over large areas. We studied a harvested coral reef fish, Lutjanus apodus (schoolmaster snapper), using eight large, isolated natural reefs (0.4-1.6 ha) in the Bahamas as replicates. An initial observational test for density dependence was followed by a manipulation of population density. The manipulation weakened an association between density and shelter-providing habitat features and revealed a positive effect of population density on recruitment and survival (inverse density dependence), but no effect of density on somatic growth. The snappers on an individual reef were organized into a few shoals, and we hypothesize that large shoals on high-density reefs were less vulnerable to large piscivores (groupers and barracudas) than the small shoals on low-density reefs. Reductions in predation risk for individuals in large social groups are well documented, but because snapper shoals occupied reefs the size of small marine reserves, these ecological interactions may influence the outcome of management actions.

Consistent individual differences and population plasticity in network-derived sociality: An experimental manipulation of density in a gregarious ungulate

PubMed Central

O’Brien, Paul P.; Vander Wal, Eric

2018-01-01

In many taxa, individual social traits appear to be consistent across time and context, thus meeting the criteria for animal personality. How these differences are maintained in response to changes in population density is unknown, particularly in large mammals, such as ungulates. Using a behavioral reaction norm (BRN) framework, we examined how among- and within-individual variation in social connectedness, measured using social network analyses, change as a function of population density. We studied a captive herd of elk (Cervus canadensis) separated into a group of male elk and a group of female elk. Males and females were exposed to three different density treatments and we recorded social associations between individuals with proximity-detecting radio-collars fitted to elk. We constructed social networks using dyadic association data and calculated three social network metrics reflective of social connectedness: eigenvector centrality, graph strength, and degree. Elk exhibited consistent individual differences in social connectedness across densities; however, they showed little individual variation in their response to changes in density, i.e., individuals oftentimes responded plastically, but in the same manner to changes in density. Female elk had highest connectedness at an intermediate density. In contrast, male elk increased connectedness with increasing density. Whereas this may suggest that the benefits of social connectedness outweigh the costs of increased competition at higher density for males, females appear to exhibit a threshold in social benefits (e.g. predator detection and forage information). Our study illustrates the importance of viewing social connectedness as a density-dependent trait, particularly in the context of plasticity. Moreover, we highlight the need to revisit our understanding of density dependence as a population-level phenomenon by accounting for consistent individual differences not only in social connectedness, but likely in other ecological processes (e.g., predator-prey dynamics, mate choice, disease transfer). PMID:29494640

Response of old-growth conifers to reduction in stand density in western Oregon forests

USGS Publications Warehouse

Latham, P.; Tappeiner, J. C.

2002-01-01

The positive growth response of healthy young trees to density reduction is well known. In contrast, large old trees are usually thought to be intrinsically limited in their ability to respond to increased growing space; therefore, density reduction is seldom used in stands of old-growth trees. We tested the null hypothesis that old-growth trees are incapable of responding with increased growth following density reduction. The diameter growth response of 271 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), ponderosa pine (Pinus ponderosa Dougl. ex Laws) and sugar pine (Pinus lambertiana Dougl.) trees ranging in age from 158 to 650 years was examined 20 to 50 years after density reduction. Density reduction involved either light thinning with removal of less vigorous trees, or shelterwood treatments in which overstory trees were not removed. Ratios of basal area growth after treatment to basal area growth before treatment, and several other measures of growth, all indicated that the old trees sometimes benefited and were not harmed by density reduction. Growth increased by 10% or more for 68% of the trees in treated stands, and nearly 30% of trees increased growth by over 50%. This growth response persisted for at least 20 years. During this 20-year period, only three trees in treated stands (1.5%) exhibited a rapid decrease in growth, whereas growth decreased in 64% of trees in untreated stands. The length of time before a growth response to density reduction occurred varied from 5 to 25 years, with the greatest growth response often occurring 20 to 25 years after treatment. These results have important implications both for the basic biology of aging in woody plants as well as for silvicultural practices in forests with old-growth trees.

Changes in sea urchins and kelp following a reduction in sea otter density as a result of the Exxon Valdez oil spill

USGS Publications Warehouse

Dean, Thomas A.; Bodkin, James L.; Jewett, Stephen C.; Monson, Daniel H.; Jung, D.

2000-01-01

Interactions between sea otters Enhydra lutris, sea urchins Strongylocentrotus droebachiensis, and kelp were investigated following the reduction in sea otter density in Prince William Sound, Alaska, after the Exxon Valdez oil spill in 1989. At northern Knight Island, a heavily oiled portion of the sound, sea otter abundance was reduced by a minimum of 50% by the oil spill, and from 1995 through 1998 remained at an estimated 66% lower than in 1973. Where sea otter densities were reduced, there were proportionally more large sea urchins. However, except in some widely scattered aggregations, both density and biomass of sea urchins were similar in an area of reduced sea otter density compared with an area where sea otters remained about 10 times more abundant. Furthermore, there was no change in kelp abundance in the area of reduced sea otter density. This is in contrast to greatly increased biomass of sea urchins and greatly reduced kelp density observed following an approximate 90% decline in sea otter abundance in the western Aleutian Islands. The variation in community response to a reduction in sea otters may be related to the magnitude of the reduction and the non-linear response by sea urchins to changes in predator abundance. The number of surviving sea otters may have been high enough to suppress sea urchin populations in Prince William Sound, but not in the Aleutians. Alternatively, differences in response may have been due to differences in the frequency or magnitude of sea urchin recruitment. Densities of small sea urchins were much higher in the Aleutian system even prior to the reduction in sea otters, suggesting a higher rate of recruitment.

Calibration procedures for the quantitative determination of membrane potential in human cells using anionic dyes.

PubMed

Klapperstück, Thomas; Glanz, Dagobert; Hanitsch, Stefan; Klapperstück, Manuela; Markwardt, Fritz; Wohlrab, Johannes

2013-07-01

Quantitative determinations of the cell membrane potential of lymphocytes (Wilson et al., J Cell Physiol 1985;125:72-81) and thymocytes (Krasznai et al., J Photochem Photobiol B 1995;28:93-99) using the anionic dye DiBAC4 (3) proved that dye depletion in the extracellular medium as a result of cellular uptake can be negligible over a wide range of cell densities. In contrast, most flow cytometric studies have not verified this condition but rather assumed it from the start. Consequently, the initially prepared extracellular dye concentration has usually been used for the calculation of the Nernst potential of the dye. In this study, however, external dye depletion could be observed in both large IGR-1 and small LCL-HO cells under experimental conditions, which have often been applied routinely in spectrofluorimetry and flow cytometry. The maximum cell density at which dye depletion could be virtually avoided was dependent on cell size and membrane potential and definitely needed to be taken into account to ensure reliable results. In addition, accepted calibration procedures based on the partition of sodium and potassium (Goldman-Hodgkin-Katz equation) or potassium alone (Nernst equation) were performed by flow cytometry on cell suspensions with an appropriately low cell density. The observed extensive lack of concordance between the correspondingly calculated membrane potential and the equilibrium potential of DiBAC4 (3) revealed that these methods require the additional measurement of cation parameters (membrane permeability and/or intracellular concentration). In contrast, due to the linear relation between fluorescence and low DiBAC4 (3) concentrations, the Nernst potential of the dye for totally depolarized cells can be reliably used for calibration with an essentially lower effort and expense. Copyright © 2013 International Society for Advancement of Cytometry.

Breast fat volume measurement using wide-bore 3 T MRI: comparison of traditional mammographic density evaluation with MRI density measurements using automatic segmentation.

PubMed

Petridou, E; Kibiro, M; Gladwell, C; Malcolm, P; Toms, A; Juette, A; Borga, M; Dahlqvist Leinhard, O; Romu, T; Kasmai, B; Denton, E

2017-07-01

To compare magnetic resonance imaging (MRI)-derived breast density measurements using automatic segmentation algorithms with radiologist estimations using the Breast Imaging Reporting and Data Systems (BI-RADS) density classification. Forty women undergoing mammography and dynamic breast MRI as part of their clinical management were recruited. Fat-water separated MRI images derived from a two-point Dixon technique, phase-sensitive reconstruction, and atlas-based segmentation were obtained before and after intravenous contrast medium administration. Breast density was assessed using software from Advanced MR Analytics (AMRA), Linköping, Sweden, with results compared to the widely used four-quartile quantitative BI-RADS scale. The proportion of glandular tissue in the breast on MRI was derived from the AMRA sequence. The mean unenhanced breast density was 0.31±0.22 (mean±SD; left) and 0.29±0.21 (right). Mean breast density on post-contrast images was 0.32±0.19 (left) and 0.32±0.2 (right). There was "almost perfect" correlation between pre- and post-contrast breast density quantification: Spearman's correlation rho=0.98 (95% confidence intervals [CI]: 0.97-0.99; left) and rho=0.99 (95% CI: 0.98-0.99; right). The 95% limits of agreement were -0.11-0.08 (left) and -0.08-0.03 (right). Interobserver reliability for BI-RADS was "substantial": weighted Kappa k=0.8 (95% CI: 0.74-0.87). The Spearman correlation coefficient between BI-RADS and MRI breast density was rho=0.73 (95% CI: 0.60-0.82; left) and rho=0.75 (95% CI: 0.63-0.83; right) which was also "substantial". The AMRA sequence provides a fully automated, reproducible, objective assessment of fibroglandular breast tissue proportion that correlates well with mammographic assessment of breast density with the added advantage of avoidance of ionising radiation. Copyright © 2017 The Royal College of Radiologists. All rights reserved.

Numerical Study on Stress Heterogeneity Development in Two-Phase Rocks with Large Rheological Contrast and Implications in the Lower Crust

NASA Astrophysics Data System (ADS)

Xu, Junshan; Zhang, Baohua

2018-03-01

Development of stress heterogeneity in two-phase rocks was investigated via a finite element method at 1000-1200 K and 100 MPa. Two groups of rock models were considered: anorthite-diopside and anorthite-clinopyroxene, with a phase volume ratio of 1:1 in each group and different dislocation creep rates between phases ( 4-8 orders of magnitude). Our numerical results indicate that the stress inside the model can be several times higher than the differential stress applied to the model and stress will tend to concentrate in hard phase, especially near the sharp boundaries with soft phase. Moreover, large stress gradient in hard phase and nearly homogeneous stress in soft phase will lead to the initialization of localized dynamic recrystallization or fracture. These numerical observations suggest that the rheological contrast between two phases plays a crucial role in stress heterogeneity rather than other factors (such as grain size, the boundary conditions or mesh density), which may eventually accelerate development of stress heterogeneity in the lower crust. Our study provides new insights into the dynamic processes of grain size reduction in the lower crust, which may cause the transformation from dislocation creep to diffusion creep and enable the weakened shear zones.

Nulling Data Reduction and On-Sky Performance of the Large Binocular Telescope Interferometer

NASA Technical Reports Server (NTRS)

Defrere, D.; Hinz, P. M.; Mennesson, B.; Hoffman, W. F.; Millan-Gabet, R.; Skemer, A. J.; Bailey, V.; Danchi, W. C.; Downy, E. C.; Durney, O.;

Differential controls on soil carbon density and mineralization among contrasting forest types in a temperate forest ecosystem.

PubMed

You, Ye-Ming; Wang, Juan; Sun, Xiao-Lu; Tang, Zuo-Xin; Zhou, Zhi-Yong; Sun, Osbert Jianxin

2016-03-01

Understanding the controls on soil carbon dynamics is crucial for modeling responses of ecosystem carbon balance to global change, yet few studies provide explicit knowledge on the direct and indirect effects of forest stands on soil carbon via microbial processes. We investigated tree species, soil, and site factors in relation to soil carbon density and mineralization in a temperate forest of central China. We found that soil microbial biomass and community structure, extracellular enzyme activities, and most of the site factors studied varied significantly across contrasting forest types, and that the associations between activities of soil extracellular enzymes and microbial community structure appeared to be weak and inconsistent across forest types, implicating complex mechanisms in the microbial regulation of soil carbon metabolism in relation to tree species. Overall, variations in soil carbon density and mineralization are predominantly accounted for by shared effects of tree species, soil, microclimate, and microbial traits rather than the individual effects of the four categories of factors. Our findings point to differential controls on soil carbon density and mineralization among contrasting forest types and highlight the challenge to incorporate microbial processes for constraining soil carbon dynamics in global carbon cycle models.

Differential controls on soil carbon density and mineralization among contrasting forest types in a temperate forest ecosystem

PubMed Central

You, Ye-Ming; Wang, Juan; Sun, Xiao-Lu; Tang, Zuo-Xin; Zhou, Zhi-Yong; Sun, Osbert Jianxin

2016-01-01

Understanding the controls on soil carbon dynamics is crucial for modeling responses of ecosystem carbon balance to global change, yet few studies provide explicit knowledge on the direct and indirect effects of forest stands on soil carbon via microbial processes. We investigated tree species, soil, and site factors in relation to soil carbon density and mineralization in a temperate forest of central China. We found that soil microbial biomass and community structure, extracellular enzyme activities, and most of the site factors studied varied significantly across contrasting forest types, and that the associations between activities of soil extracellular enzymes and microbial community structure appeared to be weak and inconsistent across forest types, implicating complex mechanisms in the microbial regulation of soil carbon metabolism in relation to tree species. Overall, variations in soil carbon density and mineralization are predominantly accounted for by shared effects of tree species, soil, microclimate, and microbial traits rather than the individual effects of the four categories of factors. Our findings point to differential controls on soil carbon density and mineralization among contrasting forest types and highlight the challenge to incorporate microbial processes for constraining soil carbon dynamics in global carbon cycle models. PMID:26925871

The use of Compton scattering in detecting anomaly in soil-possible use in pyromaterial detection

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

Abedin, Ahmad Firdaus Zainal; Ibrahim, Noorddin; Zabidi, Noriza Ahmad

The Compton scattering is able to determine the signature of land mine detection based on dependency of density anomaly and energy change of scattered photons. In this study, 4.43 MeV gamma of the Am-Be source was used to perform Compton scattering. Two detectors were placed between source with distance of 8 cm and radius of 1.9 cm. Detectors of thallium-doped sodium iodide NaI(TI) was used for detecting gamma ray. There are 9 anomalies used in this simulation. The physical of anomaly is in cylinder form with radius of 10 cm and 8.9 cm height. The anomaly is buried 5 cm deep in the bed soil measuredmore » 80 cm radius and 53.5 cm height. Monte Carlo methods indicated the scattering of photons is directly proportional to density of anomalies. The difference between detector response with anomaly and without anomaly namely contrast ratio values are in a linear relationship with density of anomalies. Anomalies of air, wood and water give positive contrast ratio values whereas explosive, sand, concrete, graphite, limestone and polyethylene give negative contrast ratio values. Overall, the contrast ratio values are greater than 2 % for all anomalies. The strong contrast ratios result a good detection capability and distinction between anomalies.« less

Development of optics for x-ray phase-contrast imaging of high energy density plasmas.

PubMed

Stutman, D; Finkenthal, M; Moldovan, N

2010-10-01

Phase-contrast or refraction-enhanced x-ray radiography can be useful for the diagnostic of low-Z high energy density plasmas, such as imploding inertial confinement fusion (ICF) pellets, due to its sensitivity to density gradients. To separate and quantify the absorption and refraction contributions to x-ray images, methods based on microperiodic optics, such as shearing interferometry, can be used. To enable applying such methods with the energetic x rays needed for ICF radiography, we investigate a new type of optics consisting of grazing incidence microperiodic mirrors. Using such mirrors, efficient phase-contrast imaging systems could be built for energies up to ∼100 keV. In addition, a simple lithographic method is proposed for the production of the microperiodic x-ray mirrors based on the difference in the total reflection between a low-Z substrate and a high-Z film. Prototype mirrors fabricated with this method show promising characteristics in laboratory tests.

The hard choice for alternative biofuels to diesel in Brazil.

PubMed

Carioca, J O B; Hiluy Filho, J J; Leal, M R L V; Macambira, F S

2009-01-01

This paper selects biofuel scenarios to substitute diesel in Brazil based on oil reserves increase, diesel imports, CO(2) emissions, crops agronomic yields, byproducts marketing and social impacts. This hard task still considers that agricultural practices in developing countries have large social impacts. Brazil presents high consumption of diesel oil in transport; low agronomic yield of traditional vegetable oil crops, which demand large cultivation areas contrasting with microalgae and palm oils which present high productivity. Concerning technologies, thermal cracking and transesterification of vegetable oils present a difficult economic situation related to vegetable oils price, food competition and glycerin market; BTL technology, meaning thermal gasification of biomass to liquids, faces problems related to low density of biomaterials and low viscosity of synthetic biodiesel produced. Biorefinery algal integrated systems and co-solvent technology to introduce up to 8% of ethanol into diesel seem to be feasible routes to reduce diesel consumption.

Optimal degrees of synaptic connectivity

PubMed Central

Litwin-Kumar, Ashok; Harris, Kameron Decker; Axel, Richard; Sompolinsky, Haim; Abbott, L. F.

2017-01-01

Summary Synaptic connectivity varies widely across neuronal types. Cerebellar granule cells receive five orders of magnitude fewer inputs than the Purkinje cells they innervate, and cerebellum-like circuits including the insect mushroom body also exhibit large divergences in connectivity. In contrast, the number of inputs per neuron in cerebral cortex is more uniform and large. We investigate how the dimension of a representation formed by a population of neurons depends on how many inputs they each receive and what this implies for learning associations. Our theory predicts that the dimensions of the cerebellar granule-cell and Drosophila Kenyon-cell representations are maximized at degrees of synaptic connectivity that match those observed anatomically, showing that sparse connectivity is sometimes superior to dense connectivity. When input synapses are subject to supervised plasticity, however, dense wiring becomes advantageous, suggesting that the type of plasticity exhibited by a set of synapses is a major determinant of connection density. PMID:28215558

Prey density and the behavioral flexibility of a marine predator: The common murre (Uria aalge)

USGS Publications Warehouse

Harding, A.M.A.; Piatt, John F.; Schmutz, J.A.; Shultz, M.T.; van Pelt, Thomas I.; Kettle, Arthur B.; Speckman, Suzann G.

2007-01-01

Flexible time budgets allow individual animals to buffer the effects of variable food availability by allocating more time to foraging when food density decreases. This trait should be especially important for marine predators that forage on patchy and ephemeral food resources. We examined flexible time allocation by a long-lived marine predator, the Common Murre (Uria aalge), using data collected in a five-year study at three colonies in Alaska (USA) with contrasting environmental conditions. Annual hydroacoustic surveys revealed an order-of-magnitude variation in food density among the 15 colony-years of study. We used data on parental time budgets and local prey density to test predictions from two hypotheses: Hypothesis A, the colony attendance of seabirds varies nonlinearly with food density; and Hypothesis B, flexible time allocation of parent murres buffers chicks against variable food availability. Hypothesis A was supported; colony attendance by murres was positively correlated with food over a limited range of poor-to-moderate food densities, but independent of food over a broader range of higher densities. This is the first empirical evidence for a nonlinear response of a marine predator's time budget to changes in prey density. Predictions from Hypothesis B were largely supported: (1) chick-feeding rates were fairly constant over a wide range of densities and only dropped below 3.5 meals per day at the low end of prey density, and (2) there was a nonlinear relationship between chick-feeding rates and time spent at the colony, with chick-feeding rates only declining after time at the colony by the nonbrooding parent was reduced to a minimum. The ability of parents to adjust their foraging time by more than 2 h/d explains why they were able to maintain chick-feeding rates of more than 3.5 meals/d across a 10-fold range in local food density. ?? 2007 by the Ecological Society of America.

Reconstructing cortical current density by exploring sparseness in the transform domain

NASA Astrophysics Data System (ADS)

Ding, Lei

2009-05-01

In the present study, we have developed a novel electromagnetic source imaging approach to reconstruct extended cortical sources by means of cortical current density (CCD) modeling and a novel EEG imaging algorithm which explores sparseness in cortical source representations through the use of L1-norm in objective functions. The new sparse cortical current density (SCCD) imaging algorithm is unique since it reconstructs cortical sources by attaining sparseness in a transform domain (the variation map of cortical source distributions). While large variations are expected to occur along boundaries (sparseness) between active and inactive cortical regions, cortical sources can be reconstructed and their spatial extents can be estimated by locating these boundaries. We studied the SCCD algorithm using numerous simulations to investigate its capability in reconstructing cortical sources with different extents and in reconstructing multiple cortical sources with different extent contrasts. The SCCD algorithm was compared with two L2-norm solutions, i.e. weighted minimum norm estimate (wMNE) and cortical LORETA. Our simulation data from the comparison study show that the proposed sparse source imaging algorithm is able to accurately and efficiently recover extended cortical sources and is promising to provide high-accuracy estimation of cortical source extents.

The effects of the spatial influence function on orthotropic femur remodelling.

PubMed

Shang, Y; Bai, J; Peng, L

2008-07-01

The morphology and internal structure of bone are modulated by the mechanical stimulus. The osteocytes can sense the stimulus signals from the adjacent regions and respond to them through bone growth or bone absorption. This mechanism can be modelled as the spatial influence function (SIF) in bone adaptation algorithm. In this paper, the remodelling process was simulated in human femurs using an adaptation algorithm with and without SIF, and the trabecular bone was assumed to be orthotropic. A different influence radius and weighting factor were adopted to study the effects of the SIF on the bone density distribution and trabecular alignment. The results have shown that the mean density and L-T ratio (the ratio of longitudinal modulus to transverse modulus) had an excellent linear relationship with the weighting factor when the influence radius was small. The characteristics of density distribution and L-T ratio accorded with the actual observation or measurement when a small weighting factor was used. The large influence radius and weighting factor led to unrealistic results. In contrast, the SIF hardly affected the trabecular alignment, as the mean variation angles of principal axes were less than 1.0 degree for any influence radius and weighting factor.

Assessing predation risks for small fish in a large river ecosystem between contrasting habitats and turbidity conditions

USGS Publications Warehouse

Dodrill, Michael J.; Yard, Mike; Pine, William E.

2016-01-01

This study examined predation risk for juvenile native fish between two riverine shoreline habitats, backwater and debris fan, across three discrete turbidity levels (low, intermediate, high) to understand environmental risks associated with habitat use in a section of the Colorado River in Grand Canyon, AZ. Inferences are particularly important to juvenile native fish, including the federally endangered humpback chub Gila cypha. This species uses a variety of habitats including backwaters which are often considered important rearing areas. Densities of two likely predators, adult rainbow trout Oncorhynchus mykiss and adult humpback chub, were estimated between habitats using binomial mixture models to examine whether higher predator density was associated with patterns of predation risk. Tethering experiments were used to quantify relative predation risk between habitats and turbidity conditions. Under low and intermediate turbidity conditions, debris fan habitat showed higher relative predation risk compared to backwaters. In both habitats the highest predation risk was observed during intermediate turbidity conditions. Density of likely predators did not significantly differ between these habitats. This information can help managers in Grand Canyon weigh flow policy options designed to increase backwater availability or extant turbidity conditions.

Evolution of subband structure with gate-tuning at LaAlO3/SrTiO3 interfaces

NASA Astrophysics Data System (ADS)

Tang, Lucas; Smink, Sander; van Heeringen, Linde; Geessinck, Jaap; Rana, Abimanuya; Rastogi, Ankur; Maan, Jan Kees; Brinkman, Alexander; Zeitler, Uli; Hilgenkamp, Hans; McCollam, Alix

The outstanding characteristic of LaAlO3/SrTiO3 heterostructures is the formation of a high mobility 2D electron gas (2DEG) at the interface. The additional presence of superconductivity, magnetism and large spin-orbit coupling in these systems suggests that strong correlations play an important role in the electronic properties, in contrast to conventional semiconductor-based 2DEGs. Knowledge of the electronic bandstructure, and the interdependence of conduction electron density and properties is therefore essential for our understanding of these materials. We present new results of low temperature transport measurements in a high mobility LaAlO3/SrTiO3-based heterostructure, in magnetic fields up to 33 T. Shubnikov de-Haas oscillations are observed, revealing several subbands with different carrier densities. By application of an electric field in the back gate geometry, the Fermi level is tuned and thus we are able to map the smooth evolution of the subbands and their properties with carrier density. These results are in good agreement with recent theoretical work, such that we can disentangle the complex band structure, and quantify aspects such as Rashba spin-splitting and the mixing of orbital character.

Coarse-grained description of cosmic structure from Szekeres models

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

Sussman, Roberto A.; Gaspar, I. Delgado; Hidalgo, Juan Carlos, E-mail: sussman@nucleares.unam.mx, E-mail: ismael.delgadog@uaem.edu.mx, E-mail: hidalgo@fis.unam.mx

2016-03-01

We show that the full dynamical freedom of the well known Szekeres models allows for the description of elaborated 3-dimensional networks of cold dark matter structures (over-densities and/or density voids) undergoing ''pancake'' collapse. By reducing Einstein's field equations to a set of evolution equations, which themselves reduce in the linear limit to evolution equations for linear perturbations, we determine the dynamics of such structures, with the spatial comoving location of each structure uniquely specified by standard early Universe initial conditions. By means of a representative example we examine in detail the density contrast, the Hubble flow and peculiar velocities ofmore » structures that evolved, from linear initial data at the last scattering surface, to fully non-linear 10–20 Mpc scale configurations today. To motivate further research, we provide a qualitative discussion on the connection of Szekeres models with linear perturbations and the pancake collapse of the Zeldovich approximation. This type of structure modelling provides a coarse grained—but fully relativistic non-linear and non-perturbative —description of evolving large scale cosmic structures before their virialisation, and as such it has an enormous potential for applications in cosmological research.« less

Symmetries, invariants and generating functions: higher-order statistics of biased tracers

NASA Astrophysics Data System (ADS)

Munshi, Dipak

2018-01-01

Gravitationally collapsed objects are known to be biased tracers of an underlying density contrast. Using symmetry arguments, generalised biasing schemes have recently been developed to relate the halo density contrast δh with the underlying density contrast δ, divergence of velocity θ and their higher-order derivatives. This is done by constructing invariants such as s, t, ψ,η. We show how the generating function formalism in Eulerian standard perturbation theory (SPT) can be used to show that many of the additional terms based on extended Galilean and Lifshitz symmetry actually do not make any contribution to the higher-order statistics of biased tracers. Other terms can also be drastically simplified allowing us to write the vertices associated with δh in terms of the vertices of δ and θ, the higher-order derivatives and the bias coefficients. We also compute the cumulant correlators (CCs) for two different tracer populations. These perturbative results are valid for tree-level contributions but at an arbitrary order. We also take into account the stochastic nature bias in our analysis. Extending previous results of a local polynomial model of bias, we express the one-point cumulants Script SN and their two-point counterparts, the CCs i.e. Script Cpq, of biased tracers in terms of that of their underlying density contrast counterparts. As a by-product of our calculation we also discuss the results using approximations based on Lagrangian perturbation theory (LPT).

An x-ray backlit Talbot-Lau deflectometer for high-energy-density electron density diagnostics

DOE PAGES

Valdivia, M. P.; Stutman, D.; Stoeckl, C.; ...

2016-02-10

X-ray phase-contrast techniques can measure electron density gradients in high-energy-density plasmas through refraction induced phase shifts. An 8 keV Talbot-Lau interferometer consisting of free standing ultrathin gratings was deployed at an ultra-short, high-intensity laser system using K-shell emission from a 1-30 J, 8 ps laser pulse focused on thin Cu foil targets. Grating survival was demonstrated for 30 J, 8 ps laser pulses. The first x-ray deflectometry images obtained under laser backlighting showed up to 25% image contrast and thus enabled detection of electron areal density gradients with a maximum value of 8.1 ± 0.5 × 10 23 cm ₋3more » in a low-Z millimeter sized sample. An electron density profile was obtained from refraction measurements with an error of <8%. We found the 50 ± 15 μm spatial resolution achieved across the full field of view was limited by the x-ray source-size, similar to conventional radiography.« less

Gravity data inversion to determine 3D topographycal density contrast of Banten area, Indonesia based on fast Fourier transform

NASA Astrophysics Data System (ADS)

Windhari, Ayuty; Handayani, Gunawan

2015-04-01

The 3D inversion gravity anomaly to estimate topographical density using a matlab source code from gridded data provided by Parker Oldenburg algorithm based on fast Fourier transform was computed. We extend and improved the source code of 3DINVERT.M invented by Gomez Ortiz and Agarwal (2005) using the relationship between Fourier transform of the gravity anomaly and the sum of the Fourier transform from the topography density. We gave density contrast between the two media to apply the inversion. FFT routine was implemented to construct amplitude spectrum to the given mean depth. The results were presented as new graphics of inverted topography density, the gravity anomaly due to the inverted topography and the difference between the input gravity data and the computed ones. It terminates when the RMS error is lower than pre-assigned value used as convergence criterion or until maximum of iterations is reached. As an example, we used the matlab program on gravity data of Banten region, Indonesia.

Development of the Ni-based Metallic glassy bipolar plates for Proton Exchange Membrane Fuel Cell (PEMFC)

NASA Astrophysics Data System (ADS)

Yamaura, S.; Yokoyama, M.; Kimura, H. M.; Inoue, A.

2009-01-01

Alloy optimization in the Ni80-xCrxP16B4 (x = 9-30 at%) alloy system was conducted in order to achieve low Tg, Tx and a large ΔTx. From this study, the Ni65Cr15P16B4 glassy alloy was found to be the optimal alloy. The static and potentiodynamic corrosion behaviours of this alloy were measured. As a result of polarization measurements, it was found that the current density of the non-polished glassy alloy sample was smaller than that of a SUS316L sample. By contrast, the current density of the surface-polished glassy sample was slightly larger than that of the SUS316L sample in the voltage range of 0.3-0.8 V. A bipolar plate was successfully produced by hot-pressing the glassy alloy sheet in a supercooled liquid state. The I-V characteristics of a single cell with the glassy bipolar plates were measured.

Λ-enhanced grey molasses on the D2 transition of Rubidium-87 atoms.

PubMed

Rosi, Sara; Burchianti, Alessia; Conclave, Stefano; Naik, Devang S; Roati, Giacomo; Fort, Chiara; Minardi, Francesco

2018-01-22

Laser cooling based on dark states, i.e. states decoupled from light, has proven to be effective to increase the phase-space density of cold trapped atoms. Dark-states cooling requires open atomic transitions, in contrast to the ordinary laser cooling used for example in magneto-optical traps (MOTs), which operate on closed atomic transitions. For alkali atoms, dark-states cooling is therefore commonly operated on the D 1 transition nS 1/2  → nP 1/2 . We show that, for 87 Rb, thanks to the large hyperfine structure separations the use of this transition is not strictly necessary and that "quasi-dark state" cooling is efficient also on the D 2 line, 5S 1/2  → 5P 3/2 . We report temperatures as low as (4.0 ± 0.3) μK and an increase of almost an order of magnitude in the phase space density with respect to ordinary laser sub-Doppler cooling.

Development of scanning graphene Hall probes for magnetic microscopy

NASA Astrophysics Data System (ADS)

Schaefer, Brian T.; Wang, Lei; McEuen, Paul L.; Nowack, Katja C.

We discuss our progress on developing scanning Hall probes fabricated from hexagonal boron nitride (hBN)-encapsulated graphene, with the goal to image magnetic fields with submicron resolution. In contrast to scanning superconducting quantum interference device (SQUID) microscopy, this technique is compatible with a large applied magnetic field and not limited to cryogenic temperatures. The field sensitivity of a Hall probe depends inversely on carrier density, while the primary source of noise in the measurement is Johnson noise originating from the device resistance. hBN-encapsulated graphene demonstrates high carrier mobility at low carrier densities, therefore making it an ideal material for sensitive Hall probes. Furthermore, engineering the dielectric environment of graphene by encapsulating in hBN reduces low-frequency charge noise and disorder from the substrate. We outline our plans for adapting these devices for scanning, including characterization of the point spread function with a scanned current loop and fabrication of a deep-etched structure that enables positioning the sensitive area within 100 nanometers of the sample surface.

Excess electrons in ice: a density functional theory study.

PubMed

Bhattacharya, Somesh Kr; Inam, Fakharul; Scandolo, Sandro

2014-02-21

We present a density functional theory study of the localization of excess electrons in the bulk and on the surface of crystalline and amorphous water ice. We analyze the initial stages of electron solvation in crystalline and amorphous ice. In the case of crystalline ice we find that excess electrons favor surface states over bulk states, even when the latter are localized at defect sites. In contrast, in amorphous ice excess electrons find it equally favorable to localize in bulk and in surface states which we attribute to the preexisting precursor states in the disordered structure. In all cases excess electrons are found to occupy the vacuum regions of the molecular network. The electron localization in the bulk of amorphous ice is assisted by its distorted hydrogen bonding network as opposed to the crystalline phase. Although qualitative, our results provide a simple interpretation of the large differences observed in the dynamics and localization of excess electrons in crystalline and amorphous ice films on metals.

Experimental investigation of standing wave effect in dual-frequency capacitively coupled argon discharges: role of a low-frequency source

NASA Astrophysics Data System (ADS)

Zhao, Kai; Liu, Yong-Xin; Kawamura, E.; Wen, De-Qi; Lieberman, M. A.; Wang, You-Nian

2018-05-01

It is well known that the plasma non-uniformity caused by the standing wave effect has brought about great challenges for plasma material processing. To improve the plasma uniformity, a low-frequency (LF) power source is introduced into a 100 MHz very-high-frequency (VHF) capacitively coupled argon plasma reactor. The effect of the LF parameters (LF voltage amplitude ϕ L and LF source f L) on the radial profile of plasma density has been investigated by utilizing a hairpin probe. The result at a low pressure (1 Pa) is compared to the one obtained by a 2D fluid-analytical capacitively coupled plasma model, showing good agreement in the plasma density radial profile. The experimental results show that the plasma density profile exhibits different dependences on ϕ L and f L at different gas pressures/electrode driven types (i.e., the two rf sources are applied on one electrode (case I) and separate electrodes (case II)). At low pressures (e.g., 8 Pa), the pronounced standing wave effect revealed in a VHF discharge can be suppressed at a relatively high ϕ L or a low f L in case I, because the HF sheath heating is largely weakened due to strong modulation by the LF source. By contrast, ϕ L and f L play insignificant roles in suppressing the standing wave effect in case II. At high pressures (e.g., 20 Pa), the opposite is true. The plasma density radial profile is more sensitive to ϕ L and f L in case II than in case I. In case II, the standing wave effect is surprisingly enhanced with increasing ϕ L at higher pressures; however, the center-high density profile caused by the standing wave effect can be compensated by increasing f L due to the enhanced electrostatic edge effect dominated by the LF source. In contrast, the density radial profile shows a much weaker dependence on ϕ L and f L in case I at higher pressures. To understand the different roles of ϕ L and f L, the electron excitation dynamics in each case are analyzed based on the measured spatio-temporal distributions of the electron-impact excitation rate by phase resolved optical emission spectroscopy.

Century Scale Evaporation Trend: An Observational Study

NASA Technical Reports Server (NTRS)

Bounoui, Lahouari

2012-01-01

Several climate models with different complexity indicate that under increased CO2 forcing, runoff would increase faster than precipitation overland. However, observations over large U.S watersheds indicate otherwise. This inconsistency between models and observations suggests that there may be important feedbacks between climate and land surface unaccounted for in the present generation of models. We have analyzed century-scale observed annual runoff and precipitation time-series over several United States Geological Survey hydrological units covering large forested regions of the Eastern United States not affected by irrigation. Both time-series exhibit a positive long-term trend; however, in contrast to model results, these historic data records show that the rate of precipitation increases at roughly double the rate of runoff increase. We considered several hydrological processes to close the water budget and found that none of these processes acting alone could account for the total water excess generated by the observed difference between precipitation and runoff. We conclude that evaporation has increased over the period of observations and show that the increasing trend in precipitation minus runoff is correlated to observed increase in vegetation density based on the longest available global satellite record. The increase in vegetation density has important implications for climate; it slows but does not alleviate the projected warming associated with greenhouse gases emission.

Structural and mechanical properties of glassy water in nanoscale confinement.

PubMed

Lombardo, Thomas G; Giovambattista, Nicolás; Debenedetti, Pablo G

2009-01-01

We investigate the structure and mechanical properties of glassy water confined between silica-based surfaces with continuously tunable hydrophobicity and hydrophilicity by computing and analyzing minimum energy, mechanically stable configurations (inherent structures). The structured silica substrate imposes long-range order on the first layer of water molecules under hydrophobic confinement at high density (p > or = 1.0 g cm(-3)). This proximal layer is also structured in hydrophilic confinement at very low density (p approximately 0.4 g cm(-3)). The ordering of water next to the hydrophobic surface greatly enhances the mechanical strength of thin films (0.8 nm). This leads to a substantial stress anisotropy; the transverse strength of the film exceeds the normal strength by 500 MPa. The large transverse strength results in a minimum in the equation of state of the energy landscape that does not correspond to a mechanical instability, but represents disruption of the ordered layer of water next to the wall. In addition, we find that the mode of mechanical failure is dependent on the type of confinement. Under large lateral strain, water confined by hydrophilic surfaces preferentially forms voids in the middle of the film and fails cohesively. In contrast, water under hydrophobic confinement tends to form voids near the walls and fails by loss of adhesion.

Development of a hybrid image processing algorithm for automatic evaluation of intramuscular fat content in beef M. longissimus dorsi.

PubMed

Du, Cheng-Jin; Sun, Da-Wen; Jackman, Patrick; Allen, Paul

2008-12-01

An automatic method for estimating the content of intramuscular fat (IMF) in beef M. longissimus dorsi (LD) was developed using a sequence of image processing algorithm. To extract IMF particles within the LD muscle from structural features of intermuscular fat surrounding the muscle, three steps of image processing algorithm were developed, i.e. bilateral filter for noise removal, kernel fuzzy c-means clustering (KFCM) for segmentation, and vector confidence connected and flood fill for IMF extraction. The technique of bilateral filtering was firstly applied to reduce the noise and enhance the contrast of the beef image. KFCM was then used to segment the filtered beef image into lean, fat, and background. The IMF was finally extracted from the original beef image by using the techniques of vector confidence connected and flood filling. The performance of the algorithm developed was verified by correlation analysis between the IMF characteristics and the percentage of chemically extractable IMF content (P<0.05). Five IMF features are very significantly correlated with the fat content (P<0.001), including count densities of middle (CDMiddle) and large (CDLarge) fat particles, area densities of middle and large fat particles, and total fat area per unit LD area. The highest coefficient is 0.852 for CDLarge.

Experimental power spectral density analysis for mid- to high-spatial frequency surface error control.

PubMed

Hoyo, Javier Del; Choi, Heejoo; Burge, James H; Kim, Geon-Hee; Kim, Dae Wook

2017-06-20

The control of surface errors as a function of spatial frequency is critical during the fabrication of modern optical systems. A large-scale surface figure error is controlled by a guided removal process, such as computer-controlled optical surfacing. Smaller-scale surface errors are controlled by polishing process parameters. Surface errors of only a few millimeters may degrade the performance of an optical system, causing background noise from scattered light and reducing imaging contrast for large optical systems. Conventionally, the microsurface roughness is often given by the root mean square at a high spatial frequency range, with errors within a 0.5×0.5  mm local surface map with 500×500 pixels. This surface specification is not adequate to fully describe the characteristics for advanced optical systems. The process for controlling and minimizing mid- to high-spatial frequency surface errors with periods of up to ∼2-3  mm was investigated for many optical fabrication conditions using the measured surface power spectral density (PSD) of a finished Zerodur optical surface. Then, the surface PSD was systematically related to various fabrication process parameters, such as the grinding methods, polishing interface materials, and polishing compounds. The retraceable experimental polishing conditions and processes used to produce an optimal optical surface PSD are presented.

Patch size and landscape effects on density and nesting success of grassland birds

USGS Publications Warehouse

Winter, Maiken; Johnson, Douglas H.; Shaffer, Jill A.; Donovan, Therese M.; Svedarsky, W. Daniel

2006-01-01

Current management recommendations for grassland birds in North America emphasize providing large patches of grassland habitat within landscapes that have few forest or shrubland areas. These Bird Conservation Areas are being proposed under the assumption that large patches of habitat in treeless landscapes will maintain viable populations of grassland birds. This assumption requires that patch size and landscape features affect density and nesting success of grassland birds, and that these effects are consistent among years and regions and across focal species. However, these assumptions have not yet been validated for grassland birds, and the relative importance of local vegetation structure, patch size, and landscape composition on grassland bird populations is not well known. In addition, factors influencing grassland bird nesting success have been investigated mostly in small-scale and short-duration studies. To develop management guidelines for grassland birds, we tested the spatial and temporal repeatability of the influence of patch size and landscape composition on density and nesting success of 3 grassland passerines, after controlling for local-scale vegetation structure, climate, and—when analyzing nest success—bird density. We conducted our study during 4 years (1998–2001) in 44 study plots that were set up in 3 regions of the northern tallgrass prairie in Minnesota and North Dakota, USA. In these study plots we measured density and nesting success of clay-colored sparrows (Spizella pallida), Savannah sparrows (Passerculus sandwichensis), and bobolinks (Dolichonyx oryzivorus). Statistical models indicated that density was influenced by patch size, landscape, region, and local vegetation structure more so than by local vegetation structure alone. Both magnitude and direction of the response of density to patch size varied among regions, years, and species. In contrast, the direction of landscape effects was consistent among regions, years, and between Savannah sparrows and bobolinks. In each species, this landscape effect was independent of patch size. Nesting success was not clearly influenced by patch size or landscape composition, and none of the factors that influenced avian density also influenced nesting success in any of the 3 species. General statements on “optimal habitat” for grassland birds should therefore be viewed cautiously. Instead, long-term studies in different regions as well as a deeper understanding of the local system are needed to determine which factors are most important for grassland birds in a particular area.

