WorldWideScience

Sample records for singleton earth convection

  1. Might electrical earthing affect convection of light

    International Nuclear Information System (INIS)

    Budrikis, Z.L.

    1982-01-01

    Partial convection of light by moving media was predicted by Fresnel and verified by Fizeau, Zeeman and others. It is accepted as an important argument in favour of the Special Theory of Relativity. The suggestion is made here that the convection is partial only when the propagating medium is moved with respect to its electrically earthed surroundings and that it would be total if an earthed shield was co-moving with the medium. This is based on a reinterpretation of Maxwell's equations wherein they are seen as macroscopic relationships that are in each case valid only in respect of a particular inertial frame of reference, the local electrical earth frame. (Auth.)

  2. Translation and convection of Earth's inner core

    Science.gov (United States)

    Monnereau, M.; Calvet, M.; Margerin, L.; Mizzon, H.; Souriau, A.

    2012-12-01

    The image of the inner core growing slowly at the center of the Earth by gradual cooling and solidification of the surrounding liquid outer core is being replaced by the more vigorous image of a ``deep foundry'', where melting and crystallization rates exceed by many times the net growth rate. Recently, a particular mode of convection, called translation, has been put forward as an important mode of inner core dynamics because this mechanism is able to explain the observed East-West asymmetry of P-wave velocity and attenuation (Monnereau et al. 2010). Translation is a pure solid displacement of the inner core material (solid iron) within its envelop, implying crystallization of entering iron on one side of the inner core and melting on the opposite side. Translation is consistent with multiple scattering models of wave propagation. If they do not experience deformation, iron crystals grow as they transit from one hemisphere to the other. Larger crystals constituting a faster and more attenuating medium, a translation velocity of some cm/yr (about ten times the growth rate) is enough to account for the superficial asymmetry observed for P-wave velocity and attenuation, with grains of a few hundred meters on the crystallizing side (West) growing up to a few kilometers before melting on the East side, and a drift direction located in the equatorial plane. Among all hypotheses that have been proposed to account for the seismic asymmetry, translation is the only one based on a demonstrated link between the seismic data and the proposed dynamics, notably through a model of seismic wave propagation. This mechanism was also proposed to be responsible for the formation of a dense layer at the bottom of the outer core, since the high rate of melting and crystallization would release a liquid depleted in light elements at the surface of the inner core (Alboussiere et al 2010). This would explain the anomalously low gradient of P wave velocity in the lowermost 200 km of the

  3. Scaling of Convection and Plate Tectonics in Super-Earths

    Science.gov (United States)

    Valencia, D. C.; O'Connell, R. J.; Sasselov, D. D.

    2006-12-01

    The discovery of three Super-Earths around different stars, possible only in the last year, prompts us to study the characteristics of our planet within a general context. The Earth, being the most massive terrestrial object in the solar system is the only planet that exhibits plate tectonics. We think this might not be a coincidence and explore the role that mass plays in determining the mode of convection. We use the scaling of convective vigor with Rayleigh number commonly used in parameterized convection. We study how the parameters controlling convection: Rayleigh number (Ra), boundary layer thickness (δ), internal temperature (T_i) and convective velocities (u) scale with mass. This is possible from the scaling of heat flux, mantle density, size and gravity with mass which we reported in Valencia, et. al 2006. The extrapolation to massive rocky planets is done from our knowledge of the Earth. Even though uncertainties arise from extrapolation and assumptions are needed we consider this simple scaling to be a first adequate step. As the mass of a planet increases, Ra increases, yielding a decrease in δ and an increase in u, while T_i increases very slightly. This is true for an isoviscous case and is more accentuated in a temperature dependent viscosity scenario. In a planet with vigorous convection (high u), a thin lithosphere (low δ) is easier to subduct and hence, initiate plate tectonics. The lithosphere also has to be dense enough (cold and thick) to have the bouyancy necessary for subduction. We calculate that a convective cycle for an isoviscous planet is τ ~ M^{-0.3} considering whole mantle convection. Meaning that if these planets have continents, the timescale for continental rearrangement is shorter (about half the Earth's for a 5 earth-mass planet). Additionally, we explore the negative feedback cycle between convection and temperature dependent viscosity and estimate a timescale for this effect.