Coronal loop seismology using damping of standing kink oscillations by mode coupling

NASA Astrophysics Data System (ADS)

Pascoe, D. J.; Goddard, C. R.; Nisticò, G.; Anfinogentov, S.; Nakariakov, V. M.

2016-05-01

Context. Kink oscillations of solar coronal loops are frequently observed to be strongly damped. The damping can be explained by mode coupling on the condition that loops have a finite inhomogeneous layer between the higher density core and lower density background. The damping rate depends on the loop density contrast ratio and inhomogeneous layer width. Aims: The theoretical description for mode coupling of kink waves has been extended to include the initial Gaussian damping regime in addition to the exponential asymptotic state. Observation of these damping regimes would provide information about the structuring of the coronal loop and so provide a seismological tool. Methods: We consider three examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) for which the general damping profile (Gaussian and exponential regimes) can be fitted. Determining the Gaussian and exponential damping times allows us to perform seismological inversions for the loop density contrast ratio and the inhomogeneous layer width normalised to the loop radius. The layer width and loop minor radius are found separately by comparing the observed loop intensity profile with forward modelling based on our seismological results. Results: The seismological method which allows the density contrast ratio and inhomogeneous layer width to be simultaneously determined from the kink mode damping profile has been applied to observational data for the first time. This allows the internal and external Alfvén speeds to be calculated, and estimates for the magnetic field strength can be dramatically improved using the given plasma density. Conclusions: The kink mode damping rate can be used as a powerful diagnostic tool to determine the coronal loop density profile. This information can be used for further calculations such as the magnetic field strength or phase mixing rate.

Leaf δ18O of remaining trees is affected by thinning intensity in a semiarid pine forest.

PubMed

Moreno-Gutiérrez, Cristina; Barberá, Gonzalo G; Nicolás, Emilio; DE Luis, Martín; Castillo, Víctor M; Martínez-Fernández, Faustino; Querejeta, José I

2011-06-01

Silvicultural thinning usually improves the water status of remaining trees in water-limited forests. We evaluated the usefulness of a dual stable isotope approach (δ¹³C, δ¹⁸O) for comparing the physiological performance of remaining trees between forest stands subjected to two different thinning intensities (moderate versus heavy) in a 60-year-old Pinus halepensis Mill. plantation in semiarid southeastern Spain. We measured bulk leaf δ¹³C and δ¹⁸O, foliar elemental concentrations, stem water content, stem water δ¹⁸O (δ¹⁸O(stem water)), tree ring widths and leaf gas exchange rates to assess the influence of forest stand density on tree performance. Remaining trees in low-density stands (heavily thinned) showed lower leaf δ¹⁸O, and higher stomatal conductance (g(s)), photosynthetic rate and radial growth than those in moderate-density stands (moderately thinned). By contrast, leaf δ¹³C, intrinsic water-use efficiency, foliar elemental concentrations and δ¹⁸O(stem water) were unaffected by stand density. Lower foliar δ¹⁸O in heavily thinned stands reflected higher g(s) of remaining trees due to decreased inter-tree competition for water, whereas higher photosynthetic rate was largely attributable to reduced stomatal limitation to CO₂ uptake. The dual isotope approach provided insight into the early (12 months) effects of stand density manipulation on the physiological performance of remaining trees. © 2011 Blackwell Publishing Ltd.

Structure of Weakly Charged Polyelectrolyte Brushes: Monomer Density Profiles

NASA Astrophysics Data System (ADS)

Borisov, O. V.; Zhulina, E. B.

1997-03-01

The internal structure (the monomer density profiles) of weakly charged polyelectrolyte brushes of different morphologies has been analyzed on the basis of the self-consistent-field approach. In contrast to previous studies based on the local electroneutrality approximation valid for sufficiently strongly charged or densely grafted (“osmotic") brushes we consider the opposite limit of sparse brushes which are unable to retain the counterions inside the brush. We have shown that an exact analytical solution of the SCF-equations is available in the case of a planar brush. In contrast to Gaussian monomer density profile known for “osmotic" polyelectrolyte brushes we have found that weakly charged brushes are characterized by constant monomer density. At the same time free ends of grafted polyions are distributed throughout the brush. Thus, the structural cross-over between polyelectrolyte “mushrooms" and dense brush regimes is established.

Solar Wind Speed Structure in the Inner Corona at 3-12 Ro

NASA Technical Reports Server (NTRS)

Woo, Richard

1995-01-01

Estimates of solar wind speed obtained by Armstrong et al. [1986] based on 1983 VLA multiple-station intensity scintillation measurements inside 12 R(sub o) have been correlated with the electron density structure observed in white-light coronagraph measurements. The observed large- scale and apparently systematic speed variations are found to depend primarily on changes in heliographic latitude and longitude, which leads to the first results on large-scale speed structure in the acceleration region of the solar wind. Over an equatorial hole, solar wind speed is relatively steady, with peak-to-peak variations of 50 km/s and an average of 230 km/s. In contrast, the near-Sun flow speed across the streamer belt shows regular large-scale variations in the range of 100-300 km/s. Based on four groups of data, the gradient is 36 km/s per degree in heliocentric coordinates (corresponding to a rise of 260 km/s over a spatial distance on the Sun of two arcmin) with a standard deviation of 2.4 km/s per degree. The lowest speeds most likely coincide with the stalks of coronal streamers observed in white-light measurements. The detection of significant wind shear over the streamer belt is consistent with in situ and scintillation measurements showing that the density spectrum has a power-law form characteristic of fully developed turbulence over a much broader range of scales than in neighboring regions.

A new bias field correction method combining N3 and FCM for improved segmentation of breast density on MRI.

PubMed

Lin, Muqing; Chan, Siwa; Chen, Jeon-Hor; Chang, Daniel; Nie, Ke; Chen, Shih-Ting; Lin, Cheng-Ju; Shih, Tzu-Ching; Nalcioglu, Orhan; Su, Min-Ying

2011-01-01

Quantitative breast density is known as a strong risk factor associated with the development of breast cancer. Measurement of breast density based on three-dimensional breast MRI may provide very useful information. One important step for quantitative analysis of breast density on MRI is the correction of field inhomogeneity to allow an accurate segmentation of the fibroglandular tissue (dense tissue). A new bias field correction method by combining the nonparametric nonuniformity normalization (N3) algorithm and fuzzy-C-means (FCM)-based inhomogeneity correction algorithm is developed in this work. The analysis is performed on non-fat-sat T1-weighted images acquired using a 1.5 T MRI scanner. A total of 60 breasts from 30 healthy volunteers was analyzed. N3 is known as a robust correction method, but it cannot correct a strong bias field on a large area. FCM-based algorithm can correct the bias field on a large area, but it may change the tissue contrast and affect the segmentation quality. The proposed algorithm applies N3 first, followed by FCM, and then the generated bias field is smoothed using Gaussian kernal and B-spline surface fitting to minimize the problem of mistakenly changed tissue contrast. The segmentation results based on the N3+FCM corrected images were compared to the N3 and FCM alone corrected images and another method, coherent local intensity clustering (CLIC), corrected images. The segmentation quality based on different correction methods were evaluated by a radiologist and ranked. The authors demonstrated that the iterative N3+FCM correction method brightens the signal intensity of fatty tissues and that separates the histogram peaks between the fibroglandular and fatty tissues to allow an accurate segmentation between them. In the first reading session, the radiologist found (N3+FCM > N3 > FCM) ranking in 17 breasts, (N3+FCM > N3 = FCM) ranking in 7 breasts, (N3+FCM = N3 > FCM) in 32 breasts, (N3+FCM = N3 = FCM) in 2 breasts, and (N3 > N3+FCM > FCM) in 2 breasts. The results of the second reading session were similar. The performance in each pairwise Wilcoxon signed-rank test is significant, showing N3+FCM superior to both N3 and FCM, and N3 superior to FCM. The performance of the new N3+FCM algorithm was comparable to that of CLIC, showing equivalent quality in 57/60 breasts. Choosing an appropriate bias field correction method is a very important preprocessing step to allow an accurate segmentation of fibroglandular tissues based on breast MRI for quantitative measurement of breast density. The proposed algorithm combining N3+FCM and CLIC both yield satisfactory results.

Food portion size and energy density evoke different patterns of brain activation in children12

PubMed Central

Fearnbach, S Nicole; Wilson, Stephen J; Fisher, Jennifer O; Savage, Jennifer S; Rolls, Barbara J; Keller, Kathleen L

2017-01-01

Background: Large portions of food promote intake, but the mechanisms that drive this effect are unclear. Previous neuroimaging studies have identified the brain-reward and decision-making systems that are involved in the response to the energy density (ED) (kilocalories per gram) of foods, but few studies have examined the brain response to the food portion size (PS). Objective: We used functional MRI (fMRI) to determine the brain response to food images that differed in PSs (large and small) and ED (high and low). Design: Block-design fMRI was used to assess the blood oxygen level–dependent (BOLD) response to images in 36 children (7–10 y old; girls: 50%), which was tested after a 2-h fast. Pre-fMRI fullness and liking were rated on visual analog scales. A whole-brain cluster-corrected analysis was used to compare BOLD activation for main effects of the PS, ED, and their interaction. Secondary analyses were used to associate BOLD contrast values with appetitive traits and laboratory intake from meals for which the portions of all foods were increased. Results: Compared with small-PS cues, large-PS cues were associated with decreased activation in the inferior frontal gyrus (P < 0.01). Compared with low-ED cues, high-ED cues were associated with increased activation in multiple regions (e.g., in the caudate, cingulate, and precentral gyrus) and decreased activation in the insula and superior temporal gyrus (P < 0.01 for all). A PS × ED interaction was shown in the superior temporal gyrus (P < 0.01). BOLD contrast values for high-ED cues compared with low-ED cues in the insula, declive, and precentral gyrus were negatively related to appetitive traits (P < 0.05). There were no associations between the brain response to the PS and either appetitive traits or intake. Conclusions: Cues regarding food PS may be processed in the lateral prefrontal cortex, which is a region that is implicated in cognitive control, whereas ED activates multiple areas involved in sensory and reward processing. Possible implications include the development of interventions that target decision-making and reward systems differently to moderate overeating. PMID:27881393

The use of high altitude remote sensing in determining existing vegetation and monitoring ecological stress

NASA Technical Reports Server (NTRS)

Foster, K.; Garcia, A.

1972-01-01

High altitude color and multispectral black and white photography was used to survey existing vegetation and soil conditions on the Empire Ranch where large scale development will soon begin. Utilizing stereo pairs of the high altitude color photography, four vegetation classifications were discernable as a function of topography and foliage characteristics. In contrast to the undeveloped Ranch, the same photography was used to detect environmental changes in the Tucson metropolitan area as a result of rapid urbanization. The most prevalent change related to development is the removal of vegetation in high density areas to allow for housing starts. Erosion then occurs where vegetation has been removed.

Communications: Complete description of re-entrant phase behavior in a charge variable colloidal model system.

PubMed

Wette, Patrick; Klassen, Ina; Holland-Moritz, Dirk; Herlach, Dieter M; Schöpe, Hans Joachim; Lorenz, Nina; Reiber, Holger; Palberg, Thomas; Roth, Stephan V

2010-04-07

In titration experiments with NaOH, we have determined the full phase diagram of charged colloidal spheres in dependence on the particle density n, the particle effective charge Z(eff) and the concentration of screening electrolyte c using microscopy, light and ultrasmall angle x-ray scattering (USAXS). For sufficiently large n, the system crystallizes upon increasing Z(eff) at constant c and melts upon increasing c at only slightly altered Z(eff). In contrast to earlier work, equilibrium phase boundaries are consistent with a universal melting line prediction from computer simulation, if the elasticity effective charge is used. This charge accounts for both counterion condensation and many-body effects.

Radiation-Driven Flame Spread Over Thermally-Thick Fuels in Quiescent Microgravity Environments

NASA Technical Reports Server (NTRS)

Honda, Linton K.; Son, Youngjin; Ronney, Paul D.; Olson, Sandra (Technical Monitor); Gokoglu, Suleyman (Technical Monitor)

2001-01-01

Microgravity experiments on flame spread over thermally thick fuels were conducted using foam fuels to obtain low density and thermal conductivity, and thus large spread rate (Sf) compared to dense fuels such as PMMA. This scheme enabled meaningful results to lie obtained even in 2.2 second drop tower experiments. It was found that, in contrast conventional understanding; steady spread can occur over thick fuels in quiescent microgravity environments, especially when a radiatively active diluent gas such as CO2 is employed. This is proposed to be due to radiative transfer from the flame to the fuel surface. Additionally, the transition from thermally thick to thermally thin behavior with decreasing bed thickness is demonstrated.

Spectral characteristics of earth-space paths at 2 and 30 FHz

NASA Technical Reports Server (NTRS)

Baxter, R. A.; Hodge, D. B.

1978-01-01

Spectral characteristics of 2 and 30 GHz signals received from the Applications Technology Satellite-6 (ATS-6) are analyzed in detail at elevation angles ranging from 0 deg to 44 deg. The spectra of the received signals are characterized by slopes and break frequencies. Statistics of these parameters are presented as probability density functions. Dependence of the spectral characteristics on elevation angle is investigated. The 2 and 30 GHz spectral shapes are contrasted through the use of scatter diagrams. The results are compared with those predicted from turbulence theory. The average spectral slopes are in close agreement with theory, although the departure from the average value at any given elevation angle is quite large.

PHOTOMETRIC TRENDS IN THE VISIBLE SOLAR CONTINUUM AND THEIR SENSITIVITY TO THE CENTER-TO-LIMB PROFILE

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

Peck, C. L.; Rast, M. P.

2015-08-01

Solar irradiance variations over solar rotational timescales are largely determined by the passage of magnetic structures across the visible solar disk. Variations on solar cycle timescales are thought to be similarly due to changes in surface magnetism with activity. Understanding the contribution of magnetic structures to total solar irradiance and solar spectral irradiance requires assessing their contributions as a function of disk position. Since only relative photometry is possible from the ground, the contrasts of image pixels are measured with respect to a center-to-limb intensity profile. Using nine years of full-disk red and blue continuum images from the Precision Solarmore » Photometric Telescope at the Mauna Loa Solar Observatory, we examine the sensitivity of continuum contrast measurements to the center-to-limb profile definition. Profiles which differ only by the amount of magnetic activity allowed in the pixels used to determine them yield oppositely signed solar cycle length continuum contrast trends, either agreeing with previous results and showing negative correlation with solar cycle or disagreeing and showing positive correlation with solar cycle. Changes in the center-to-limb profile shape over the solar cycle are responsible for the contradictory contrast results, and we demonstrate that the lowest contrast structures, internetwork and network, are most sensitive to these. Thus the strengths of the full-disk, internetwork, and network photometric trends depend critically on the magnetic flux density used in the quiet-Sun definition. We conclude that the contributions of low contrast magnetic structures to variations in the solar continuum output, particularly to long-term variations, are difficult, if not impossible, to determine without the use of radiometric imaging.« less

Best density and structure for uneven-aged northern hardwood management in New England

Treesearch

William B. Leak

2003-01-01

Choice of the best residual density (basal area per acre) and structure (diameter distribution) for uneven-aged management of northern hardwoods is a complex decision that depends on the manager's decision rules, product objectives, site conditions, and - perhaps most important - current stand conditions. In contrast to other recommendations on residual density...

The ATLASGAL survey: distribution of cold dust in the Galactic plane. Combination with Planck data

NASA Astrophysics Data System (ADS)

Csengeri, T.; Weiss, A.; Wyrowski, F.; Menten, K. M.; Urquhart, J. S.; Leurini, S.; Schuller, F.; Beuther, H.; Bontemps, S.; Bronfman, L.; Henning, Th.; Schneider, N.

2016-01-01

Context. Sensitive ground-based submillimeter surveys, such as ATLASGAL, provide a global view on the distribution of cold dense gas in the Galactic plane at up to two-times better angular-resolution compared to recent space-based surveys with Herschel. However, a drawback of ground-based continuum observations is that they intrinsically filter emission, at angular scales larger than a fraction of the field-of-view of the array, when subtracting the sky noise in the data processing. The lost information on the distribution of diffuse emission can be, however, recovered from space-based, all-sky surveys with Planck. Aims: Here we aim to demonstrate how this information can be used to complement ground-based bolometer data and present reprocessed maps of the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey. Methods: We use the maps at 353 GHz from the Planck/HFI instrument, which performed a high sensitivity all-sky survey at a frequency close to that of the APEX/LABOCA array, which is centred on 345 GHz. Complementing the ground-based observations with information on larger angular scales, the resulting maps reveal the distribution of cold dust in the inner Galaxy with a larger spatial dynamic range. We visually describe the observed features and assess the global properties of dust distribution. Results: Adding information from large angular scales helps to better identify the global properties of the cold Galactic interstellar medium. To illustrate this, we provide mass estimates from the dust towards the W43 star-forming region and estimate a column density contrast of at least a factor of five between a low intensity halo and the star-forming ridge. We also show examples of elongated structures extending over angular scales of 0.5°, which we refer to as thin giant filaments. Corresponding to > 30 pc structures in projection at a distance of 3 kpc, these dust lanes are very extended and show large aspect ratios. We assess the fraction of dense gas by determining the contribution of the APEX/LABOCA maps to the combined maps, and estimate 2-5% for the dense gas fraction (corresponding to Av> 7 mag) on average in the Galactic plane. We also show probability distribution functions of the column density (N-PDF), which reveal the typically observed log-normal distribution for low column density and exhibit an excess at high column densities. As a reference for extragalactic studies, we show the line-of-sight integrated N-PDF of the inner Galaxy, and derive a contribution of this excess to the total column density of ~ 2.2%, corresponding to NH2 = 2.92 × 1022 cm-2. Taking the total flux density observed in the maps, we provide an independent estimate of the mass of molecular gas in the inner Galaxy of ~ 1 × 109 M⊙, which is consistent with previous estimates using CO emission. From the mass and dense gas fraction (fDG), we estimate a Galactic SFR of Ṁ = 1.3 M⊙ yr-1. Conclusions: Retrieving the extended emission helps to better identify massive giant filaments which are elongated and confined structures. We show that the log-normal distribution of low column density gas is ubiquitous in the inner Galaxy. While the distribution of diffuse gas is relatively homogenous in the inner Galaxy, the central molecular zone (CMZ) stands out with a higher dense gas fraction despite its low star formation efficiency.Altogether our findings explain well the observed low star formation efficiency of the Milky Way by the low fDG in the Galactic ISM. In contrast, the high fDG observed towards the CMZ, despite its low star formation activity, suggests that, in that particular region of our Galaxy, high density gas is not the bottleneck for star formation.

Contrast of artificial subcutaneous hematomas in MRI over time.

PubMed

Hassler, Eva Maria; Ogris, Kathrin; Petrovic, Andreas; Neumayer, Bernhard; Widek, Thomas; Yen, Kathrin; Scheurer, Eva

2015-03-01

In clinical forensic medicine, hematomas and other externally visible injuries build the basis for the reconstruction of events. However, dating of subcutaneous hematomas based on their external aspect is difficult. Magnetic resonance imaging (MRI) has proven its use in dating intracranial hemorrhage. Thus, the aim was to investigate if MRI can also be used for dating subcutaneous hematomas and to analyze an eventual influence of the hematoma shape. In 20 healthy volunteers (11 females, 9 males, aged 26.9 ± 3.8 years), 4 ml of autologous blood were injected subcutaneously in the thigh. The hematoma was scanned immediately after the injection, after 3 and 24 h and 3, 7, and 14 days using three sequences with different contrast. Data was analyzed by measuring signal intensities of the hematoma, the muscle, and the subcutaneous tissue over time, and the Michelson contrast coefficients between the tissues were calculated. In the analysis, hematoma shape was considered. Signal intensity of blood in the proton density-weighted sequence reached its maximum 3 h after the injection with a subsequent decrease, whereas the signal intensities of muscle and fatty tissue remained constant. The time course of the Michelson coefficient of blood versus muscle decreased exponentially with a change from hyperintensity to hypointensity at 116.9 h, depending on hematoma shape. In the other sequences, either variability was large or contrast coefficients stayed constant over time. The observed change of contrast of blood versus muscle permits a quick estimate of a hematoma's age. The consideration of the hematoma shape is expected to further enhance dating using MRI.

Exon definition as a potential negative force against intron losses in evolution.

PubMed

Niu, Deng-Ke

2008-11-13

Previous studies have indicated that the wide variation in intron density (the number of introns per gene) among different eukaryotes largely reflects varying degrees of intron loss during evolution. The most popular model, which suggests that organisms lose introns through a mechanism in which reverse-transcribed cDNA recombines with the genomic DNA, concerns only one mutational force. Using exons as the units of splicing-site recognition, exon definition constrains the length of exons. An intron-loss event results in fusion of flanking exons and thus a larger exon. The large size of the newborn exon may cause splicing errors, i.e., exon skipping, if the splicing of pre-mRNAs is initiated by exon definition. By contrast, if the splicing of pre-mRNAs is initiated by intron definition, intron loss does not matter. Exon definition may thus be a selective force against intron loss. An organism with a high frequency of exon definition is expected to experience a low rate of intron loss throughout evolution and have a high density of spliceosomal introns. The majority of spliceosomal introns in vertebrates may be maintained during evolution not because of potential functions, but because of their splicing mechanism (i.e., exon definition). Further research is required to determine whether exon definition is a negative force in maintaining the high intron density of vertebrates. This article was reviewed by Dr. Scott W. Roy (nominated by Dr. John Logsdon), Dr.Eugene V. Koonin, and Dr. Igor B. Rogozin (nominated by Dr. Mikhail Gelfand). For the full reviews,please go to the Reviewers' comments section.

Three-dimensional printing and deformation behavior of low-density target structures by two-photon polymerization

NASA Astrophysics Data System (ADS)

Liu, Ying; Stein, Ori; Campbell, John H.; Jiang, Lijia; Petta, Nicole; Lu, Yongfeng

2017-08-01

Two-photon polymerization (2PP), a 3D nano to microscale additive manufacturing process, is being used for the first time to fabricate small custom experimental packages ("targets") to support laser-driven high-energy-density (HED) physics research. Of particular interest is the use of 2PP to deterministically print low-density, low atomic-number (CHO) polymer matrices ("foams") at millimeter scale with sub-micrometer resolution. Deformation during development and drying of the foam structures remains a challenge when using certain commercial photo-resins; here we compare use of acrylic resins IP-S and IP-Dip. The mechanical strength of polymeric beam and foam structures is examined particularly the degree of deformation that occurs during the development and drying processes. The magnitude of the shrinkage in the two resins in quantified by printing sample structures and by use of FEA to simulate the deformation. Capillary drying forces are shown to be small and likely below the elastic limit of the core foam structure. In contrast the substantial shrinkage in IP-Dip ( 5-10%) cause large shear stresses and associated plastic deformation particularly near constrained boundaries such as the substrate and locations with sharp density variation. The inherent weakness of stitching boundaries is also evident and in certain cases can lead to delamination. Use of IP-S shows marked reduction in deformation with a minor loss of print resolution

Changes in Structure and Functioning of Protist (Testate Amoebae) Communities Due to Conversion of Lowland Rainforest into Rubber and Oil Palm Plantations.

PubMed

Krashevska, Valentyna; Klarner, Bernhard; Widyastuti, Rahayu; Maraun, Mark; Scheu, Stefan

2016-01-01

Large areas of tropical rainforest are being converted to agricultural and plantation land uses, but little is known of biodiversity and ecological functioning under these replacement land uses. We investigated the effects of conversion of rainforest into jungle rubber, intensive rubber and oil palm plantations on testate amoebae, diverse and functionally important protists in litter and soil. Living testate amoebae species richness, density and biomass were all lower in replacement land uses than in rainforest, with the impact being more pronounced in litter than in soil. Similar abundances of species of high and low trophic level in rainforest suggest that trophic interactions are more balanced, with a high number of functionally redundant species, than in rubber and oil palm. In contrast, plantations had a low density of high trophic level species indicating losses of functions. This was particularly so in oil palm plantations. In addition, the relative density of species with siliceous shells was >50% lower in the litter layer of oil palm and rubber compared to rainforest and jungle rubber. This difference suggests that rainforest conversion changes biogenic silicon pools and increases silicon losses. Overall, the lower species richness, density and biomass in plantations than in rainforest, and the changes in the functional composition of the testate amoebae community, indicate detrimental effects of rainforest conversion on the structure and functioning of microbial food webs.

Impact of large-scale dynamics on the microphysical properties of midlatitude cirrus

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

Muhlbauer, Andreas; Ackerman, Thomas P.; Comstock, Jennifer M.

2014-04-16

In situ microphysical observations 3 of mid-latitude cirrus collected during the Department of Energy Small Particles in Cirrus (SPAR-TICUS) field campaign are combined with an atmospheric state classification for the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site to understand statistical relationships between cirrus microphysics and the large-scale meteorology. The atmospheric state classification is informed about the large-scale meteorology and state of cloudiness at the ARM SGP site by combining ECMWF ERA-Interim reanalysis data with 14 years of continuous observations from the millimeter-wavelength cloud radar. Almost half of the cirrus cloud occurrences in the vicinity of the ARM SGPmore » site during SPARTICUS can be explained by three distinct synoptic condi- tions, namely upper-level ridges, mid-latitude cyclones with frontal systems and subtropical flows. Probability density functions (PDFs) of cirrus micro- physical properties such as particle size distributions (PSDs), ice number con- centrations and ice water content (IWC) are examined and exhibit striking differences among the different synoptic regimes. Generally, narrower PSDs with lower IWC but higher ice number concentrations are found in cirrus sam- pled in upper-level ridges whereas cirrus sampled in subtropical flows, fronts and aged anvils show broader PSDs with considerably lower ice number con- centrations but higher IWC. Despite striking contrasts in the cirrus micro- physics for different large-scale environments, the PDFs of vertical velocity are not different, suggesting that vertical velocity PDFs are a poor predic-tor for explaining the microphysical variability in cirrus. Instead, cirrus mi- crophysical contrasts may be driven by differences in ice supersaturations or aerosols.« less

The cosmological dependence of cluster density profiles

NASA Technical Reports Server (NTRS)

Crone, Mary M.; Evrard, August E.; Richstone, Douglas O.

1994-01-01

We use N-body simulations to study the shape of mean cluster density and velocity profiles in the nonlinear regime formed via gravitational instability. The dependence of the final structure on both cosmology and initial density field is examined, using a grid of cosmologies and scale-free initial power spectra P(k) varies as k(exp n). Einstein-de Sitter, open (Omega(sub 0) = 0.2 and 0.1) and flat, low density (Omega(sub 0) = 0.2 lambda(sub 0) = 0.8) models are examined, with initial spectral indices n = -2, -1 and 0. For each model, we stack clusters in an appropriately scaled manner to define an average density profile in the nonlinear regime. The profiles are well fit by a power law rho(r) varies as r(exp -alpha) for radii whereat the local density contrast is between 100 and 3000. This covers 99% of the cluster volume. We find a clear trend toward steeper slopes (larger alphas) with both increasing n and decreasing Omega(sub 0). The Omega(sub 0) dependence is partially masked by the n dependence; there is degeneracy in the values of alpha between the Einstein-de Sitter and flat, low-density cosmologies. However, the profile slopes in the open models are consistently higher than the Omega = 1 values for the range of n examined. Cluster density profiles are thus potentially useful cosmological diagnostics. We find no evidence for a constant density core in any of the models, although the density profiles do tend to flatten at small radii. Much of the flattening is due to the force softening required by the simulations. An attempt is made to recover the unsoftened profiles assuming angular momentum invariance. The recovered profiles in Einstein-de Sitter cosmologies are consistent with a pure power law up to the highest density contrasts (10(exp 6)) accessible with our resolution. The low-density models show significant deviation from a power law above density contrasts approximately 10(exp 5). We interpret this curvature as reflecting the non-scale-invariant nature of the background cosmology in these models. These results are at the limit of our resolution and so should be tested in the future using simulations with larger numbers of particles. Such simulations will also provide insight on the broader problem of understanding, in a statistical sense, the full phase space structure of collapsed, cosmological halos.

Nanoscale X-Ray Microscopic Imaging of Mammalian Mineralized Tissue

PubMed Central

Andrews, Joy C.; Almeida, Eduardo; van der Meulen, Marjolein C.H.; Alwood, Joshua S.; Lee, Chialing; Liu, Yijin; Chen, Jie; Meirer, Florian; Feser, Michael; Gelb, Jeff; Rudati, Juana; Tkachuk, Andrei; Yun, Wenbing; Pianetta, Piero

2010-01-01

A novel hard transmission X-ray microscope (TXM) at the Stanford Synchrotron Radiation Light-source operating from 5 to 15 keV X-ray energy with 14 to 30 µm2 field of view has been used for high-resolution (30–40 nm) imaging and density quantification of mineralized tissue. TXM is uniquely suited for imaging of internal cellular structures and networks in mammalian mineralized tissues using relatively thick (50 µm), untreated samples that preserve tissue micro- and nanostructure. To test this method we performed Zernike phase contrast and absorption contrast imaging of mouse cancellous bone prepared under different conditions of in vivo loading, fixation, and contrast agents. In addition, the three-dimensional structure was examined using tomography. Individual osteocytic lacunae were observed embedded within trabeculae in cancellous bone. Extensive canalicular networks were evident and included processes with diameters near the 30–40 nm instrument resolution that have not been reported previously. Trabecular density was quantified relative to rod-like crystalline apatite, and rod-like trabecular struts were found to have 51–54% of pure crystal density and plate-like areas had 44–53% of crystal density. The nanometer resolution of TXM enables future studies for visualization and quantification of ultrastructural changes in bone tissue resulting from osteoporosis, dental disease, and other pathologies. PMID:20374681

A River Runs Under It: Modeling the Distribution of Streams and Stream Burial in Large River Basins

NASA Astrophysics Data System (ADS)

Elmore, A. J.; Julian, J.; Guinn, S.; Weitzell, R.; Fitzpatrick, M.

2011-12-01

Stream network density exerts a strong control on hydrologic processes in watersheds. Over land and through soil and bedrock substrate, water moves slowly and is subject to chemical transformations unique to conditions of continuous contact with geologic materials. In contrast, once water enters stream channels it is efficiently transported out of watersheds, reducing the amount of time for biological uptake and stream nutrient processing. Therefore, stream network density dictates both the relative importance of terrestrial and aquatic influences to stream chemistry and the residence time of water in watersheds, and is critical to modeling and empirical studies aimed at understanding the impact of land use on stream water quantity and quality. Stream network density is largely a function of the number and length of the smallest streams. Methods for mapping and measuring these headwater streams range from simple measurement of stream length from existing maps, to detailed field mapping efforts, which are difficult to implement over large areas. Confounding the simplest approaches, many headwater stream reaches are not included in hydrographical maps, such as the U.S. National Hydrography Dataset (NHD), either because they were buried during the course of urban development or because they were seen as smaller than the minimum mapping size at the time of map generation. These "missing streams" severely limit the effective analyses of stream network density based on the NHD, constituting a major problem for many efforts to understand land-use impacts on streams. Here we report on research that predicts stream presence and absence by coupling field observations of headwater stream channels with maximum entropy models (MaxEnt) commonly implemented in biogeographical studies to model species distributions. The model utilizes terrain variables that are continuously accumulated along hydrologic flowpaths derived from a 10-m digital elevation model. In validation, the model correctly predicts the presence of 91% of all 10-m stream segments, and rarely miscalculates tributary numbers. We apply this model to the entire Potomac River Basin (37,800 km2) and several adjacent basins to map stream channel density and compare our results with NHD flowline data. We find that NHD underestimates stream channel density by a factor of two in most sub watersheds and this effect is strongest in the densely urbanized cities of Washington, DC and Baltimore, MD. We then apply a second predictive model based on impervious surface area data to map the extent of stream burial. Results demonstrate that the extent of stream burial increases with decreasing stream catchment area. When applied at four time steps (1975, 1990, 2001, and 2006), we find that although stream burial rates have slowed in the recent decade, streams that are not mapped in NHD flowline data continue to be buried during development. This work is the most ambitious attempt yet to map stream network density over a large region and will have lasting implications for modeling and conservation efforts.

Social causes of correlational selection and the resolution of a heritable throat color polymorphism in a lizard.

PubMed

Sinervo, B; Bleay, C; Adamopoulou, C

2001-10-01

When selection acts on social or behavioral traits, the fitness of an individual depends on the phenotypes of its competitors. Here, we describe methods and statistical inference for measuring natural selection in small social groups. We measured selection on throat color alleles that arises from microgeographic variation in allele frequency at natal sites of side-blotched lizards (Uta stansburiana). Previous game-theoretic analysis indicates that two color morphs of female side-blotched lizards are engaged in an offspring quantity-quality game that promotes a density- and frequency-dependent cycle. Orange-throated females are r-strategists. They lay large clutches of small progeny, which have poor survival at high density, but good survival at low density. In contrast, yellow-throated females are K-strategists. They lay small clutches of large progeny, which have good survival at high density. We tested three predictions of the female game: (1) orange progeny should have a fitness advantage at low density; (2) correlational selection acts to couple color alleles and progeny size; and (3) this correlational selection arises from frequency-dependent selection in which large hatchling size confers an advantage, but only when yellow alleles are rare. We also confirmed the heritability of color, and therefore its genetic basis, by producing progeny from controlled matings. A parsimonious cause of the high heritability is that three alleles (o, b, y) segregate as one genetic factor. We review the physiology of color formation to explain the possible genetic architecture of the throat color trait. Heritability of color was nearly additive in our breeding study, allowing us to compute a genotypic value for each individual and thus predict the frequency of progeny alleles released on 116 plots. Rather than study the fitness of individual progeny, we studied how the fitness of their color alleles varied with allele frequency on plots. We confirmed prediction 1: When orange alleles are present in female progeny, they have higher fitness at low density when compared to other alleles. Even though the difference in egg size of the female morphs was small (0.02 g), it led to knife-edged survival effects for their progeny depending on local social context. Selection on hatchling survival was not only dependent on color alleles, but on a fitness interaction between color alleles and hatchling size, which confirmed prediction 2. Sire effects, which are not confounded by maternal phenotype, allowed us to resolve the frequency dependence of correlational selection on egg size and color alleles and thereby confirmed prediction 3. Selection favored large size when yellow sire alleles were rare, but small size when they were common. Correlational selection promotes the formation of a self-reinforcing genetic correlation between the morphs and life-history variation, which causes selection in the next density and frequency cycle to be exacerbated. We discuss general conditions for the evolution of self-reinforcing genetic correlations that arise from social selection associated with frequency-dependent sexual and natural selection.

Numerical Model of Hydraulic Fracturing Fluid Transport in the Subsurface with Pressure Transient, Density Effects, and Imbibition

NASA Astrophysics Data System (ADS)

Birdsell, D.; Rajaram, H.; Dempsey, D.; Viswanathan, H.

2014-12-01

Understanding the transport of hydraulic fracturing (HF) fluid that is injected into the deep subsurface for shale gas extraction is important to ensure that shallow drinking water aquifers are not contaminated from an environmental and public health perspective and to understand formation damage from an oil and gas production perspective. Upward pressure gradients, permeable pathways such as faults or improperly abandoned wellbores, and the density contrast of the HF fluid to the surrounding brine encourages upward HF fluid migration. In contrast, the very low shale permeability and the imbibition of water into partially-saturated shale may sequester much of the HF fluid. Using the Finite Element Heat and Mass Transfer Code (FEHM), single-phase flow and transport simulations are performed to quantify how much HF fluid is removed via the wellbore as flowback and produced water and how much reaches overlying aquifers; imbibition is calculated with a semi-analytical one-dimensional solution and treated as a sink term. The travel time for HF fluid to reach the shallow aquifers is highly dependent on the amount of water imbibed and the suction applied to the well. If imbibition rates and suction are small, the pressure transient due to injection and the density contrast allows rapid upward plume migration at early times. The density contrast diminishes considerably within tens to hundreds of years as mixing occurs. We present estimates of HF fluid migration to shallow aquifers during the first 1,000 years after hydraulic fracturing begins for ranges of subsurface properties.

Analytic Ballistic Performance Model of Whipple Shields

NASA Technical Reports Server (NTRS)

Miller, J. E.; Bjorkman, M. D.; Christiansen, E. L.; Ryan, S. J.

2015-01-01

The dual-wall, Whipple shield is the shield of choice for lightweight, long-duration flight. The shield uses an initial sacrificial wall to initiate fragmentation and melt an impacting threat that expands over a void before hitting a subsequent shield wall of a critical component. The key parameters to this type of shield are the rear wall and its mass which stops the debris, as well as the minimum shock wave strength generated by the threat particle impact of the sacrificial wall and the amount of room that is available for expansion. Ensuring the shock wave strength is sufficiently high to achieve large scale fragmentation/melt of the threat particle enables the expansion of the threat and reduces the momentum flux of the debris on the rear wall. Three key factors in the shock wave strength achieved are the thickness of the sacrificial wall relative to the characteristic dimension of the impacting particle, the density and material cohesion contrast of the sacrificial wall relative to the threat particle and the impact speed. The mass of the rear wall and the sacrificial wall are desirable to minimize for launch costs making it important to have an understanding of the effects of density contrast and impact speed. An analytic model is developed here, to describe the influence of these three key factors. In addition this paper develops a description of a fourth key parameter related to fragmentation and its role in establishing the onset of projectile expansion.

Optimization of return electrodes in neurostimulating arrays

NASA Astrophysics Data System (ADS)

Flores, Thomas; Goetz, Georges; Lei, Xin; Palanker, Daniel

2016-06-01

Objective. High resolution visual prostheses require dense stimulating arrays with localized inputs of individual electrodes. We study the electric field produced by multielectrode arrays in electrolyte to determine an optimal configuration of return electrodes and activation sequence. Approach. To determine the boundary conditions for computation of the electric field in electrolyte, we assessed current dynamics using an equivalent circuit of a multielectrode array with interleaved return electrodes. The electric field modeled with two different boundary conditions derived from the equivalent circuit was then compared to measurements of electric potential in electrolyte. To assess the effect of return electrode configuration on retinal stimulation, we transformed the computed electric fields into retinal response using a model of neural network-mediated stimulation. Main results. Electric currents at the capacitive electrode-electrolyte interface redistribute over time, so that boundary conditions transition from equipotential surfaces at the beginning of the pulse to uniform current density in steady state. Experimental measurements confirmed that, in steady state, the boundary condition corresponds to a uniform current density on electrode surfaces. Arrays with local return electrodes exhibit improved field confinement and can elicit stronger network-mediated retinal response compared to those with a common remote return. Connecting local return electrodes enhances the field penetration depth and allows reducing the return electrode area. Sequential activation of the pixels in large monopolar arrays reduces electrical cross-talk and improves the contrast in pattern stimulation. Significance. Accurate modeling of multielectrode arrays helps optimize the electrode configuration to maximize the spatial resolution, contrast and dynamic range of retinal prostheses.

Proposed imaging of the ultrafast electronic motion in samples using x-ray phase contrast.

PubMed

Dixit, Gopal; Slowik, Jan Malte; Santra, Robin

2013-03-29

Tracing the motion of electrons has enormous relevance to understanding ubiquitous phenomena in ultrafast science, such as the dynamical evolution of the electron density during complex chemical and biological processes. Scattering of ultrashort x-ray pulses from an electronic wave packet would appear to be the most obvious approach to image the electronic motion in real time and real space with the notion that such scattering patterns, in the far-field regime, encode the instantaneous electron density of the wave packet. However, recent results by Dixit et al. [Proc. Natl. Acad. Sci. U.S.A. 109, 11636 (2012)] have put this notion into question and have shown that the scattering in the far-field regime probes spatiotemporal density-density correlations. Here, we propose a possible way to image the instantaneous electron density of the wave packet via ultrafast x-ray phase contrast imaging. Moreover, we show that inelastic scattering processes, which plague ultrafast scattering in the far-field regime, do not contribute in ultrafast x-ray phase contrast imaging as a consequence of an interference effect. We illustrate our general findings by means of a wave packet that lies in the time and energy range of the dynamics of valence electrons in complex molecular and biological systems. This present work offers a potential to image not only instantaneous snapshots of nonstationary electron dynamics, but also the laplacian of these snapshots which provide information about the complex bonding and topology of the charge distributions in the systems.

Proposed Imaging of the Ultrafast Electronic Motion in Samples using X-Ray Phase Contrast

NASA Astrophysics Data System (ADS)

Dixit, Gopal; Slowik, Jan Malte; Santra, Robin

2013-03-01

Tracing the motion of electrons has enormous relevance to understanding ubiquitous phenomena in ultrafast science, such as the dynamical evolution of the electron density during complex chemical and biological processes. Scattering of ultrashort x-ray pulses from an electronic wave packet would appear to be the most obvious approach to image the electronic motion in real time and real space with the notion that such scattering patterns, in the far-field regime, encode the instantaneous electron density of the wave packet. However, recent results by Dixit et al. [Proc. Natl. Acad. Sci. U.S.A. 109, 11 636 (2012)] have put this notion into question and have shown that the scattering in the far-field regime probes spatiotemporal density-density correlations. Here, we propose a possible way to image the instantaneous electron density of the wave packet via ultrafast x-ray phase contrast imaging. Moreover, we show that inelastic scattering processes, which plague ultrafast scattering in the far-field regime, do not contribute in ultrafast x-ray phase contrast imaging as a consequence of an interference effect. We illustrate our general findings by means of a wave packet that lies in the time and energy range of the dynamics of valence electrons in complex molecular and biological systems. This present work offers a potential to image not only instantaneous snapshots of nonstationary electron dynamics, but also the Laplacian of these snapshots which provide information about the complex bonding and topology of the charge distributions in the systems.

Aversive properties of negative incentive shifts in Fischer 344 and Lewis rats

PubMed Central

Brewer, Adam; Johnson, Patrick; Stein, Jeff; Schlund, Michael; Williams, Dean C.

2018-01-01

Research on incentive contrast highlights that reward value is not absolute but rather is based upon comparisons we make to rewards we have received and expect to receive. Both human and nonhuman studies on incentive contrast show that shifting from a larger more-valued reward to a smaller less-valued reward is associated with long periods of nonresponding—a negative contrast effect. In this investigation, we used two different genetic rat strains, Fischer 344 and Lewis rats that putatively differ in their sensitivity to aversive stimulation, to assess the aversive properties of large-to-small reward shifts (negative incentive shifts). Additionally, we examined the extent to which increasing cost (fixed-ratio requirements) modulates negative contrast effects. In the presence of a cue that signaled the upcoming reward magnitude, lever pressing was reinforced with one of two different magnitudes of food (large or small). This design created two contrast shifts (small-to-large, large-to-small) and two shifts used as control conditions (small-to-small, large-to-large). Results showed a significant interaction between rat strain and cost requirements only during the negative incentive shift with the emotionally reactive Fischer 344 rats exhibiting significantly longer response latencies with increasing cost, highlighting greater negative contrast. These findings are more consistent with emotionality accounts of negative contrast and results of neurophysiological research that suggests shifting from a large to a small reward is aversive. Findings also highlight how subjective reward value and motivation is a product of gene-environment interactions. PMID:27864048

Soil fate of agricultural fumigants in raised-bed, plasticulture systems in the southeastern United States.

PubMed

Chellemi, Dan O; Ajwa, Husein A; Sullivan, David A; Alessandro, Rocco; Gilreath, James P; Yates, Scott R

2011-01-01

Soil concentrations and degradation rates of methyl isothio-cyanate (MITC), chloropicrin (CP), 1,3-dichloropropene (1,3-D), and dimethyl disulfide (DMDS) were determined under fumigant application scenarios representative of commercial raised bed, plastic mulched vegetable production systems. Five days after application, 1,3-D, MITC, and CP were detected at concentrations up to 3.52, 0.72, and 2.45 μg cm, respectively, in the soil atmosphere when applications were made in uniformly compacted soils with a water content >200% of field capacity and covered by a virtually impermeable or metalized film. By contrast, DMDS, MITC, and CP concentrations in the soil atmosphere were 0.81, 0.02, and 0.05 μg cm, respectively, 5 d after application in soil containing undecomposed plant residue, numerous large (>3 mm) clods, and water content below field capacity and covered by low-density polyethylene. Ranked in order of impact on the persistence of fumigants in soil were soil water content (moisture), soil tilth (the physical condition of soil as related to its fitness as a planting bed), the type of plastic film used to cover fumigated beds, and soil texture. Fumigants were readily detected 13 d after application when applied in uniformly compacted soils with water contents >200% of capacity and covered by a virtually impermeable or metalized film. By contrast, 1,3-D and MITC had dissipated 5 d after application in soils with numerous large (>3 mm) clods and water contents below field capacity that were covered by low-density polyethylene. Soil degradation of CP, DMDS, and MITC were primarily attributed to biological mechanisms, whereas degradation of 1,3-D was attributed principally to abiotic factors. This study demonstrates improved soil retention of agricultural fumigants in application scenarios representative of good agricultural practices. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Immortality of Cu damascene interconnects

NASA Astrophysics Data System (ADS)

Hau-Riege, Stefan P.

2002-04-01

We have studied short-line effects in fully-integrated Cu damascene interconnects through electromigration experiments on lines of various lengths and embedded in different dielectric materials. We compare these results with results from analogous experiments on subtractively-etched Al-based interconnects. It is known that Al-based interconnects exhibit three different behaviors, depending on the magnitude of the product of current density, j, and line length, L: For small values of (jL), no void nucleation occurs, and the line is immortal. For intermediate values, voids nucleate, but the line does not fail because the current can flow through the higher-resistivity refractory-metal-based shunt layers. Here, the resistance of the line increases but eventually saturates, and the relative resistance increase is proportional to (jL/B), where B is the effective elastic modulus of the metallization system. For large values of (jL/B), voiding leads to an unacceptably high resistance increase, and the line is considered failed. By contrast, we observed only two regimes for Cu-based interconnects: Either the resistance of the line stays constant during the duration of the experiment, and the line is considered immortal, or the line fails due to an abrupt open-circuit failure. The absence of an intermediate regime in which the resistance saturates is due to the absence of a shunt layer that is able to support a large amount of current once voiding occurs. Since voids nucleate much more easily in Cu- than in Al-based interconnects, a small fraction of short Cu lines fails even at low current densities. It is therefore more appropriate to consider the probability of immortality in the case of Cu rather than assuming a sharp boundary between mortality and immortality. The probability of immortality decreases with increasing amount of material depleted from the cathode, which is proportional to (jL2/B) at steady state. By contrast, the immortality of Al-based interconnects is described by (jL) if no voids nucleate, and (jL/B) if voids nucleate.

Dietary change of the rock lobster Jasus lalandii after an ‘invasive’ geographic shift: Effects of size, density and food availability

NASA Astrophysics Data System (ADS)

Haley, C. N.; Blamey, L. K.; Atkinson, L. J.; Branch, G. M.

2011-06-01

During the 1990s the rock lobster Jasus lalandii shifted its focus of distribution south-eastwards along the coast of South Africa, to establish a dense population in an area where it was previously rare. This coincided with a marked decrease in the sea urchin Parechinus angulosus, a preferred prey item of J. lalandii and a vital source of shelter for juveniles of the abalone Haliotis midae. The range expansion of lobsters has thus economic and ecological ripple effects. We determined the diets of small (50-65 mm carapace length) and large (>69 mm CL) rock lobsters from gut content analyses, and compared them between three 'lobster invaded' sites and three adjacent 'non-invaded' sites where densities are still low. At the non-invaded sites, diets were collectively heterogeneous but the dietary breadth of individual lobsters was narrow (in contradiction to generally accepted ecological theory), and the lobsters fed mainly on large, individual, mobile, high-energy prey such as sea urchins and large winkles. Conversely, at invaded sites where lobster densities were high, they consumed predominantly small, colonial or sessile low-energy prey such as sponges, barnacles and foliar algae, and the diet was significantly more uniform among individuals, but broader within individuals. This was a direct result of the contrasting benthic community structure of the two areas, and consequent prey availability - itself caused by differences in intensity of rock-lobster predation. Cannibalism was unexpectedly greater at non-invaded sites, possibly as a result of lobsters being larger there. The diet of small and large lobsters also differed significantly. Large rock lobsters predominantly consumed large individual prey such as lobsters, urchins and crabs, while small rock lobsters ate mainly colonial, sessile prey such as sponges and barnacles, and small prey such as tiny winkles and crustaceans. Dietary selectivity indices revealed that algae and sponges were negatively selected (avoided) in non-invaded areas but positively or neutrally selected in invaded areas. These dietary differences have important ramifications not only for the lobster populations but also for the structure and functioning of the radically different communities that have developed in invaded areas, reflecting a regime shift induced by lobster predation.

The Effects of Magnetic-field Geometry on Longitudinal Oscillaitons of Solar Prominences

NASA Technical Reports Server (NTRS)

Luna, M.; Diaz, A. J.; Karpen, J.

2013-01-01

We investigate the influence of the geometry of the solar filament magnetic structure on the large-amplitude longitudinal oscillations. A representative filament flux tube is modeled as composed of a cool thread centered in a dipped part with hot coronal regions on either side.We have found the normal modes of the system and establish that the observed longitudinal oscillations are well described with the fundamental mode. For small and intermediate curvature radii and moderate to large density contrast between the prominence and the corona, the main restoring force is the solar gravity. In this full wave description of the oscillation a simple expression for the oscillation frequencies is derived in which the pressure-driven term introduces a small correction. We have also found that the normal modes are almost independent of the geometry of the hot regions of the tube. We conclude that observed large-amplitude longitudinal oscillations are driven by the projected gravity along the flux tubes and are strongly influenced by the curvature of the dips of the magnetic field in which the threads reside.

Toward single-chirality carbon nanotube device arrays.

PubMed

Vijayaraghavan, Aravind; Hennrich, Frank; Stürzl, Ninette; Engel, Michael; Ganzhorn, Marc; Oron-Carl, Matti; Marquardt, Christoph W; Dehm, Simone; Lebedkin, Sergei; Kappes, Manfred M; Krupke, Ralph

2010-05-25

The large-scale integration of devices consisting of individual single-walled carbon nanotubes (SWCNT), all of the same chirality, is a critical step toward their electronic, optoelectronic, and electromechanical application. Here, the authors realize two related goals, the first of which is the fabrication of high-density, single-chirality SWCNT device arrays by dielectrophoretic assembly from monodisperse SWCNT solution obtained by polymer-mediated sorting. Such arrays are ideal for correlating measurements using various techniques across multiple identical devices, which is the second goal. The arrays are characterized by voltage-contrast scanning electron microscopy, electron transport, photoluminescence (PL), and Raman spectroscopy and show identical signatures as expected for single-chirality SWCNTs. In the assembled nanotubes, a large D peak in Raman spectra, a large dark-exciton peak in PL spectra as well as lowered conductance and slow switching in electron transport are all shown to be correlated to each other. By comparison to control samples, we conclude that these are the result of scattering from electronic and not structural defects resulting from the polymer wrapping, similar to what has been predicted for DNA wrapping.

Investigation of anatomical anomalies in Hanford Site mule deer

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

Tiller, B.L.; Cadwell, L.L.; Poston, T.M.

Rocky Mountain mule deer (Odocoileus hemionus hemionus), common residents of the Hanford Site, are an important part of the shrub-steppe ecosystem as well as being valued for aesthetics and hunting. Because mule deer have been protected from hunting on the Site for 50 years, the herd has developed unique population characteristics, including a large number of old animals and males with either large or atypically developed antlers, in contrast to other herds in the semi-arid regions of the Northwest. Hanford Site mule deer have been studied since 1991 because of the herd`s unique nature and high degree of public interest.more » A special study of the mule deer herd was initiated in 1993 after observations were made of a relatively large number of male deer with atypical, velvet-covered antlers. This report specifically describes our analyses of adult male deer found on the Site with atypical antlers. The report includes estimates of population densities and composition; home ranges, habitat uses, and dietary habits; natural and human-induced causes of mortality; and the herd`s overall health and reproductive status.« less

Large-field high-contrast hard x-ray Zernike phase-contrast nano-imaging beamline at Pohang Light Source.

PubMed

Lim, Jun; Park, So Yeong; Huang, Jung Yun; Han, Sung Mi; Kim, Hong-Tae

2013-01-01

We developed an off-axis-illuminated zone-plate-based hard x-ray Zernike phase-contrast microscope beamline at Pohang Light Source. Owing to condenser optics-free and off-axis illumination, a large field of view was achieved. The pinhole-type Zernike phase plate affords high-contrast images of a cell with minimal artifacts such as the shade-off and halo effects. The setup, including the optics and the alignment, is simple and easy, and allows faster and easier imaging of large bio-samples.

Noncontact 3-D Speckle Contrast Diffuse Correlation Tomography of Tissue Blood Flow Distribution.

PubMed

Huang, Chong; Irwin, Daniel; Zhao, Mingjun; Shang, Yu; Agochukwu, Nneamaka; Wong, Lesley; Yu, Guoqiang

2017-10-01

Recent advancements in near-infrared diffuse correlation techniques and instrumentation have opened the path for versatile deep tissue microvasculature blood flow imaging systems. Despite this progress there remains a need for a completely noncontact, noninvasive device with high translatability from small/testing (animal) to large/target (human) subjects with trivial application on both. Accordingly, we discuss our newly developed setup which meets this demand, termed noncontact speckle contrast diffuse correlation tomography (nc_scDCT). The nc_scDCT provides fast, continuous, portable, noninvasive, and inexpensive acquisition of 3-D tomographic deep (up to 10 mm) tissue blood flow distributions with straightforward design and customization. The features presented include a finite-element-method implementation for incorporating complex tissue boundaries, fully noncontact hardware for avoiding tissue compression and interactions, rapid data collection with a diffuse speckle contrast method, reflectance-based design promoting experimental translation, extensibility to related techniques, and robust adjustable source and detector patterns and density for high resolution measurement with flexible regions of interest enabling unique application-specific setups. Validation is shown in the detection and characterization of both high and low contrasts in flow relative to the background using tissue phantoms with a pump-connected tube (high) and phantom spheres (low). Furthermore, in vivo validation of extracting spatiotemporal 3-D blood flow distributions and hyperemic response during forearm cuff occlusion is demonstrated. Finally, the success of instrument feasibility in clinical use is examined through the intraoperative imaging of mastectomy skin flap.

Twentieth-century decline of large-diameter trees in Yosemite National Park, California, USA

USGS Publications Warehouse

Lutz, J.A.; van Wagtendonk, J.W.; Franklin, J.F.

2009-01-01

Studies of forest change in western North America often focus on increased densities of small-diameter trees rather than on changes in the large tree component. Large trees generally have lower rates of mortality than small trees and are more resilient to climate change, but these assumptions have rarely been examined in long-term studies. We combined data from 655 historical (1932-1936) and 210 modern (1988-1999) vegetation plots to examine changes in density of large-diameter trees in Yosemite National Park (3027 km2). We tested the assumption of stability for large-diameter trees, as both individual species and communities of large-diameter trees. Between the 1930s and 1990s, large-diameter tree density in Yosemite declined 24%. Although the decrease was apparent in all forest types, declines were greatest in subalpine and upper montane forests (57.0% of park area), and least in lower montane forests (15.3% of park area). Large-diameter tree densities of 11 species declined while only 3 species increased. Four general patterns emerged: (1) Pinus albicaulis, Quercus chrysolepis, and Quercus kelloggii had increases in density of large-diameter trees occur throughout their ranges; (2) Pinus jeffreyi, Pinus lambertiana, and Pinus ponderosa, had disproportionately larger decreases in large-diameter tree densities in lower-elevation portions of their ranges; (3) Abies concolor and Pinus contorta, had approximately uniform decreases in large-diameter trees throughout their elevational ranges; and (4) Abies magnifica, Calocedrus decurrens, Juniperus occidentalis, Pinus monticola, Pseudotsuga menziesii, and Tsuga mertensiana displayed little or no change in large-diameter tree densities. In Pinus ponderosa-Calocedrus decurrens forests, modern large-diameter tree densities were equivalent whether or not plots had burned since 1936. However, in unburned plots, the large-diameter trees were predominantly A. concolor, C. decurrens, and Q. chrysolepis, whereas P. ponderosa dominated the large-diameter component of burned plots. Densities of large-diameter P. ponderosa were 8.1 trees ha-1 in plots that had experienced fire, but only 0.5 trees ha-1 in plots that remained unburned. ?? 2009 Elsevier B.V. All rights reserved.

HUNTING FOR PLANETS IN THE HL TAU DISK

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

Testi, L.; Skemer, A.; Bailey, V.

2015-10-20

Recent ALMA images of HL Tau show gaps in the dusty disk that may be caused by planetary bodies. Given the young age of this system, if confirmed, this finding would imply very short timescales for planet formation, probably in a gravitationally unstable disk. To test this scenario, we searched for young planets by means of direct imaging in the L′ band using the Large Binocular Telescope Interferometer mid-infrared camera. At the location of two prominent dips in the dust distribution at ∼70 AU (∼0.″5) from the central star, we reach a contrast level of ∼7.5 mag. We did notmore » detect any point sources at the location of the rings. Using evolutionary models we derive upper limits of ∼10–15 M{sub Jup} at ≤0.5–1 Ma for the possible planets. With these sensitivity limits we should have been able to detect companions sufficiently massive to open full gaps in the disk. The structures detected at millimeter wavelengths could be gaps in the distributions of large grains on the disk midplane caused by planets not massive enough to fully open the gaps. Future ALMA observations of the molecular gas density profile and kinematics as well as higher contrast infrared observations may be able to provide a definitive answer.« less

The Global Evolution of Giant Molecular Clouds. I. Model Formulation and Quasi-Equilibrium Behavior

NASA Astrophysics Data System (ADS)

Krumholz, Mark R.; Matzner, Christopher D.; McKee, Christopher F.

2006-12-01

We present semianalytic dynamical models for giant molecular clouds evolving under the influence of H II regions launched by newborn star clusters. In contrast to previous work, we neither assume that clouds are in virial or energetic equilibrium, nor do we ignore the effects of star formation feedback. The clouds, which we treat as spherical, can expand and contract homologously. Photoionization drives mass ejection; the recoil of cloud material both stirs turbulent motions and leads to an effective confining pressure. The balance between these effects and the decay of turbulent motions through isothermal shocks determines clouds' dynamical and energetic evolution. We find that for realistic values of the rates of turbulent dissipation, photoevaporation, and energy injection by H II regions, the massive clouds where most molecular gas in the Galaxy resides live for a few crossing times, in good agreement with recent observational estimates that large clouds in Local Group galaxies survive roughly 20-30 Myr. During this time clouds remain close to equilibrium, with virial parameters of 1-3 and column densities near 1022 H atoms cm-2, also in agreement with observed cloud properties. Over their lives they convert 5%-10% of their mass into stars, after which point most clouds are destroyed when a large H II region unbinds them. In contrast, small clouds like those found in the solar neighborhood only survive ~1 crossing time before being destroyed.

Correlation Between Contrast Time-Density Time on Digital Subtraction Angiography and Flow: An in Vitro Study.

PubMed

Brunozzi, Denise; Shakur, Sophia F; Ismail, Rahim; Linninger, Andreas; Hsu, Chih-Yang; Charbel, Fady T; Alaraj, Ali

2018-02-01

Digital subtraction angiography (DSA) provides an excellent anatomic characterization of cerebral vasculature, but hemodynamic assessment is often qualitative and subjective. Various clinical algorithms have been produced to semiquantify flow from the data obtained from DSA, but few have tested them against reliable flow values. An arched flow model was created and injected with contrast material. Seventeen injections were acquired in anterior-posterior and lateral DSA projections, and 4 injections were acquired in oblique projection. Image intensity change over the angiogram cycle of each DSA run was analyzed through a custom MATLAB code. Time-density plots obtained were divided into 3 components (time-density times, TDTs): TDT 10%-100% (time needed for contrast material to change image intensity from 10% to 100%), TDT 100%-10% (time needed for contrast material to change image intensity from 100% to 10%), and TDT 25%-25% (time needed for contrast material to change from 25% image intensity to 25%). Time-density index (TDI) was defined as model cross-sectional area to TDT ratio, and it was measured against different flow rates. TDI 10%-100% , TDI 100%-10% , and TDI 25%-25% all correlated significantly with flow (P < 0.001). TDI 10%-100% , TDI 100%-10% , and TDI 25%-25% showed, respectively, a correlation coefficient of 0.91, 0.91, and 0.97 in the anterior-posterior DSA projections (P < 0.001). In the lateral DSA projection, TDI 100%-10% showed a weaker correlation (r = 0.57; P = 0.03). Also in the oblique DSA projection, TDIs correlated significantly with flow. TDI on DSA correlates significantly with flow. Although in vitro studies might overlook conditions that occur in patients, this method appears to correlate with the flow and could offer a semiquantitative method to evaluate the cerebral blood flow. Copyright © 2017 Elsevier Inc. All rights reserved.

Detectability comparison between a high energy x-ray phase sensitive and mammography systems in imaging phantoms with varying glandular-adipose ratios

NASA Astrophysics Data System (ADS)

Ghani, Muhammad U.; Wong, Molly D.; Wu, Di; Zheng, Bin; Fajardo, Laurie L.; Yan, Aimin; Fuh, Janis; Wu, Xizeng; Liu, Hong

2017-05-01

The objective of this study was to demonstrate the potential benefits of using high energy x-rays in comparison with the conventional mammography imaging systems for phase sensitive imaging of breast tissues with varying glandular-adipose ratios. This study employed two modular phantoms simulating the glandular (G) and adipose (A) breast tissue composition in 50 G-50 A and 70 G-30 A percentage densities. Each phantom had a thickness of 5 cm with a contrast detail test pattern embedded in the middle. For both phantoms, the phase contrast images were acquired using a micro-focus x-ray source operated at 120 kVp and 4.5 mAs, with a magnification factor (M) of 2.5 and a detector with a 50 µm pixel pitch. The mean glandular dose delivered to the 50 G-50 A and 70 G-30 A phantom sets were 1.33 and 1.3 mGy, respectively. A phase retrieval algorithm based on the phase attenuation duality that required only a single phase contrast image was applied. Conventional low energy mammography images were acquired using GE Senographe DS and Hologic Selenia systems utilizing their automatic exposure control (AEC) settings. In addition, the automatic contrast mode (CNT) was also used for the acquisition with the GE system. The AEC mode applied higher dose settings for the 70 G-30 A phantom set. As compared to the phase contrast images, the dose levels for the AEC mode acquired images were similar while the dose levels for the CNT mode were almost double. The observer study, contrast-to-noise ratio and figure of merit comparisons indicated a large improvement with the phase retrieved images in comparison to the AEC mode images acquired with the clinical systems for both density levels. As the glandular composition increased, the detectability of smaller discs decreased with the clinical systems, particularly with the GE system, even at higher dose settings. As compared to the CNT mode (double dose) images, the observer study also indicated that the phase retrieved images provided similar or improved detection for all disc sizes except for the disk diameters of 2 mm and 1 mm for the 50 G-50 A phantom and 3 mm and 0.5 mm for the 70 G-30 A phantom. This study demonstrated the potential of utilizing a high energy phase sensitive x-ray imaging system to improve lesion detection and reduce radiation dose when imaging breast tissues with varying glandular compositions.

Use of CT Hounsfield unit density to identify ablated tumor after laparoscopic radiofrequency ablation of hepatic tumors.

PubMed

Berber, E; Foroutani, A; Garland, A M; Rogers, S J; Engle, K L; Ryan, T L; Siperstein, A E

2000-09-01

When attempting to interpret CT scans after radiofrequency thermal ablation (RFA) of liver tumors, it is sometimes difficult to distinguish ablated from viable tumor tissue. Identification of the two types of tissue is specially problematic for lesions that are hypodense before ablation. The aim of this study was to determine whether quantitative Hounsfield unit (HU) density measurements can be used to document the lack of tumor perfusion and thereby identify ablated tissue. Liver spiral CT scans of 13 patients with 51 lesions undergoing laparoscopic RFA for metastatic liver tumors within a 2-year time period were reviewed. HU density of the lesions as well as normal liver were measured pre- and postoperatively in each CT phase (noncontrast, arterial, portovenous). Statistical analyses were performed using Student's paired t-test and ANOVA. Normal liver parenchyma, which was used as a control, showed a similar increase with contrast injection in both pre- and postprocedure CT scans (56.4 +/- 2.4 vs 57.1 +/- 2.4 HU, respectively; p = 0.3). In contrast, ablated liver lesions showed a preablation increase of 45.7 +/- 3.4 HU but only a minimal postablation increase of 6.6 +/- 0.7 HU (p < 0.0001). This was true for highly vascular tumors (neuroendocrine) as well as hypovascular ones (adenocarcinoma). This is the first study to define quantitative radiological criteria using HU density for the evaluation of ablated tissues. A lack of increase in HU density with contrast injection indicates necrotic tissue, whereas perfused tissue shows an increase in HU density. This technique can be used in the evaluation of patients undergoing RFA.

Ecological drivers of guanaco recruitment: variable carrying capacity and density dependence.

PubMed

Marino, Andrea; Pascual, Miguel; Baldi, Ricardo

2014-08-01

Ungulates living in predator-free reserves offer the opportunity to study the influence of food limitation on population dynamics without the potentially confounding effects of top-down regulation or livestock competition. We assessed the influence of relative forage availability and population density on guanaco recruitment in two predator-free reserves in eastern Patagonia, with contrasting scenarios of population density. We also explored the relative contribution of the observed recruitment to population growth using a deterministic linear model to test the assumption that the studied populations were closed units. The observed densities increased twice as fast as our theoretical populations, indicating that marked immigration has taken place during the recovery phase experienced by both populations, thus we rejected the closed-population assumption. Regarding the factors driving variation in recruitment, in the low- to medium-density setting, we found a positive linear relationship between recruitment and surrogates of annual primary production, whereas no density dependence was detected. In contrast, in the high-density scenario, both annual primary production and population density showed marked effects, indicating a positive relationship between recruitment and per capita food availability above a food-limitation threshold. Our results support the idea that environmental carrying capacity fluctuates in response to climatic variation, and that these fluctuations have relevant consequences for herbivore dynamics, such as amplifying density dependence in drier years. We conclude that including the coupling between environmental variability in resources and density dependence is crucial to model ungulate population dynamics; to overlook temporal changes in carrying capacity may even mask density dependence as well as other important processes.

Astrophysical radiation environments of habitable worlds

NASA Astrophysics Data System (ADS)

Smith, David Samuel

Numerous astrophysical sources of radiation affect the environment of planets orbiting within the liquid-water habitable zone of main-sequence stars. This dissertation reaches a number of conclusions about the ionizing radiation environment of the habitable zone with respect to X-rays and gamma-rays from stellar flares and background Galactic cosmic rays. Gamma-rays and X-rays incident on terrestrial-like exoplanet atmospheres can be efficiently reprocessed into diffuse UV emission that, depending on the presence of atmospheric UV absorbers, can reach the surface. Extreme solar X-ray flares over the last 4.6 Gyr could have delivered large enough radiation doses to the Martian surface to sterilize any unprotected organisms, depending on the largest energy releases possible. These flares also pose a significant hazard to manned space missions, since a large flare can occur with little or no warning during an extravehicular activity. A flare as large as the largest observed could deliver radiation doses exceeding safety limits to an astronaut protected by only a spacesuit. With respect to particle radiation, the nature of Galactic cosmic-ray modulation by astrospheres means that habitable-zone cosmic-ray fluxes change by much larger magnitudes when passing through low- densities regions of the interstellar medium. In contrast to the popular idea that passages through dense molecular clouds are required to significantly enhance Galactic cosmic-ray fluxes and affect planets' electrical circuits, background mutation rates, and climates, we find that densities of only 0.1-10 cm -3 , the densities of most interstellar clouds, are sufficient to bring fluxes close to the full, interstellar level. Finally, passages through dense molecular clouds are necessary to shrink astrospheres to within the habitable zone, but such events produce even higher interstellar hydrogen and dust accretion rates than have been estimated because of the combination of enhanced charge-exchange rates between stellar-wind ions and interstellar neutrals and the growing importance of the central star's gravity on particle trajectories as the astrosphere shrinks.

Association between a variation in the phosphodiesterase 4D gene and bone mineral density.

PubMed

Reneland, Richard H; Mah, Steven; Kammerer, Stefan; Hoyal, Carolyn R; Marnellos, George; Wilson, Scott G; Sambrook, Philip N; Spector, Tim D; Nelson, Matthew R; Braun, Andreas

2005-03-07

Fragility fractures caused by osteoporosis are a major cause of morbidity and mortality in aging populations. Bone mineral density (BMD) is a useful surrogate marker for risk of fracture and is a highly heritable trait. The genetic variants underlying this genetic contribution are largely unknown. We performed a large-scale association study investigating more than 25,000 single nucleotide polymorphisms (SNPs) located within 16,000 genes. Allele frequencies were estimated in contrasting DNA pools from white females selected for low (<0.87 g/cm2, n = 319) and high (> 1.11 g/cm2, n = 321) BMD at the lumbar spine. Significant findings were verified in two additional sample collections. Based on allele frequency differences between DNA pools and subsequent individual genotyping, one of the candidate loci indicated was the phosphodiesterase 4D (PDE4D) gene region on chromosome 5q12. We subsequently tested the marker SNP, rs1498608, in a second sample of 138 white females with low (<0.91 g/cm2) and 138 females with high (>1.04 g/cm2) lumbar spine BMD. Odds ratios were 1.5 (P = 0.035) in the original sample and 2.1 (P = 0.018) in the replication sample. Association fine mapping with 80 SNPs located within 50 kilobases of the marker SNP identified a 20 kilobase region of association containing exon 6 of PDE4D. In a second, family-based replication sample with a preponderance of females with low BMD, rs1498608 showed an opposite relationship with BMD at different sites (p = 0.00044-0.09). We also replicated the previously reported association of the Ser37Ala polymorphism in BMP2, known to interact biologically with PDE4D, with BMD. This study indicates that variants in the gene encoding PDE4D account for some of the genetic contribution to bone mineral density variation in humans. The contrasting results from different samples indicate that the effect may be context-dependent. PDE4 inhibitors have been shown to increase bone mass in normal and osteopenic mice, but up until now there have been no reports implicating any member of the PDE4 gene family in human osteoporosis.

Fragmentation and matrix contrast favor understory plants through negative cascading effects on a strong competitor palm.

PubMed

Hernández-Ruedas, Manuel A; Arroyo-Rodríguez, Víctor; Morante-Filho, José Carlos; Meave, Jorge A; Martínez-Ramos, Miguel

2018-05-04

Understanding the patterns and processes driving biodiversity maintenance in fragmented tropical forests is urgently needed for conservation planning, especially in species-rich forest reserves. Of particular concern are the effects that habitat modifications at the landscape scale may have on forest regeneration and ecosystem functioning: a topic that has received limited attention. Here, we assessed the effects of landscape structure (i.e., forest cover, open area matrices, forest fragmentation, and mean inter-patch isolation distance) on understory plant assemblages in the Los Tuxtlas Biosphere Reserve, Mexico. Previous studies suggest that the demographic burst of the strong competitor palm Astrocaryum mexicanum in the core area of this reserve limits plant recruitment and imperils biodiversity conservation within this protected area. Yet, the local and landscape predictors of this palm, and its impact on tree recruitment at a regional scale are unknown. Thus, we used structural equation modeling to assess the direct and cascading effects of landscape structure on stem and species density in the understory of 20 forest sites distributed across this biodiversity hotspot. Indirect paths included the effect of landscape structure on tree basal area (a proxy of local disturbance), and the effects of these variables on A. mexicanum. Density of A. mexicanum mainly increased with decreasing both fragmentation and open areas in the matrix (matrix contrast, hereafter), and such an increase in palm density negatively affected stem and species density in the understory. The negative direct effect of matrix contrast on stem density was overridden by the indirect positive effects (i.e., through negative cascading effects on A. mexicanum), resulting in a weak effect of matrix contrast on stem density. These findings suggest that dispersal limitation and negative edge effects in more fragmented landscapes dominated by open areas prevent the proliferation of this palm species, enhancing the diversity and abundance of understory trees. This "positive" news adds to an increasing line of evidence suggesting that fragmentation may have some positive effects on biodiversity, in this case by preventing the proliferation of species that can jeopardize biodiversity conservation within tropical reserves. © 2018 by the Ecological Society of America.

Early renal dysfunction after contrast media administration despite prophylactic hydration.

PubMed

Burchardt, Pawel; Guzik, Przemyslaw; Tabaczewski, Piotr; Synowiec, Tomasz; Bogdan, Monika; Faner, Paula; Chmielarz-Sobocińska, Anna; Palasz, Anna

2013-06-01

The actual incidence of renal dysfunction after contrast media administration seems to be underestimated, especially in the context of epidemiological data. There are only few data concerning the monitoring of impaired kidney function within a few hours after iodine contrast medium application. Hence, the purpose of this study is to observe the incidence of early renal function deterioration within 12-18 h after administration of iodine contrast media in patients scheduled for elective coronary angiography, who were intravenously and orally hydrated. In addition, the project aims to reclassify the contrast induced nephropathy phenomenon, by identification of early markers of renal dysfunction. Morphology, electrolytes, blood urea nitrogen (BUN), creatinine, low-density lipoprotein cholesterol, triglycerides, high-density lipoprotein, and total cholesterol levels were assessed with the use of typical laboratory techniques in 319 patients referred for coronary angiography. We demonstrated that early deterioration of renal function in patients 12-18 h after administration of contrast during imaging tests (even when appropriate prophylactic hydration was used), may occurred just as an increase (or no change) of serum creatinine level and BUN level and a decrease of creatinine clearance and glomerular filtration rate. Depending on the parameter, the phenomenon can be found in 13-28 % of all respondents. Early renal function impairment defined as above was almost 2 and 2.22 × 10(3) times (respectively) more frequently observed in our study than contrast induced nephropathy defined by current definitions.

Evaluating the importance of faecal sources in human-impacted waters.

PubMed

Schoen, Mary E; Soller, Jeffrey A; Ashbolt, Nicholas J

2011-04-01

Quantitative microbial risk assessment (QMRA) was used to evaluate the relative contribution of faecal indicators and pathogens when a mixture of human sources impacts a recreational waterbody. The waterbody was assumed to be impacted with a mixture of secondary-treated disinfected municipal wastewater and untreated (or poorly treated) sewage, using Norovirus as the reference pathogen and enterococci as the reference faecal indicator. The contribution made by each source to the total waterbody volume, indicator density, pathogen density, and illness risk was estimated for a number of scenarios that accounted for pathogen and indicator inactivation based on the age of the effluent (source-to-receptor), possible sedimentation of microorganisms, and the addition of a non-pathogenic source of faecal indicators (such as old sediments or an animal population with low occurrence of human-infectious pathogens). The waterbody indicator density was held constant at 35 CFU 100 mL(-1) enterococci to compare results across scenarios. For the combinations evaluated, either the untreated sewage or the non-pathogenic source of faecal indicators dominated the recreational waterbody enterococci density assuming a culture method. In contrast, indicator density assayed by qPCR, pathogen density, and bather gastrointestinal illness risks were largely dominated by secondary disinfected municipal wastewater, with untreated sewage being increasingly less important as the faecal indicator load increased from a non-pathogenic source. The results support the use of a calibrated qPCR total enterococci indicator, compared to a culture-based assay, to index infectious human enteric viruses released in treated human wastewater, and illustrate that the source contributing the majority of risk in a mixture may be overlooked when only assessing faecal indicators by a culture-based method. Published by Elsevier Ltd.

The use of clinical contrast media for lymphangiography in cadaveric studies.

PubMed

Pan, Wei-Ren; Le Roux, Cara Michelle; Rozen, Warren M

2009-01-01

Radiographic contrast media have not been previously used in human lymphatic cadaver studies. As these will have further clinical applications, we sought to investigate their use in this role. Both lower legs from an unembalmed human cadaver were studied. We used hydrogen peroxide to identify the lymphatics of the dorsum of the foot, and a single lymphatic was microsurgically injected with 1 ml of 76% 'Urografin.' A series of radiographs were taken 1 min after injection and for 2.5 h until the Urografin vanished. Images were digitalized for analysis. The series of lymphangiograms generated showed the size, location, and course of the lymphatics in the leg. Over time, the density of the iodinated contrast in the lymphatic vessels reduced and disappeared completely after 2.5 hours postinjection. A 'digitally subtracted' image provided a clear and high-contrast lymphangiogram. The lymphatic network identified was shown to diverge and converge twice as it coursed proximally up the limb. Urografin, a clinical radiographic contrast medium, was shown to lose contrast density 2.5 h following cadaveric intralymphatic injection. The use of a new technique, that of 'digital subtraction lymphangiography,' was able to demonstrate the lymphatic vessel pathways clearly, and is a useful technique for cadaveric lymphatic studies.

Particle in cell simulation on plasma grating contrast enhancement induced by infrared laser pulse

NASA Astrophysics Data System (ADS)

Li, M.; Yuan, T.; Xu, Y. X.; Wang, J. X.; Luo, S. N.

2018-05-01

The dynamics of plasma grating contrast enhancement (PGCE) irradiated by an infrared laser pulse is investigated with one dimensional particle-in-cell simulation where field ionization and impact ionization are simultaneously considered for the first time. The numeric results show that the impact ionization dominates the PGCE process. Upon the interaction with the laser pulse, abundant free electrons are efficiently accelerated and subsequently triggered massive impact ionizations in the density ridges of the plasma grating for the higher local plasma energy density, which efficiently enhances the grating contrast. Besides the dynamic analysis of PGCE, we explore the parameter space of the incident infrared laser pulse to optimize the PGCE effect, which can provide useful guidance to experiments related to laser-plasma-grating interactions and may find applications in prolonging the duration of the plasma grating.

Homogenization of sample absorption for the imaging of large and dense fossils with synchrotron microtomography.

PubMed

Sanchez, Sophie; Fernandez, Vincent; Pierce, Stephanie E; Tafforeau, Paul

2013-09-01

Propagation phase-contrast synchrotron radiation microtomography (PPC-SRμCT) has proved to be very successful for examining fossils. Because fossils range widely in taphonomic preservation, size, shape and density, X-ray computed tomography protocols are constantly being developed and refined. Here we present a 1-h procedure that combines a filtered high-energy polychromatic beam with long-distance PPC-SRμCT (sample to detector: 4-16 m) and an attenuation protocol normalizing the absorption profile (tested on 13-cm-thick and 5.242 g cm(-3) locally dense samples but applicable to 20-cm-thick samples). This approach provides high-quality imaging results, which show marked improvement relative to results from images obtained without the attenuation protocol in apparent transmission, contrast and signal-to-noise ratio. The attenuation protocol involves immersing samples in a tube filled with aluminum or glass balls in association with a U-shaped aluminum profiler. This technique therefore provides access to a larger dynamic range of the detector used for tomographic reconstruction. This protocol homogenizes beam-hardening artifacts, thereby rendering it effective for use with conventional μCT scanners.

Structure and Distribution of Centromeric Retrotransposons at Diploid and Allotetraploid Coffea Centromeric and Pericentromeric Regions

PubMed Central

de Castro Nunes, Renata; Orozco-Arias, Simon; Crouzillat, Dominique; Mueller, Lukas A.; Strickler, Suzy R.; Descombes, Patrick; Fournier, Coralie; Moine, Deborah; de Kochko, Alexandre; Yuyama, Priscila M.; Vanzela, André L. L.; Guyot, Romain

2018-01-01

Centromeric regions of plants are generally composed of large array of satellites from a specific lineage of Gypsy LTR-retrotransposons, called Centromeric Retrotransposons. Repeated sequences interact with a specific H3 histone, playing a crucial function on kinetochore formation. To study the structure and composition of centromeric regions in the genus Coffea, we annotated and classified Centromeric Retrotransposons sequences from the allotetraploid C. arabica genome and its two diploid ancestors: Coffea canephora and C. eugenioides. Ten distinct CRC (Centromeric Retrotransposons in Coffea) families were found. The sequence mapping and FISH experiments of CRC Reverse Transcriptase domains in C. canephora, C. eugenioides, and C. arabica clearly indicate a strong and specific targeting mainly onto proximal chromosome regions, which can be associated also with heterochromatin. PacBio genome sequence analyses of putative centromeric regions on C. arabica and C. canephora chromosomes showed an exceptional density of one family of CRC elements, and the complete absence of satellite arrays, contrasting with usual structure of plant centromeres. Altogether, our data suggest a specific centromere organization in Coffea, contrasting with other plant genomes. PMID:29497436

High abundance and diversity of consumers associated with eutrophic areas in a semi-desert macrotidal coastal ecosystem in Patagonia, Argentina

NASA Astrophysics Data System (ADS)

Martinetto, Paulina; Daleo, Pedro; Escapa, Mauricio; Alberti, Juan; Isacch, Juan Pablo; Fanjul, Eugenia; Botto, Florencia; Piriz, Maria Luz; Ponce, Gabriela; Casas, Graciela; Iribarne, Oscar

2010-07-01

Here we evaluated the response to eutrophication in terms of abundance and diversity of flora and fauna in a semi-desert macrotidal coastal system (San Antonio bay, Patagonia, Argentina, 40° 48' S) where signs of eutrophication (high nutrient concentration, seaweed blooms, high growth rate of macroalgae) have been reported. We compared abundances and species composition of macroalgae, small infaunal and epifaunal invertebrates, and birds associated with tidal channels of the San Antonio Bay subject to contrasting anthropogenic influence. Macroalgae were more abundant and diverse in the channel closer to human activity where nutrient concentrations were also higher. In contrast to what others have observed in eutrophic sites, small invertebrates and birds were also more abundant and diverse in the channel with macroalgal blooms and high nutrient concentration. The large water flushing during the tidal cycle could prevent anoxic or hypoxic events, making the environment suitable for consumers. Thus, this could be a case in which eutrophication supports high densities of consumers by increasing food availability, rather than negatively affecting the survival of organisms.

Predicting wading bird and aquatic faunal responses to ecosystem restoration scenarios

USGS Publications Warehouse

Beerens, James M.; Trexler, Joel C.; Catano, Christopher P.