  4. Convection and waves on Small Earth and Deep Atmosphere

    Directory of Open Access Journals (Sweden)

    Noureddine Semane

    2015-06-01

    Full Text Available A scaled version of the European Centre for Medium-Range Weather Forecasts (ECMWF spectral hydrostatic forecast model (IFS has been developed with full physics using an Aqua planet configuration. This includes Kuang et al.'s Small Earth Diabatic Acceleration and REscaling (DARE/SE approach bringing the synoptic scale a factor γ closer to the convective scale by reducing the Earth radius by γ, and increasing the rotation rate and all diabatic processes by the same factor. Furthermore, the scaled version also provides an alternative system to DARE/SE, dubbed ‘Deep Atmosphere Diabatic Acceleration and REscaling’ (DARE/DA, which reduces gravity by a factor γ and thereby increases the horizontal scale of convection by γ, while only weakly affecting the large-scale flow. The two approaches have been evaluated using a T159 spectral truncation and γ = 8 with the deep convection scheme switched off. The evaluation is against the baseline unscaled model at T1279 spectral resolution without deep convection parametrisation, as well as the unscaled T159 model using the deep convection parametrisation. It is shown that the DARE/SE and DARE/DA systems provide fairly equivalent results, while the DARE/DA system seems to be the preferred choice as it damps divergent modes, providing a better climatology, and is technically easier to implement. However, neither of the systems could reproduce the motion range and modes of the high-resolution spectral model. Higher equivalent horizontal resolution in the 1–10 km range and the full non-hydrostatic system might be necessary to successfully simulate the convective and large-scale explicitly at reduced cost.

  5. Earth's core convection: Boussinesq approximation or incompressible approach?

    Czech Academy of Sciences Publication Activity Database

    Anufriev, A. P.; Hejda, Pavel

    2010-01-01

    Roč. 104, č. 1 (2010), s. 65-83 ISSN 0309-1929 R&D Projects: GA AV ČR IAA300120704 Grant - others:INTAS(XE) 03-51-5807 Institutional research plan: CEZ:AV0Z30120515 Keywords : geodynamic models * core convection * Boussinesq approximation Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 0.831, year: 2010

  6. Water-induced convection in the Earth's mantle transition zone

    Science.gov (United States)

    Richard, Guillaume C.; Bercovici, David

    2009-01-01

    Water enters the Earth's mantle by subduction of oceanic lithosphere. Most of this water immediately returns to the atmosphere through arc volcanism, but a part of it is expected as deep as the mantle transition zone (410-660 km depth). There, slabs can be deflected and linger before sinking into the lower mantle. Because it lowers the density and viscosity of the transition zone minerals (i.e., wadsleyite and ringwoodite), water is likely to affect the dynamics of the transition zone mantle overlying stagnant slabs. The consequences of water exchange between a floating slab and the transition zone are investigated. In particular, we focus on the possible onset of small-scale convection despite the adverse thermal gradient (i.e., mantle is cooled from below by the slab). The competition between thermal and hydrous effects on the density and thus on the convective stability of the top layer of the slab is examined numerically, including water-dependent density and viscosity and temperature-dependent water solubility. For plausible initial water content in a slab (≥0.5 wt %), an episode of convection is likely to occur after a relatively short time delay (5-20 Ma) after the slab enters the transition zone. However, water induced rheological weakening is seen to be a controlling parameter for the onset time of convection. Moreover, small-scale convection above a stagnant slab greatly enhances the rate of slab dehydration. Small-scale convection also facilitates heating of the slab, which in itself may prolong the residence time of the slab in the transition zone.

  7. First Principles Analysis of Convection in the Earth's Mantle, Eustatic Sea Level and Earth Volume

    Science.gov (United States)

    Kinsland, G. L.

    2011-12-01

    Steady state convection (convection whereby heat leaving the mantle at the top is equal to the heat entering the mantle across the core mantle boundary and that created within the mantle) of the Earth's mantle is, to a very good approximation, both a constant mass and constant volume process. Mass or volume which moves to one place; e.g., an oceanic ridge; must be accompanied by mass or volume removed from another place. The location of removal, whether from underneath of an ocean or a continent, determines the relationship between oceanic ridge volume and eustatic sea level. If all of the volume entering a ridge were to come from under an oceanic basin then the size of the ridge would not affect eustatic sea level as it would be compensated by a lowering of the sea floor elsewhere. If the volume comes from under a continent then the hypsometry of the continent becomes important. Thus, eustatic sea level is not simply related to convection rate and oceanic ridge volume as posited by Hays and Pitman(1973). Non-steady state convection is still a constant mass process but is not a constant volume process. The mantle experiences a net gain of heat, warms and expands during periods of relatively slow convection (that being convection rate which is less than that necessary to transport incoming and internally created heat to the surface). Conversely, the mantle has a net loss of heat, cools and contracts during periods of relatively rapid convection. The Earth itself expands and contracts as the mantle does. During rapid convection more volume is delivered from the interior of the mantle to the Earth's ridge system than during slow convection. The integral of the difference of ridge system volume between fast and slow convection over a fast-slow convection cycle is a measure of the difference in volume of the mantle over a cycle. The magnitude of the Earth's volume expansion and contraction as calculated from published values for the volume of ocean ridges and is about

  8. Convectively driven decadal zonal accelerations in Earth's fluid core

    Science.gov (United States)

    More, Colin; Dumberry, Mathieu

    2018-04-01

    Azimuthal accelerations of cylindrical surfaces co-axial with the rotation axis have been inferred to exist in Earth's fluid core on the basis of magnetic field observations and changes in the length-of-day. These accelerations have a typical timescale of decades. However, the physical mechanism causing the accelerations is not well understood. Scaling arguments suggest that the leading order torque averaged over cylindrical surfaces should arise from the Lorentz force. Decadal fluctuations in the magnetic field inside the core, driven by convective flows, could then force decadal changes in the Lorentz torque and generate zonal accelerations. We test this hypothesis by constructing a quasi-geostrophic model of magnetoconvection, with thermally driven flows perturbing a steady, imposed background magnetic field. We show that when the Alfvén number in our model is similar to that in Earth's fluid core, temporal fluctuations in the torque balance are dominated by the Lorentz torque, with the latter generating mean zonal accelerations. Our model reproduces both fast, free Alfvén waves and slow, forced accelerations, with ratios of relative strength and relative timescale similar to those inferred for the Earth's core. The temporal changes in the magnetic field which drive the time-varying Lorentz torque are produced by the underlying convective flows, shearing and advecting the magnetic field on a timescale associated with convective eddies. Our results support the hypothesis that temporal changes in the magnetic field deep inside Earth's fluid core drive the observed decadal zonal accelerations of cylindrical surfaces through the Lorentz torque.

  9. Singleton strings

    International Nuclear Information System (INIS)

    Engquist, J.; Sundell, P.; Tamassia, L.

    2007-01-01

    The group theoretical structure underlying physics in anti de Sitter (AdS) spacetime is intrinsically different with respect to the flat case, due to the presence of special ultra-short representations, named singletons, that do not admit a flat space limit. The purpose of this collaboration is to exploit this feature in the study of string and brane dynamics in AdS spacetime, in particular while trying to establish a connection between String Theory in AdS backgrounds (in the tensionless limit) and Higher-Spin Gauge Theory. (orig.)