2017-01-01

In large-scale conservation decisions, scenario planning identifies key uncertainties of ecosystem function linked to ecological drivers affected by management, incorporates ecological feedbacks, and scales up to answer questions robust to alternative futures. Wetland restoration planning requires an understanding of how proposed changes in surface hydrology, water storage, and landscape connectivity affect aquatic animal composition, productivity, and food-web function. In the Florida Everglades, reintroduction of historical hydrologic patterns is expected to increase productivity of all trophic levels. Highly mobile indicator species such as wading birds integrate secondary productivity from aquatic prey (small fishes and crayfish) over the landscape. To evaluate how fish, crayfish, and wading birds may respond to alternative hydrologic restoration plans, we compared predicted small fish density, crayfish density and biomass, and wading bird occurrence for existing conditions to four restoration scenarios that varied water storage and removal of levees and canals (i.e. decompartmentalization). Densities of small fish and occurrence of wading birds are predicted to increase throughout most of the Everglades under all restoration options because of increased flows and connectivity. Full decompartmentalization goes furthest toward recreating hypothesized historical patterns of fish density by draining excess water ponded by levees and hydrating areas that are currently drier than in the past. In contrast, crayfish density declined and species composition shifted under all restoration options because of lengthened hydroperiods (i.e. time of inundation). Under full decompartmentalization, the distribution of increased prey available for wading birds shifted south, closer to historical locations of nesting activity in Everglades National Park.

Comparison of sampling methodologies and estimation of population parameters for a temporary fish ectoparasite.

PubMed

Artim, J M; Sikkel, P C

2016-08-01

Characterizing spatio-temporal variation in the density of organisms in a community is a crucial part of ecological study. However, doing so for small, motile, cryptic species presents multiple challenges, especially where multiple life history stages are involved. Gnathiid isopods are ecologically important marine ectoparasites, micropredators that live in substrate for most of their lives, emerging only once during each juvenile stage to feed on fish blood. Many gnathiid species are nocturnal and most have distinct substrate preferences. Studies of gnathiid use of habitat, exploitation of hosts, and population dynamics have used various trap designs to estimate rates of gnathiid emergence, study sensory ecology, and identify host susceptibility. In the studies reported here, we compare and contrast the performance of emergence, fish-baited and light trap designs, outline the key features of these traps, and determine some life cycle parameters derived from trap counts for the Eastern Caribbean coral-reef gnathiid, Gnathia marleyi. We also used counts from large emergence traps and light traps to estimate additional life cycle parameters, emergence rates, and total gnathiid density on substrate, and to calibrate the light trap design to provide estimates of rate of emergence and total gnathiid density in habitat not amenable to emergence trap deployment.

Calculation of the critical overdensity in the spherical-collapse approximation

NASA Astrophysics Data System (ADS)

Herrera, D.; Waga, I.; Jorás, S. E.

2017-03-01

Critical overdensity δc is a key concept in estimating the number count of halos for different redshift and halo-mass bins, and therefore, it is a powerful tool to compare cosmological models to observations. There are currently two different prescriptions in the literature for its calculation, namely, the differential-radius and the constant-infinity methods. In this work we show that the latter yields precise results only if we are careful in the definition of the so-called numerical infinities. Although the subtleties we point out are crucial ingredients for an accurate determination of δc both in general relativity and in any other gravity theory, we focus on f (R )-modified gravity models in the metric approach; in particular, we use the so-called large (F =1 /3 ) and small-field (F =0 ) limits. For both of them, we calculate the relative errors (between our method and the others) in the critical density δc, in the comoving number density of halos per logarithmic mass interval nln M, and in the number of clusters at a given redshift in a given mass bin Nbin, as functions of the redshift. We have also derived an analytical expression for the density contrast in the linear regime as a function of the collapse redshift zc and Ωm 0 for any F .

Chandra and XMM-Newton Observations of the Abell 3395/Abell 3391 Intercluster Filament

NASA Astrophysics Data System (ADS)

Alvarez, Gabriella E.; Randall, Scott W.; Bourdin, Hervé; Jones, Christine; Holley-Bockelmann, Kelly

2018-05-01

We present Chandra and XMM-Newton X-ray observations of the Abell 3391/Abell 3395 intercluster filament. It has been suggested that the galaxy clusters Abell 3395, Abell 3391, and the galaxy group ESO-161 -IG 006 located between the two clusters, are in alignment along a large-scale intercluster filament. We find that the filament is aligned close to the plane of the sky, in contrast to previous results. We find a global projected filament temperature kT = {4.45}-0.55+0.89 keV, electron density {n}e={1.08}-0.05+0.06× {10}-4 cm‑3, and {M}gas}={2.7}-0.1+0.2 × {10}13 M ⊙. The thermodynamic properties of the filament are consistent with that of the intracluster medium (ICM) of Abell 3395 and Abell 3391, suggesting that the filament emission is dominated by ICM gas that has been tidally disrupted during an early stage merger between these two clusters. We present temperature, density, entropy, and abundance profiles across the filament. We find that the galaxy group ESO-161 may be undergoing ram-pressure-stripping in the low-density environment at or near the virial radius of both clusters, due to its rapid motion through the filament.

Giant increase of critical current density and vortex pinning in Mn doped K{sub x}Fe{sub 2−y}Se{sub 2} single crystals

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

Li, Mingtao; Zhang, Jincang, E-mail: jczhang@staff.shu.edu.cn; Materials Genome Institute, Shanghai University, Shanghai 200444

2014-11-10

We report a comparative study of the critical current density (J{sub c}) and vortex pinning among pure and Mn doped K{sub x}Fe{sub 2−y}Se{sub 2} single crystals. It is found that the J{sub c} values can be greatly improved by Mn doping and post-quenching treatment when comparing to pristine pure sample. In contrast to pure samples, an anomalous second magnetization peak (SMP) effect is observed in both 1% and 2% Mn doped samples at T = 3 K for H∥ab but not for H∥c. Referring to Dew-Hughes and Kramer's model, we performed scaling analyses of the vortex pinning force density vs magnetic field inmore » 1% Mn doped and quenched pristine crystals. The results show that the normal point defects are the dominant pinning sources, which probably originate from the variations of intercalated K atoms. We propose that the large nonsuperconducting K-Mn-Se inclusions may contribute to the partial normal surface pinning and give rise to the anomalous SMP effect for H∥ab in Mn doped crystals. These results may facilitate further understanding of the superconductivity and vortex pinning in intercalated iron-selenides superconductors.« less

Genetic predisposition to low bone mass is paralleled by an enhanced sensitivity to signals anabolic to the skeleton

NASA Technical Reports Server (NTRS)

Judex, Stefan; Donahue, Leah-Rae; Rubin, Clinton

2002-01-01

The structure of the adult skeleton is determined, in large part, by its genome. Whether genetic variations may influence the effectiveness of interventions to combat skeletal diseases remains unknown. The differential response of trabecular bone to an anabolic (low-level mechanical vibration) and a catabolic (disuse) mechanical stimulus were evaluated in three strains of adult mice. In low bone-mineral-density C57BL/6J mice, the low-level mechanical signal caused significantly larger bone formation rates (BFR) in the proximal tibia, but the removal of functional weight bearing did not significantly alter BFR. In mid-density BALB/cByJ mice, mechanical stimulation also increased BFR, whereas disuse significantly decreased BFR. In contrast, neither anabolic nor catabolic mechanical signals influenced any index of bone formation in high-density C3H/HeJ mice. Together, data from this study indicate that the sensitivity of trabecular tissue to both anabolic and catabolic stimuli is influenced by the genome. Extrapolated to humans, these results may explain in part why prophylaxes for low bone mass are not universally effective, yet also indicate that there may be a genotypic indication of people who are at reduced risk of suffering from bone loss.

Comparing laser-based open- and closed-path gas analyzers to measure methane fluxes using the eddy covariance method

USGS Publications Warehouse

Detto, Matteo; Verfaillie, Joseph; Anderson, Frank; Xu, Liukang; Baldocchi, Dennis

2011-01-01

Closed- and open-path methane gas analyzers are used in eddy covariance systems to compare three potential methane emitting ecosystems in the Sacramento-San Joaquin Delta (CA, USA): a rice field, a peatland pasture and a restored wetland. The study points out similarities and differences of the systems in field experiments and data processing. The closed-path system, despite a less intrusive placement with the sonic anemometer, required more care and power. In contrast, the open-path system appears more versatile for a remote and unattended experimental site. Overall, the two systems have comparable minimum detectable limits, but synchronization between wind speed and methane data, air density corrections and spectral losses have different impacts on the computed flux covariances. For the closed-path analyzer, air density effects are less important, but the synchronization and spectral losses may represent a problem when fluxes are small or when an undersized pump is used. For the open-path analyzer air density corrections are greater, due to spectroscopy effects and the classic Webb–Pearman–Leuning correction. Comparison between the 30-min fluxes reveals good agreement in terms of magnitudes between open-path and closed-path flux systems. However, the scatter is large, as consequence of the intensive data processing which both systems require.

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

Kunal, Bhagatwala, E-mail: kunalbhagatwala@gmail.com; Nidhi, Karia

A 91 years old female presented with chest pain and shortness of breath after a fall. Chest radiograph showed a very large left-sided fluid collection surrounded by calcified pleura and collapse of the left lung (Figure 1). CT scan of chest with contrast revealed a chronic appearing increased density left pleural effusion contained within thick calcified pleura (). Upon further questioning patient reported that when she was 20 years old she had repeated punctures to her left chest to collapse the lung for the treatment of suspected tuberculosis. The air-filled pleural space eventually got transformed into calcified pleura with containedmore » effusion. No further intervention was performed for this effusion as the patient’s symptoms improved. She did not have any symptoms before the fall.« less

Nearly-free-electron system of monolayer Na on the surface of single-crystal HfSe 2

DOE PAGES

Eknapakul, T.; Fongkaew, I.; Siriroj, S.; ...

2016-11-15

Here, the electronic structure of a single Na monolayer on the surface of single-crystal HfSe 2 is investigated using angle-resolved photoemission spectroscopy. We find that this system exhibits an almost perfect "nearly-free-electron" behavior with an extracted effective mass of ~1m e, in contrast to heavier masses found previously for alkali-metal monolayers on other substrates. Our density-functional-theory calculations indicate that this is due to the large lattice constant, causing both exchange and correlation interactions to be suppressed, and to the weak hybridization between the overlayer and the substrate. This is therefore an ideal model system for understanding the properties of two-dimensionalmore » materials.« less

Image quality comparison between single energy and dual energy CT protocols for hepatic imaging

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

Yao, Yuan, E-mail: yuanyao@stanford.edu; Pelc, Nor

Purpose: Multi-detector computed tomography (MDCT) enables volumetric scans in a single breath hold and is clinically useful for hepatic imaging. For simple tasks, conventional single energy (SE) computed tomography (CT) images acquired at the optimal tube potential are known to have better quality than dual energy (DE) blended images. However, liver imaging is complex and often requires imaging of both structures containing iodinated contrast media, where atomic number differences are the primary contrast mechanism, and other structures, where density differences are the primary contrast mechanism. Hence it is conceivable that the broad spectrum used in a dual energy acquisition maymore » be an advantage. In this work we are interested in comparing these two imaging strategies at equal-dose and more complex settings. Methods: We developed numerical anthropomorphic phantoms to mimic realistic clinical CT scans for medium size and large size patients. MDCT images based on the defined phantoms were simulated using various SE and DE protocols at pre- and post-contrast stages. For SE CT, images from 60 kVp through 140 with 10 kVp steps were considered; for DE CT, both 80/140 and 100/140 kVp scans were simulated and linearly blended at the optimal weights. To make a fair comparison, the mAs of each scan was adjusted to match the reference radiation dose (120 kVp, 200 mAs for medium size patients and 140 kVp, 400 mAs for large size patients). Contrast-to-noise ratio (CNR) of liver against other soft tissues was used to evaluate and compare the SE and DE protocols, and multiple pre- and post-contrasted liver-tissue pairs were used to define a composite CNR. To help validate the simulation results, we conducted a small clinical study. Eighty-five 120 kVp images and 81 blended 80/140 kVp images were collected and compared through both quantitative image quality analysis and an observer study. Results: In the simulation study, we found that the CNR of pre-contrast SE image mostly increased with increasing kVp while for post-contrast imaging 90 kVp or lower yielded higher CNR images, depending on the differential iodine concentration of each tissue. Similar trends were seen in DE blended CNR and those from SE protocols. In the presence of differential iodine concentration (i.e., post-contrast), the CNR curves maximize at lower kVps (80–120), with the peak shifted rightward for larger patients. The combined pre- and post-contrast composite CNR study demonstrated that an optimal SE protocol has better performance than blended DE images, and the optimal tube potential for SE scan is around 90 kVp for a medium size patients and between 90 and 120 kVp for large size patients (although low kVp imaging requires high x-ray tube power to avoid photon starvation). Also, a tin filter added to the high kVp beam is not only beneficial for material decomposition but it improves the CNR of the DE blended images as well. The dose adjusted CNR of the clinical images also showed the same trend and radiologists favored the SE scans over blended DE images. Conclusions: Our simulation showed that an optimized SE protocol produces up to 5% higher CNR for a range of clinical tasks. The clinical study also suggested 120 kVp SE scans have better image quality than blended DE images. Hence, blended DE images do not have a fundamental CNR advantage over optimized SE images.« less

Generation of large-scale density fluctuations by buoyancy

NASA Technical Reports Server (NTRS)

Chasnov, J. R.; Rogallo, R. S.

1990-01-01

The generation of fluid motion from a state of rest by buoyancy forces acting on a homogeneous isotropic small-scale density field is considered. Nonlinear interactions between the generated fluid motion and the initial isotropic small-scale density field are found to create an anisotropic large-scale density field with spectrum proportional to kappa(exp 4). This large-scale density field is observed to result in an increasing Reynolds number of the fluid turbulence in its final period of decay.

Influence of deer abundance on the abundance of questing adult Ixodes scapularis (Acari: Ixodidae)

USGS Publications Warehouse

Ginsberg, H.S.; Zhioua, E.

1999-01-01

Nymphal and adult Ixodes scapularis Say were sampled by flagging at 2 sites on a barrier island, Fire Island, NY, and at 2 sites on the nearby mainland. Nymphal densities did not differ consistently between island and mainland sites, but adult densities were consistently lower on the island. We tested whether lower adult densities on the island resulted from greater nymphal mortality on the island than the mainland, or whether adult ticks on the island were poorly sampled by flagging because they had attached abundantly to deer, which were common on Fire Island. Differential nymphal mortality on islands vs. mainland did not explain this difference in adult densities because survival of flat and engorged nymphs in enclosures was the same at island and mainland sites. Ticks were infected by parasitic wasps on the island and not the mainland, but the infection rate (4.3%) was too low to explain the difference in adult tick densities. In contrast, exclusion of deer by game fencing on Fire Island resulted in markedly increased numbers of adult ticks in flagging samples inside compared to samples taken outside the exclosures. Therefore, the scarcity of adult ticks in flagging samples on Fire Island resulted, at least in part, from the ticks being unavailable to flagging samples because they were on deer hosts. Differences in the densities of flagged ticks inside and outside the exclosures were used to estimate the percentage of questing adults on Fire Island that found deer hosts, excluding those that attached to other host species. Approximately 56% of these questing adult ticks found deer hosts in 1995 and 50% found deer hosts in 1996. Therefore, in areas where vertebrate hosts are highly abundant, large proportions of the questing tick population can find hosts. Moreover, comparisons of tick densities at different sites by flagging can potentially be biased by differences in host densities among sites.

Biotic interactions at hydrothermal vents: Recruitment inhibition by the mussel Bathymodiolus thermophilus

NASA Astrophysics Data System (ADS)

Lenihan, H. S.; Mills, S. W.; Mullineaux, L. S.; Peterson, C. H.; Fisher, C. R.; Micheli, F.

2008-12-01

The structure and dynamics of marine communities are regulated in part by variation in recruitment. As in other ecosystems, recruitment at deep-sea hydrothermal vents is controlled by the interplay of propagule supply and behavior, gradients in physical-chemical conditions, and biotic interactions during pre- and post-settlement periods. Recent research along the East Pacific Rise indicates that inhibition of recently settled larvae by mobile predators (mainly limpets) influences patterns of recruitment and subsequent community succession. We conducted a manipulative experiment at the same sites (˜2510 m water depth) to test whether high-density assemblages of the mussel Bathymodiolus thermophilus also inhibit recruitment. In a preliminary study, recruitment of vent invertebrates within the faunal zone dominated by B. thermophilus was strikingly different at two sites, East Wall and Worm Hole. East Wall had high densities of mussels but very low total recruitment. In contrast, Worm Hole had few mussels but high recruitment. Using the submersible Alvin, we transplanted a large number of mussels from East Wall to Worm Hole and quantified recruitment on basalt blocks placed in three treatments: (1) naturally high densities of mussels at East Wall; (2) naturally low densities of mussels at Worm Hole; and (3) high densities of transplanted mussels at Worm Hole. After 11 months, a total of 24 taxa had recruited to the basalt blocks. Recruitment was 44-60% lower in the transplanted high-density mussel patch at Worm Hole and the natural high-density patch at East Wall than within the natural low-density patch at Worm Hole. Biotic processes that may have caused the pattern of recruitment observed included predation of larvae via water filtration by mussels, larval avoidance of superior competitors, interference competition, and enhanced predation by species within the mussel-bed community. Our results indicate that biotic interactions affecting recruitment must be understood to explain patterns of invertebrate community organization and dynamics at hydrothermal vents.

Coupled Boltzmann computation of mixed axion neutralino dark matter in the SUSY DFSZ axion model

NASA Astrophysics Data System (ADS)

Bae, Kyu Jung; Baer, Howard; Lessa, Andre; Serce, Hasan

2014-10-01

The supersymmetrized DFSZ axion model is highly motivated not only because it offers solutions to both the gauge hierarchy and strong CP problems, but also because it provides a solution to the SUSY μ-problem which naturally allows for a Little Hierarchy. We compute the expected mixed axion-neutralino dark matter abundance for the SUSY DFSZ axion model in two benchmark cases—a natural SUSY model with a standard neutralino underabundance (SUA) and an mSUGRA/CMSSM model with a standard overabundance (SOA). Our computation implements coupled Boltzmann equations which track the radiation density along with neutralino, axion, axion CO (produced via coherent oscillations), saxion, saxion CO, axino and gravitino densities. In the SUSY DFSZ model, axions, axinos and saxions go through the process of freeze-in—in contrast to freeze-out or out-of-equilibrium production as in the SUSY KSVZ model—resulting in thermal yields which are largely independent of the re-heat temperature. We find the SUA case with suppressed saxion-axion couplings (ξ=0) only admits solutions for PQ breaking scale falesssim 6× 1012 GeV where the bulk of parameter space tends to be axion-dominated. For SUA with allowed saxion-axion couplings (ξ =1), then fa values up to ~ 1014 GeV are allowed. For the SOA case, almost all of SUSY DFSZ parameter space is disallowed by a combination of overproduction of dark matter, overproduction of dark radiation or violation of BBN constraints. An exception occurs at very large fa~ 1015-1016 GeV where large entropy dilution from CO-produced saxions leads to allowed models.

3D CT cerebral angiography technique using a 320-detector machine with a time-density curve and low contrast medium volume: comparison with fixed time delay technique.

PubMed

Das, K; Biswas, S; Roughley, S; Bhojak, M; Niven, S

2014-03-01

To describe a cerebral computed tomography angiography (CTA) technique using a 320-detector CT machine and a small contrast medium volume (35 ml, 15 ml for test bolus). Also, to compare the quality of these images with that of the images acquired using a larger contrast medium volume (90 or 120 ml) and a fixed time delay (FTD) of 18 s using a 16-detector CT machine. Cerebral CTA images were acquired using a 320-detector machine by synchronizing the scanning time with the time of peak enhancement as determined from the time-density curve (TDC) using a test bolus dose. The quality of CTA images acquired using this technique was compared with that obtained using a FTD of 18 s (by 16-detector CT), retrospectively. Average densities in four different intracranial arteries, overall opacification of arteries, and the degree of venous contamination were graded and compared. Thirty-eight patients were scanned using the TDC technique and 40 patients using the FTD technique. The arterial densities achieved by the TDC technique were higher (significant for supraclinoid and basilar arteries, p < 0.05). The proportion of images deemed as having "good" arterial opacification was 95% for TDC and 90% for FTD. The degree of venous contamination was significantly higher in images produced by the FTD technique (p < 0.001%). Good diagnostic quality CTA images with significant reduction of venous contamination can be achieved with a low contrast medium dose using a 320-detector machine by coupling the time of data acquisition with the time of peak enhancement. Copyright © 2013 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

A speeded-up saliency region-based contrast detection method for small targets

NASA Astrophysics Data System (ADS)

Li, Zhengjie; Zhang, Haiying; Bai, Jiaojiao; Zhou, Zhongjun; Zheng, Huihuang

2018-04-01

To cope with the rapid development of the real applications for infrared small targets, the researchers have tried their best to pursue more robust detection methods. At present, the contrast measure-based method has become a promising research branch. Following the framework, in this paper, a speeded-up contrast measure scheme is proposed based on the saliency detection and density clustering. First, the saliency region is segmented by saliency detection method, and then, the Multi-scale contrast calculation is carried out on it instead of traversing the whole image. Second, the target with a certain "integrity" property in spatial is exploited to distinguish the target from the isolated noises by density clustering. Finally, the targets are detected by a self-adaptation threshold. Compared with time-consuming MPCM (Multiscale Patch Contrast Map), the time cost of the speeded-up version is within a few seconds. Additional, due to the use of "clustering segmentation", the false alarm caused by heavy noises can be restrained to a lower level. The experiments show that our method has a satisfied FASR (False alarm suppression ratio) and real-time performance compared with the state-of-art algorithms no matter in cloudy sky or sea-sky background.

Vacuum statistics and stability in axionic landscapes

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

Masoumi, Ali; Vilenkin, Alexander, E-mail: ali@cosmos.phy.tufts.edu, E-mail: vilenkin@cosmos.phy.tufts.edu

2016-03-01

We investigate vacuum statistics and stability in random axionic landscapes. For this purpose we developed an algorithm for a quick evaluation of the tunneling action, which in most cases is accurate within 10%. We find that stability of a vacuum is strongly correlated with its energy density, with lifetime rapidly growing as the energy density is decreased. On the other hand, the probability P(B) for a vacuum to have a tunneling action B greater than a given value declines as a slow power law in B. This is in sharp contrast with the studies of random quartic potentials, which foundmore » a fast exponential decline of P(B). Our results suggest that the total number of relatively stable vacua (say, with B>100) grows exponentially with the number of fields N and can get extremely large for N∼> 100. The problem with this kind of model is that the stable vacua are concentrated near the absolute minimum of the potential, so the observed value of the cosmological constant cannot be explained without fine-tuning. To address this difficulty, we consider a modification of the model, where the axions acquire a quadratic mass term, due to their mixing with 4-form fields. This results in a larger landscape with a much broader distribution of vacuum energies. The number of relatively stable vacua in such models can still be extremely large.« less

Redox control of ferrocene-based complexes with systematically extended π-conjugated connectors: switchable and tailorable second order nonlinear optics.

PubMed

Wang, Wen-Yong; Ma, Na-Na; Sun, Shi-Ling; Qiu, Yong-Qing

2014-03-14

The studies of geometrical structures, thermal stabilities, redox properties, nonlinear responses and optoelectronic properties have been carried out on a series of novel ferrocenyl (Fc) chromophores with the view of assessing their switchable and tailorable second order nonlinear optics (NLO). The use of a constant Fc donor and a 4,4'-bipyridinium acceptor and varied conjugated bridges makes it possible to systematically determine the contribution of organic connectors to chromophore nonlinear optical activities. The structures reveal that both the reduction reactions and organic connectors have a significant influence on 4,4'-bipyridinium. The potential energy surface maps along with plots of reduced density gradient mirror the thermal stabilities of the Fc-based chromophores. The first and second reductions take place preferentially at the 4,4'-bipyridinium moieties. Significantly, the reduction processes result in the molecular switches with large NLO contrast varying from zero or very small to a large value. Moreover, time-dependent density functional theory results indicate that the absorption peaks are mainly attributed to Fc to 4,4'-bipyridinium charge transfer and the mixture of intramolecular charge transfer within the two respective 4,4'-bipyridinium moieties coupled with interlayer charge transfer between the two 4,4'-bipyridinium moieties. This provides us with comprehensive information on the effect of organic connectors on the NLO properties.

Laser Remediation of Threats Posed by Small Orbital Debris

NASA Technical Reports Server (NTRS)

Fork, Richard L.; Rogers, Jan R.; Hovater, Mary A.

2012-01-01

The continually increasing amount of orbital debris in near Earth space poses an increasing challenge to space situational awareness. Recent collisions of spacecraft caused abrupt increases in the density of both large and small debris in near Earth space. An especially challenging class of threats is that due to the increasing density of small (1 mm to 10 cm dimension) orbital debris. This small debris poses a serious threat since: (1) The high velocity enables even millimeter dimension debris to cause serious damage to vulnerable areas of space assets, e.g., detector windows; (2) The small size and large number of debris elements prevent adequate detection and cataloguing. We have identified solutions to this threat in the form of novel laser systems and novel ways of using these laser systems. While implementation of the solutions we identify is challenging we find approaches offering threat mitigation within time frames and at costs of practical interest. We base our analysis on the unique combination of coherent light specifically structured in both space and time and applied in novel ways entirely within the vacuum of space to deorbiting small debris. We compare and contrast laser based small debris removal strategies using ground based laser systems with strategies using space based laser systems. We find laser systems located and used entirely within space offer essential and decisive advantages over groundbased laser systems.

Damping Measurements of Plasma Modes

NASA Astrophysics Data System (ADS)

Anderegg, F.; Affolter, M.; Driscoll, C. F.

2010-11-01

For azimuthally symmetric plasma modes in a magnesium ion plasma, confined in a 3 Tesla Penning-Malmberg trap with a density of n ˜10^7cm-3, we measure a damping rate of 2s-1< γ< 10^4s-1 over a wide range in temperature (5 x10-6 eV< T < 5eV) and aspect ratio (0.25 < α< 25), with a wave amplitude of δn / n ˜5%. Changing the aspect ratio, α= Lp/ 2rp, of the plasma column, alters the frequency of the mode from 16 KHz to 192 KHz. The oscillatory fluid displacement is small compared to the wavelength of the mode; in contrast, the fluid velocity, δvf, can be large compared to v. The real part of the frequency satisfies a linear dispersion relation. In long thin plasmas (α> 10) these modes are Trivelpiece-Gould (TG) modes, and for smaller values of α they are Dubin spheroidal modes. However the damping appears to be non-linear; initially large waves have weaker exponential damping, which is not yet understood. Recent theoryootnotetextM.W. Anderson and T.M. O'Neil, Phys. Plasmas 14, 112110 (2007). calculates the damping of TG modes expected from viscosity due to ion-ion collisions; but the measured damping, while having a similar temperature and density dependence, is about 40 times larger than calculated. This discrepancy might be due to an external damping mechanism.

Reconstructing the metric of the local Universe from number counts observations

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

Vallejo, Sergio Andres; Romano, Antonio Enea, E-mail: antonio.enea.romano@cern.ch

Number counts observations available with new surveys such as the Euclid mission will be an important source of information about the metric of the Universe. We compute the low red-shift expansion for the energy density and the density contrast using an exact spherically symmetric solution in presence of a cosmological constant. At low red-shift the expansion is more precise than linear perturbation theory prediction. We then use the local expansion to reconstruct the metric from the monopole of the density contrast. We test the inversion method using numerical calculations and find a good agreement within the regime of validity ofmore » the red-shift expansion. The method could be applied to observational data to reconstruct the metric of the local Universe with a level of precision higher than the one achievable using perturbation theory.« less

Constraints on the design of core-shell resonators of locally resonant acoustic metamaterials

NASA Astrophysics Data System (ADS)

Bos, Lionel; Lukyanova, Lyubov; Wunenburger, Régis

2012-11-01

We perform a parametric study of the analytic model of Liu [Z. Liu , Phys. Rev. B10.1103/PhysRevB.71.014103 71, 014103 (2005)] describing the mechanical response of a core-shell particle to an acoustic excitation in order to help in selecting the constitutive materials and in designing innovative processes of fabrication of downsized core-shell resonators, which are key constituents of locally resonant acoustic metamaterials. We show that the value of the first Lamé coefficient of the material constituting the shell has no marked influence on the value of the resonance frequency of the core-shell resonator, that is, it does not necessarily need to be small for satisfying the condition of subwavelength resonator dimension at resonance. Moreover, we show that the larger the density contrast between the core and the shell and the thinner the shell, the broader is the frequency band over which the effective density of the resonator suspension is negative, but that it is practically useless to decrease the dimensionless shell thickness below 0.6. Finally, we show that the dissipation is also less perceptible the thinner is the shell and the larger is the density contrast. The effect of the density contrast between the core and the shell and of the dissipation on the resonance width are explained by comparing with the harmonic oscillator and the mass-in-mass 1D lattice.

Correlation between blood and lymphatic vessel density and results of contrast-enhanced spectral mammography.

PubMed

Luczynska, Elzbieta; Niemiec, Joanna; Ambicka, Aleksandra; Adamczyk, Agnieszka; Walasek, Tomasz; Ryś, Janusz; Sas-Korczyńska, Beata

2015-09-01

Contrast-enhanced spectral mammography (CESM) is a novel technique used for detection of tumour vascularity by imaging the moment in which contrast, delivered to the lesion by blood vessels, leaks out of them, and flows out through lymphatic vessels. In our study, we included 174 women for whom spectral mammography was performed for diagnostic purposes. The relationship between enhancement in CESM and blood vessel density (BVD), lymphatic vessel density (LVD) or the percentage of fields with at least one lymphatic vessel (distribution of podoplanin-positive vessels - DPV) and other related parameters was assessed in 55 cases. BVD, LVD and DPV were assessed immunohistochemically, applying podoplanin and CD31/CD34 as markers of lymphatic and blood vessels, respectively. The sensitivity (in detection of malignant lesions) of CESM was 100%, while its specificity - 39%. We found a significant positive correlation between the intensity of enhancement in CESM and BVD (p = 0.007, r = 0.357) and a negative correlation between the intensity of enhancement in CESM and DPV (p = 0.003, r = -0.390). Lesions with the highest enhancement in CESM showed a high number of blood vessels and a low number of lymphatics. 1) CESM is a method characterized by high sensitivity and acceptable specificity; 2) the correlation between CESM results and blood/lymphatic vessel density confirms its utility in detection of tissue angiogenesis and/or lymphangiogenesis.

Modelling the effect of wheat canopy architecture as affected by sowing density on Septoria tritici epidemics using a coupled epidemic–virtual plant model

PubMed Central

Baccar, Rim; Fournier, Christian; Dornbusch, Tino; Andrieu, Bruno; Gouache, David; Robert, Corinne

2011-01-01

Background and Aims The relationship between Septoria tritici, a splash-dispersed disease, and its host is complex because of the interactions between the dynamic plant architecture and the vertical progress of the disease. The aim of this study was to test the capacity of a coupled virtual wheat–Septoria tritici epidemic model (Septo3D) to simulate disease progress on the different leaf layers for contrasted sowing density treatments. Methods A field experiment was performed with winter wheat ‘Soissons’ grown at three contrasted densities. Plant architecture was characterized to parameterize the wheat model, and disease dynamic was monitored to compare with simulations. Three simulation scenarios, differing in the degree of detail with which plant variability of development was represented, were defined. Key Results Despite architectural differences between density treatments, few differences were found in disease progress; only the lower-density treatment resulted in a slightly higher rate of lesion development. Model predictions were consistent with field measurements but did not reproduce the higher rate of lesion progress in the low density. The canopy reconstruction scenario in which inter-plant variability was taken into account yielded the best agreement between measured and simulated epidemics. Simulations performed with the canopy represented by a population of the same average plant deviated strongly from the observations. Conclusions It was possible to compare the predicted and measured epidemics on detailed variables, supporting the hypothesis that the approach is able to provide new insights into the processes and plant traits that contribute to the epidemics. On the other hand, the complex and dynamic responses to sowing density made it difficult to test the model precisely and to disentangle the various aspects involved. This could be overcome by comparing more contrasted and/or simpler canopy architectures such as those resulting from quasi-isogenic lines differing by single architectural traits. PMID:21724656

Younger and older adults' perception of the Wundt-Hering illusion as a function of display illumination and reflectance contrast.

PubMed

Astor-Stetson, E; Lane, S

1991-08-01

Reflectance contrast (i.e., black as compared to grey figures on white ground) and display illumination were manipulated to vary the brightness contrast of Wundt-Hering figures. 16 college students and 16 older adults were presented with high, medium, and low reflectance contrast figures. For half the participants, display illumination was manipulated by covering the figures with a .5 yellow neutral density filter. Magnitude of the illusion increased significantly with increased reflectance contrast for college students, and college students were significantly more susceptible to the high contrast figures than were older adults. Display illumination had no effect on the performance of either group.

Improvements in Diagnostic Accuracy with Quantitative Dynamic Contrast-Enhanced MRI

DTIC Science & Technology

2011-12-01

Magnetic   Resonance   Imaging  during  the  Menstrual  Cylce:  Perfusion   Imaging  Signal   Enhanceent,  and  Influence  of...acquisition of quantitative images displaying the concentration of contrast media as well as MRI -detectable proton density. To date 21 patients have...truly  quantitative   images  of  a  dynamic  contrast-­‐enhanced  (DCE)   MRI  of  the

Modeling Mars Cyclogenesis and Frontal Waves: Seasonal Variations and Implications on Dust Activity

NASA Technical Reports Server (NTRS)

Hollingsworth, J. L.; Kahre, M. A.

2014-01-01

Between late autumn through early spring,middle and high latitudes onMars exhibit strong equator-to-polemean temperature contrasts (i.e., "baroclinicity"). Data collected during the Viking era and observations from both the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) indicate that such strong baroclinicity supports vigorous, large-scale eastward traveling weather systems (i.e., transient synoptic period waves) [1, 2]. For a rapidly rotating, differentially heated, shallow atmosphere such as on Earth and Mars, these large-scale, extratropical weather disturbances are critical components of the global circulation. The wave-like disturbances serve as agents in the transport of heat and momentum between low and high latitudes of the planet. Through cyclonic/anticyclonic winds, intense shear deformations, contractions-dilatations in temperature and density, and sharp perturbations amongst atmospheric tracers (i.e., dust, volatiles (e.g., water vapor) and condensates (e.g., water-ice cloud particles)), Mars' extratropical weather systems have significant sub-synoptic scale ramifications by supporting atmospheric frontal waves (Fig. 1).

Extratropical Cyclogenesis and Frontal Waves on Mars: Influences on Dust, Weather and the Planet's climate

NASA Technical Reports Server (NTRS)

Hollingsworth, J. L.; Kahre, Melinda A.

2012-01-01

Between late autumn and early spring, middle and high latitudes on Mars exhibit strong equatortopole mean temperature contrasts (i.e., "baroclinicity"). Data collected during the Viking era and observations from both the Mars Global Surveyor (MGS) and Mars Reconnaissance Orbiter (MRO) indicate that this strong baroclinicity supports vigorous, large-scale eastward traveling weather systems (i.e., transient synoptic periodwaves) [1,2]. For a rapidly rotating, differentially heated, shallow atmosphere such as on Earth and Mars, these large-scale, extratropical weather disturbances are critical components of the global circulation. The wavelike disturbances act as agents in the transport of heat and momentum between low and high latitudes of the planet. Through cyclonic/anticyclonic winds, intense shear deformations, contractions-dilatations in temperature and density, and sharp perturbations amongst atmospheric tracers (i.e., dust, volatiles (e.g., water vapor) and condensates (e.g., water-ice cloud particles)), Mars extratropical weather systems have significant subsynoptic scale ramifications by supporting atmospheric frontal waves (Fig. 1).

Contrastive thermoelectric properties of strained SnSe crystals from the first-principles calculations

NASA Astrophysics Data System (ADS)

Tang, Yu; Cheng, Feng; Li, Decong; Deng, Shuping; Chen, Zhong; Sun, Luqi; Liu, Wenting; Shen, Lanxian; Deng, Shukang

2018-06-01

SnSe is a promising thermoelectric material with a record high dimensionless figure of merit ZT at high temperature ∼923 K. However, the ZT values for low-Temperature Pnma phase SnSe are just 0.1-0.9. Here, we use First-principle combine with Boltzmann transport theory methods to study the effect of tensile and compressible strain on the thermoelectric transport properties. The power factor of SnSe with -4% strain have a large boost along b and c directions of 7.7 and 3.9 μW cm-1 K-2, respectively, which are 2.5 and 2 times as large as those pristine SnSe. The charge density distributions reveal that the overlap of wave function has significant change due to the changed bond lengths and bond angles under different strain, which lead to the change of band gap and band dispersion. Our work provides a new effective strategy to enhance the thermoelectric properties of materials.

Bubble-induced microstreaming: guiding and destroying lipid vesicles

NASA Astrophysics Data System (ADS)

Marmottant, Philippe; Hilgenfeldt, Sascha

2002-11-01

Micron-sized bubbles respond with strong oscillations when submitted to ultrasound. This has led to their use as echographic contrast enhancers. The large energy and force densities generated by the collapsing bubbles also make them non-invasive mechanical tools: Recently, it has been reported that the interaction of cavitating bubbles with nearby cells can render the latter permeable to large molecules (sonoporation), suggesting prospects for drug delivery and gene transfection. We have developed a laboratory setup that allows for a controlled study of the interaction of single microbubbles with single lipid bilayer vesicles. Substituting vesicles for cell membranes is advantageous because the mechanical properties of vesicles are well-known. Microscopic observations reveal that vesicles near a bubble follow the vivid streaming motion set up by the bubble. The vesicles "bounce" off the bubble, being periodically accelerated towards and away from it, and undergo well-defined shape deformations along their trajectory in accordance with fluid-dynamical theory. Break-up of vesicles could also be observed.

The DiskMass Survey. II. Error Budget

NASA Astrophysics Data System (ADS)

Bershady, Matthew A.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.; Martinsson, Thomas

2010-06-01

We present a performance analysis of the DiskMass Survey. The survey uses collisionless tracers in the form of disk stars to measure the surface density of spiral disks, to provide an absolute calibration of the stellar mass-to-light ratio (Υ_{*}), and to yield robust estimates of the dark-matter halo density profile in the inner regions of galaxies. We find that a disk inclination range of 25°-35° is optimal for our measurements, consistent with our survey design to select nearly face-on galaxies. Uncertainties in disk scale heights are significant, but can be estimated from radial scale lengths to 25% now, and more precisely in the future. We detail the spectroscopic analysis used to derive line-of-sight velocity dispersions, precise at low surface-brightness, and accurate in the presence of composite stellar populations. Our methods take full advantage of large-grasp integral-field spectroscopy and an extensive library of observed stars. We show that the baryon-to-total mass fraction ({F}_bar) is not a well-defined observational quantity because it is coupled to the halo mass model. This remains true even when the disk mass is known and spatially extended rotation curves are available. In contrast, the fraction of the rotation speed supplied by the disk at 2.2 scale lengths (disk maximality) is a robust observational indicator of the baryonic disk contribution to the potential. We construct the error budget for the key quantities: dynamical disk mass surface density (Σdyn), disk stellar mass-to-light ratio (Υ^disk_{*}), and disk maximality ({F}_{*,max}^disk≡ V^disk_{*,max}/ V_c). Random and systematic errors in these quantities for individual galaxies will be ~25%, while survey precision for sample quartiles are reduced to 10%, largely devoid of systematic errors outside of distance uncertainties.

Effects of combined dimension reduction and tabulation on the simulations of a turbulent premixed flame using a large-eddy simulation/probability density function method

NASA Astrophysics Data System (ADS)

Kim, Jeonglae; Pope, Stephen B.

2014-05-01

A turbulent lean-premixed propane-air flame stabilised by a triangular cylinder as a flame-holder is simulated to assess the accuracy and computational efficiency of combined dimension reduction and tabulation of chemistry. The computational condition matches the Volvo rig experiments. For the reactive simulation, the Lagrangian Large-Eddy Simulation/Probability Density Function (LES/PDF) formulation is used. A novel two-way coupling approach between LES and PDF is applied to obtain resolved density to reduce its statistical fluctuations. Composition mixing is evaluated by the modified Interaction-by-Exchange with the Mean (IEM) model. A baseline case uses In Situ Adaptive Tabulation (ISAT) to calculate chemical reactions efficiently. Its results demonstrate good agreement with the experimental measurements in turbulence statistics, temperature, and minor species mass fractions. For dimension reduction, 11 and 16 represented species are chosen and a variant of Rate Controlled Constrained Equilibrium (RCCE) is applied in conjunction with ISAT to each case. All the quantities in the comparison are indistinguishable from the baseline results using ISAT only. The combined use of RCCE/ISAT reduces the computational time for chemical reaction by more than 50%. However, for the current turbulent premixed flame, chemical reaction takes only a minor portion of the overall computational cost, in contrast to non-premixed flame simulations using LES/PDF, presumably due to the restricted manifold of purely premixed flame in the composition space. Instead, composition mixing is the major contributor to cost reduction since the mean-drift term, which is computationally expensive, is computed for the reduced representation. Overall, a reduction of more than 15% in the computational cost is obtained.

Effect of settling particles on the stability of a particle-laden flow in a vertical plane channel

NASA Astrophysics Data System (ADS)

Boronin, S. A.; Osiptsov, A. N.