  10. Thermal histories of convective earth models and constraints on radiogenic heat production in the earth

    International Nuclear Information System (INIS)

    Davies, G.F.

    1980-01-01

    Thermal histories have been calculated for simple models of the earth which assume that heat is transported by convection throughout the interior. The application of independent constraints to these solutions limits the acceptable range of the ratio of present radiogenic heat production in the earth to the present surface heat flux. The models use an empirical relation between the rate of convective heat transport and the temperature difference across a convecting fluid. This is combined with an approximate proportionality between effective mantle viscosity and T/sup -n/, where T is temperature and it is argued that n is about 30 throughout the mantle. The large value of n causes T to be strongly buffered against changes in the earth's energy budget and shortens by an order of magnitude the response time of surface heat flux to changes in energy budget as compared to less temperature-dependent heat transport mechanisms. Nevertheless, response times with n=30 are still as long as 1 or 2 b.y. Assuming that the present heat flux is entirely primordial (i.e., nonradiogenic) in a convective model leads back to unrealistically high temperatures about 1.7 b.y. ago. Inclusion of exponentially decaying (i.e., radiogenic) heat sources moves the high temperatures further into the past and leads to a transition from 'hot' to 'cool' calculated thermal histories for the case when the present rate of heat production is near 50% of the present rate of heat loss. Requiring the calculated histories to satisfy minimal geological constraints limits the present heat production/heat loss ratio to between about 0.3 and 0.85. Plausible stronger constraints narrow this range to between 0.45 and 0.65. These results are compatible with estimated radiogentic heat production rates in some meteorites and terrestrial rocks, with a whole-earth K/U ratio of 1--2 x 10 4 giving optimal agreement

  11. Convective cells of internal gravity waves in the earth's atmosphere with finite temperature gradient

    Directory of Open Access Journals (Sweden)

    O. Onishchenko

    2013-03-01

    Full Text Available In this paper, we have investigated vortex structures (e.g. convective cells of internal gravity waves (IGWs in the earth's atmosphere with a finite vertical temperature gradient. A closed system of nonlinear equations for these waves and the condition for existence of solitary convective cells are obtained. In the atmosphere layers where the temperature decreases with height, the presence of IGW convective cells is shown. The typical parameters of such structures in the earth's atmosphere are discussed.

  12. Mixing properties of thermal convection in the earth's mantle

    NARCIS (Netherlands)

    Schmalzl, J.T.

    1996-01-01

    The structure of mantle convection will greatly influence the generation and the survival of compositional heterogeneities. Conversely, geochemical observations can be used to obtain information about heterogeneities in the mantle and then, with certain model assumptions, information about the

  13. Preconception and prenatal urinary concentrations of phenols and birth size of singleton infants born to mothers and fathers from the Environment and Reproductive Health (EARTH) study.

    Science.gov (United States)

    Messerlian, Carmen; Mustieles, Vicente; Minguez-Alarcon, Lidia; Ford, Jennifer B; Calafat, Antonia M; Souter, Irene; Williams, Paige L; Hauser, Russ

    2018-05-01

    Although pregnancy concentrations of some phenols have been associated with infant size at birth, there is limited data on the effect of preconception exposure. We aimed to examine paternal and maternal preconception and maternal prenatal urinary phenol concentrations in relation to birth weight and head circumference. We evaluated 346 singletons born to 346 mothers and 184 fathers (184 couples) from a prospective preconception cohort of subfertile couples from the Environment and Reproductive Health (EARTH) Study in Boston, USA. We used multiple urine samples collected before the index pregnancy in both men and women to estimate mean preconception urinary benzophenone-3, triclosan, butylparaben, propylparaben, methylparaben, or ethylparaben concentrations. We also estimated mean maternal prenatal urinary phenol concentrations by averaging trimester-specific urine samples. Birth weight and head circumference were abstracted from delivery records. We estimated the association of natural log-phenol concentrations with birth outcomes using multivariable linear regression models, adjusting for known confounders. In adjusted models, each log-unit increase in paternal preconception benzophenone-3 concentration was associated with a 137 g increase in birth weight (95% CI: 60, 214). Additional adjustment for prenatal benzophenone-3 concentration strengthened this association. None of the maternal preconception phenol concentrations were associated with birth weight. However, maternal prenatal triclosan concentrations were associated with a 38 g decrease in birth weight (95% CI: -76, 0). Few associations were observed between phenols and head circumference except for a decrease of 0.27 cm (95% CI: -54, 0) in relation to maternal preconception methylparaben concentration. Although our findings should be interpreted in light of inherent study limitations, these results suggest potential evidence of associations between some paternal or maternal phenol concentrations and

  14. Geodynamo and mantle convection simulations on the Earth Simulator using the Yin-Yang grid

    International Nuclear Information System (INIS)

    Kageyama, Akira; Yoshida, Masaki

    2005-01-01

    We have developed finite difference codes based on the Yin-Yang grid for the geodynamo simulation and the mantle convection simulation. The Yin-Yang grid is a kind of spherical overset grid that is composed of two identical component grids. The intrinsic simplicity of the mesh configuration of the Yin-Yang grid enables us to develop highly optimized simulation codes on massively parallel supercomputers. The Yin-Yang geodynamo code has achieved 15.2 Tflops with 4096 processors on the Earth Simulator. This represents 46% of the theoretical peak performance. The Yin-Yang mantle code has enabled us to carry out mantle convection simulations in realistic regimes with a Rayleigh number of 10 7 including strongly temperature dependent viscosity with spatial contrast up to 10 6

  15. Microwave heating device for internal heating convection experiments, applied to Earth's mantle dynamics.

    Science.gov (United States)

    Surducan, E; Surducan, V; Limare, A; Neamtu, C; Di Giuseppe, E

    2014-12-01

    We report the design, construction, and performances of a microwave (MW) heating device for laboratory experiments with non-contact, homogeneous internal heating. The device generates MW radiation at 2.47 GHz from a commercial magnetron supplied by a pulsed current inverter using proprietary, feedback based command and control hardware and software. Specially designed MW launchers direct the MW radiation into the sample through a MW homogenizer, devised to even the MW power distribution into the sample's volume. An adjustable MW circuit adapts the MW generator to the load (i.e., the sample) placed in the experiment chamber. Dedicated heatsinks maintain the MW circuits at constant temperature throughout the experiment. Openings for laser scanning for image acquisition with a CCD camera and for the cooling circuits are protected by special MW filters. The performances of the device are analyzed in terms of heating uniformity, long term output power stability, and load matching. The device is used for small scale experiments simulating Earth's mantle convection. The 30 × 30 × 5 cm(3) convection tank is filled with a water‑based viscous fluid. A uniform and constant temperature is maintained at the upper boundary by an aluminum heat exchanger and adiabatic conditions apply at the tank base. We characterize the geometry of the convective regime as well as its bulk thermal evolution by measuring the velocity field by Particle Image Velocimetry and the temperature field by using Thermochromic Liquid Crystals.

  16. Tomographic and Geodynamic Constraints on Convection-Induced Mixing in Earth's Deep Mantle

    Science.gov (United States)

    Hafter, D. P.; Forte, A. M.; Bremner, P. M.; Glisovic, P.