2018-03-01

The stability of a viscous particle-laden flow in a vertical plane channel in the presence of the gravity force is studied. The flow is described using a two-fluid "dusty-gas" model with negligibly small volume fraction of fines and two-way coupling of the phases. Two different profiles of the particle number density in the main flow are considered: homogeneous and non-homogeneous in the form of two layers symmetric about the channel axis. The novel element of the linear-stability problem formulation is a particle velocity slip in the main flow caused by the gravity-induced settling of the dispersed phase. The eigenvalue problem for a linearized system of governing equations is solved using the orthonormalization and QZ algorithms. For a uniform particle number density distribution, it is found that there exists a domain in the plane of Froude and Stokes numbers, in which the two-phase flow in a vertical channel is stable for an arbitrary Reynolds number. This stability domain corresponds to relatively small-inertia particles and large velocity-slip in the main flow. In contrast to the flow with a uniform particle number density distribution, the stratified dusty-gas flow in a vertical channel is unstable over a wide range of governing parameters. The instability at small Reynolds numbers is determined by the gravitational mode characterized by small wavenumbers (long-wave instability), while at larger Reynolds numbers the instability is dominated by the shear mode with the time-amplification factor larger than that of the gravitational mode. The results of the study can be used for optimization of a large number of technological processes, including those in riser reactors, pneumatic conveying in pipeline systems, hydraulic fracturing, and well cementing.

The Infrared Properties of Sources Matched in the Wise All-Sky and Herschel ATLAS Surveys

NASA Technical Reports Server (NTRS)

Bond, Nicholas A.; Benford, Dominic J.; Gardner, Jonathan P.; Amblard, Alexandre; Fleuren, Simone; Blain, Andrew W.; Dunne, Loretta; Smith, Daniel J. B.; Maddox, Steve J.; Hoyos, Carlos;

Ecological structure and function differs between habitats dominated by seagrasses and green seaweeds.

PubMed

Tuya, Fernando; Png-Gonzalez, Lydia; Riera, Rodrigo; Haroun, Ricardo; Espino, Fernando

2014-07-01

Marine vegetated habitats, e.g. seagrass meadows, deliver essential functions and services to coastal ecosystems and human welfare. Impacts induced by humans, however, have facilitated the replacement of seagrasses by alternative vegetation, e.g. green rhizophytic seaweeds. The implications of habitat shifts for ecosystem attributes and processes and the services they deliver remain poorly known. In this study, we compared ecosystem structure and function between Cymodocea nodosa seagrass meadows and bottoms dominated by Caulerpa prolifera, a green, native, rhizophytic seaweed, through 5 ecological proxies: (i) primary production (via community metabolism), (ii) composition and abundance of epifauna (a proxy for provision of habitat for epifauna), composition and abundance of (iii) small-sized (juvenile) and (iv) large-sized (adult) fishes (proxies for provision of habitat for fishes), and (v) sediment retention (a proxy for sediment stabilization). Four of these proxies were greater in C. nodosa seagrass meadows than in C. prolifera beds: gross primary productivity (∼1.4 times), the total abundance, species density and biomass of small-sized fishes (∼2.1, 1.3 and 1.3 times, respectively), the total abundance and species density of large-sized fishes (∼3.6 and 1.5 times, respectively), and sediment stabilization (∼1.4 times). In contrast, the total abundance and species density of epifauna was larger (∼3.1 and 1.7 times, respectively) in C. prolifera than in C. nodosa seagrass beds. These results suggest that ecosystem structure and function may differ if seagrasses are replaced by green rhizophytic seaweeds. Importantly, ecosystem functions may not be appropriate surrogates for one another. As a result, assessments of ecosystem services associated with ecosystem functions cannot be based on exclusively one service that is expected to benefit other services. Copyright © 2014 Elsevier Ltd. All rights reserved.

The Infrared Properties of Sources Matched in the WISE All-Sky and Herschel Atlas Surveys

NASA Technical Reports Server (NTRS)

Bond, Nicholas A.; Benford, Dominic J.; Gardner, Jonathan P.; Eisenhardt, Peter; Amblard, Alexandre; Temi, Pasquale; Fleuren, Simone; Blain, Andrew W.; Dunne, Loretta; Smith, Daniel J.;

State-of-stress in magmatic rift zones: Predicting the role of surface and subsurface topography

NASA Astrophysics Data System (ADS)

Oliva, S. J. C.; Ebinger, C.; Rivalta, E.; Williams, C. A.

2017-12-01

Continental rift zones are segmented along their length by large fault systems that form in response to extensional stresses. Volcanoes and crustal magma chambers cause fundamental changes to the density structure, load the plates, and alter the state-of-stress within the crust, which then dictates fracture orientation. In this study, we develop geodynamic models scaled to a < 7 My rift sector in the Eastern rift, East Africa where geophysical imaging provides tight constraints on subsurface structure, petrologic and thermodynamic studies constrain material densities, and seismicity and structural analyses constrain active and time-averaged kinematics. This area is an ideal test area because a 60º stress rotation is observed in time-averaged fault and magma intrusion, and in local seismicity, and because this was the site of a large volume dike intrusion and seismic sequence in 2007. We use physics-based 2D and 3D models (analytical and finite elements) constrained by data from active rift zones to quantify the effects of loading on state-of-stress. By modeling varying geometric arrangements, and density contrasts of topographic and subsurface loads, and with reasonable regional extensional forces, the resulting state-of-stress reveals the favored orientation for new intrusions. Although our models are generalized, they allow us to evaluate whether a magmatic system (surface and subsurface) can explain the observed stress rotation, and enable new intrusions, new faults, or fault reactivation with orientations oblique to the main border faults. Our results will improve our understanding of the different factors at play in these extensional regimes, as well as contribute to a better assessment of the hazards in the area.

Tvashtar's Plume during the New Horizons Flyby of the Jovian System

NASA Astrophysics Data System (ADS)

Trafton, Laurence M.; Hoey, William Andrew; Ackley, Peter; Goldstein, David B.; Varghese, Philip L.

2016-10-01

During the gravity-assist flyby of the Jovian system from 26 Feb 2007 to 3 Mar 2007, the New Horizons spacecraft obtained multiple images of Io's Pele-class plume "Tvashtar" using the panchromatic LORRI camera, including a unique "movie" sequence of 5 images taken 2 minutes apart that provide the only record of dynamical activity for an extra-terrestrial volcanic plume. Prominent plume activity included a single traveling wave traveling down the west side of the canopy and a semi-regular particulate pattern that evolved down the canopy. The spout was detected in an average of the 5 movie images and its intensity may constrain the refractory complement of the plume. Comparison with the observed plume irradiance may then constrain the condensate complement. Other features, more apparent after subtracting the mean movie image, include semi-periodic azimuthal density variation in the canopy at plausibly common flight times from the vent, implying an azimuthal component to the dust density distribution at the vent. There are features that show a few large tendrils distributed in azimuth around the canopy that extend all the way to the surface, like the canopy projection, while the rest of the canopy appears to have a large discontinuity in density at the rim, as if the canopy were suspended. Successive waves having contrasting mean wavefront density suggest a fundamental-mode temporal pulsing at the vent. The scattering phase function for the plume particulates was found to be strongly forward scattering, increasing nearly monotonically during the flyby by an order of magnitude over the solar phase angle range 57 - 150 deg. Rathbun et al. (2014; Icarus 231, 261) reported that neither the Girru nor Tvashtar surface eruptions varied dramatically over 1-2 Mar 2007; however, most of the growth we found in Tvashtar's brightness during the flyby occurred by these dates. Therefore, increasing eruption activity, rising refractory dust density, or condensation may have contributed to the brightness increase with phase angle, along with forward scattering. Any transition in the mode of eruption (e.g., lava lake to fire fountain) was continuous and gradual. [NASA grant NNX14A039G

Magnetic and gravity gradiometry framework for Mesoproterozoic iron oxide-apatite and iron oxide-copper-gold deposits, southeast Missouri, USA

USGS Publications Warehouse

McCafferty, Anne E.; Phillips, Jeffrey; Driscoll, Rhonda L.

2016-01-01

High-resolution airborne magnetic and gravity gradiometry data provide the geophysical framework for evaluating the exploration potential of hidden iron oxide deposits in Mesoproterozoic basement rocks of southeast Missouri. The data are used to calculate mineral prospectivity for iron oxide-apatite (IOA) ± rare earth element (REE) and iron oxide-copper-gold (IOCG) deposits. Results delineate the geophysical footprints of all known iron oxide deposits and reveal several previously unrecognized prospective areas. The airborne data are also inverted to three-dimensional density and magnetic susceptibility models over four concealed deposits at Pea Ridge (IOA ± REE), Boss (IOCG), Kratz Spring (IOA), and Bourbon (IOCG). The Pea Ridge susceptibility model shows a magnetic source that is vertically extensive and traceable to a depth of greater than 2 km. A smaller density source, located within the shallow Precambrian basement, is partly coincident with the magnetic source at Pea Ridge. In contrast, the Boss models show a large (625-m-wide), vertically extensive, and coincident dense and magnetic stock with shallower adjacent lobes that extend more than 2,600 m across the shallow Precambrian paleosurface. The Kratz Spring deposit appears to be a smaller volume of iron oxides and is characterized by lower density and less magnetic rock compared to the other iron deposits. A prospective area identified south of the Kratz Spring deposit shows the largest volume of coincident dense and nonmagnetic rock in the subsurface, and is interpreted as prospective for a hematite-dominant lithology that extends from the top of the Precambrian to depths exceeding 2 km. The Bourbon deposit displays a large bowl-shaped volume of coincident high density and high-magnetic susceptibility rock, and a geometry that suggests the iron mineralization is vertically restricted to the upper parts of the Precambrian basement. In order to underpin the evaluation of the prospectivity and three-dimensional models, an extensive statistical summary of density and apparent magnetic susceptibility measurements is presented that includes data on several hundred samples taken from the deposits, altered wall rocks, and unaltered country rocks.

Generating Converged Accurate Free Energy Surfaces for Chemical Reactions with a Force-Matched Semiempirical Model.

PubMed

Kroonblawd, Matthew P; Pietrucci, Fabio; Saitta, Antonino Marco; Goldman, Nir

2018-04-10

We demonstrate the capability of creating robust density functional tight binding (DFTB) models for chemical reactivity in prebiotic mixtures through force matching to short time scale quantum free energy estimates. Molecular dynamics using density functional theory (DFT) is a highly accurate approach to generate free energy surfaces for chemical reactions, but the extreme computational cost often limits the time scales and range of thermodynamic states that can feasibly be studied. In contrast, DFTB is a semiempirical quantum method that affords up to a thousandfold reduction in cost and can recover DFT-level accuracy. Here, we show that a force-matched DFTB model for aqueous glycine condensation reactions yields free energy surfaces that are consistent with experimental observations of reaction energetics. Convergence analysis reveals that multiple nanoseconds of combined trajectory are needed to reach a steady-fluctuating free energy estimate for glycine condensation. Predictive accuracy of force-matched DFTB is demonstrated by direct comparison to DFT, with the two approaches yielding surfaces with large regions that differ by only a few kcal mol -1 .

Generating Converged Accurate Free Energy Surfaces for Chemical Reactions with a Force-Matched Semiempirical Model

DOE PAGES

Kroonblawd, Matthew P.; Pietrucci, Fabio; Saitta, Antonino Marco; ...

2018-03-15

Here, we demonstrate the capability of creating robust density functional tight binding (DFTB) models for chemical reactivity in prebiotic mixtures through force matching to short time scale quantum free energy estimates. Molecular dynamics using density functional theory (DFT) is a highly accurate approach to generate free energy surfaces for chemical reactions, but the extreme computational cost often limits the time scales and range of thermodynamic states that can feasibly be studied. In contrast, DFTB is a semiempirical quantum method that affords up to a thousandfold reduction in cost and can recover DFT-level accuracy. Here, we show that a force-matched DFTBmore » model for aqueous glycine condensation reactions yields free energy surfaces that are consistent with experimental observations of reaction energetics. Convergence analysis reveals that multiple nanoseconds of combined trajectory are needed to reach a steady-fluctuating free energy estimate for glycine condensation. Predictive accuracy of force-matched DFTB is demonstrated by direct comparison to DFT, with the two approaches yielding surfaces with large regions that differ by only a few kcal mol –1.« less

Estimation of alluvial-fill thickness in the Mimbres ground-water basin, New Mexico, from interpretation of isostatic residual gravity anomalies

USGS Publications Warehouse

Heywood, Charles E.

2002-01-01

The geologic structure of the Mimbres ground-water basin in southwest New Mexico is characterized by north- and northwest-trending structural subbasins. Sedimentation of Miocene and Pliocene age has filled and obscured the boundaries of these subbasins and formed poten- tially productive aquifers of varied thickness. The location and depth of the subbasins can be esti- mated from analysis of isostatic residual gravity anomalies. Density contrasts of various basement lithologies generate complex regional gravity trends, which are convolved with the gravity signal from the Miocene and Pliocene alluvial fill. An iterative scheme was used to separate these regional gravity trends from the alluvial-fill grav- ity signal, which was inverted with estimated depth-density relations to compute the thickness of the alluvial fill at 1-kilometer spacing. The thickness estimates were constrained by explor- atory drill-hole information, interpreted seismic- refraction profiles, and location of bedrock lithol- ogy from surficial geologic mapping. The result- ing map of alluvial-fill thickness suggests large areas of thin alluvium that separate deep structural subbasins.

Generating Converged Accurate Free Energy Surfaces for Chemical Reactions with a Force-Matched Semiempirical Model

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

Kroonblawd, Matthew P.; Pietrucci, Fabio; Saitta, Antonino Marco

Here, we demonstrate the capability of creating robust density functional tight binding (DFTB) models for chemical reactivity in prebiotic mixtures through force matching to short time scale quantum free energy estimates. Molecular dynamics using density functional theory (DFT) is a highly accurate approach to generate free energy surfaces for chemical reactions, but the extreme computational cost often limits the time scales and range of thermodynamic states that can feasibly be studied. In contrast, DFTB is a semiempirical quantum method that affords up to a thousandfold reduction in cost and can recover DFT-level accuracy. Here, we show that a force-matched DFTBmore » model for aqueous glycine condensation reactions yields free energy surfaces that are consistent with experimental observations of reaction energetics. Convergence analysis reveals that multiple nanoseconds of combined trajectory are needed to reach a steady-fluctuating free energy estimate for glycine condensation. Predictive accuracy of force-matched DFTB is demonstrated by direct comparison to DFT, with the two approaches yielding surfaces with large regions that differ by only a few kcal mol –1.« less

Dendrimer Nanoscaffolds for Potential Theranostics of Prostate Cancer with a Focus on Radiochemistry

PubMed Central

Lo, Su-Tang; Kumar, Amit; Hsieh, Jer-Tsong; Sun, Xiankai

2013-01-01

Dendrimers are a class of structurally defined macromolecules featured with a central core, a low-density interior formed by repetitive branching units, and a high-density exterior terminated with surface functional groups. In contrast to their polymeric counterparts, dendrimers are nano-sized and symmetrically shaped, which can be reproducibly synthesized in a large scale with monodispersity. These unique features have made dendrimers of increasing interest for drug delivery and other biomedical applications as a nanoscaffold system. Intended to address the potential use of dendrimers for the development of theranostic agents, which combines therapeutics and diagnostics in a single entity for personalized medicine, this review focuses on the reported methodologies of using dendrimer nanoscaffolds for targeted imaging and therapy of prostate cancer. Of particular interest, relevant chemistry strategies are discussed due to their important roles in the design and synthesis of diagnostic and therapeutic dendrimer-based nanoconjugates and potential theranostic agents, targeted or non-targeted. Given the developing status of nanoscaffolded theranostics, major challenges and potential hurdles are discussed along with the examples representing current advances. PMID:23294202

Soft resonator of omnidirectional resonance for acoustic metamaterials with a negative bulk modulus

PubMed Central

Jing, Xiaodong; Meng, Yang; Sun, Xiaofeng

2015-01-01

Monopolar resonance is of fundamental importance in the acoustic field. Here, we present the realization of a monopolar resonance that goes beyond the concept of Helmholtz resonators. The balloon-like soft resonator (SR) oscillates omnidirectionally and radiates from all parts of its spherical surface, eliminating the need for a hard wall for the cavity and baffle effects. For airborne sound, such a low-modulus resonator can be made extremely lightweight. Deep subwavelength resonance is achieved when the SR is tuned by adjusting the shell thickness, benefiting from the large density contrast between the shell material and the encapsulated gas. The SR resonates with near-perfect monopole symmetry, as demonstrated by the theoretical and experimental results, which are in excellent agreement. For a lattice of SRs, a band gap occurs and blocks near-total transmission, and the effective bulk modulus exhibits a prominent negative band, while the effective mass density remains unchanged. Our study shows that the SR is suitable for building 3D acoustic metamaterials and provides a basis for constructing left-handed materials as a new means of creating a negative bulk modulus. PMID:26538085

Joint properties of a tool machining process to guarantee fluid-proof abilities

NASA Astrophysics Data System (ADS)

Bataille, C.; Deltombe, R.; Jourani, A.; Bigerelle, M.

2017-12-01

This study addressed the impact of rod surface topography in contact with reciprocating seals. Rods were tooled with and without centreless grinding. All rods tooled with centreless grinding were fluid-proof, in contrast to rods tooled without centreless grinding that either had leaks or were fluid-proof. A method was developed to analyse the machining signature, and the software Mesrug™ was used in order to discriminate roughness parameters that can be used to characterize the sealing functionality. According to this surface roughness analysis, a fluid-proof rod tooled without centreless grinding presents aperiodic large plateaus, and the relevant roughness parameter for characterizing the sealing functionality is the density of summits S DS. Increasing the density of summits counteracts leakage, which may be because motif decomposition integrates three topographical components: circularity (perpendicular long-wave roughness), longitudinal waviness, and roughness thanks to the Wolf pruning algorithm. A 3D analytical contact model was applied to analyse the contact area of each type of sample with the seal surface. This model provides a leakage probability, and the results were consistent with the interpretation of the topographical analysis.

Collective motion of squirmers in a quasi-2D geometry

NASA Astrophysics Data System (ADS)

Zöttl, Andreas; Stark, Holger

2013-03-01

Microorganisms like bacteria, algae or spermatozoa typically move in an aqueous environment where they interact via hydrodynamic flow fields. Recent experiments studied the collective motion of dense suspensions of bacteria where swarming and large-scale turbulence emerged. Moreover, spherical artificial microswimmers, so-called squirmers, have been constructed and studied in a quasi-2D geometry. Here we present a numerical study of the collective dynamics of squirmers confined in quasi-2D between two parallel walls. Because of their spherical shape the reorientation of squirmers is solely due to noise and hydrodynamic interactions via induced flow fields. This is in contrast to elongated swimmers like bacteria which locally align due to steric interactions. We study the collective motion of pushers, pullers and potential swimmers at different densities. At small densities the squirmers are oriented parallel to the walls and pairwise collisions determine the reorientation rate. In dense suspensions rotational diffusion is greatly enhanced and pushers, in particular, tend to orient perpendicular to the walls. This effects the dynamics of the emerging clusters. In very dense suspensions we observe active jamming and long-lived crystalline structures.

Large Scale Density Estimation of Blue and Fin Whales (LSD)

DTIC Science & Technology

2014-09-30

172. McDonald, MA, Hildebrand, JA, and Mesnick, S (2009). Worldwide decline in tonal frequencies of blue whale songs . Endangered Species Research 9...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Large Scale Density Estimation of Blue and Fin Whales ...estimating blue and fin whale density that is effective over large spatial scales and is designed to cope with spatial variation in animal density utilizing

Risk of large-scale evacuation based on the effectiveness of rescue strategies under different crowd densities.

PubMed

Wang, Jinghong; Lo, Siuming; Wang, Qingsong; Sun, Jinhua; Mu, Honglin

2013-08-01

Crowd density is a key factor that influences the moving characteristics of a large group of people during a large-scale evacuation. In this article, the macro features of crowd flow and subsequent rescue strategies were considered, and a series of characteristic crowd densities that affect large-scale people movement, as well as the maximum bearing density when the crowd is extremely congested, were analyzed. On the basis of characteristic crowd densities, the queuing theory was applied to simulate crowd movement. Accordingly, the moving characteristics of the crowd and the effects of typical crowd density-which is viewed as the representation of the crowd's arrival intensity in front of the evacuation passageways-on rescue strategies was studied. Furthermore, a "risk axle of crowd density" is proposed to determine the efficiency of rescue strategies in a large-scale evacuation, i.e., whether the rescue strategies are able to effectively maintain or improve evacuation efficiency. Finally, through some rational hypotheses for the value of evacuation risk, a three-dimensional distribution of the evacuation risk is established to illustrate the risk axle of crowd density. This work aims to make some macro, but original, analysis on the risk of large-scale crowd evacuation from the perspective of the efficiency of rescue strategies. © 2012 Society for Risk Analysis.

Reconnaissance of the β Pictoris system down to 1.75 AU with the L' - b and vector vortex coronagraph on VLT/NACO

NASA Astrophysics Data System (ADS)

Milli, J.; Absil, O.; Mawet, D.; Lagrange, A.-M.

2013-09-01

High contrast imaging has thoroughly combed through the limited parameter space accessible with first-generation ground-based adaptive optics instruments and the HST. Only a few objects were discovered, and many non-detections reported and statistically interpreted. The field is now in need of a technological breakthrough. We aim at opening a new parameter space with first-generation systems such as NACO at the Very Large Telescope, by providing ground-breaking inner working angle (IWA) capabilities in the L' band. This mid-infrared wavelength range is a sweet spot for high contrast coronagraphy since the planets-to-star brightness ratio is favorable, while Strehl ratio is naturally higher. An annular groove phase mask (AGPM) vector vortex coronagraph optimized for the L' band, made out of diamond subwavelength gratings has been manufactured and qualified in the lab. The AGPM enables high contrast imaging at very small IWA (here 0".09), potentially being the key to a new parameter space. Here we present the results of the installation and successful commissioning of an L'- band AGPM on VLT/NACO. During a recent science verification run, we imaged the inner regions of Beta Pictoris down to the previously unexplored projected radius of 1.75 AU with unprecedented point source sensitivity. The disk was also clearly resolved down to its inner truncation . The new NACO mode is an opportunity to introduce a more rigorous framework for deriving detection limits at very small angles, which is also relevant for SPHERE and GPI and every high contrast imaging instrument with small IWA ambitions. Indeed, classical tools assuming Gaussian statistics, perfectly valid at large separations, loose significance close to the center simply because the sample size decreases dramatically (fewer resolution elements at a given radius). Moreover, the probability density function (PDF) of speckle noise and associated confidence level for detection depend on radius. ADI was shown to transform speckles'modified Rician PDF into quasi-Gaussian PDF at large separations, but it is expected that this property of ADI does not hold true at small angles. Finally, the flux attenuation induced by ADI, potentially significant at small angles, does not scale linearly with the companion brightness, which makes its calibration more difficult.

Exchange and correlation effects on plasmon dispersions and Coulomb drag in low-density electron bilayers

NASA Astrophysics Data System (ADS)

Badalyan, S. M.; Kim, C. S.; Vignale, G.; Senatore, G.

2007-03-01

We investigate the effect of exchange and correlation (XC) on the plasmon spectrum and the Coulomb drag between spatially separated low-density two-dimensional electron layers. We adopt a different approach, which employs dynamic XC kernels in the calculation of the bilayer plasmon spectra and of the plasmon-mediated drag, and static many-body local field factors in the calculation of the particle-hole contribution to the drag. The spectrum of bilayer plasmons and the drag resistivity are calculated in a broad range of temperatures taking into account both intra- and interlayer correlation effects. We observe that both plasmon modes are strongly affected by XC corrections. After the inclusion of the complex dynamic XC kernels, a decrease of the electron density induces shifts of the plasmon branches in opposite directions. This is in stark contrast with the tendency observed within random phase approximation that both optical and acoustical plasmons move away from the boundary of the particle-hole continuum with a decrease in the electron density. We find that the introduction of XC corrections results in a significant enhancement of the transresistivity and qualitative changes in its temperature dependence. In particular, the large high-temperature plasmon peak that is present in the random phase approximation is found to disappear when the XC corrections are included. Our numerical results at low temperatures are in good agreement with the results of recent experiments by Kellogg [Solid State Commun. 123, 515 (2002)].

Textural evolution of magma during the 9.4-ka trachytic explosive eruption at Kilian Volcano, Chaîne des Puys, France

NASA Astrophysics Data System (ADS)

Colombier, M.; Gurioli, L.; Druitt, T. H.; Shea, T.; Boivin, P.; Miallier, D.; Cluzel, N.

2017-02-01

Textural parameters such as density, porosity, pore connectivity, permeability, and vesicle size distributions of vesiculated and dense pyroclasts from the 9.4-ka eruption of Kilian Volcano, were quantified to constrain conduit and eruptive processes. The eruption generated a sequence of five vertical explosions of decreasing intensity, producing pyroclastic density currents and tephra fallout. The initial and final phases of the eruption correspond to the fragmentation of a degassed plug, as suggested by the increase of dense juvenile clasts (bimodal density distributions) as well as non-juvenile clasts, resulting from the reaming of a crater. In contrast, the intermediate eruptive phases were the results of more open-conduit conditions (unimodal density distributions, decreases in dense juvenile pyroclasts, and non-juvenile clasts). Vesicles within the pyroclasts are almost fully connected; however, there are a wide range of permeabilities, especially for the dense juvenile clasts. Textural analysis of the juvenile clasts reveals two vesiculation events: (1) an early nucleation event at low decompression rates during slow magma ascent producing a population of large bubbles (>1 mm) and (2) a syn-explosive nucleation event, followed by growth and coalescence of small bubbles controlled by high decompression rates immediately prior to or during explosive fragmentation. The similarities in pyroclast textures between the Kilian explosions and those at Soufrière Hills Volcano on Montserrat, in 1997, imply that eruptive processes in the two systems were rather similar and probably common to vulcanian eruptions in general.

Exposure to cadmium and persistent organochlorine pollutants and its association with bone mineral density and markers of bone metabolism on postmenopausal women

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

Rignell-Hydbom, A., E-mail: anna.rignell-hydbom@med.lu.se; Skerfving, S.; Lundh, T.

Environmental contaminants such as cadmium and persistent organochlorine pollutants have been proposed as risk factors of osteoporosis, and women may be at an increased risk. To assess associations between exposure to cadmium and two different POPs (2,2',4,4',5,5'-hexachlorobiphenyl CB-153, 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethylene p,p'-DDE), on one hand, and bone effects, on the other, in a population-based study among postmenopausal (60-70 years) Swedish women with biobanked blood samples. The study included 908 women and was designed to have a large contrast of bone mineral densities, measured with a single photon absorptiometry technique in the non-dominant forearm. Biochemical markers related to bone metabolism were analyzed inmore » serum. Exposure assessment was based on cadmium concentrations in erythrocytes and serum concentrations of CB-153 and p,p'-DDE. Cadmium was negatively associated with bone mineral density and parathyroid hormone, positively with the marker of bone resorption. However, this association disappeared after adjustment for smoking. The major DDT metabolite (p,p'-DDE) was positively associated with bone mineral density, an association which remained after adjustment for confounders, but the effect was weak. There was no evidence that the estrogenic congener (CB-153) was associated with any of the bone markers. In conclusion, no convincing associations were observed between cadmium and POPs, on one hand, and bone metabolism markers and BMD, on the other.« less

Changes in Structure and Functioning of Protist (Testate Amoebae) Communities Due to Conversion of Lowland Rainforest into Rubber and Oil Palm Plantations

PubMed Central

Krashevska, Valentyna; Klarner, Bernhard; Widyastuti, Rahayu; Maraun, Mark; Scheu, Stefan

2016-01-01

Large areas of tropical rainforest are being converted to agricultural and plantation land uses, but little is known of biodiversity and ecological functioning under these replacement land uses. We investigated the effects of conversion of rainforest into jungle rubber, intensive rubber and oil palm plantations on testate amoebae, diverse and functionally important protists in litter and soil. Living testate amoebae species richness, density and biomass were all lower in replacement land uses than in rainforest, with the impact being more pronounced in litter than in soil. Similar abundances of species of high and low trophic level in rainforest suggest that trophic interactions are more balanced, with a high number of functionally redundant species, than in rubber and oil palm. In contrast, plantations had a low density of high trophic level species indicating losses of functions. This was particularly so in oil palm plantations. In addition, the relative density of species with siliceous shells was >50% lower in the litter layer of oil palm and rubber compared to rainforest and jungle rubber. This difference suggests that rainforest conversion changes biogenic silicon pools and increases silicon losses. Overall, the lower species richness, density and biomass in plantations than in rainforest, and the changes in the functional composition of the testate amoebae community, indicate detrimental effects of rainforest conversion on the structure and functioning of microbial food webs. PMID:27463805

[Donor supply of scalp and specificities of hair transplantation in Asians].

PubMed

Tsilosani, A Z; Mshvenieradze, E G

2008-01-01

In 2005--2007 in a hair transplantation clinic 'Talizi' the flow of international patients increased dramatically, including those from Central and Eastern Asia. During this period 211 ethnic Asian patients underwent operations, including 146 patients from South Korea, 2--from China, 62-- from Kazakhstan and 1--from Philippines. Black and straight hair give impact of low density due to considerable contrast with characteristic for Asians light color scalp; therefore, from the very beginning we tried to transplant as many grafts (follicular units - FU) as possible. For the operation we chose strip version (FUSS) that enables to receive large number of grafts. The scale of transplantation varied in a range of 1200-3800 FU, on average--2500-3000 FU. Though, even from the very first cases we faced specificities of ethnic Asian scalp that significantly complicated our work: low density and low hair/graft ratio in donor zone in contrast to information from special literature, and low laxity (flexibility) of the scalp. We set an objective to specify indicators of donor density (number of FU on a sq.cm and hair/FU ratio), to study bio-mechanical specificities of ethnic Asian scalp and develop optimal surgical tactics for these patients after the evaluation of transplantation results. Observation group was composed of 211 patients from abovementioned countries and a sub-group--50 Korean patients for medium-scale hair transplantation (2000-3000 FU) by strip version. Study of donor characteristics of these patients revealed low density--74 FU/cm2; on 1 cm2 grow only 121 hairs, whereas hair/FU ration was 1,63. Strength required to close would edges (scalp tension power) varied from 1,4 kg-f to 2,6 kg-f depending on scalp flexibility and number of transplanted grafts (strip width), and amounted on average to 2,16 +/- 0,02 kg-f, p < 0,001%. This indicator is about 1,5 times exceeding the one of ethnic Caucasian patient group (1,47 +/- 0,02 kg-f, p < 0,001%). Low donor density of our Korean patients compelled us to increase width of the obtained skin strip (sometimes to 2,5 cm) in order to get required number of grafts (FU). In case of low flexibility of the scalps this resulted in high percentage (10-15%) of wide (4-10 mm) scar formation in donor area. In order to find the way out from this situation (restrict the width of the strip to 1,5 cm without affecting FU to be transplanted in one operation), we proposed the combination of the strip version (FUSS) with FU extraction (FUE). While this solution increased the duration and price of the operation, we believe that it is the most optimal version in case of large-scale hair transplantation for the ethnic Asian patients.

Density perturbation in the models reconstructed from jerk parameter

NASA Astrophysics Data System (ADS)

Sinha, Srijita; Banerjee, Narayan

2018-06-01

The present work deals with the late time evolution of the linear density contrast in the dark energy models reconstructed from the jerk parameter. It is found that the non-interacting models are favoured compared to the models where an interaction is allowed in the dark sector.

Mechanized Symmetrical Sowing

Treesearch

Kirk D. Howell

2005-01-01

With hundreds of variables to investigate, and thousands of combinations, seldom is there found such appeal to the investigator as an organism’s response to density. Loblolly pine (Pinus taeda L.) was grown at several levels of seedbed density and sowing configurations in order to display unique contrasts between consequent morphological traits,...

Effects of Habitual Physical Activity and Fitness on Tibial Cortical Bone Mass, Structure and Mass Distribution in Pre-pubertal Boys and Girls: The Look Study.

PubMed

Duckham, Rachel L; Rantalainen, Timo; Ducher, Gaele; Hill, Briony; Telford, Richard D; Telford, Rohan M; Daly, Robin M

2016-07-01

Targeted weight-bearing activities during the pre-pubertal years can improve cortical bone mass, structure and distribution, but less is known about the influence of habitual physical activity (PA) and fitness. This study examined the effects of contrasting habitual PA and fitness levels on cortical bone density, geometry and mass distribution in pre-pubertal children. Boys (n = 241) and girls (n = 245) aged 7-9 years had a pQCT scan to measure tibial mid-shaft total, cortical and medullary area, cortical thickness, density, polar strength strain index (SSIpolar) and the mass/density distribution through the bone cortex (radial distribution divided into endo-, mid- and pericortical regions) and around the centre of mass (polar distribution). Four contrasting PA and fitness groups (inactive-unfit, inactive-fit, active-unfit, active-fit) were generated based on daily step counts (pedometer, 7-days) and fitness levels (20-m shuttle test and vertical jump) for boys and girls separately. Active-fit boys had 7.3-7.7 % greater cortical area and thickness compared to inactive-unfit boys (P < 0.05), which was largely due to a 6.4-7.8 % (P < 0.05) greater cortical mass in the posterior-lateral, medial and posterior-medial 66 % tibial regions. Cortical area was not significantly different across PA-fitness categories in girls, but active-fit girls had 6.1 % (P < 0.05) greater SSIpolar compared to inactive-fit girls, which was likely due to their 6.7 % (P < 0.05) greater total bone area. There was also a small region-specific cortical mass benefit in the posterior-medial 66 % tibia cortex in active-fit girls. Higher levels of habitual PA-fitness were associated with small regional-specific gains in 66 % tibial cortical bone mass in pre-pubertal children, particularly boys.

Esophageal abnormalities in gastroesophageal reflux disease.

PubMed

Levine, Marc S; Carucci, Laura R

2018-06-01

Fluoroscopic esophagography is a widely available, safe, and inexpensive test for detecting gastroesophageal reflux disease. In this article, we review the technique for performing a high-quality esophagram, including upright, double-contrast views of the esophagus and cardia with high-density barium; prone, single-contrast views of the esophagus with low-density barium; and evaluation of gastroesophageal reflux. We then discuss the radiographic findings associated with gastroesophageal reflux disease, including esophageal dysmotility, reflux esophagitis, peptic strictures, and Barrett's esophagus. Finally, we consider the differential diagnosis for the various radiographic findings associated with this condition. When carefully performed and interpreted, the esophagram is a useful test for evaluating gastroesophageal reflux disease and its complications.

X-ray spatial frequency heterodyne imaging of protein-based nanobubble contrast agents

PubMed Central

Rand, Danielle; Uchida, Masaki; Douglas, Trevor; Rose-Petruck, Christoph

2014-01-01

Spatial Frequency Heterodyne Imaging (SFHI) is a novel x-ray scatter imaging technique that utilizes nanoparticle contrast agents. The enhanced sensitivity of this new technique relative to traditional absorption-based x-ray radiography makes it promising for applications in biomedical and materials imaging. Although previous studies on SFHI have utilized only metal nanoparticle contrast agents, we show that nanomaterials with a much lower electron density are also suitable. We prepared protein-based “nanobubble” contrast agents that are comprised of protein cage architectures filled with gas. Results show that these nanobubbles provide contrast in SFHI comparable to that of gold nanoparticles of similar size. PMID:25321797

The phanerozoic impact cratering rate: Evidence from the farside of the Moon

USGS Publications Warehouse

McEwen, A.S.; Moore, Johnnie N.; Shoemaker, E.M.

1997-01-01

The relatively recent (< 1 b.y.) flux of asteroids and comets forming large craters on the Earth and Moon may be accurately recorded by craters with bright rays on the Moon's farside. Many previously unknown farside rayed craters are clearly distinguished in the low-phase-angle images returned by the Clementine spacecraft. Some large rayed craters on the lunar nearside are probably significantly older than 1 Ga; rays remain visible over the maria due to compositional contrasts long after soils have reached optical maturity. Most of the farside crust has a more homogeneous composition and only immature rays are visible. The size-frequency distribution of farside rayed craters is similar to that measured for Eratosthenian craters (up to 3.2 b.y.) at diameters larger than 15 km. The areal density of farside rayed craters matches that of a corrected tabulation of nearside Copernican craters. Hence the presence of bright rays due to immature soils around large craters provides a consistent time-stratigraphic basis for defining the base of the Copernican System. The density of large craters less than ???3.2 b.y. old is ???3.2 times higher than that of large farside rayed craters alone. This observation can be interpreted in two ways: (1) the average cratering rate has been constant over the past 3.2 b.y. and the base of the Copernican is ???1 Ga, or (2) the cratering rate has increased in recent geologic time and the base of the Copernican is less than 1 Ga. We favor the latter interpretation because the rays of Copernicus (800-850 m.y. old) appear to be very close to optical maturity, suggesting that the average Copernican cratering rate was ???35% higher than the average Eratosthenian rate. Other lines of evidence for an increase in the Phanerozoic (545 Ga) cratering rate are (1) the densities of small craters superimposed on Copernicus and Apollo landing sites, (2) the rates estimated from well-dated terrestrial craters (??? 120 m.y.) and from present-day astronomical observations, and (3) the Proterozoic rate suggested by the crater record of Australia. The hypothesis most consistent with several key observations is that the cratering rate has increased by ???2x during the past ???300 m.y. Copyright 1997 by the American Geophysical Union.

Spectroscopic Measurement Techniques for Aerospace Flows

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Bathel, Brett F.; Johansen, Craig T.; Cutler, Andrew D.; Hurley, Samantha

2014-01-01

The conditions that characterize aerospace flows are so varied, that a single diagnostic technique is not sufficient for its measurement. Fluid dynamists use knowledge of similarity to help categorize and focus on different flow conditions. For example, the Reynolds number represents the ratio of inertial to viscous forces in a flow. When the velocity scales, length scales, and gas density are large and the magnitude of the molecular viscosity is low, the Reynolds number becomes large. This corresponds to large scale vehicles (e.g Airbus A380), fast moving objects (e.g. artillery projectiles), vehicles in dense fluids (e.g. submarine in water), or flows with low dynamic viscosity (e.g. skydiver in air). In each of these cases, the inertial forces dominate viscous forces, and unsteady turbulent fluctuations in the flow variables are observed. In contrast, flows with small length scales (e.g. dispersion of micro-particles in a solid rocket nozzle), slow moving objects (e.g. micro aerial vehicles), flows with low density gases (e.g. atmospheric re-entry), or fluids with a large magnitude of viscosity (e.g. engine coolant flow), all have low Reynolds numbers. In these cases, viscous forces become very important and often the flows can be steady and laminar. The Mach number, which is the ratio of the velocity to the speed of sound in the medium, also helps to differentiate types of flows. At very low Mach numbers, acoustic waves travel much faster than the object, and the flow can be assumed to be incompressible (e.g. Cessna 172 aircraft). As the object speed approaches the speed of sound, the gas density can become variable (e.g. flow over wing of Learjet 85). When the object speed is higher than the speed of sound (Ma > 1), the presences of shock waves and other gas dynamic features can become important to the vehicle performance (e.g. SR-71 Blackbird). In the hypersonic flow regime (Ma > 5), large changes in temperature begin to affect flow properties, causing real-gas effects to occur (e.g. X-43 Scramjet). At even higher Mach numbers, chemistry and nonequilibrium effects come into play (e.g. Startdust re-entry capsule), further complicating the measurement. These limits can be predicted by calculating the ratio of chemical and thermal relaxation time to the flow time scales. Other non-dimensional numbers can be used to further differentiate types of aerospace flows.

Large Scale Density Estimation of Blue and Fin Whales: Utilizing Sparse Array Data to Develop and Implement a New Method for Estimating Blue and Fin Whale Density

DTIC Science & Technology

2015-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Large Scale Density Estimation of Blue and Fin Whales ...Utilizing Sparse Array Data to Develop and Implement a New Method for Estimating Blue and Fin Whale Density Len Thomas & Danielle Harris Centre...to develop and implement a new method for estimating blue and fin whale density that is effective over large spatial scales and is designed to cope

Segregation of large granules from close-packed cluster of small granules due to buoyancy.

PubMed

Yang, Xian-qing; Zhou, Kun; Qiu, Kang; Zhao, Yue-min

2006-03-01

Segregation of large granules in a vibrofluidized granular bed with inhomogeneous granular number density distribution is studied by an event-driven algorithm. Simulation results show that the mean vertical position of large granules decreases with the increase of the density ration of the large granules to the small ones. This conclusion is consistent with the explanation that the net pressure due to the small surrounding particle impacts balances the large granular weight, and indict that the upward movement of the large granules is driven by the buoyancy. The values of temperature, density, and pressure of the systems are also computed by changing the conditions such as heating temperature on the bottom and restitution coefficient of particles. These results indicate that the segregation of large granules also happen in the systems with density inversion or even close-packed cluster of particles floating on a low-density fluid, due to the buoyancy. An equation of state is proposed to explain the buoyancy.

T1 and susceptibility contrast at high fields

NASA Astrophysics Data System (ADS)

Neelavalli, Jaladhar

Clinical imaging at high magnetic field strengths (≥ 3Tesla) is sought after primarily due to the increased signal strength available at these fields. This increased SNR can be used to perform: (a) high resolution imaging in the same time as at lower field strengths; (b) the same resolution imaging with much faster acquisition; and (c) functional MR imaging (fMRI), dynamic perfusion and diffusion imaging with increased sensitivity. However they are also associated with increased power deposition (SAR) due to increase in imaging frequency and longer T1 relaxation times. Longer T1s mean longer imaging times for generating good T1 contrast images. On the other hand for faster imaging, at high fields fast spin echo or magnetization prepared sequences are conventionally proposed which are, however, associated with high SAR values. Imaging with low SAR is more and more important as we move towards high fields and particularly for patients with metallic implants like pacemakers or deep brain stimulator. The SAR limit acceptable for these patients is much less than the limit acceptable for normal subjects. A new method is proposed for imaging at high fields with good contrast with simultaneous reduction in power deposition. Further, T1 based contrast optimization problem in FLASH imaging is considered for tissues with different T1s but same spin densities. The solution providing optimal imaging parameters is simplified for quick and easy computation in a clinical setting. The efficacy of the simplification is evaluated and practical limits under which the simplification can be applied are worked out. The phase difference due to variation in magnetic susceptibility property among biological tissues is another unique source of contrast which is different from the conventional T1, T2 and T2* contrast. This susceptibility based phase contrast has become more and more important at high fields, partly due to contrast generation issues due to longer T 1s and shorter T2s and partly because of the invariance of most tissue susceptibilities with field strength. This essentially ensures a constant available phase contrast between tissues across field strengths. In fact, with the increased SNR at high fields, the phase CNR actually increases with field strength which is even better. Susceptibility weighted imaging, which uniquely combines this phase and magnitude information to generate enhanced susceptibility contrast magnitude images, has proven to be an important tool in the study of various neurological conditions like, Alzheimer's, Parkinson's, Huntington's disease and multiple sclerosis even at conventional field strength of 1.5T and should have more applicability at high fields. A major issue in using phase images for susceptibility contrast, directly or as processed SWI magnitude images, is the large scale background phase variations that obscure the local susceptibility based contrast. A novel method is proposed for removing such geometrically induced large scale phase variations using a Fourier Transform based field calculation method. It is shown that the new method is capable of successfully removing the background field effects. It is shown that the new method is not only capable of successfully removing the background field effects but also helps in preserving more local phase information.

Contrasting Effects of Vocabulary Knowledge on Temporal and Parietal Brain Structure across Lifespan

ERIC Educational Resources Information Center

Richardson, Fiona M.; Thomas, Michael S. C.; Filippi, Roberto; Harth, Helen; Price, Cathy J.

2010-01-01

Using behavioral, structural, and functional imaging techniques, we demonstrate contrasting effects of vocabulary knowledge on temporal and parietal brain structure in 47 healthy volunteers who ranged in age from 7 to 73 years. In the left posterior supramarginal gyrus, vocabulary knowledge was positively correlated with gray matter density in…

Adaptive typography for dynamic mapping environments

NASA Astrophysics Data System (ADS)

Bardon, Didier

1991-08-01

When typography moves across a map, it passes over areas of different colors, densities, and textures. In such a dynamic environment, the aspect of typography must be constantly adapted to provide disernibility for every new background. Adaptive typography undergoes two adaptive operations: background control and contrast control. The background control prevents the features of the map (edges, lines, abrupt changes of densities) from destroying the integrity of the letterform. This is achieved by smoothing the features of the map in the area where a text label is displayed. The modified area is limited to the space covered by the characters of the label. Dispositions are taken to insure that the smoothing operation does not introduce any new visual noise. The contrast control assures that there are sufficient lightness differences between the typography and its ever-changing background. For every new situation, background color and foreground color are compared and the foreground color lightness is adjusted according to a chosen contrast value. Criteria and methods of choosing the appropriate contrast value are presented as well as the experiments that led to them.

X-ray clusters in a cold dark matter + lambda universe: A direct, large-scale, high-resolution, hydrodynamic simulation

NASA Technical Reports Server (NTRS)

Cen, Renyue; Ostriker, Jeremiah P.

1994-01-01

A new, three-dimensional, shock-capturing, hydrodynamic code is utilized to determine the distribution of hot gas in a cold dark matter (CDM) + lambda model universe. Periodic boundary conditions are assumed: a box with size 85/h Mpc, having cell size 0.31/h Mpc, is followed in a simulation with 270(exp 3) = 10(exp 7.3) cells. We adopt omega = 0.45, lambda = 0.55, h identically equal to H/100 km/s/Mpc = 0.6, and then, from the cosmic background explorer (COBE) and light element nucleosynthesis, sigma(sub 8) = 0.77, omega(sub b) = 0.043. We identify the X-ray emitting clusters in the simulation box, compute the luminosity function at several wavelength bands, the temperature function and estimated sizes, as well as the evolution of these quantities with redshift. This open model succeeds in matching local observations of clusters in contrast to the standard omega = 1, CDM model, which fails. It predicts an order of magnitude decline in the number density of bright (h nu = 2-10 keV) clusters from z = 0 to z = 2 in contrast to a slight increase in the number density for standard omega = 1, CDM model. This COBE-normalized CDM + lambda model produces approximately the same number of X-ray clusters having L(sub x) greater than 10(exp 43) erg/s as observed. The background radiation field at 1 keV due to clusters is approximately the observed background which, after correction for numerical effects, again indicates that the model is consistent with observations.

The role of North African rivers in driving Mediterranean-Atlantic exchange

NASA Astrophysics Data System (ADS)

Flecker, Rachel; Marzocchi, Alice; van der Schee, Marlies; Meijer, Paul; Lofi, Johanna; Lunt, Dan

2014-05-01

The main driver for exchange through the Gibraltar Strait today is the density contrast between Mediterranean and Atlantic water. Mediterranean water is more saline than Atlantic water because the amount of water the Mediterranean loses through evaporation exceeds both precipitation and freshwater input from rivers. This means it has a negative hydrologic budget. In the Late Miocene however, a very large river known as the Esohabi River drained across North Africa and had its mouth in the Gulf of Sirt. This river was sourced in palaeo-Lake Chad and was strongly influenced by precession-driven monsoonal rainfall. Multiple General Circulation Model simulations through a single precessional cycle indicate that river water may only have reached the Mediterranean in significant quantities in summer during particular orbital configurations e.g. precession minima combined with eccentricity maxima. However, during high amplitude eccentricity maxima, the volume of water supplied through the Esohabi and Nile rivers may have been sufficient to switch the hydrologic budget from negative to positive. In doing so, the fresh water supply should have reduced the salinity of the Mediterranean and consequently the density contrast with adjacent Atlantic water leading to a reduction in exchange. In this presentation we explore the evidence for the timing and nature of freshwater input to the Mediterranean from North Africa. We also consider how relevant this freshwater flux may be in determining some of the major environmental and sedimentological changes in the Late Miocene to early Pliocene including some of the salinity changes that occurred during the Messinian Salinity Crisis.

New magnetic phase and magnetic coherence in Nd/Sm(001) superlattices

NASA Astrophysics Data System (ADS)

Soriano, S.; Dufour, C.; Dumesnil, K.; Stunault, A.

2006-06-01

In order to investigate magnetic phenomena in Nd and Sm layers separately, resonant x-ray magnetic scattering experiments have been performed to study Nd/Sm(001) superlattices with different relative layers thickness. The samples were grown using molecular beam epitaxy, and optimized to yield dhcp Sm growth and thus a coherent dhcp stacking across the Nd/Sm superlattices. The magnetic phases in Sm layers are very close to the ones evidenced in dhcp thick films. In contrast, the magnetism in Nd layers shows strong differences with the bulk case. In superlattices with a large Sm thickness (>8 nm), no magnetic scattering usually associated with Nd magnetic structure was detected. In superlattices with smaller Sm thickness (<4 nm), new Nd magnetic phases have been observed. A detailed analysis of the propagation of the magnetic structures in the cubic and hexagonal sublattices of both Sm and Nd is presented. Both Sm hexagonal and cubic magnetic phases propagate coherently through 3.7 nm thick Nd layers but remain confined in Sm layers when the Nd layers are 7.1 nm thick. In contrast, the critical Sm thickness allowing a coherent propagation of Nd magnetic order is different for the hexagonal and cubic sublattices above 5 K. Finally, we show that: (i) a spin-density wave and a 4f magnetic order with perpendicular polarization are exclusive on a given crystallographic site (either hexagonal or cubic); (ii) a 4f magnetic order on a crystallographic site does not perturb the establishment of a spin-density wave with a perpendicular polarization on the other site.

Advances in equine computed tomography and use of contrast media.

PubMed

Puchalski, Sarah M

2012-12-01

Advances in equine computed tomography have been made as a result of improvements in software and hardware and an increasing body of knowledge. Contrast media can be administered intravascularly or intrathecally. Contrast media is useful to differentiate between tissues of similar density. Equine computed tomography can be used for many different clinical conditions, including lameness diagnosis, fracture identification and characterization, preoperative planning, and characterization of skull diseases. Copyright © 2012 Elsevier Inc. All rights reserved.

Stabilization of a finite slice in miscible displacement in homogeneous porous media

NASA Astrophysics Data System (ADS)

Pramanik, Satyajit; Mishra, Manoranjan

2016-11-01

We numerically studied the miscible displacement of a finite slice of variable viscosity and density. The stability of the finite slice depends on different flow parameters, such as displacement velocity U, mobility ratio R , and the density contrast. Series of numerical simulations corresponding to different ordered pair (R, U) in the parameter space, and a given density contrast reveal six different instability regions. We have shown that independent of the width of the slice, there always exists a region of stable displacement, and below a critical value of the slice width, this stable region increases with decreasing slice width. Further we observe that the viscous fingering (buoyancy-induced instability) at the upper interface induces buoyancy-induced instability (viscous fingering) at the lower interface. Besides the fundamental fluid dynamics understanding, our results can be helpful to model CO2 sequestration and chromatographic separation.

Migration in the shearing sheet and estimates for young open cluster migration

NASA Astrophysics Data System (ADS)

Quillen, Alice C.; Nolting, Eric; Minchev, Ivan; De Silva, Gayandhi; Chiappini, Cristina

2018-04-01

Using tracer particles embedded in self-gravitating shearing sheet N-body simulations, we investigate the distance in guiding centre radius that stars or star clusters can migrate in a few orbital periods. The standard deviations of guiding centre distributions and maximum migration distances depend on the Toomre or critical wavelength and the contrast in mass surface density caused by spiral structure. Comparison between our simulations and estimated guiding radii for a few young supersolar metallicity open clusters, including NGC 6583, suggests that the contrast in mass surface density in the solar neighbourhood has standard deviation (in the surface density distribution) divided by mean of about 1/4 and larger than measured using COBE data by Drimmel and Spergel. Our estimate is consistent with a standard deviation of ˜0.07 dex in the metallicities measured from high-quality spectroscopic data for 38 young open clusters (<1 Gyr) with mean galactocentric radius 7-9 kpc.

Imported fire ants near the edge of their range: disturbance and moisture determine prevalence and impact of an invasive social insect.

PubMed

LeBrun, Edward G; Plowes, Robert M; Gilbert, Lawrence E

2012-07-01

1. Habitat disturbance and species invasions interact in natural systems, making it difficult to isolate the primary cause of ecosystem degradation. A general understanding requires case studies of how disturbance and invasion interact across a variety of ecosystem - invasive species combinations. 2. Dramatic losses in ant diversity followed the invasion of central Texas by red imported fire ants (Solenopsis invicta). However, recent manipulative studies in Florida revealed no effect on ant diversity following the removal of S. invicta from a disturbed pasture habitat, but moderate loss of diversity associated with their introduction into undisturbed habitat and no invasion occurred without disturbance. Thus, the importance of S. invicta in driving diversity loss and its ability to invade undisturbed systems is unresolved. 3. We examine the distribution and abundance of a large monogyne S. invicta population and its association with the co-occurring ant assemblage at a site in south Texas close to the aridity tolerance limit of S. invicta. 4. We document that moisture modulates S. invicta densities. Further, soil disturbing habitat manipulations greatly increase S. invicta population densities. However, S. invicta penetrates all habitats regardless of soil disturbance history. In contrast, controlled burns depress S. invicta densities. 5. In habitats where S. invicta is prevalent, it completely replaces native fire ants. However, S. invicta impacts native ants as a whole less strongly. Intriguingly, native ants responded distinctly to S. invicta in different environments. In wet, undisturbed environments, high S. invicta abundance disrupts the spatial structure of the ant assemblage by increasing clumping and is associated with reduced species density, while in dry-disturbed habitats, sites with high S. invicta abundance possess high numbers of native species. Analyses of co-occurrence indicate that reduced species density in wet-undisturbed sites arises from negative species interactions between native ants and S. invicta. However, these same data suggest that the high native species density of abundant S. invicta sites in dry-disturbed environments does not result from facilitation. 6. Monogyne S. invicta populations play different roles in different environments, driving ant diversity loss in some, but being largely symptomatic of habitat disturbance in others. © 2012 The Authors. Journal of Animal Ecology © 2012 British Ecological Society.

Forward and inverse functional variations in rotationally inelastic scattering

NASA Astrophysics Data System (ADS)

Guzman, Robert; Rabitz, Herschel

1986-09-01

This paper considers the response of various rotational energy transfer processes to functional variations about an assumed model intermolecular potential. Attention is focused on the scattering of an atom and a linear rigid rotor. The collision dynamics are approximated by employing both the infinite order sudden (IOS) and exponential distorted wave (EDW) methods to describe Ar-N2 and He-H2, respectively. The following cross sections are considered: state-to-state differential and integral, final state summed differential and integral, and effective diffusion and viscosity cross sections. Attention is first given to the forward sensitivity densities δ0/δV(R,r) where 0 denotes any of the aforementioned cross sections, R is the intermolecular distance, and r is the internal coordinates. These forward sensitivity densities (functional derivatives) offer a quantitative measure of the importance of different regions of the potential surface to a chosen cross section. Via knowledge of the forward sensitivities and a particular variation δV(R,r) the concomitant response δ0 is generated. It was found that locally a variation in the potential can give rise to a large response in the cross sections as measured by these forward densities. In contrast, a unit percent change in the overall potential produced a 1%-10% change in the cross sections studied indicating that the large + and - responses to local variations tend to cancel. In addition, inverse sensitivity densities δV(R,r)/δ0 are obtained. These inverse densities are of interest since they are the exact solution to the infinitesimal inverse scattering problem. Although the inverse sensitivity densities do not in themselves form an inversion algorithm, they do offer a quantitative measure of the importance of performing particular measurements for the ultimate purpose of inversion. Using a set of state-to-state integral cross sections we found that the resultant responses from the infinitesimal inversion were typically small such that ‖δV(R,r)‖≪‖V(R,r)‖. From the viewpoint of an actual inversion, these results indicate that only through an extensive effort will significant knowledge of the potential be gained from the cross sections. All of these calculations serve to illustrate the methodology, and other observables as well as dynamical schemes could be explored as desired.

Selective PEGylation of Parylene-C/SiO2 Substrates for Improved Astrocyte Cell Patterning.

PubMed

Raos, B J; Doyle, C S; Simpson, M C; Graham, E S; Unsworth, C P

2018-02-09

Controlling the spatial distribution of glia and neurons in in vitro culture offers the opportunity to study how cellular interactions contribute to large scale network behaviour. A recently developed approach to cell-patterning uses differential adsorption of animal-serum protein on parylene-C and SiO 2 surfaces to enable patterning of neurons and glia. Serum, however, is typically poorly defined and generates reproducibility challenges. Alternative activation methods are highly desirable to enable patterning without relying on animal serum. We take advantage of the innate contrasting surface chemistries of parylene-C and SiO 2 to enable selective bonding of polyethylene glycol SiO 2 surfaces, i.e. PEGylation, rendering them almost completely repulsive to cell adhesion. As the reagents used in the PEGylation protocol are chemically defined, the reproducibility and batch-to-batch variability complications associated with the used of animal serum are avoided. We report that PEGylated parylene-C/SiO 2 substrates achieve a contrast in astrocyte density of 65:1 whereas the standard serum-immersion protocol results in a contrast of 5.6:1. Furthermore, single-cell isolation was significantly improved on PEGylated substrates when astrocytes were grown on close-proximity parylene-C nodes, whereas isolation was limited on serum-activated substrates due tolerance for cell adhesion on serum-adsorbed SiO 2 surfaces.

Empirical gradient threshold technique for automated segmentation across image modalities and cell lines.

PubMed

Chalfoun, J; Majurski, M; Peskin, A; Breen, C; Bajcsy, P; Brady, M

2015-10-01

New microscopy technologies are enabling image acquisition of terabyte-sized data sets consisting of hundreds of thousands of images. In order to retrieve and analyze the biological information in these large data sets, segmentation is needed to detect the regions containing cells or cell colonies. Our work with hundreds of large images (each 21,000×21,000 pixels) requires a segmentation method that: (1) yields high segmentation accuracy, (2) is applicable to multiple cell lines with various densities of cells and cell colonies, and several imaging modalities, (3) can process large data sets in a timely manner, (4) has a low memory footprint and (5) has a small number of user-set parameters that do not require adjustment during the segmentation of large image sets. None of the currently available segmentation methods meet all these requirements. Segmentation based on image gradient thresholding is fast and has a low memory footprint. However, existing techniques that automate the selection of the gradient image threshold do not work across image modalities, multiple cell lines, and a wide range of foreground/background densities (requirement 2) and all failed the requirement for robust parameters that do not require re-adjustment with time (requirement 5). We present a novel and empirically derived image gradient threshold selection method for separating foreground and background pixels in an image that meets all the requirements listed above. We quantify the difference between our approach and existing ones in terms of accuracy, execution speed, memory usage and number of adjustable parameters on a reference data set. This reference data set consists of 501 validation images with manually determined segmentations and image sizes ranging from 0.36 Megapixels to 850 Megapixels. It includes four different cell lines and two image modalities: phase contrast and fluorescent. Our new technique, called Empirical Gradient Threshold (EGT), is derived from this reference data set with a 10-fold cross-validation method. EGT segments cells or colonies with resulting Dice accuracy index measurements above 0.92 for all cross-validation data sets. EGT results has also been visually verified on a much larger data set that includes bright field and Differential Interference Contrast (DIC) images, 16 cell lines and 61 time-sequence data sets, for a total of 17,479 images. This method is implemented as an open-source plugin to ImageJ as well as a standalone executable that can be downloaded from the following link: https://isg.nist.gov/. © 2015 The Authors Journal of Microscopy © 2015 Royal Microscopical Society.

A robust generalized fuzzy operator approach to film contrast correction in digital subtraction radiography.

PubMed

Leung, Chung-Chu

2006-03-01

Digital subtraction radiography requires close matching of the contrast in each pair of X-ray images to be subtracted. Previous studies have shown that nonparametric contrast/brightness correction methods using the cumulative density function (CDF) and its improvements, which are based on gray-level transformation associated with the pixel histogram, perform well in uniform contrast/brightness difference conditions. However, for radiographs with nonuniform contrast/ brightness, the CDF produces unsatisfactory results. In this paper, we propose a new approach in contrast correction based on the generalized fuzzy operator with least square method. The result shows that 50% of the contrast/brightness errors can be corrected using this approach when the contrast/brightness difference between a radiographic pair is 10 U. A comparison of our approach with that of CDF is presented, and this modified GFO method produces better contrast normalization results than the CDF approach.

Field and Experimental Constraints on the Dynamics of Replenished Silicic Magma Chambers

NASA Astrophysics Data System (ADS)

Bain, A. A.; Jellinek, M.

2008-12-01

The underlying causes of catastrophic caldera-forming volcanic eruptions remain poorly understood. However, the occurrence of magma mixing within bimodal systems has become increasingly linked with such eruptions. In particular, buoyancy effects related to unstable density contrasts arising as a result of silicic- basaltic magma interactions may play an important role in the growth, differentiation and catastrophic eruption of silicic magma chambers. Evidence of such magmatic interactions can be found in layered intrusions from the Coastal Maine Magmatic Province (USA), where well-exposed cross-sections reveal hundreds of laterally-extensive basaltic sheets, apparently injected as intrusive lava flows onto the growing floors of silicic magma chambers. Interfaces between mafic and silicic layers are commonly sharply defined and exhibit deformation parallel to the inferred direction of palaeo-gravity. Our field observations suggest that the cooling, settling and buckling of gravitationally-unstable mafic replenishments may have driven large-scale (basalt layer depth) and small- scale (crystal diameter) upwelling and/or overturning of underlying buoyant silicic cumulate material. In order to characterize the full range of buoyancy effects, we carried out extensive spectral analysis of high- resolution digital field measurements from the Pleasant Bay and Mount Desert Island intrusions. In many cases, Rayleigh-Taylor theory and the longest measured wavelength of deformation indicate that a large and potentially-quantifiable fraction of the original, pre-replenishment silicic cumulate thickness may be missing, implying that vertical mass transfer has occurred. In addition, the shortest wavelengths of deformation are generally consistent with observed length-scales of crystals and clumps of crystals at these localities. With the aim of understanding the initial conditions that gave rise to these field observations, we conduct a series of laboratory experiments in which we observe the development of a Rayleigh-Taylor instability between a buoyant basal fluid layer overlain by a denser fluid layer. In order to identify the important parameters in the problem, we perform these experiments for a wide range of density contrasts, layer thicknesses and fluid rheologies (i.e. we vary particle concentration from the dilute to highly-crystalline limits to simulate freezing basalt and re-heated silicic cumulate rheologies). Regimes in which the entire silicic layer becomes unstable are potentially responsible for overturning the system and iniating large volcanic eruptions.

Judder-Induced Edge Flicker at Zero Spatial Contrast

NASA Technical Reports Server (NTRS)

Larimer, James; Feng, Christine; Gille, Jennifer; Cheung, Victor

2004-01-01

Judder is a motion artifact that degrades the quality of video imagery. Smooth motion appears jerky and can appear to flicker along the leading and trailing edge of the moving object. In a previous paper, we demonstrated that the strength of the edge flicker signal depended upon the brightness of the scene and the contrast of the moving object relative to the background. Reducing the contrast between foreground and background reduced the flicker signal. In this report, we show that the contrast signal required for judder-induced edge flicker is due to temporal contrast and not simply to spatial contrast. Bars made of random dots of the same dot density as the background exhibit edge flicker when moved at sufficient rate.

Interactions between terrestrial mammals and the fruits of two neotropical rainforest tree species

NASA Astrophysics Data System (ADS)

Camargo-Sanabria, Angela A.; Mendoza, Eduardo

2016-05-01

Mammalian frugivory is a distinctive biotic interaction of tropical forests; however, most efforts in the Neotropics have focused on cases of animals foraging in the forest canopy, in particular primates and bats. In contrast much less is known about this interaction when it involves fruits deposited on the forest floor and terrestrial mammals. We conducted a camera-trapping survey to analyze the characteristics of the mammalian ensembles visiting fruits of Licania platypus and Pouteria sapota deposited on the forest floor in a well preserved tropical rainforest of Mexico. Both tree species produce large fruits but contrast in their population densities and fruit chemical composition. In particular, we expected that more species of terrestrial mammals would consume P. sapota fruits due to its higher pulp:seed ratio, lower availability and greater carbohydrate content. We monitored fruits at the base of 13 trees (P. sapota, n = 4 and L. platypus, n = 9) using camera-traps. We recorded 13 mammal species from which we had evidence of 8 consuming or removing fruits. These eight species accounted for 70% of the species of mammalian frugivores active in the forest floor of our study area. The ensemble of frugivores associated with L. platypus (6 spp.) was a subset of that associated with P. sapota (8 spp). Large body-sized species such as Tapirus bairdii, Pecari tajacu and Cuniculus paca were the mammals more frequently interacting with fruits of the focal species. Our results further our understanding of the characteristics of the interaction between terrestrial mammalian frugivores and large-sized fruits, helping to gain a more balanced view of its importance across different tropical forests and providing a baseline to compare against defaunated forests.

Searching for filaments and large-scale structure around DAFT/FADA clusters

NASA Astrophysics Data System (ADS)

Durret, F.; Márquez, I.; Acebrón, A.; Adami, C.; Cabrera-Lavers, A.; Capelato, H.; Martinet, N.; Sarron, F.; Ulmer, M. P.

2016-04-01

Context. Clusters of galaxies are located at the intersection of cosmic filaments and are still accreting galaxies and groups along these preferential directions. However, because of their relatively low contrast on the sky, filaments are difficult to detect (unless a large amount of spectroscopic data are available), and unambiguous detections have been limited until now to relatively low redshifts (z< ~ 0.3). Aims: This project is aimed at searching for extensions and filaments around clusters, traced by galaxies selected to be at the cluster redshift based on the red sequence. In the 0.4

Combined Dynamic Contrast Enhanced Liver MRI and MRA Using Interleaved Variable Density Sampling

PubMed Central

Rahimi, Mahdi Salmani; Korosec, Frank R.; Wang, Kang; Holmes, James H.; Motosugi, Utaroh; Bannas, Peter; Reeder, Scott B.

2014-01-01

Purpose To develop and evaluate a method for volumetric contrast-enhanced MR imaging of the liver, with high spatial and temporal resolutions, for combined dynamic imaging and MR angiography using a single injection of contrast. Methods An interleaved variable density (IVD) undersampling pattern was implemented in combination with a real-time-triggered, time-resolved, dual-echo 3D spoiled gradient echo sequence. Parallel imaging autocalibration lines were acquired only once during the first time-frame. Imaging was performed in ten subjects with focal nodular hyperplasia (FNH) and compared with their clinical MRI. The angiographic phase of the proposed method was compared to a dedicated MR angiogram acquired during a second injection of contrast. Results A total of 21 FNH, 3 cavernous hemangiomas, and 109 arterial segments were visualized in 10 subjects. The temporally-resolved images depicted the characteristic arterial enhancement pattern of the lesions with a 4 s update rate. Images were graded as having significantly higher quality compared to the clinical MRI. Angiograms produced from the IVD method provided non-inferior diagnostic assessment compared to the dedicated MRA. Conclusion Using an undersampled IVD imaging method, we have demonstrated the feasibility of obtaining high spatial and temporal resolution dynamic contrast-enhanced imaging and simultaneous MRA of the liver. PMID:24639130

Exploiting Optical Contrasts for Cervical Precancer Diagnosis via Diffuse Reflectance Spectroscopy

NASA Astrophysics Data System (ADS)

Chang, Vivide Tuan-Chyan

Among women worldwide, cervical cancer is the third most common cancer with an incidence rate of 15.3 per 100,000 and a mortality rate of 7.8 per 100,000 women. This is largely attributed to the lack of infrastructure and resources in the developing countries to support the organized screening and diagnostic programs that are available to women in developed nations. Hence, there is a critical global need for a screening and diagnostic paradigm that is effective in low-resource settings. Various strategies are described to design an optical spectroscopic sensor capable of collecting reliable diffuse reflectance data to extract quantitative optical contrasts for cervical cancer screening and diagnosis. A scalable Monte Carlo based optical toolbox can be used to extract absorption and scattering contrasts from diffuse reflectance acquired in the cervix in vivo. [Total Hb] was shown to increase significantly in high-grade cervical intraepithelial neoplasia (CIN 2+), clinically the most important tissue grade to identify, compared to normal and low-grade intraepithelial neoplasia (CIN 1). Scattering was not significantly decreased in CIN 2+ versus normal and CIN 1, but was significantly decreased in CIN relative to normal cervical tissues. Immunohistochemistry via anti-CD34, which stains the endothelial cells that line blood vessels, was used to validate the observed absorption contrast. The concomitant increase in microvessel density and [total Hb] suggests that both are reactive to angiogenic forces from up-regulated expression of VEGF in CIN 2+. Masson's trichrome stain was used to assess collagen density changes associated with dysplastic transformation of the cervix, hypothesized as the dominant source of decreased scattering observed. Due to mismatch in optical and histological sampling, as well as the small sample size, collagen density and scattering did not change in a similar fashion with tissue grade. Dysplasia may also induce changes in cross-linking of collagen without altering the amount of collagen present. Further work would be required to elucidate the exact sources of scattering contrast observed. Common confounding variables that limit the accuracy and clinical acceptability of optical spectroscopic systems are calibration requirements and variable probe-tissue contact pressures. Our results suggest that using a real-time self-calibration channel, as opposed to conventional post-experiment diffuse reflectance standard calibration measurements, significantly improved data integrity for the extraction of scattering contrast. Extracted [total Hb] and scattering were also significantly associated with applied contact probe pressure in colposcopically normal sites. Hence, future contact probe spectroscopy or imaging systems should incorporate a self-calibration channel and ensure spectral acquisition at a consistent contact pressure to collect reliable data with enhanced absorption and scattering contrasts. Another method to enhance optical contrast is to selectively interrogate different depths in the dysplastic cervix. For instance, scattering has been shown to increase in the epithelium (increase in nuclear-to-cytoplasmic ratio) while decrease in the stroma (re-organization of the extra-cellular matrix and changes in of collagen fiber cross-links). A fiber-optic probe with 45° illumination and collection fibers with a separation distance of 330 μm was designed and constructed to selectively interrogate the cervical epithelium. Mean extraction errors from liquid phantoms with optical properties mimicking the cervical epithelium for μa and μs' were 11.3 % and 12.7 %, respectively. Diffuse reflectance spectra from 9 sites in four loop electrosurgical excision procedure (LEEP) patients were analyzed. Preliminary data demonstrate the utility of the oblique fiber geometry in extracting scattering contrast in the cervical epithelium. Further work is needed to study the systematic error in optical property extraction and to incorporate simultaneous extraction of epithelial and stromal contrasts using both flat and oblique illumination and collection fibers. Various strategies, namely self-calibration, consistent contact pressure, and the incorporation of depth-selective sensing, have been proposed to improve the data integrity of an optical spectroscopic system for maximal contrast. In addition to addressing field operation requirements (such as power and operator training requirement), these improvements should enable the collection of reliable spectral data to aid in the adoption of optical smart sensors in the screening and diagnosis of cervical precancer, especially in a global health setting.

Recent land-use and land-cover changes and its driving factors in a fire-prone area of southwestern Turkey.

PubMed

Viedma, Olga; Moreno, José M; Güngöroglu, Cumhur; Cosgun, Ufuk; Kavgacı, Ali

2017-07-15

During the last decades, contrasted trends in forest fires among countries around the Mediterranean basin have been observed. In the northern/western countries, Land Use-Land Cover (LULC) changes led to more hazardous landscapes, with consequent increases in fires. This contrasted with fire trends in southern/eastern countries. The recent incidence of large fires in some of the latter prompted the question of whether they are now following the path of their neighbors decades earlier. In this study, we investigated recent LULC changes in southwestern Turkey, focusing on those that could affect fire, and the factors driving them. To this end, LULC maps at different time steps (1975, 1990, 2000 and 2010) were obtained from Landsat images, together with relevant socioeconomic data. Generalized linear mixed models (GLMMs) were applied to assess the effects of socioeconomic and geophysical factors on the dominant LULC changes over time. Over the whole period studied, the most important LULC changes were deforestation followed by afforestation. Deforestation was positively related to high livestock density and proximity to villages and increased forest interfaces with other LULC types. We found no evidence that LULC changes were making the landscape more hazardous as there was a net decrease in fuels biomass and the landscape became more fragmented over time. However, despite the area being heavily used and relatively fragmented, large fires can occur driven by severe weather. Copyright © 2017 Elsevier Ltd. All rights reserved.

Changes in habitat complexity negatively affect diverse gastropod assemblages in coralline algal turf.

PubMed

Kelaher, B P

2003-05-01

The physical structure of a habitat generally has a strong influence on the diversity and abundance of associated organisms. I investigated the role of coralline algal turf structure in determining spatial variation of gastropod assemblages at different tidal heights of a rocky shore near Sydney, Australia. The structural characteristics of algal turf tested were frond density (or structural complexity) and frond length (the vertical scale over which structural complexity was measured). This definition of structural complexity assumes that complexity of the habitat increases with increasing frond density. While frond length was unrelated to gastropod community structure, I found significant correlations between density of fronds and multivariate and univariate measures of gastropod assemblages, indicating the importance of structural complexity. In contrast to previous studies, here there were negative relationships between the density of fronds and the richness and abundance of gastropods. Artificial habitat mimics were used to manipulate the density of fronds to test the hypothesis that increasing algal structural complexity decreases the richness and abundance of gastropods. As predicted, there were significantly more species of gastropods in loosely packed than in tightly packed turf at both low- and mid-shore levels. Despite large differences between gastropod assemblages at different tidal heights, the direction and magnitude of these negative effects were similar at low- and mid-shore levels and, therefore, relatively independent of local environmental conditions. These novel results extend our previous understanding of the ecological effects of habitat structure because they demonstrate possible limitations of commonly used definitions of structural complexity, as well as distinct upper thresholds in the relationship between structural complexity and faunal species richness.

A cross-sectional prevalence study of ethnically targeted and general audience outdoor obesity-related advertising.

PubMed

Yancey, Antronette K; Cole, Brian L; Brown, Rochelle; Williams, Jerome D; Hillier, Amy; Kline, Randolph S; Ashe, Marice; Grier, Sonya A; Backman, Desiree; McCarthy, William J

2009-03-01

Commercial marketing is a critical but understudied element of the sociocultural environment influencing Americans' food and beverage preferences and purchases. This marketing also likely influences the utilization of goods and services related to physical activity and sedentary behavior. A growing literature documents the targeting of racial/ethnic and income groups in commercial advertisements in magazines, on billboards, and on television that may contribute to sociodemographic disparities in obesity and chronic disease risk and protective behaviors. This article examines whether African Americans, Latinos, and people living in low-income neighborhoods are disproportionately exposed to advertisements for high-calorie, low nutrient-dense foods and beverages and for sedentary entertainment and transportation and are relatively underexposed to advertising for nutritious foods and beverages and goods and services promoting physical activities. Outdoor advertising density and content were compared in zip code areas selected to offer contrasts by area income and ethnicity in four cities: Los Angeles, Austin, New York City, and Philadelphia. Large variations were observed in the amount, type, and value of advertising in the selected zip code areas. Living in an upper-income neighborhood, regardless of its residents' predominant ethnicity, is generally protective against exposure to most types of obesity-promoting outdoor advertising (food, fast food, sugary beverages, sedentary entertainment, and transportation). The density of advertising varied by zip code area race/ethnicity, with African American zip code areas having the highest advertising densities, Latino zip code areas having slightly lower densities, and white zip code areas having the lowest densities. The potential health and economic implications of differential exposure to obesity-related advertising are substantial. Although substantive legal questions remain about the government's ability to regulate advertising, the success of limiting tobacco advertising offers lessons for reducing the marketing contribution to the obesigenicity of urban environments.

Anomalous electronic structure and magnetoresistance in TaAs2

NASA Astrophysics Data System (ADS)

Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

2016-06-01

The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions.

Anomalous electronic structure and magnetoresistance in TaAs2

PubMed Central

Luo, Yongkang; McDonald, R. D.; Rosa, P. F. S.; Scott, B.; Wakeham, N.; Ghimire, N. J.; Bauer, E. D.; Thompson, J. D.; Ronning, F.

2016-01-01

The change in resistance of a material in a magnetic field reflects its electronic state. In metals with weakly- or non-interacting electrons, the resistance typically increases upon the application of a magnetic field. In contrast, negative magnetoresistance may appear under some circumstances, e.g., in metals with anisotropic Fermi surfaces or with spin-disorder scattering and semimetals with Dirac or Weyl electronic structures. Here we show that the non-magnetic semimetal TaAs2 possesses a very large negative magnetoresistance, with an unknown scattering mechanism. Density functional calculations find that TaAs2 is a new topological semimetal [ℤ2 invariant (0;111)] without Dirac dispersion, demonstrating that a negative magnetoresistance in non-magnetic semimetals cannot be attributed uniquely to the Adler-Bell-Jackiw chiral anomaly of bulk Dirac/Weyl fermions. PMID:27271852

Attractive and Repulsive Forces on Particles in Oscillatory Flow

NASA Astrophysics Data System (ADS)

Agarwal, Siddhansh; Rallabandi, Bhargav; Raju, David; Thameem, Raqeeb; Hilgenfeldt, Sascha

2016-11-01

A large class of oscillating flows gives rise to rectified streaming motion of the fluid. It has recently been shown that particle transport in such flows, excited by bubbles oscillating at ultrasound frequencies, leads to differential displacement and efficient sorting of microparticles by size. We derive a general expression for the instantaneous radial force experienced by a small spherical particle in the vicinity of an oscillating interface, and generalize the radial projection of the Maxey-Riley equation to include this effect. Varying relevant system parameters, we show that the net effect on the particle can be either an attraction to or a repulsion from the bubble surface, depending in particular on the particle size and the particle/fluid density contrast. We demonstrate that these predictions are in agreement with a variety of experiments.

Strong interplay between structure and electronic properties in CuIn(S,Se){2}: a first-principles study.

PubMed

Vidal, Julien; Botti, Silvana; Olsson, Pär; Guillemoles, Jean-François; Reining, Lucia

2010-02-05

We present a first-principles study of the electronic properties of CuIn(S,Se){2} (CIS) using state-of-the-art self-consistent GW and hybrid functionals. The calculated band gap depends strongly on the anion displacement u, an internal structural parameter that measures lattice distortion. This contrasts with the observed stability of the band gap of CIS solar panels under operating conditions, where a relatively large dispersion of values for u occurs. We solve this apparent paradox considering the coupled effect on the band gap of copper vacancies and lattice distortions. The correct treatment of d electrons in these materials requires going beyond density functional theory, and GW self-consistency is critical to evaluate the quasiparticle gap and the valence band maximum.

A mechanism for deep chromospheric heating during solar flares

NASA Technical Reports Server (NTRS)

Machado, M. E.; Emslie, A. G.; Mauas, P. J.

1986-01-01

The role of the negative hydrogen ion, H(-), in the energy balance of the deep solar chromosphere is reexamined and it is found, in contrast with earlier authors, that H(-) is a source of heating at these levels. The response of this region to an ionizing flux of flare-associated UV radiation (1500 to 1900 A) is then addressed: it is found that the excess ionization of Si to Si(+) increases the local electron number density considerably, since most species are largely neutral at deep chromospheric levels. This in turn increases the electron-hydrogen atom association rate, the H(-) abundance, and the rate of absorption of photospheric radiation by this ion. It is found that the excess absorption by this process may lead to a substantial temperature enhancement at temperature minimum levels during flares.

Application of ECH to the study of transport in ITER baseline scenario-like discharges in DIII-D

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

Pinsker, R. I.; Austin, M. E.; Ernst, D. R.

Recent DIII-D experiments in the ITER Baseline Scenario (IBS) have shown strong increases in fluctuations and correlated reduction of confinement associated with entering the electron-heating-dominated regime with strong electron cyclotron heating (ECH). The addition of 3.2 MW of 110 GHz EC power deposited at ρ~0.42 to IBS discharges with ~3 MW of neutral beam injection causes large increases in low-k and medium-k turbulent density fluctuations observed with Doppler backscatter (DBS), beam emission spectroscopy (BES) and phase-contrast imaging (PCI) diagnostics, correlated with decreases in the energy, particle, and momentum confinement times. Power balance calculations show the electron heat diffusivity χ emore » increases significantly in the mid-radius region 0.4« less

Application of ECH to the study of transport in ITER baseline scenario-like discharges in DIII-D

DOE PAGES

Pinsker, R. I.; Austin, M. E.; Ernst, D. R.; ...

2015-03-12

Recent DIII-D experiments in the ITER Baseline Scenario (IBS) have shown strong increases in fluctuations and correlated reduction of confinement associated with entering the electron-heating-dominated regime with strong electron cyclotron heating (ECH). The addition of 3.2 MW of 110 GHz EC power deposited at ρ~0.42 to IBS discharges with ~3 MW of neutral beam injection causes large increases in low-k and medium-k turbulent density fluctuations observed with Doppler backscatter (DBS), beam emission spectroscopy (BES) and phase-contrast imaging (PCI) diagnostics, correlated with decreases in the energy, particle, and momentum confinement times. Power balance calculations show the electron heat diffusivity χ emore » increases significantly in the mid-radius region 0.4« less

Current-induced changes of migration energy barriers in graphene and carbon nanotubes.

PubMed

Obodo, J T; Rungger, I; Sanvito, S; Schwingenschlögl, U

2016-05-21

An electron current can move atoms in a nanoscale device with important consequences for the device operation and breakdown. We perform first principles calculations aimed at evaluating the possibility of changing the energy barriers for atom migration in carbon-based systems. In particular, we consider the migration of adatoms and defects in graphene and carbon nanotubes. Although the current-induced forces are large for both the systems, in graphene the force component along the migration path is small and therefore the barrier height is little affected by the current flow. In contrast, the same barrier is significantly reduced in carbon nanotubes as the current increases. Our work also provides a real-system numerical demonstration that current-induced forces within density functional theory are non-conservative.

Validation of the Contrast Attenuation Technique (CAT) for Deducing Dust Densities from Photographic Records Taken during the MILL RACE High Explosive Test.

DTIC Science & Technology

1982-02-28

BRE O STNDADS 193- rC low& L --. -: !’- • ,- r;4; [.9 ’- DNA-TR-81-81 VALIDATION OF THE CONTRAST ATTENUATION TECHNIQUE ( CAT ) FOR DEDUCING DUST...TITLE (and Sublitle) S. TYPE OF REPORT & PERIOD COVERED VALIDATION OF THE CONTRAST ATTENUATION TECHNIQUE Technical Report ( CAT ) FOR DEDUCING DUST...SCATTERING AND EXTINCTION CONSIDERATIONS- -------- 77 C DATA ON FILMS*USED FOR THE MILL RACE CAT TEST -- ------- 85 2

A Search for Plasma "Fingers" in the Io Torus

NASA Astrophysics Data System (ADS)

Jaggar, S.; Schneider, N. M.; Bagenal, F.; Trauger, J. T.