    2017-12-01

    Seismological studies reveal two large low-shear-velocity provinces (LLSVPs) in the lowermost mantle (e.g., Su et al. 1994; Wang & Wen 2007; He & Wen 2012), which may represent accumulations of subducted slabs at the CMB (Tan & Gurnis 2005; Christensen & Hoffman 1994) or primordial material generated in the early differentiation of Earth (e.g. Li et al. 2014). The longevity or stability of these large-scale heterogeneities in the deep mantle depends on the vigor and spatial distribution of the convective circulation, which is in turn dependent on the distribution of mantle buoyancy and viscosity (e.g. Glisovic & Forte 2015). Here we explore the state of convective mixing in the mantle using the ASPECT convection code (Kronbichler et al. 2012). A series of experiments are conducted to consider the geochemical and dynamical contributions of LLSVPs to deep-mantle upwellings and corresponding plume-sourced volcanism. The principal feature of these experiments is the use of particle tracers to track geochemical changes in the LLSVPs and mantle plumes in addition to identifying those parts of the mantle that may remain unmixed. We employ 3-D mantle density anomalies derived from joint inversions of seismic, geodynamic and mineral physics constraints and geodynamically-constrained viscosity distributions (Glisovic et al. 2015) to ensure that the predicted flow fields yield a good match to key geophysical constraints (e.g. heat flow, global gravity anomalies and plate velocities).

  17. Microwave heating device for internal heating convection experiments, applied to Earth's mantle dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Surducan, E.; Surducan, V.; Neamtu, C., E-mail: camelia.neamtu@itim-cj.ro [National Institute for Research and Development of Isotopic and Molecular Technologies (INCDTIM), 67-103 Donat St., 400293, Cluj‑Napoca (Romania); Limare, A.; Di Giuseppe, E. [Institut de Physique du Globe de Paris (IPGP), Univ. Paris Diderot, UMR CNRS 7154, 1 rue Jussieu, 75005, Paris (France)

    2014-12-15

    We report the design, construction, and performances of a microwave (MW) heating device for laboratory experiments with non-contact, homogeneous internal heating. The device generates MW radiation at 2.47 GHz from a commercial magnetron supplied by a pulsed current inverter using proprietary, feedback based command and control hardware and software. Specially designed MW launchers direct the MW radiation into the sample through a MW homogenizer, devised to even the MW power distribution into the sample's volume. An adjustable MW circuit adapts the MW generator to the load (i.e., the sample) placed in the experiment chamber. Dedicated heatsinks maintain the MW circuits at constant temperature throughout the experiment. Openings for laser scanning for image acquisition with a CCD camera and for the cooling circuits are protected by special MW filters. The performances of the device are analyzed in terms of heating uniformity, long term output power stability, and load matching. The device is used for small scale experiments simulating Earth's mantle convection. The 30 × 30 × 5 cm{sup 3} convection tank is filled with a water‑based viscous fluid. A uniform and constant temperature is maintained at the upper boundary by an aluminum heat exchanger and adiabatic conditions apply at the tank base. We characterize the geometry of the convective regime as well as its bulk thermal evolution by measuring the velocity field by Particle Image Velocimetry and the temperature field by using Thermochromic Liquid Crystals.

  18. Stochastic generation of MAC waves and implications for convection in Earth's core

    Science.gov (United States)

    Buffett, Bruce; Knezek, Nicholas

    2018-03-01

    Convection in Earth's core can sustain magnetic-Archemedes-Coriolis (MAC) waves through a variety of mechanisms. Buoyancy and Lorentz forces are viable sources for wave motion, together with the effects of magnetic induction. We develop a quantitative description for zonal MAC waves and assess the source mechanisms using a numerical dynamo model. The largest sources at conditions accessible to the dynamo model are due to buoyancy forces and magnetic induction. However, when these sources are extrapolated to conditions expected in Earth's core, the Lorentz force emerges as the dominant generation mechanism. This source is expected to produce wave velocities of roughly 2 km yr-1 when the internal magnetic field is characterized by a dimensionless Elsasser number of roughly Λ ≈ 10 and the root-mean-square convective velocity defines a magnetic Reynolds number of Rm ≈ 103. Our preferred model has a radially varying stratification and a constant (radial) background magnetic field. It predicts a broad power spectrum for the wave velocity with most power distributed across periods from 30 to 100 yr.

  19. Numerical experiments on thermal convection of highly compressible fluids with variable viscosity and thermal conductivity: Implications for mantle convection of super-Earths

    Science.gov (United States)

    Kameyama, Masanori; Yamamoto, Mayumi

    2018-01-01

    We conduct a series of numerical experiments of thermal convection of highly compressible fluids in a two-dimensional rectangular box, in order to study the mantle convection on super-Earths. The thermal conductivity and viscosity are assumed to exponentially depend on depth and temperature, respectively, while the variations in thermodynamic properties (thermal expansivity and reference density) with depth are taken to be relevant for the super-Earths with 10 times the Earth's. From our experiments we identified a distinct regime of convecting flow patterns induced by the interplay between the adiabatic temperature change and the spatial variations in viscosity and thermal conductivity. That is, for the cases with strong temperature-dependent viscosity and depth-dependent thermal conductivity, a "deep stratosphere" of stable thermal stratification is formed at the base of the mantle, in addition to thick stagnant lids at their top surfaces. In the "deep stratosphere", the fluid motion is insignificant particularly in the vertical direction in spite of smallest viscosity owing to its strong dependence on temperature. Our finding may further imply that some of super-Earths which are lacking in mobile tectonic plates on their top surfaces may have "deep stratospheres" at the base of their mantles.

  20. Flat-space singletons

    International Nuclear Information System (INIS)

    Fronsdal, C.

    1987-01-01

    Singletons exist, as particles and as local fields, only in 3+2 de Sitter space. Their kinematical properties make them natural candidates for constituents of massless fields, and perhaps for quarks. It is interesting to find out how to describe this type of compositeness in flat space. A theory of interacting singleton fields in de Sitter space is now available, and in this paper we study the flat-space limit of the Green's functions of that theory. The flat-space limit is an autonomous theory of Green's functions, but is not an operator field theory. The three-point function is calculated and its flat-space limit is found to reveal glimpses of a physical interpretation. Causal and spectral properties are in accord with the tenets of axiomatic field theory. The theory is a generalization of local field theory, in which photons appear as composite objects although the physical S matrix is the same as in conventional QED

  1. Empirical links between the local runaway greenhouse, super-greenhouse, and deep convection in Earth's tropics

    Science.gov (United States)

    Dewey, M. C.; Goldblatt, C.

    2017-12-01

    Energy balance requires that energy absorbed and emitted at the top of the atmosphere equal; this is maintained via the Planck feedback whereby outgoing longwave radiation (OLR) increases as surface temperature increases. There are two cases where this breaks down: the runaway greenhouse (known from planetary sciences theory) characterized by an asymptotic limit on OLR from moist atmospheres, and the super-greenhouse (known from tropical meteorology observations) where OLR decreases with surface temperature when the atmosphere is moist aloft. Here we show that the runaway greenhouse limit can be empirically observed and constrained in Earth's tropics, that the runaway and super-greenhouse occur as part of the same physical phenomenon, and that the transition through the super-greenhouse to a local runaway greenhouse is intimately linked to the onset of deep convection. A runaway greenhouse occurs when water vapour causes the troposphere to become optically thick to thermal radiation from the surface and a limit on OLR emerges as thermal emission is from a constant temperature level aloft. This limit is modelled as 282 W/m/m [Goldblatt et al, 2013]. Using satellite data from Earth's tropics, we find an empirical value of this limit of 280 W/m/m, in excellent agreement with the model.A column transitioning to a runaway greenhouse typically overshoots the runaway limit and then OLR decreases with increasing surface temperature until the runaway limit is reached after which OLR remains constant. The term super-greenhouse effect (SGE) has been used to describe OLR decreasing with surface warming, observed in these satellite measurements. We show the SGE is one and the same as the transition to a local runaway greenhouse, and represents a fundamental shift in the radiation response of the earth system, rather than simply an extension of water vapour feedback. This transition via SGE from an optically thin to optically thick troposphere is facilitated by enhanced

  2. An Invitation to Kitchen Earth Sciences, an Example of MISO Soup Convection Experiment in Classroom

    Science.gov (United States)

    Kurita, K.; Kumagai, I.; Davaille, A.