1996-09-01

We have compared model and data images of the Io plasma torus to test the radial diffusion model of Yang et al. (J. Geophys. Res., Vol 99, p. 8755, 1994). They predict that radial diffusion takes the form of `fingers' of dense plasma flowing outward due to the centrifugal force. Furthermore, they show that the spatial scale of these significant longitudinal variations is approximately 15(o) . The observations used in this study were obtained using a 2.4m telescope at Las Campanas Observatory using a narrowband filter to isolate emissions from S(++) at 9531 Angstroms. S(++) images are dominated by emission from the warm torus where outward radial transport is expected. Although S(+) images are brighter, they are contaminated by emission from the cold torus where fingers are not expected. We used the Colorado Io Torus Emission Package (CITEP)(Taylor et al., J. Geophys. Res., Vol. 100, p. 19541, 1995) to simulate images of the torus with fingers. CITEP is a comprehensive program which incorporates accurate atomic physics, plasma physics and magnetic field models to simulate the brightness and morphology or torus emissions. We used a Voyager empirical model (Bagenal, J. Geophys. Res., Vol. 99, p. 11043, 1994) modulated by a sinusoidal longitudinal density variation with a 15(o) period and an amplitude proportional to the density at that L-shell. We compared simulated images with data to determine the minimum density contrast necessary to make fingers detectable. We place an upper limit on the density contrast of +/- 20% on a 15(o) spatial scale. We conclude that either the density contrast of this mode of transport is small, or other processes are more important for radial transport. This constraint can also be used in other radial diffusion models which predict density variations on this spatial scale. This work has been supported by NASA's Planetary Astronomy and Planetary Atmospheres programs.

Highly-stretchable 3D-architected Mechanical Metamaterials

NASA Astrophysics Data System (ADS)

Jiang, Yanhui; Wang, Qiming

2016-09-01

Soft materials featuring both 3D free-form architectures and high stretchability are highly desirable for a number of engineering applications ranging from cushion modulators, soft robots to stretchable electronics; however, both the manufacturing and fundamental mechanics are largely elusive. Here, we overcome the manufacturing difficulties and report a class of mechanical metamaterials that not only features 3D free-form lattice architectures but also poses ultrahigh reversible stretchability (strain > 414%), 4 times higher than that of the existing counterparts with the similar complexity of 3D architectures. The microarchitected metamaterials, made of highly stretchable elastomers, are realized through an additive manufacturing technique, projection microstereolithography, and its postprocessing. With the fabricated metamaterials, we reveal their exotic mechanical behaviors: Under large-strain tension, their moduli follow a linear scaling relationship with their densities regardless of architecture types, in sharp contrast to the architecture-dependent modulus power-law of the existing engineering materials; under large-strain compression, they present tunable negative-stiffness that enables ultrahigh energy absorption efficiencies. To harness their extraordinary stretchability and microstructures, we demonstrate that the metamaterials open a number of application avenues in lightweight and flexible structure connectors, ultraefficient dampers, 3D meshed rehabilitation structures and stretchable electronics with designed 3D anisotropic conductivity.

Highly-stretchable 3D-architected Mechanical Metamaterials.

PubMed

Jiang, Yanhui; Wang, Qiming

2016-09-26

Soft materials featuring both 3D free-form architectures and high stretchability are highly desirable for a number of engineering applications ranging from cushion modulators, soft robots to stretchable electronics; however, both the manufacturing and fundamental mechanics are largely elusive. Here, we overcome the manufacturing difficulties and report a class of mechanical metamaterials that not only features 3D free-form lattice architectures but also poses ultrahigh reversible stretchability (strain > 414%), 4 times higher than that of the existing counterparts with the similar complexity of 3D architectures. The microarchitected metamaterials, made of highly stretchable elastomers, are realized through an additive manufacturing technique, projection microstereolithography, and its postprocessing. With the fabricated metamaterials, we reveal their exotic mechanical behaviors: Under large-strain tension, their moduli follow a linear scaling relationship with their densities regardless of architecture types, in sharp contrast to the architecture-dependent modulus power-law of the existing engineering materials; under large-strain compression, they present tunable negative-stiffness that enables ultrahigh energy absorption efficiencies. To harness their extraordinary stretchability and microstructures, we demonstrate that the metamaterials open a number of application avenues in lightweight and flexible structure connectors, ultraefficient dampers, 3D meshed rehabilitation structures and stretchable electronics with designed 3D anisotropic conductivity.

Contrast medium extravasation injury: guidelines for prevention and management.

PubMed

Bellin, Marie-France; Jakobsen, Jarl A; Tomassin, Isabelle; Thomsen, Henrik S; Morcos, Sameh K; Thomsen, H S; Morcos, S K; Almén, T; Aspelin, P; Bellin, M F; Clauss, W; Flaten, H; Grenier, N; Ideé, J-M; Jakobsen, J A; Krestin, G P; Stacul, F; Webb, J A W

2002-11-01

Extravasation of contrast material is a well-recognized complication of contrast-enhanced imaging studies. The management of this complication is contentious; therefore, the Contrast Media Safety Committee of The European Society of Urogenital Radiology decided to review the literature and issue guidelines. A comprehensive literature search was carried out. The resulting report was discussed at the 8th European Symposium on Urogenital Radiology in Genoa, Italy. Automated power injection may result in extravasation of large volumes and may or can lead to severe tissue damage. Infants, young children and unconscious and debilitated patients are particularly at risk of extravasation during contrast media injection. Fortunately, most extravasations result in minimal swelling or erythema, with no long-term sequelae; however, severe skin necrosis and ulceration may occur. Large volumes of high osmolar contrast media are known to induce significant tissue damage. Compartment syndrome may be seen associated with extravasation of large volumes. Conservative management is often adequate, but in serious cases the advice of a plastic surgeon is recommended. Based on the review simple guidelines for prophylaxis and management of contrast medium extravasation injuries are proposed.

The Dissolution of an Interfween Miscible Liquids

NASA Technical Reports Server (NTRS)

Vlad, D.H.; Maher, J.V.

1999-01-01

The disappearance of the surface tension of the interface of a binary mixture, measured using the dynamic surface light scattering technique, is slower for a binary mixture of higher density contrast. A comparison with a naive diffusion model, expected to provide a lower limit for the speed of dissolution in the absence of gravity shows that the interfacial surface tension disappears much slower than even by diffusion with the effect becoming much more pronounced when density contrast between the liquid phases is increased. Thus, the factor most likely to be responsible for this anomalously slow dissolution is gravity. A mechanism could be based on the competition between diffusive relaxation and sedimentation at the dissolving interface.

Modification of YAPE keypoint detection algorithm for wide local contrast range images

NASA Astrophysics Data System (ADS)

Lukoyanov, A.; Nikolaev, D.; Konovalenko, I.

2018-04-01

Keypoint detection is an important tool of image analysis, and among many contemporary keypoint detection algorithms YAPE is known for its computational performance, allowing its use in mobile and embedded systems. One of its shortcomings is high sensitivity to local contrast which leads to high detection density in high-contrast areas while missing detections in low-contrast ones. In this work we study the contrast sensitivity of YAPE and propose a modification which compensates for this property on images with wide local contrast range (Yet Another Contrast-Invariant Point Extractor, YACIPE). As a model example, we considered the traffic sign recognition problem, where some signs are well-lighted, whereas others are in shadows and thus have low contrast. We show that the number of traffic signs on the image of which has not been detected any keypoints is 40% less for the proposed modification compared to the original algorithm.

Quality evaluation of radiographic contrast media in large-volume prefilled syringes and vials.

PubMed

Sendo, T; Hirakawa, M; Yaginuma, M; Aoyama, T; Oishi, R

1998-06-01

The authors compared the particle contaminations of radiographic contrast media packaged in large-volume prefilled syringes and vials. Particle counting was performed for four contrast media packaged in large-volume prefilled syringes (iohexol, ioversol, ioversol for angiography, and ioxaglate) and three contrast media packaged in vials (iohexol, ioversol, and ioxaglate). X-ray emission spectrometry was performed to characterize the individual particles. The amount of silicone oil in the syringe was quantified with infrared spectrophotometry. The particle contamination in syringes containing ioversol was higher than that in syringes containing iohexol or ioxaglate. Particle contamination in the vials was relatively low, except with ioxaglate. X-ray emission spectrometry of the components of the syringe and vial showed that the source of particles was internal material released from the rubber stopper or inner surface. The particle counts for contrast media packaged in syringes and vials varied considerably among the different contrast media and were related to the amount of silicone oil on the inner surface and rubber piston of the syringe.

In Vitro Validation of an Artefact Suppression Algorithm in X-Ray Phase-Contrast Computed Tomography.

PubMed

Sunaguchi, Naoki; Yuasa, Tetsuya; Hirano, Shin-Ichi; Gupta, Rajiv; Ando, Masami

2015-01-01

X-ray phase-contrast tomography can significantly increase the contrast-resolution of conventional attenuation-contrast imaging, especially for soft-tissue structures that have very similar attenuation. Just as in attenuation-based tomography, phase contrast tomography requires a linear dependence of aggregate beam direction on the incremental direction alteration caused by individual voxels along the path of the X-ray beam. Dense objects such as calcifications in biological specimens violate this condition. There are extensive beam deflection artefacts in the vicinity of such structures because they result in large distortion of wave front due to the large difference of refractive index; for such large changes in beam direction, the transmittance of the silicon analyzer crystal saturates and is no longer linearly dependent on the angle of refraction. This paper describes a method by which these effects can be overcome and excellent soft-tissue contrast of phase tomography can be preserved in the vicinity of such artefact-producing structures.

Preliminary Geophysical Investigations of the Ship Rock Diatreme, Navajo Nation, New Mexico

NASA Astrophysics Data System (ADS)

Gruen, E. M.; McCarthy, L.; Namingha, G.; Bank, C.; Noblett, J.; Semken, S.

2003-12-01

Magnetic and gravity data were collected at the Ship Rock minette neck and dikes, part of the Navajo volcanic field in the central Colorado Plateau, to investigate their subsurface structure. The deep root system of Ship Rock, an exhumed Oligocene maar-diatreme complex, has not been resolved. The diatreme is largely composed of minette tuff-breccia with a large wallrock fraction, whereas the dikes are composed of hypabyssal minette. The country rock is the Upper Cretaceous Mancos Shale. Density and magnetic contrasts between the igneous rock and surrounding shale suggest that the buried structure of Ship Rock can be imaged. Preliminary geophysical investigations were carried out in order to test this hypothesis. We collected magnetic and gravitational data along four lines selected to transect the major south and northeast dikes and to partly encircle the diatreme. Modeling differently sized, oriented and shaped intrusions, we created theoretical Free Air anomaly curves to try to match the two clearest anomalies. Modeling necessitates (i) that the major north-south dike dips west and (ii) the presence of a high-density, deep body near the diatreme. The Free Air anomaly curves show that smaller dikes might not be detected from gravity data; however, they are necessary to determine the presence of large, dense bodies. Although not modeled, the magnetics curves show that smaller dikes can easily be detected. Our study results are promising, and we plan a more thorough investigation in the future which will produce a magnetic map to determine if further buried dikes exist in the vicinity, and measure gravity along additional profiles to better constrain the location of the dense body at depth.

Factors influencing the distribution of native bull trout and westslope cutthroat trout in western Glacier National Park, Montana

USGS Publications Warehouse

D'Angelo, Vincent S.; Muhlfeld, Clint C.

2013-01-01

The widespread declines of native bull trout (Salvelinus confluentus) and westslope cutthroat trout (Oncorhynchus clarkii lewisi) populations prompted researchers to investigate factors influencing their distribution and status in western Glacier National Park, Montana. We evaluated the association of a suite of abiotic factors (stream width, elevation, gradient, large woody debris density, pool density, August mean stream temperature, reach surface area) with the occurrence (presence or absence) of bull trout and westslope cutthroat trout in 79 stream reaches in five sub-drainages containing glacial lakes. We modeled the occurrence of each species using logistic regression and evaluated competing models using an information theoretic approach. Westslope cutthroat trout were widely distributed (47 of 79 reaches), and there appeared to be no restrictions on their distribution other than physical barriers. Westslope cutthroat trout were most commonly found in relatively warm reaches downstream of lakes and in headwater reaches with large amounts of large woody debris and abundant pools. By contrast, bull trout were infrequently detected (10 of 79 reaches), with 7 of the 10 (70%) detections in sub-drainages that have not been compromised by non-native lake trout (S. namaycush). Bull trout were most often found in cold, low-gradient reaches upstream of glacial lakes. Our results indicate that complex stream habitats in sub-drainages free of non-native species are important to the persistence of native salmonids in western Glacier National Park. Results from this study may help managers monitor and protect important habitats and populations, inform conservation and recovery programs, and guide non-native species suppression efforts in Glacier National Park and elsewhere.

GW-BSE approach on S1 vertical transition energy of large charge transfer compounds: A performance assessment.

PubMed

Ziaei, Vafa; Bredow, Thomas

2016-11-07

In this work, we apply many-body perturbation theory (MBPT) on large critical charge transfer (CT) complexes to assess its performance on the S 1 excitation energy. Since the S 1 energy of CT compounds is heavily dependent on the Hartree-Fock (HF) exchange fraction in the reference density functional, MBPT opens a new way for reliable prediction of CT S 1 energy without explicit knowledge of suitable amount of HF-exchange, in contrary to the time-dependent density functional theory (TD-DFT), where depending on various functionals, large errors can arise. Thus, simply by starting from a (semi-)local reference functional and performing update of Kohn-Sham (KS) energies in the Green's function G while keeping dynamical screened interaction (W(ω)) frozen to the mean-field level, we obtain impressingly highly accurate S 1 energy at slightly higher computational cost in comparison to TD-DFT. However, this energy-only updating mechanism in G fails to work if the initial guess contains a fraction or 100% HF-exchange, and hence considerably inaccurate S 1 energy is predicted. Furthermore, eigenvalue updating both in G and W(ω) overshoots the S 1 energy due to enhanced underscreening of W(ω), independent of the (hybrid-)DFT starting orbitals. A full energy-update on top of HF orbitals even further overestimates the S 1 energy. An additional update of KS wave functions within the Quasi-Particle Self-Consistent GW (QSGW) deteriorates results, in stark contrast to the good results obtained from QSGW for periodic systems. For the sake of transferability, we further present data of small critical non-charge transfer systems, confirming the outcomes of the CT-systems.

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

Bae, Kyu Jung; Baer, Howard; Serce, Hasan

The supersymmetrized DFSZ axion model is highly motivated not only because it offers solutions to both the gauge hierarchy and strong CP problems, but also because it provides a solution to the SUSY μ-problem which naturally allows for a Little Hierarchy. We compute the expected mixed axion-neutralino dark matter abundance for the SUSY DFSZ axion model in two benchmark cases—a natural SUSY model with a standard neutralino underabundance (SUA) and an mSUGRA/CMSSM model with a standard overabundance (SOA). Our computation implements coupled Boltzmann equations which track the radiation density along with neutralino, axion, axion CO (produced via coherent oscillations), saxion,more » saxion CO, axino and gravitino densities. In the SUSY DFSZ model, axions, axinos and saxions go through the process of freeze-in—in contrast to freeze-out or out-of-equilibrium production as in the SUSY KSVZ model—resulting in thermal yields which are largely independent of the re-heat temperature. We find the SUA case with suppressed saxion-axion couplings (ξ=0) only admits solutions for PQ breaking scale f{sub a}∼< 6× 10{sup 12} GeV where the bulk of parameter space tends to be axion-dominated. For SUA with allowed saxion-axion couplings (ξ =1), then f{sub a} values up to ∼ 10{sup 14} GeV are allowed. For the SOA case, almost all of SUSY DFSZ parameter space is disallowed by a combination of overproduction of dark matter, overproduction of dark radiation or violation of BBN constraints. An exception occurs at very large f{sub a}∼ 10{sup 15}–10{sup 16} GeV where large entropy dilution from CO-produced saxions leads to allowed models.« less

A Theoretical Investigation of Optical Emission in Solar Flares

NASA Astrophysics Data System (ADS)

Abbett, William Paul

A dynamic theoretical model of a flare loop from its footpoints in the photosphere to its apex in the corona is presented, and the effects of non-thermal heating of the lower atmosphere by accelerated electrons and soft X-ray irradiation from the flare heated transition region and corona are investigated. Important transitions of hydrogen, helium, and singly ionized calcium and magnesium are treated in non-LTE. Three main conclusions are drawn from the models. First, even the strongest of impulsive events can be described as having two phases: a gentle phase characterized by a state of near equilibrium, and an explosive phase characterized by large material flows, and strong hydrodynamic waves and shocks. During the gentle phase, one or possibly two temperature 'plateaus' form in the upper chromosphere. The line emission generated in these regions produces profiles that are generally symmetric and undistorted, in contrast to emission produced during the explosive phase, where large velocity gradients that occur in the upper atmosphere produce line profiles that are highly asymmetric and show large emission peaks and troughs. Second, a significant continuum (or 'white light') brightening results from increased hydrogen recombination radiation in the upper chromosphere at the point where the accelerated electrons deposit the bulk of their energy. Third, there exists a measurable time lag between the brightening of the near wings of Hα and the brightening of the Paschen continuum. This delay is controlled by the amount of time it takes for electron densities in the upper chromosphere to become high enough, and the densities of hydrogen atoms in high energy bound states to become low enough, to allow the number of recombinations to dominate the number of photoionizations in the region.

Clinical study of contrast-enhanced digital mammography and the evaluation of blood and lymphatic microvessel density

PubMed Central

Cruz-Bastida, Juan P; Rosado-Méndez, Iván M; Villaseñor-Navarro, Yolanda; Pérez-Ponce, Héctor; Galván, Héctor A; Trujillo-Zamudio, Flavio E; Sánchez-Suárez, Patricia; Benítez-Bribiesca, Luis

2016-01-01

Objective: To correlate image parameters in contrast-enhanced digital mammography (CEDM) with blood and lymphatic microvessel density (MVD). Methods: 18 Breast Imaging-Reporting and Data System (BI-RADS)-4 to BI-RADS-5 patients were subjected to CEDM. Craniocaudal views were acquired, two views (low and high energy) before iodine contrast medium (CM) injection and four views (high energy) 1–5 min afterwards. Processing included registration and two subtraction modalities, traditional single-energy temporal (high-energy) and “dual-energy temporal with a matrix”, proposed to improve lesion conspicuity. Images were calibrated into iodine thickness, and iodine uptake, contrast, time–intensity and time–contrast kinetic curves were quantified. Image indicators were compared with MVD evaluated by anti-CD105 and anti-podoplanin (D2-40) immunohistochemistry. Results: 11 lesions were cancerous and 7 were benign. CEDM subtraction strongly increased conspicuity of lesions enhanced by iodine uptake. A strong correlation was observed between lymphatic vessels and blood vessels; all benign lesions had <30 blood microvessels per field, and all cancers had more than this value. MVD showed no correlation with iodine uptake, nor with contrast. The most frequent curve was early uptake followed by plateau for uptake and contrast in benign and malignant lesions. The positive-predictive value of uptake dynamics was 73% and that of contrast was 64%. Conclusion: CEDM increased lesion visibility and showed additional features compared with conventional mammography. Lack of correlation between image parameters and MVD is probably due to tumour tissue heterogeneity, mammography projective nature and/or dependence of extracellular iodine irrigation on tissue composition. Advances in knowledge: Quantitative analysis of CEDM images was performed. Image parameters and MVD showed no correlation. Probably, this is indication of the complex dependence of CM perfusion on tumour microenvironment. PMID:27376457

X-ray Emission Characteristics of Ultra-High Energy Density Relativistic Plasmas Created by Ultrafast Laser Irradiation of Nanowire Arrays

NASA Astrophysics Data System (ADS)

Hollinger, R. C.; Bargsten, C.; Shlyaptsev, V. N.; Pukhov, A.; Purvis, M. A.; Townsend, A.; Keiss, D.; Wang, Y.; Wang, S.; Prieto, A.; Rocca, J. J.

2014-10-01

Irradiation of ordered nanowire arrays with high contrast femtosecond laser pulses of relativistic intensity creates volumetrically heated near solid density plasmas characterized by multi-KeV temperatures and extreme degrees of ionization. The large hydrodynamic-to-radiative lifetime ratio of these plasmas results in very efficient X-ray generation. Au nanowire array plasmas irradiated at I 5×1018 Wcm-2 are measured to convert ~ 5 percent of the laser energy into h ν > 0.9 KeV X-rays, and >1 × 10-4 into h ν > 9 KeV photons, creating bright picosecond X-ray sources. The angular distribution of the higher energy photons is measured to change from isotropic into annular as the intensity increases, while softer X-ray emission (h ν >1 KeV) remains isotropic and nearly unchanged. Model simulations suggest the unexpected annular distribution of the hard X-rays might result from bremsstrahlung of fast electrons confined in a high aspect ratio near solid density plasma in which the electron-ion collision mean free-path is of the order of the plasma thickness. Work supported by the U.S Department of Energy, Fusion Energy Sciences and the Defense Threat Reduction Agency Grant HDTRA-1-10-1-0079. A.P was supported by of DFG-funded project TR18.

Tree Productivity Enhanced with Conversion from Forest to Urban Land Covers.

PubMed

Briber, Brittain M; Hutyra, Lucy R; Reinmann, Andrew B; Raciti, Steve M; Dearborn, Victoria K; Holden, Christopher E; Dunn, Allison L

2015-01-01

Urban areas are expanding, changing the structure and productivity of landscapes. While some urban areas have been shown to hold substantial biomass, the productivity of these systems is largely unknown. We assessed how conversion from forest to urban land uses affected both biomass structure and productivity across eastern Massachusetts. We found that urban land uses held less than half the biomass of adjacent forest expanses with a plot level mean biomass density of 33.5 ± 8.0 Mg C ha(-1). As the intensity of urban development increased, the canopy cover, stem density, and biomass decreased. Analysis of Quercus rubra tree cores showed that tree-level basal area increment nearly doubled following development, increasing from 17.1 ± 3.0 to 35.8 ± 4.7 cm(2) yr(-1). Scaling the observed stem densities and growth rates within developed areas suggests an aboveground biomass growth rate of 1.8 ± 0.4 Mg C ha(-1) yr(-1), a growth rate comparable to nearby, intact forests. The contrasting high growth rates and lower biomass pools within urban areas suggest a highly dynamic ecosystem with rapid turnover. As global urban extent continues to grow, cities consider climate mitigation options, and as the verification of net greenhouse gas emissions emerges as critical for policy, quantifying the role of urban vegetation in regional-to-global carbon budgets will become ever more important.

The variation of rotation curve shapes as a signature of the effects of baryons on dark matter density profiles

NASA Astrophysics Data System (ADS)

Brook, Chris B.

2015-12-01

Rotation curves of galaxies show a wide range of shapes, which can be paramaterized as scatter in Vrot(1 kpc)/Vmax , i.e. the ratio of the rotation velocity measured at 1 kpc and the maximum measured rotation velocity. We examine whether the observed scatter can be accounted for by combining scatters in disc scalelengths, the concentration-halo mass relation, and the M⋆-Mhalo relation. We use these scatters to create model galaxy populations; when housed within dark matter haloes that have universal, Navarro, Frenk & White density profiles, the model does not match the lowest observed values of Vrot(1 kpc)/Vmax and has too little scatter in Vrot(1 kpc)/Vmax compared to observations. By contrast, a model using a mass-dependent dark matter profile, where the inner slope is determined by the ratio of M⋆/Mhalo, produces galaxies with low values of Vrot(1 kpc)/Vmax and a much larger scatter, both in agreement with observation. We conclude that the large observed scatter in Vrot(1 kpc)/Vmax favours density profiles that are significantly affected by baryonic processes. Alternative dark matter core formation models such as self-interacting dark matter may also account for the observed variation in rotation curve shapes, but these observations may provide important constraints in terms of core sizes, and whether they vary with halo mass and/or merger history.

Quantum corral effects on competing orders and electronic states in chiral d + id or f-wave superconductors.

PubMed

Zuo, Xian-Jun

2018-03-07

Self-consistent calculations are performed to characterize the quantum corral effects on the electronic states of chiral d + id or f-wave superconductors in this paper. A variety of spatial structures of competing orders are revealed in the presence of ferromagnetic nano-corrals, and superconducting islands are found to be absent in the case of small corrals while being seen for large corrals. Compared with the local suppression of superconductivity by a magnetic impurity inside the corral, surprisingly, an additional remarkable feature, i.e., obvious oscillations or enhancement of superconductivity around a non-magnetic impurity, is observed inside the magnetic corral. This is important in view of applications, especially in view of the demand for devices to locally produce strong superconductivity. Meanwhile, the charge density displays obvious modulations due to quantum confinement but in contrast, the spin density pattern exhibits its robustness against the corral effect. Furthermore, we explore the local density of states so as to be directly checked by experiments. We demonstrate that a magnetic corral can suppress the formation of quasi-particle bound states induced by an impurity inside the corral in the chiral d + id state while the f-wave case shows different behaviors. These results also propose a new route to make a distinction between the two competing pairing states in triangular-lattice superconductors.

Interplay between mast cells, enterochromaffin cells, and sensory signaling in the aging human bowel.

PubMed

Yu, Y; Daly, D M; Adam, I J; Kitsanta, P; Hill, C J; Wild, J; Shorthouse, A; Grundy, D; Jiang, W

2016-10-01

Advanced age is associated with a reduction in clinical visceral pain perception. However, the underlying mechanisms remain largely unknown. Previous studies have suggested that an abnormal interplay between mast cells, enterochromaffin (EC) cells, and afferent nerves contribute to nociception in gastrointestinal disorders. The aim of this study was to investigate how aging affects afferent sensitivity and neuro-immune association in the human bowel. Mechanical and chemical sensitivity of human bowel afferents were examined by ex vivo afferent nerve recordings. Age-related changes in the density of mast cells, EC cells, sensory nerve terminals, and mast cell-nerve micro-anatomical association were investigated by histological and immune staining. Human afferents could be broadly classified into subpopulations displaying mechanical and chemical sensitivity, adaptation, chemo-sensitization, and recruitment. Interestingly human bowel afferent nerve sensitivity was attenuated with age. The density of substance P-immunoreactive (SP-IR) nerve varicosities was also reduced with age. In contrast, the density of ileal and colonic mucosal mast cells was increased with age, as was ileal EC cell number. An increased proportion of mast cells was found in close apposition to SP-IR nerves. Afferent sensitivity in human bowel was reduced with advancing age. Augmentation of mast cells and EC cell numbers and the mast cell-nerve association suggest a compensatory mechanism for sensory neurodegeneration. © 2016 The Authors. Neurogastroenterology & Motility Published by John Wiley & Sons Ltd.

Tree Productivity Enhanced with Conversion from Forest to Urban Land Covers

PubMed Central

Briber, Brittain M.; Hutyra, Lucy R.; Reinmann, Andrew B.; Raciti, Steve M.; Dearborn, Victoria K.; Holden, Christopher E.; Dunn, Allison L.

2015-01-01

Urban areas are expanding, changing the structure and productivity of landscapes. While some urban areas have been shown to hold substantial biomass, the productivity of these systems is largely unknown. We assessed how conversion from forest to urban land uses affected both biomass structure and productivity across eastern Massachusetts. We found that urban land uses held less than half the biomass of adjacent forest expanses with a plot level mean biomass density of 33.5 ± 8.0 Mg C ha-1. As the intensity of urban development increased, the canopy cover, stem density, and biomass decreased. Analysis of Quercus rubra tree cores showed that tree-level basal area increment nearly doubled following development, increasing from 17.1 ± 3.0 to 35.8 ± 4.7 cm2 yr-1. Scaling the observed stem densities and growth rates within developed areas suggests an aboveground biomass growth rate of 1.8 ± 0.4 Mg C ha-1 yr-1, a growth rate comparable to nearby, intact forests. The contrasting high growth rates and lower biomass pools within urban areas suggest a highly dynamic ecosystem with rapid turnover. As global urban extent continues to grow, cities consider climate mitigation options, and as the verification of net greenhouse gas emissions emerges as critical for policy, quantifying the role of urban vegetation in regional-to-global carbon budgets will become ever more important. PMID:26302444

Improved locality of the phase-field lattice-Boltzmann model for immiscible fluids at high density ratios

NASA Astrophysics Data System (ADS)

Fakhari, Abbas; Mitchell, Travis; Leonardi, Christopher; Bolster, Diogo

2017-11-01

Based on phase-field theory, we introduce a robust lattice-Boltzmann equation for modeling immiscible multiphase flows at large density and viscosity contrasts. Our approach is built by modifying the method proposed by Zu and He [Phys. Rev. E 87, 043301 (2013), 10.1103/PhysRevE.87.043301] in such a way as to improve efficiency and numerical stability. In particular, we employ a different interface-tracking equation based on the so-called conservative phase-field model, a simplified equilibrium distribution that decouples pressure and velocity calculations, and a local scheme based on the hydrodynamic distribution functions for calculation of the stress tensor. In addition to two distribution functions for interface tracking and recovery of hydrodynamic properties, the only nonlocal variable in the proposed model is the phase field. Moreover, within our framework there is no need to use biased or mixed difference stencils for numerical stability and accuracy at high density ratios. This not only simplifies the implementation and efficiency of the model, but also leads to a model that is better suited to parallel implementation on distributed-memory machines. Several benchmark cases are considered to assess the efficacy of the proposed model, including the layered Poiseuille flow in a rectangular channel, Rayleigh-Taylor instability, and the rise of a Taylor bubble in a duct. The numerical results are in good agreement with available numerical and experimental data.

The growth of aspherical structure in the universe - Is the Local Supercluster an unusual system

NASA Technical Reports Server (NTRS)

White, S. D. M.; Silk, J.

1979-01-01

The growth and subsequent collapse of homogeneous ellipsoidal perturbations in a uniform expanding background is considered as a simple model for the formation of large-scale aspherical structures in the observed universe. Numerical calculations of the evolution of such perturbations turn out to be well described by an approximate analytic solution of the equations of motion, and simple relationships are found between the initial shape of a perturbation and its shape and kinematic properties at the time of collapse. Perturbations do not change their shape significantly until they reach a density contrast of order unity. As a result, structures with the kinematic properties of the Local Supercluster should form much more commonly in a low-density universe than in a flat universe. The homogeneity of the local Hubble flow, the motion of the Milky Way with respect to the microwave background, and the flattening of the Local Supercluster can be successfully accounted for by these models, provided that the initial perturbation is sufficiently flattened. Viable models are obtained only if the ratio of the lengths of the two smaller axes of the initial perturbation is at least 3:1 in an Einstein-de Sitter universe or at least 1.8:1 in a universe for which the density parameter (Omega) is of order 0.1, when the protocluster pancakes.

Information in a Network of Neuronal Cells: Effect of Cell Density and Short-Term Depression

PubMed Central

Onesto, Valentina; Cosentino, Carlo; Di Fabrizio, Enzo; Cesarelli, Mario; Amato, Francesco; Gentile, Francesco

2016-01-01

Neurons are specialized, electrically excitable cells which use electrical to chemical signals to transmit and elaborate information. Understanding how the cooperation of a great many of neurons in a grid may modify and perhaps improve the information quality, in contrast to few neurons in isolation, is critical for the rational design of cell-materials interfaces for applications in regenerative medicine, tissue engineering, and personalized lab-on-a-chips. In the present paper, we couple an integrate-and-fire model with information theory variables to analyse the extent of information in a network of nerve cells. We provide an estimate of the information in the network in bits as a function of cell density and short-term depression time. In the model, neurons are connected through a Delaunay triangulation of not-intersecting edges; in doing so, the number of connecting synapses per neuron is approximately constant to reproduce the early time of network development in planar neural cell cultures. In simulations where the number of nodes is varied, we observe an optimal value of cell density for which information in the grid is maximized. In simulations in which the posttransmission latency time is varied, we observe that information increases as the latency time decreases and, for specific configurations of the grid, it is largely enhanced in a resonance effect. PMID:27403421

High resolution reconstruction of monthly precipitation of Iberian Peninsula using circulation weather types

NASA Astrophysics Data System (ADS)

Cortesi, N.; Trigo, R.; Gonzalez-Hidalgo, J. C.; Ramos, A. M.

2012-06-01

Precipitation over the Iberian Peninsula (IP) is highly variable and shows large spatial contrasts between wet mountainous regions, to the north, and dry regions in the inland plains and southern areas. In this work, a high-density monthly precipitation dataset for the IP was coupled with a set of 26 atmospheric circulation weather types (Trigo and DaCamara, 2000) to reconstruct Iberian monthly precipitation from October to May with a very high resolution of 3030 precipitation series (overall mean density one station each 200 km2). A stepwise linear regression model with forward selection was used to develop monthly reconstructed precipitation series calibrated and validated over 1948-2003 period. Validation was conducted by means of a leave-one-out cross-validation over the calibration period. The results show a good model performance for selected months, with a mean coefficient of variation (CV) around 0.6 for validation period, being particularly robust over the western and central sectors of IP, while the predicted values in the Mediterranean and northern coastal areas are less acute. We show for three long stations (Lisbon, Madrid and Valencia) the comparison between model and original data as an example to how these models can be used in order to obtain monthly precipitation fields since the 1850s over most of IP for this very high density network.

Transverse Space-Charge Field-Induced Plasma Dynamics for Ultraintense Electron-Beam Characterization

NASA Astrophysics Data System (ADS)

Tarkeshian, R.; Vay, J. L.; Lehe, R.; Schroeder, C. B.; Esarey, E. H.; Feurer, T.; Leemans, W. P.

2018-04-01

Similarly to laser or x-ray beams, the interaction of sufficiently intense particle beams with neutral gases will result in the creation of plasma. In contrast to photon-based ionization, the strong unipolar field of a particle beam can generate a plasma where the electron population receives a large initial momentum kick and escapes, leaving behind unshielded ions. Measuring the properties of the ensuing Coulomb exploding ions—such as their kinetic energy distribution, yield, and spatial distribution—can provide information about the peak electric fields that are achieved in the electron beams. Particle-in-cell simulations and analytical models are presented for high-brightness electron beams of a few femtoseconds or even hundreds of attoseconds, and transverse beam sizes on the micron scale, as generated by today's free electron lasers. Different density regimes for the utilization as a potential diagnostics are explored, and the fundamental differences in plasma dynamical behavior for e-beam or photon-based ionization are highlighted. By measuring the dynamics of field-induced ions for different gas and beam densities, a lower bound on the beam charge density can be obtained in a single shot and in a noninvasive way. The exponential dependency of the ionization yield on the beam properties can provide unprecedented spatial and temporal resolution, at the submicrometer and subfemtosecond scales, respectively, offering a practical and powerful approach to characterizing beams from accelerators at the frontiers of performance.

Material properties of Pacific hake, Humboldt squid, and two species of myctophids in the California Current.

PubMed

Becker, Kaylyn N; Warren, Joseph D

2015-05-01

Material properties of the flesh from three fish species (Merluccius productus, Symbolophorus californiensis, and Diaphus theta), and several body parts of the Humboldt squid (Dosidicus gigas) collected from the California Current ecosystem were measured. The density contrast relative to seawater varied within and among taxa for fish flesh (0.9919-1.036), squid soft body parts (mantle, arms, tentacle, braincase, eyes; 1.009-1.057), and squid hard body parts (beak and pen; 1.085-1.459). Effects of animal length and environmental conditions on nekton density contrast were investigated. The sound speed contrast relative to seawater varied within and among taxa for fish flesh (0.986-1.027) and Humboldt squid mantle and braincase (0.937-1.028). Material properties in this study are similar to values from previous studies on species with similar life histories. In general, the sound speed and density of soft body parts of fish and squid were 1%-3% and 1%-6%, respectively, greater than the surrounding seawater. Hard parts of the squid were significantly more dense (6%-46%) than seawater. The material properties reported here can be used to improve target strength estimates from acoustic scattering models, which could increase the accuracy of biomass estimates from acoustic surveys for these nekton.

Comparison of the detectability of high- and low-contrast details on a TFT screen and a CRT screen designed for radiologic diagnosis.

PubMed

Kotter, Elmar; Bley, Thorsten A; Saueressig, Ulrich; Fisch, Dagmar; Springer, Oliver; Winterer, Jan Torsten; Schaefer, Oliver; Langer, Mathias

2003-11-01

To evaluate the detection rate of fine details of a new thin-film transistor (TFT) grayscale monitor designed for radiologic diagnosis, compared with a type of cathode ray tube (CRT) screen used routinely for diagnostic radiology. Fifteen radiographs of a statistical phantom presenting low- and high-contrast details were obtained and read out with an Agfa ADC compact storage phosphor system. Each radiograph presented 60 high-density (high-contrast) and 60 low-density (low-contrast) test bodies. Approximately half the test bodies contained holes with different diameters. Observers were asked to detect the presence or absence of a hole in the test body on a 5-point confidence range. The total of 1800 test bodies was reviewed by 5 radiologists on the TFT monitor (20.8 inches; 1536 x 2048 pixels; maximum luminance, 650 cd/m2; contrast, 600:1) and the CRT monitor (21 inches; P45 Phosphor; 2048 x 2560 pixels operated at 1728 x 2304 pixels; maximum luminance, 600 cd/m2; contrast, 300:1). The data were analyzed by receiver-operator characteristic analysis. For high-contrast details, the mean area under the curve rated 0.9336 for the TFT monitor and 0.9312 for the CRT monitor. For low-contrast details, the mean area under the curve rated 0.9189 for the TFT monitor and 0.9224 for the CRT monitor. At P

Quantifications of dendrochronological information from contrasting microdensitometric measuring circumstances of experimental wood samples.

PubMed

Helama, S; Bégin, Y; Vartiainen, M; Peltola, H; Kolström, T; Meriläinen, J

2012-06-01

We analyzed how the pretreatment method of Scots pine (Pinus sylvestris L.) wood specimens together with X-ray methodology applied for density analyses affect resulting tree-ring data and derived proxy-based climate information. We also evaluated whether these results from two contrasting laboratory circumstances could be homogenized by applying dendroclimatic statistical methods. For this study, we measured a pair of X-ray based microdensitometry datasets using double samples of subfossil and recent wood specimens. Dendrochronological information of earlywood and latewood series was examined to determine for alterations in the resulting data. We found that the level of overall density, its trend over cambial ages and the growth amplitude altered due to the sample pretreatment/density measuring exercise, which means that comparisons of heterogeneous datasets should be, in general, regarded cautiously. Dendrochronological standardization did, however, even out several potentially biasing influences from the differing overall densities and their trends. The two latewood (maximum) density chronologies yielded paleoclimatic reconstructions which both calibrated and verified satisfactorily with the instrumental warm-season (March-September) mean temperatures. The transfer functions were found to further equalize the differences between the two proxy records. We recommend (if no strictly homogenous data are available) reconciling similar data assemblages through transfer functions with multiple independent variables. Copyright © 2012 Elsevier Ltd. All rights reserved.

Automated, contour-based tracking and analysis of cell behaviour over long time scales in environments of varying complexity and cell density.

PubMed

Baker, Richard M; Brasch, Megan E; Manning, M Lisa; Henderson, James H

2014-08-06

Understanding single and collective cell motility in model environments is foundational to many current research efforts in biology and bioengineering. To elucidate subtle differences in cell behaviour despite cell-to-cell variability, we introduce an algorithm for tracking large numbers of cells for long time periods and present a set of physics-based metrics that quantify differences in cell trajectories. Our algorithm, termed automated contour-based tracking for in vitro environments (ACTIVE), was designed for adherent cell populations subject to nuclear staining or transfection. ACTIVE is distinct from existing tracking software because it accommodates both variability in image intensity and multi-cell interactions, such as divisions and occlusions. When applied to low-contrast images from live-cell experiments, ACTIVE reduced error in analysing cell occlusion events by as much as 43% compared with a benchmark-tracking program while simultaneously tracking cell divisions and resulting daughter-daughter cell relationships. The large dataset generated by ACTIVE allowed us to develop metrics that capture subtle differences between cell trajectories on different substrates. We present cell motility data for thousands of cells studied at varying densities on shape-memory-polymer-based nanotopographies and identify several quantitative differences, including an unanticipated difference between two 'control' substrates. We expect that ACTIVE will be immediately useful to researchers who require accurate, long-time-scale motility data for many cells. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

The Changing Sensory and Sympathetic Innervation of the Young, Adult and Aging Mouse Femur.

PubMed

Chartier, Stephane R; Mitchell, Stefanie A T; Majuta, Lisa A; Mantyh, Patrick W

2018-02-10

Although bone is continually being remodeled and ultimately declines with aging, little is known whether similar changes occur in the sensory and sympathetic nerve fibers that innervate bone. Here, immunohistochemistry and confocal microscopy were used to examine changes in the sensory and sympathetic nerve fibers that innervate the young (10 days post-partum), adult (3 months) and aging (24 months) C57Bl/6 mouse femur. In all three ages examined, the periosteum was the most densely innervated bone compartment. With aging, the total number of sensory and sympathetic nerve fibers clearly declines as the cambium layer of the periosteum dramatically thins. Yet even in the aging femur, there remains a dense sensory and sympathetic innervation of the periosteum. In cortical bone, sensory and sympathetic nerve fibers are largely confined to vascularized Haversian canals and while there is no significant decline in the density of sensory fibers, there was a 75% reduction in sympathetic nerve fibers in the aging vs. adult cortical bone. In contrast, in the bone marrow the overall density/unit area of both sensory and sympathetic nerve fibers appeared to remain largely unchanged across the lifespan. The preferential preservation of sensory nerve fibers suggests that even as bone itself undergoes a marked decline with age, the nociceptors that detect injury and signal skeletal pain remain relatively intact. Copyright © 2018 The Author(s). Published by Elsevier Ltd.. All rights reserved.

The formation of disc galaxies in high-resolution moving-mesh cosmological simulations

NASA Astrophysics Data System (ADS)

Marinacci, Federico; Pakmor, Rüdiger; Springel, Volker

2014-01-01

We present cosmological hydrodynamical simulations of eight Milky Way-sized haloes that have been previously studied with dark matter only in the Aquarius project. For the first time, we employ the moving-mesh code AREPO in zoom simulations combined with a comprehensive model for galaxy formation physics designed for large cosmological simulations. Our simulations form in most of the eight haloes strongly disc-dominated systems with realistic rotation curves, close to exponential surface density profiles, a stellar mass to halo mass ratio that matches expectations from abundance matching techniques, and galaxy sizes and ages consistent with expectations from large galaxy surveys in the local Universe. There is no evidence for any dark matter core formation in our simulations, even so they include repeated baryonic outflows by supernova-driven winds and black hole quasar feedback. For one of our haloes, the object studied in the recent `Aquila' code comparison project, we carried out a resolution study with our techniques, covering a dynamic range of 64 in mass resolution. Without any change in our feedback parameters, the final galaxy properties are reassuringly similar, in contrast to other modelling techniques used in the field that are inherently resolution dependent. This success in producing realistic disc galaxies is reached, in the context of our interstellar medium treatment, without resorting to a high density threshold for star formation, a low star formation efficiency, or early stellar feedback, factors deemed crucial for disc formation by other recent numerical studies.

Weak lensing by galaxy troughs in DES Science Verification data

DOE PAGES

Gruen, D.; Friedrich, O.; Amara, A.; ...

2015-11-29

In this study, we measure the weak lensing shear around galaxy troughs, i.e. the radial alignment of background galaxies relative to underdensities in projections of the foreground galaxy field over a wide range of redshift in Science Verification data from the Dark Energy Survey. Our detection of the shear signal is highly significant (10σ–15σ for the smallest angular scales) for troughs with the redshift range z ϵ [0.2, 0.5] of the projected galaxy field and angular diameters of 10 arcmin…1°. These measurements probe the connection between the galaxy, matter density, and convergence fields. By assuming galaxies are biased tracers ofmore » the matter density with Poissonian noise, we find agreement of our measurements with predictions in a fiducial Λ cold dark matter model. The prediction for the lensing signal on large trough scales is virtually independent of the details of the underlying model for the connection of galaxies and matter. Our comparison of the shear around troughs with that around cylinders with large galaxy counts is consistent with a symmetry between galaxy and matter over- and underdensities. In addition, we measure the two-point angular correlation of troughs with galaxies which, in contrast to the lensing signal, is sensitive to galaxy bias on all scales. The lensing signal of troughs and their clustering with galaxies is therefore a promising probe of the statistical properties of matter underdensities and their connection to the galaxy field.« less

Double inflation - A possible resolution of the large-scale structure problem

NASA Technical Reports Server (NTRS)

Turner, Michael S.; Villumsen, Jens V.; Vittorio, Nicola; Silk, Joseph; Juszkiewicz, Roman

1987-01-01

A model is presented for the large-scale structure of the universe in which two successive inflationary phases resulted in large small-scale and small large-scale density fluctuations. This bimodal density fluctuation spectrum in an Omega = 1 universe dominated by hot dark matter leads to large-scale structure of the galaxy distribution that is consistent with recent observational results. In particular, large, nearly empty voids and significant large-scale peculiar velocity fields are produced over scales of about 100 Mpc, while the small-scale structure over less than about 10 Mpc resembles that in a low-density universe, as observed. Detailed analytical calculations and numerical simulations are given of the spatial and velocity correlations.

Non-invasive, Multimodal Functional Imaging of the Intestine with Frozen Micellar Naphthalocyanines

PubMed Central

Zhang, Yumiao; Jeon, Mansik; Rich, Laurie J.; Hong, Hao; Geng, Jumin; Zhang, Yin; Shi, Sixiang; Barnhart, Todd E.; Alexandridis, Paschalis; Huizinga, Jan D.; Seshadri, Mukund; Cai, Weibo; Kim, Chulhong; Lovell, Jonathan F.

2014-01-01

Overview There is a need for safer and improved methods for non-invasive imaging of the gastrointestinal tract. Modalities based on X-ray radiation, magnetic resonance and ultrasound suffer from limitations with respect to safety, accessibility or lack of adequate contrast. Functional intestinal imaging of dynamic gut processes has not been practical using existing approaches. Here, we report the development of a family of nanoparticles that can withstand the harsh conditions of the stomach and intestine, avoid systemic absorption, and give rise to good optical contrast for photoacoustic imaging. The hydrophobicity of naphthalocyanine dyes was exploited to generate purified ~20 nm frozen micelles, which we call nanonaps, with tunable and large near-infrared absorption values (>1000). Unlike conventional chromophores, nanonaps exhibited non-shifting spectra at ultrahigh optical densities and, following oral administration in mice, passed safely through the gastrointestinal tract. Non-invasive, non-ionizing photoacoustic techniques were used to visualize nanonap intestinal distribution with low background and remarkable resolution with 0.5 cm depth, and enabled real-time intestinal functional imaging with ultrasound co-registration. Positron emission tomography following seamless nanonap radiolabelling allowed complementary whole body imaging. PMID:24997526

Hexadecameric structure of an invertebrate gap junction channel.

PubMed

Oshima, Atsunori; Matsuzawa, Tomohiro; Murata, Kazuyoshi; Tani, Kazutoshi; Fujiyoshi, Yoshinori

2016-03-27

Innexins are invertebrate-specific gap junction proteins with four transmembrane helices. These proteins oligomerize to constitute intercellular channels that allow for the passage of small signaling molecules associated with neural and muscular electrical activity. In contrast to the large number of structural and functional studies of connexin gap junction channels, few structural studies of recombinant innexin channels are reported. Here we show the three-dimensional structure of two-dimensionally crystallized Caenorhabditis elegans innexin-6 (INX-6) gap junction channels. The N-terminal deleted INX-6 proteins are crystallized in lipid bilayers. The three-dimensional reconstruction determined by cryo-electron crystallography reveals that a single INX-6 gap junction channel comprises 16 subunits, a hexadecamer, in contrast to chordate connexin channels, which comprise 12 subunits. The channel pore diameters at the cytoplasmic entrance and extracellular gap region are larger than those of connexin26. Two bulb densities are observed in each hemichannel, one in the pore and the other at the cytoplasmic side of the hemichannel in the channel pore pathway. These findings imply a structural diversity of gap junction channels among multicellular organisms. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Crustal structure of the Murray Ridge, northwest Indian Ocean, from wide-angle seismic data

NASA Astrophysics Data System (ADS)

Minshull, T. A.; Edwards, R. A.; Flueh, E. R.

2015-07-01

The Murray Ridge/Dalrymple Trough system forms the boundary between the Indian and Arabian plates in the northern Arabian Sea. Geodetic constraints from the surrounding continents suggest that this plate boundary is undergoing oblique extension at a rate of a few millimetres per year. We present wide-angle seismic data that constrains the composition of the Ridge and of adjacent lithosphere beneath the Indus Fan. We infer that Murray Ridge, like the adjacent Dalrymple Trough, is underlain by continental crust, while a thin crustal section beneath the Indus Fan represents thinned continental crust or exhumed serpentinized mantle that forms part of a magma-poor rifted margin. Changes in crustal structure across the Murray Ridge and Dalrymple Trough can explain short-wavelength gravity anomalies, but a long-wavelength anomaly must be attributed to deeper density contrasts that may result from a large age contrast across the plate boundary. The origin of this fragment of continental crust remains enigmatic, but the presence of basement fabrics to the south that are roughly parallel to Murray Ridge suggests that it separated from the India/Seychelles/Madagascar block by extension during early breakup of Gondwana.

Towards the Moho depth and Moho density contrast along with their uncertainties from seismic and satellite gravity observations

NASA Astrophysics Data System (ADS)

Abrehdary, M.; Sjöberg, L. E.; Bagherbandi, M.; Sampietro, D.

2017-12-01

We present a combined method for estimating a new global Moho model named KTH15C, containing Moho depth and Moho density contrast (or shortly Moho parameters), from a combination of global models of gravity (GOCO05S), topography (DTM2006) and seismic information (CRUST1.0 and MDN07) to a resolution of 1° × 1° based on a solution of Vening Meinesz-Moritz' inverse problem of isostasy. This paper also aims modelling of the observation standard errors propagated from the Vening Meinesz-Moritz and CRUST1.0 models in estimating the uncertainty of the final Moho model. The numerical results yield Moho depths ranging from 6.5 to 70.3 km, and the estimated Moho density contrasts ranging from 21 to 650 kg/m3, respectively. Moreover, test computations display that in most areas estimated uncertainties in the parameters are less than 3 km and 50 kg/m3, respectively, but they reach to more significant values under Gulf of Mexico, Chile, Eastern Mediterranean, Timor sea and parts of polar regions. Comparing the Moho depths estimated by KTH15C and those derived by KTH11C, GEMMA2012C, CRUST1.0, KTH14C, CRUST14 and GEMMA1.0 models shows that KTH15C agree fairly well with CRUST1.0 but rather poor with other models. The Moho density contrasts estimated by KTH15C and those of the KTH11C, KTH14C and VMM model agree to 112, 31 and 61 kg/m3 in RMS. The regional numerical studies show that the RMS differences between KTH15C and Moho depths from seismic information yields fits of 2 to 4 km in South and North America, Africa, Europe, Asia, Australia and Antarctica, respectively.

Assessing tumor vascularization as a potential biomarker of imatinib resistance in gastrointestinal stromal tumors by dynamic contrast-enhanced magnetic resonance imaging.

PubMed

Consolino, Lorena; Longo, Dario Livio; Sciortino, Marianna; Dastrù, Walter; Cabodi, Sara; Giovenzana, Giovanni Battista; Aime, Silvio

2017-07-01

Most metastatic gastrointestinal stromal tumors (GISTs) develop resistance to the first-line imatinib treatment. Recently, increased vessel density and angiogenic markers were reported in GISTs with a poor prognosis, suggesting that angiogenesis is implicated in GIST tumor progression and resistance. The purpose of this study was to investigate the relationship between tumor vasculature and imatinib resistance in different GIST mouse models using a noninvasive magnetic resonance imaging (MRI) functional approach. Immunodeficient mice (n = 8 for each cell line) were grafted with imatinib-sensitive (GIST882 and GIST-T1) and imatinib-resistant (GIST430) human cell lines. Dynamic contrast-enhanced MRI (DCE-MRI) was performed on GIST xenografts to quantify tumor vessel permeability (K trans ) and vascular volume fraction (v p ). Microvessel density (MVD), permeability (mean dextran density, MDD), and angiogenic markers were evaluated by immunofluorescence and western blot assays. Dynamic contrast-enhanced magnetic resonance imaging showed significantly increased vessel density (P < 0.0001) and permeability (P = 0.0002) in imatinib-resistant tumors compared to imatinib-sensitive ones. Strong positive correlations were observed between MRI estimates, K trans and v p , and their related ex vivo values, MVD (r = 0.78 for K trans and r = 0.82 for v p ) and MDD (r = 0.77 for K trans and r = 0.94 for v p ). In addition, higher expression of vascular endothelial growth factor receptors (VEGFR2 and VEFGR3) was seen in GIST430. Dynamic contrast-enhanced magnetic resonance imaging highlighted marked differences in tumor vasculature and microenvironment properties between imatinib-resistant and imatinib-sensitive GISTs, as also confirmed by ex vivo assays. These results provide new insights into the role that DCE-MRI could play in GIST characterization and response to GIST treatment. Validation studies are needed to confirm these findings.

Contrast media controversies in 2015: imaging patients with renal impairment or risk of contrast reaction.

PubMed

Davenport, Matthew S; Cohan, Richard H; Ellis, James H

2015-06-01

The incidence and significance of complications related to intravascular contrast material administration have become increasingly controversial. This review will highlight current thinking regarding the imaging of patients with renal impairment and those at risk for an allergiclike contrast reaction. The risk of contrast-induced acute kidney injury remains uncertain for patients with an estimated glomerular filtration rate (GFR) less than 45 mL/min/1.73 m(2), but if there is a risk, it is greatest in those with estimated GFR less than 30 mL/min/1.73 m(2). In this population, low-risk gadolinium-based contrast agents appear to have a large safety margin. Corticosteroid prophylaxis remains the standard of care in the United States for patients identified to be at high risk of a contrast reaction, but it has an incomplete mitigating effect on contrast reaction rates and the number needed to treat is large.

Socioeconomic status affects mosquito (Diptera: Culicidae) larval habitat type availability and infestation level.

PubMed

Dowling, Zara; Ladeau, Shannon L; Armbruster, Peter; Biehler, Dawn; Leisnham, Paul T

2013-07-01

Mosquito populations are largely regulated by processes occurring at the larval stage. We sampled mosquito larval microhabitats (mostly water-holding containers) in six neighborhoods in the Washington, DC, area that varied in socioeconomic status (SES) and housing structure (row houses vs. stand-alone houses) to test associations among these neighborhood characteristics, microhabitat abundance and parameters, and mosquito occurrence and densities. Thirty-four percent (33.9%) of sampled microhabitats contained mosquito larvae, and 93.1% of larvae were Aedes albopictus Skuse or Culex pipiens L. Five specific container types (drains, corrugated flexible drainpipes, planters, garbage cans, and buckets) accounted for the majority of water-holding (56.0%) and mosquito-positive (50.6%) microhabitats sampled. We found no associations between SES or housing structure with total microhabitat abundance per yard, mosquito occurrence or mosquito densities per microhabitat. In contrast, container purpose varied with SES, with low SES neighborhoods having greater numbers of disused containers and lower numbers of functional containers than low and medium SES neighborhoods. Ae. albopictus were 83% more abundant in disused containers, whereas Cx. pipiens were more abundant in structural and functional containers, possibly owing to species-specific oviposition and development related to water quality. Ae. albopictus densities increased over the summer, whereas Cx. pipiens densities remained constant. Ae. albopictus is usually the dominant pest in urban areas in the eastern United States; therefore, integrated mosquito management programs should incorporate the elimination of disused containers to reduce its infestation and adult production, especially in low SES neighborhoods where they occur most frequently.

Adsorption and transport of charged vs. neutral hydrophobic molecules at the membrane of murine erythroleukemia (MEL) cells.

PubMed

Zeng, Jia; Eckenrode, Heather M; Dai, Hai-Lung; Wilhelm, Michael J

2015-03-01

The adsorption and transport of hydrophobic molecules at the membrane surface of pre- and post-DMSO induced differentiated murine erythroleukemia (MEL) cells were examined by time- and wavelength-resolved second harmonic light scattering. Two medium (<600 Da) hydrophobic molecules, cationic malachite green (MG) and neutral bromocresol purple (BCP), were investigated. While it was observed that the MG cation adsorbs onto the surface of the MEL cell, neutral BCP does not. It is suggested that an electrostatic interaction between the opposite charges of the cation and the MEL cell surface is the primary driving force for adsorption. Comparisons of adsorption density and free energy, measured at different pH and cell morphology, indicate that the interaction is predominantly through sialic acid carboxyl groups. MG cation adsorption densities have been determined as (0.6±0.3)×10(6) μm(-2) on the surface of undifferentiated MEL cells, and (1.8±0.5)×10(7) μm(-2) on differentiated MEL cells, while the deduced adsorption free energies are effectively identical (ca. -10.9±0.1 and -10.8±0.1 kcal mol(-1), respectively). The measured MG densities indicate that the total number of surface carboxyl groups is largely conserved following differentiation, and therefore the density of carboxylic groups is much larger on the differentiated cell surface than the undifferentiated one. Finally, in contrast to synthetic liposomes and bacterial membranes, surface adsorbed MG cations are unable to traverse the MEL cell membrane. Copyright © 2015 Elsevier B.V. All rights reserved.

Using simulation models to investigate the cumulative effects of sowing rate, sowing date and cultivar choice on weed competition.

PubMed

Andrew, Izzadora K S; Storkey, Jonathan

2017-05-01

With the increasing pressure on crop production from the evolution of herbicide resistance, farmers are increasingly adopting Integrated Weed Management (IWM) strategies to augment their weed control. These include measures to increase the competitiveness of the crop canopy such as increased sowing rate and the use of more competitive cultivars. While there are data on the relative impact of these non-chemical weed control methods assessed in isolation, there is uncertainty about their combined contribution, which may be hindering their adoption. In this article, the INTERCOM simulation model of crop/weed competition was used to examine the combined impact of crop density, sowing date and cultivar choice on the outcomes of competition between wheat ( Triticum aestivum ) and Alopecurus myosuroides . Alopecurus myosuroides is a problematic weed of cereal crops in North-Western Europe and the primary target for IWM in the UK because it has evolved resistance to a range of herbicides. The model was parameterised for two cultivars with contrasting competitive ability, and simulations run across 10 years at different crop densities and two sowing dates. The results suggest that sowing date, sowing density and cultivar choice largely work in a complementary fashion, allowing enhanced competitive ability against weeds when used in combination. However, the relative benefit of choosing a more competitive cultivar decreases at later sowing dates and higher crop densities. Modeling approaches could be further employed to examine the effectiveness of IWM, reducing the need for more expensive and cumbersome long-term in situ experimentation.

Disentangling trophic relationships in a High Arctic tundra ecosystem through food web modeling.

PubMed

Legagneux, P; Gauthier, G; Berteaux, D; Bêty, J; Cadieux, M C; Bilodeau, F; Bolduc, E; McKinnon, L; Tarroux, A; Therrien, J F; Morissette, L; Krebs, C J

2012-07-01

Determining the manner in which food webs will respond to environmental changes is difficult because the relative importance of top-down vs. bottom-up forces in controlling ecosystems is still debated. This is especially true in the Arctic tundra where, despite relatively simple food webs, it is still unclear which forces dominate in this ecosystem. Our primary goal was to assess the extent to which a tundra food web was dominated by plant-herbivore or predator-prey interactions. Based on a 17-year (1993-2009) study of terrestrial wildlife on Bylot Island, Nunavut, Canada, we developed trophic mass balance models to address this question. Snow Geese were the dominant herbivores in this ecosystem, followed by two sympatric lemming species (brown and collared lemmings). Arctic foxes, weasels, and several species of birds of prey were the dominant predators. Results of our trophic models encompassing 19 functional groups showed that <10% of the annual primary production was consumed by herbivores in most years despite the presence of a large Snow Goose colony, but that 20-100% of the annual herbivore production was consumed by predators. The impact of herbivores on vegetation has also weakened over time, probably due to an increase in primary production. The impact of predators was highest on lemmings, intermediate on passerines, and lowest on geese and shorebirds, but it varied with lemming abundance. Predation of collared lemmings exceeded production in most years and may explain why this species remained at low density. In contrast, the predation rate on brown lemmings varied with prey density and may have contributed to the high-amplitude, periodic fluctuations in the abundance of this species. Our analysis provided little evidence that herbivores are limited by primary production on Bylot Island. In contrast, we measured strong predator-prey interactions, which supports the hypothesis that this food web is primarily controlled by top-down forces. The presence of allochthonous resources subsidizing top predators and the absence of large herbivores may partly explain the predominant role of predation in this low-productivity ecosystem.

Improvements in Quantifying Bank Erosion for Sediment Budgets within the Chesapeake Bay Watershed by Integrating Structure-From-Motion Photogrammetry

NASA Astrophysics Data System (ADS)

Bell, J. M.; Cashman, M. J.; Nibert, L.; Jackson, S.

2017-12-01

Fine sediment is a major source of pollution due to its ability to attenuate light, smother habitat, and sorb and transport nutrients, such as phosphorus and nitrogen. Piedmont streams in the Mid-Atlantic region of the United States are frequently characterized as incised with steep, highly erodible banks of legacy sediment that can contribute to high sediment loads. Multiple sediment fingerprinting studies in this region have demonstrated that stream banks can contribute a large proportion of the total sediment load, but stream banks are frequently overlooked in sediment delivery models and Total Maximum Daily Load allocations. The direct quantification of bank erosion is therefore essential to producing accurate sediment budgets, which are needed to inform the targeted mitigation and remediation of degraded fluvial systems. This study contrasts the use of traditional bank pin measurements, structure-from-motion photogrammetric techniques, and aerial LIDAR at sites within Maryland, USA. Bank pin measurements, representing only single points in space, were found to be highly variable with subjective initial placement often missing nearby, large-scale bank failures. In contrast, photogrammetric techniques, using structure-from-motion, were able to capture a more spatially-complete streambank profile. Using a Nikon D810 camera, bank scans were able to reconstruct banks with a RMSE as low as 0.1mm and repeat scan alignment resolution of <2mm. However, during summer months, photogrammetry exhibited some coverage gaps in areas of high vegetation density. Difference-maps rendered from multiple UAV structure-from-motion scans provided an ability to rapidly assess changes to river channel morphology during leaf-off conditions. Additionally, UAV-derived scans were georeferenced over historical LIDAR data to evaluate historical bank-erosion over multi-year timescales. Future work will include difference mapping channel features at watershed scales. This photogrammetric approach of quantifying geomorphic change, when coupled with bank-sediment bulk density, has promise to accurately quantify volumetric change as well as sediment loads originating from bank erosion, and may provide valuable data of the quantification of bank erosion for incorporation into regional sediment models.

Big bang nucleosynthesis and the quark-hadron transition

NASA Technical Reports Server (NTRS)

Kurki-Suonio, Hannu; Matzner, Richard A.; Olive, Keith A.; Schramm, David N.

1990-01-01

An examination and brief review is made of the effects of quark-hadron transition induced fluctuations on Big Bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogeneous calculations might be loosened by as much as 50 percent, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N(sub nu) is less than or approximately 4. To achieve baryon densities of greater than or approximately 0.3 of critical density would require initial density contrasts R is much greater the 10(exp e), whereas the simplest models for the transition seem to restrict R to less than of approximately 10(exp 2).

Big Bang nucleosynthesis and the Quark-Hadron transition

NASA Technical Reports Server (NTRS)

Kurki-Suonio, Hannu; Matzner, Richard A.; Olive, Keith A.; Schramm, David N.

1989-01-01

An examination and brief review is made of the effects of quark-hadron transistion induced fluctuations on Big Bang nucleosynthesis. It is shown that cosmologically critical densities in baryons are difficult to reconcile with observation, but the traditional baryon density constraints from homogeneous calculations might be loosened by as much as 50 percent, to 0.3 of critical density, and the limit on the number of neutrino flavors remains about N(sub nu) is less than or approximately 4. To achieve baryon densities of greater than or approximately 0.3 of critical density would require initial density contrasts R is much greater the 10(exp 3), whereas the simplest models for the transition seem to restrict R to less than of approximately 10(exp 2).

Probing ultrafast dynamics of solid-density plasma generated by high-contrast intense laser pulses

NASA Astrophysics Data System (ADS)

Jana, Kamalesh; Blackman, David R.; Shaikh, Moniruzzaman; Lad, Amit D.; Sarkar, Deep; Dey, Indranuj; Robinson, Alex P. L.; Pasley, John; Ravindra Kumar, G.

2018-01-01

We present ultrafast dynamics of solid-density plasma created by high-contrast (picosecond contrast ˜10-9), high-intensity (˜4 × 1018 W/cm2) laser pulses using time-resolved pump-probe Doppler spectrometry. Experiments show a rapid rise in blue-shift at early time delay (2-4.3 ps) followed by a rapid fall (4.3-8.3 ps) and then a slow rise in blue-shift at later time delays (>8.3 ps). Simulations show that the early-time observations, specifically the absence of any red-shifting of the reflected probe, can only be reproduced if the front surface is unperturbed by the laser pre-pulse at the moment that the high intensity pulse arrives. A flexible diagnostic which is capable of diagnosing the presence of low-levels of pre-plasma formation would be useful for potential applications in laser-produced proton and ion production, such as cancer therapy and security imaging.

The large-scale correlations of multicell densities and profiles: implications for cosmic variance estimates

NASA Astrophysics Data System (ADS)

Codis, Sandrine; Bernardeau, Francis; Pichon, Christophe

2016-08-01

In order to quantify the error budget in the measured probability distribution functions of cell densities, the two-point statistics of cosmic densities in concentric spheres is investigated. Bias functions are introduced as the ratio of their two-point correlation function to the two-point correlation of the underlying dark matter distribution. They describe how cell densities are spatially correlated. They are computed here via the so-called large deviation principle in the quasi-linear regime. Their large-separation limit is presented and successfully compared to simulations for density and density slopes: this regime is shown to be rapidly reached allowing to get sub-percent precision for a wide range of densities and variances. The corresponding asymptotic limit provides an estimate of the cosmic variance of standard concentric cell statistics applied to finite surveys. More generally, no assumption on the separation is required for some specific moments of the two-point statistics, for instance when predicting the generating function of cumulants containing any powers of concentric densities in one location and one power of density at some arbitrary distance from the rest. This exact `one external leg' cumulant generating function is used in particular to probe the rate of convergence of the large-separation approximation.

Large-scale structure of randomly jammed spheres

NASA Astrophysics Data System (ADS)

Ikeda, Atsushi; Berthier, Ludovic; Parisi, Giorgio

2017-05-01

We numerically analyze the density field of three-dimensional randomly jammed packings of monodisperse soft frictionless spherical particles, paying special attention to fluctuations occurring at large length scales. We study in detail the two-point static structure factor at low wave vectors in Fourier space. We also analyze the nature of the density field in real space by studying the large-distance behavior of the two-point pair correlation function, of density fluctuations in subsystems of increasing sizes, and of the direct correlation function. We show that such real space analysis can be greatly improved by introducing a coarse-grained density field to disentangle genuine large-scale correlations from purely local effects. Our results confirm that both Fourier and real space signatures of vanishing density fluctuations at large scale are absent, indicating that randomly jammed packings are not hyperuniform. In addition, we establish that the pair correlation function displays a surprisingly complex structure at large distances, which is however not compatible with the long-range negative correlation of hyperuniform systems but fully compatible with an analytic form for the structure factor. This implies that the direct correlation function is short ranged, as we also demonstrate directly. Our results reveal that density fluctuations in jammed packings do not follow the behavior expected for random hyperuniform materials, but display instead a more complex behavior.

Paws without claws? Ecological effects of large carnivores in anthropogenic landscapes

PubMed Central

Sahlén, E.; Elmhagen, B.; Chamaillé-Jammes, S.; Sand, H.; Lone, K.; Cromsigt, J. P. G. M.

2016-01-01

Large carnivores are frequently presented as saviours of biodiversity and ecosystem functioning through their creation of trophic cascades, an idea largely based on studies coming primarily out of relatively natural landscapes. However, in large parts of the world, particularly in Europe, large carnivores live in and are returning to strongly human-modified ecosystems. At present, we lack a coherent framework to predict the effects of large carnivores in these anthropogenic landscapes. We review how human actions influence the ecological roles of large carnivores by affecting their density or behaviour or those of mesopredators or prey species. We argue that the potential for density-mediated trophic cascades in anthropogenic landscapes is limited to unproductive areas where even low carnivore numbers may impact prey densities or to the limited parts of the landscape where carnivores are allowed to reach ecologically functional densities. The potential for behaviourally mediated trophic cascades may be larger and more widespread, because even low carnivore densities affect prey behaviour. We conclude that predator–prey interactions in anthropogenic landscapes will be highly context-dependent and human actions will often attenuate the ecological effects of large carnivores. We highlight the knowledge gaps and outline a new research avenue to study the role of carnivores in anthropogenic landscapes. PMID:27798302

Estimation of contrast of refraction contrast imaging compared with absorption imaging-basic approach.

PubMed

Hirano, Masatsugu; Yamasaki, Katsuhito; Okada, Hiroshi; Kitazawa, Sohei; Kitazawa, Riko; Ohno, Yoshiharu; Sakurai, Takashi; Kondoh, Takeshi; Ohbayashi, Chiho; Katafuchi, Tetsuro; Maeda, Sakan; Sugimura, Kazuro; Tamura, Shinichi

2005-03-01

We discuss the usefulness of the refraction contrast method using highly parallel X-rays as a new approach to minute lung cancer detection. The advantages of refraction contrast images are discussed in terms of contrast, and a comparison is made with absorption images. We simulated refraction contrast imaging using globules with the density of water in air as models for minute lung cancer detection. The contrast intensified by bright and dark lines was compared on a globule with the contrast of absorption images. We adopted the Monte Carlo simulation to determine the strength of the profile curve of the photon counts at the detector. The obtained contrasts were more intense by two to three digits than those obtainable with the absorption contrast imaging method. The contrast in refraction contrast imaging was more intense than that obtainable with absorption contrast imaging. A two to three digit improvement in contrast means that it is possible to greatly reduce the exposure dose necessary for imaging. Therefore, it is expected to become possible to detect the interfaces of soft tissues, which are difficult to capture with conventional absorption imaging, at low dosages and high resolution.

Comparing ab initio density-functional and wave function theories: the impact of correlation on the electronic density and the role of the correlation potential.

PubMed

Grabowski, Ireneusz; Teale, Andrew M; Śmiga, Szymon; Bartlett, Rodney J

2011-09-21

The framework of ab initio density-functional theory (DFT) has been introduced as a way to provide a seamless connection between the Kohn-Sham (KS) formulation of DFT and wave-function based ab initio approaches [R. J. Bartlett, I. Grabowski, S. Hirata, and S. Ivanov, J. Chem. Phys. 122, 034104 (2005)]. Recently, an analysis of the impact of dynamical correlation effects on the density of the neon atom was presented [K. Jankowski, K. Nowakowski, I. Grabowski, and J. Wasilewski, J. Chem. Phys. 130, 164102 (2009)], contrasting the behaviour for a variety of standard density functionals with that of ab initio approaches based on second-order Møller-Plesset (MP2) and coupled cluster theories at the singles-doubles (CCSD) and singles-doubles perturbative triples [CCSD(T)] levels. In the present work, we consider ab initio density functionals based on second-order many-body perturbation theory and coupled cluster perturbation theory in a similar manner, for a range of small atomic and molecular systems. For comparison, we also consider results obtained from MP2, CCSD, and CCSD(T) calculations. In addition to this density based analysis, we determine the KS correlation potentials corresponding to these densities and compare them with those obtained for a range of ab initio density functionals via the optimized effective potential method. The correlation energies, densities, and potentials calculated using ab initio DFT display a similar systematic behaviour to those derived from electronic densities calculated using ab initio wave function theories. In contrast, typical explicit density functionals for the correlation energy, such as VWN5 and LYP, do not show behaviour consistent with this picture of dynamical correlation, although they may provide some degree of correction for already erroneous explicitly density-dependent exchange-only functionals. The results presented here using orbital dependent ab initio density functionals show that they provide a treatment of exchange and correlation contributions within the KS framework that is more consistent with traditional ab initio wave function based methods.

Global carbon sequestration in tidal, saline wetland soils

USGS Publications Warehouse

Chmura, G.L.; Anisfeld, S.C.; Cahoon, D.R.; Lynch, J.C.

2003-01-01

Wetlands represent the largest component of the terrestrial biological carbon pool and thus play an important role in global carbon cycles. Most global carbon budgets, however, have focused on dry land ecosystems that extend over large areas and have not accounted for the many small, scattered carbon-storing ecosystems such as tidal saline wetlands. We compiled data for 154 sites in mangroves and salt marshes from the western and eastern Atlantic and Pacific coasts, as well as the Indian Ocean, Mediterranean Ocean, and Gulf of Mexico. The set of sites spans a latitudinal range from 22.4??S in the Indian Ocean to 55.5??N in the northeastern Atlantic. The average soil carbon density of mangrove swamps (0.055 ?? 0.004 g cm-3) is significantly higher than the salt marsh average (0.039 ?? 0.003 g cm-3). Soil carbon density in mangrove swamps and Spartina patens marshes declines with increasing average annual temperature, probably due to increased decay rates at higher temperatures. In contrast, carbon sequestration rates were not significantly different between mangrove swamps and salt marshes. Variability in sediment accumulation rates within marshes is a major control of carbon sequestration rates masking any relationship with climatic parameters. Globally, these combined wetlands store at least 44.6 Tg C yr-1 and probably more, as detailed areal inventories are not available for salt marshes in China and South America. Much attention has been given to the role of freshwater wetlands, particularly northern peatlands, as carbon sinks. In contrast to peatlands, salt marshes and mangroves release negligible amounts of greenhouse gases and store more carbon per unit area. Copyright 2003 by the American Geophysical Union.

Multiphase Dynamics of Magma Oceans

NASA Astrophysics Data System (ADS)

Boukaré, Charles-Edouard; Ricard, Yanick; Parmentier, Edgar M.

2017-04-01

Since the earliest study of the Apollo lunar samples, the magma ocean hypothesis has received increasing consideration for explaining the early evolution of terrestrial planets. Giant impacts seem to be able to melt significantly large planets at the end of their accretion. The evolution of the resulting magma ocean would set the initial conditions (thermal and compositionnal structure) for subsequent long-term solid-state planet dynamics. However, magma ocean dynamics remains poorly understood. The major challenge relies on understanding interactions between the physical properties of materials (e.g., viscosity (at liquid or solid state), buoyancy) and the complex dynamics of an extremely vigorously convecting system. Such complexities might be neglected in cases where liquidus/adiabat interactions and density stratification leads to stable situations. However, interesting possibilities arise when exploring magma ocean dynamics in other regime. In the case of the Earth, recent studies have shown that the liquidus might intersect the adiabat at mid-mantle depth and/or that solids might be buoyant at deep mantle conditions. These results require the consideration of more sophisticated scenarios. For instance, how does bottom-up crystallization look with buoyant crystals? To understand this complex dynamics, we develop a multiphase phase numerical code that can handle simultaneously phase change, the convection in each phase and in the slurry, as well as the compaction or decompaction of the two phases. Although our code can only run in a limited parameter range (Rayleigh number, viscosity contrast between phases, Prandlt number), it provides a rich dynamics that illustrates what could have happened. For a given liquidus/adiabat configuration and density contrast between melt and solid, we explore magma ocean scenarios by varying the relative timescales of three first order processes: solid-liquid separation, thermo-chemical convective motions and magma ocean cooling.

Compensatory increases in nuclear PGC1alpha protein are primarily associated with subsarcolemmal mitochondrial adaptations in ZDF rats.

PubMed

Holloway, Graham P; Gurd, Brendon J; Snook, Laelie A; Lally, Jamie; Bonen, Arend

2010-04-01

We examined in insulin-resistant muscle if, in contrast to long-standing dogma, mitochondrial fatty acid oxidation is increased and whether this is attributed to an increased nuclear content of peroxisome proliferator-activated receptor (PPAR) gamma coactivator (PGC) 1alpha and the adaptations of specific mitochondrial subpopulations. Skeletal muscles from male control and Zucker diabetic fatty (ZDF) rats were used to determine 1) intramuscular lipid distribution, 2) subsarcolemmal and intermyofibrillar mitochondrial morphology, 3) rates of palmitate oxidation in subsarcolemmal and intermyofibrillar mitochondria, and 4) the subcellular localization of PGC1alpha. Electotransfection of PGC1alpha cDNA into lean animals tested the notion that increased nuclear PGC1alpha preferentially targeted subsarcolemmal mitochondria. Transmission electron microscope analysis revealed that in ZDF animals the number (+50%), width (+69%), and density (+57%) of subsarcolemmal mitochondria were increased (P < 0.05). In contrast, intermyofibrillar mitochondria remained largely unchanged. Rates of palmitate oxidation were approximately 40% higher (P < 0.05) in ZDF subsarcolemmal and intermyofibrillar mitochondria, potentially as a result of the increased PPAR-targeted proteins, carnitine palmitoyltransferase-I, and fatty acid translocase (FAT)/CD36. PGC1alpha mRNA and total protein were not altered in ZDF animals; however, a greater (approximately 70%; P < 0.05) amount of PGC1alpha was located in nuclei. Overexpression of PGC1alpha only increased subsarcolemmal mitochondrial oxidation rates. In ZDF animals, intramuscular lipids accumulate in the intermyofibrillar region (increased size and number), and this is primarily associated with increased oxidative capacity in subsarcolemmal mitochondria (number, size, density, and oxidation rates). These changes may result from an increased nuclear content of PGC1alpha, as under basal conditions, overexpression of PGC1alpha appears to target subsarcolemmal mitochondria.

Comparative quantitative assessment of the human corneal sub-basal nerve plexus by in vivo confocal microscopy and histological staining.

PubMed

Kowtharapu, B S; Winter, K; Marfurt, C; Allgeier, S; Köhler, B; Hovakimyan, M; Stahnke, T; Wree, A; Stachs, O; Guthoff, R F

2017-03-01

PurposeThis study was designed to compare and contrast quantitative data of the human corneal sub-basal nerve plexus (SBP) evaluated by two different methods: in vivo confocal microscopy (IVCM), and immunohistochemical staining of ex vivo donor corneas.MethodsSeven parameters of the SBP in large-scale IVCM mosaicking images from healthy subjects were compared with the identical parameters in ex vivo donor corneas stained by β-III-tubulin immunohistochemistry. Corneal nerve fiber length (CNFL), corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), average weighted corneal nerve fiber tortuosity (CNFTo), corneal nerve connection points (CNCP), average corneal nerve single-fiber length (CNSFL), and average weighted corneal nerve fiber thickness (CNFTh) were calculated using a dedicated, published algorithm and compared.ResultsOur experiments showed significantly higher values for CNFL (50.2 vs 21.4 mm/mm 2 ), CNFD (1358.8 vs 277.3 nerve fibers/mm 2 ), CNBD (847.6 vs 163.5 branches/mm 2 ), CNFTo (0.095 vs 0.081 μm -1 ), and CNCP (49.4 vs 21.6 connections/mm 2 ) in histologically staining specimens compared with IVCM images. In contrast, CNSFL values were higher in IVCM images than in histological specimens (32.1 vs 74.1 μm). No significant difference was observed in CNFTh (2.22 vs 2.20 μm) between the two groups.ConclusionsThe results of this study have shown that IVCM has an inherently lower resolution compared with ex vivo immunohistochemical staining of the corneal SBP and that this limitation leads to a systematic underestimation of several SBP parameters. Despite this shortcoming, IVCM is a vital clinical tool for in vivo characterization, quantitative clinical imaging, and evaluation of the human corneal SBP.

Canopy transpiration for two Japanese cypress forests with contrasting structures

NASA Astrophysics Data System (ADS)

Tsuruta, K.; Komatsu, H.; Kume, T.; Shinohara, Y.; Otsuki, K.

2012-12-01

Canopy transpiration (EC) could have large variations among stands with different structures. To evaluate a difference in EC between stands with different structures for Japanese cypress, we observed EC using the sap flow technique in two stands with contrasting structures (age was 19 year and 99 year, mean diameter at breast height was 13.5 cm and 44.6 cm, stem density was 2100 trees ha-1 and 350 trees ha-1, respectively) for 5 months under the same meteorological condition. The mean stand sap flux density (JS) for measurement period and stand sapwood area (AS_stand) for the old stand (0.43 m3 m-2 day-1 and 15.2 m2 ha-1) were lower than those for the young stand (0.62 m3 m-2 day-1 and 20.4 m2 ha-1) by 31.1 % and 25.4 %, respectively. EC is calculated as a product of JS and AS_stand. Therefore the EC in the old stand was lower than that in the young stand by 50 %. We calculated the contribution of the reference JS for a given meteorological conditions (JSref) and the response of JS to the meteorological conditions (JSresp) in the two stands, and examined which is a primary factor for the difference of EC between the two studied stands. The JSresp for the young stand were not considerably different from that for the old stand, whereas JSref for the young stand was greater than that for the old stand. This indicates that JSref (not JSresp) was the primary cause for the difference of EC between the two stands. Further studies observing EC from stands with various structures are needed to generalize our conclusions.

Ramsey interferometry of Rydberg ensembles inside microwave cavities

NASA Astrophysics Data System (ADS)

Sommer, Christian; Genes, Claudiu

2018-06-01

We study ensembles of Rydberg atoms in a confined electromagnetic environment such as is provided by a microwave cavity. The competition between standard free space Ising type and cavity-mediated interactions leads to the emergence of different regimes where the particle‑particle couplings range from the typical van der Waals r ‑6 behavior to r ‑3 and to r-independence. We apply a Ramsey spectroscopic technique to map the two-body interactions into a characteristic signal such as intensity and contrast decay curves. As opposed to previous treatments requiring high-densities for considerable contrast and phase decay (Takei et al 2016 Nat. Comms. 7 13449; Sommer et al 2016 Phys. Rev. A 94 053607), the cavity scenario can exhibit similar behavior at much lower densities.

Effect of copper on the recombination activity of extended defects in silicon

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

Feklisova, O. V., E-mail: feklisov@iptm.ru; Yakimov, E. B.

2015-06-15

The effect of copper atoms introduced by high-temperature diffusion on the recombination properties of dislocations and dislocation trails in p-type single-crystal silicon is studied by the electron-beam-induced current technique. It is shown that, in contrast to dislocations, dislocation trails exhibit an increase in recombination activity after the introduction of copper. Bright contrast appearance in the vicinity of dislocation trails is detected after the diffusion of copper and quenching of the samples. The contrast depends on the defect density in these trails.