    2008-12-01

    In recent frontiers of earth sciences such as computer simulations and large-scale observations/experiments involved researchers are usually remote from the targets and feel difficulty in having a sense of touching the phenomena in hands. This results in losing sympathy for natural phenomena particularly among young researchers, which we consider a serious problem. We believe the analog experiments such as the subjects of "kitchen earth sciences" proposed here can be a remedy for this. Analog experiments have been used as an important tool in various research fields of earth science, particularly in the fields of developing new ideas. The experiment by H. Ramberg by using silicone pate is famous for guiding concept of the mantle dynamics. The term, "analog" means something not directly related to the target of the research but in analogical sense parallel comparison is possible. The advantages of the analog experiments however seem to have been overwhelmed by rapid progresses of computer simulations. Although we still believe in the present-day meaning, recently we are recognizing another aspect of its significance. The essence of "kitchen earth science" as an analog experiment is to provide experimental setups and materials easily from the kitchen, by which everyone can start experiments and participate in the discussion without special preparations because of our daily-experienced matter. Here we will show one such example which can be used as a heuristic subject in the classrooms at introductory level of earth science as well as in lunch time break of advanced researchers. In heated miso soup the fluid motion can be easily traced by the motion of miso "particles". At highly heated state immiscible part of miso convects with aqueous fluid. At intermediate heating the miso part precipitates to form a sediment layer at the bottom. This layered structure is destroyed regularly by the instability caused by accumulated heat in the miso layer as a bursting. By showing

  3. Plate Tectonic Cycling and Whole Mantle Convection Modulate Earth's 3He/22Ne Ratio

    Science.gov (United States)

    Dygert, N. J.; Jackson, C.; Hesse, M. A.; Tremblay, M. M.; Shuster, D. L.; Gu, J.

    2016-12-01

    3He and 22Ne are not produced in the mantle or fractionated by partial melting, and neither isotope is recycled back into the mantle by subduction of oceanic basalt or sediment. Thus, it is a surprise that large 3He/22Ne variations exist within the mantle and that the mantle has a net elevated 3He/22Ne ratio compared to volatile-rich planetary precursor materials. Depleted subcontinental lithospheric mantle and mid-ocean ridge basalt (MORB) mantle have distinctly higher 3He/22Ne compared to ocean island basalt (OIB) sources ( 4-12.5 vs. 2.5-4.5, respectively) [1,2]. The low 3He/22Ne of OIBs approaches chondritic ( 1) and solar nebula values ( 1.5). The high 3He/22Ne of the MORB mantle is not similar to solar sources or any known family of meteorites, requiring a mechanism for fractionating He from Ne in the mantle and suggesting isolation of distinct mantle reservoirs throughout geologic time. We model the formation of a MORB source with elevated and variable 3He/22Ne though diffusive exchange between dunite channel-hosted basaltic liquids and harzburgite wallrock beneath mid-ocean ridges. Over timescales relevant to mantle upwelling beneath spreading centers, He may diffuse tens to hundreds of meters into wallrock while Ne is relatively immobile, producing a regassed, depleted mantle lithosphere with elevated 3He/22Ne. Subduction of high 3He/22Ne mantle would generate a MORB source with high 3He/22Ne. Regassed, high 3He/22Ne mantle lithosphere has He concentrations 2-3 orders of magnitude lower than undegassed mantle. To preserve the large volumes of high 3He/22Ne mantle required by the MORB source, mixing between subducted and undegassed mantle reservoirs must have been limited throughout geologic time. Using the new 3He/22Ne constraints, we ran a model similar to [3] to quantify mantle mixing timescales, finding they are on the order of Gyr assuming physically reasonable seafloor spreading rates, and that Earth's convecting mantle has lost >99% of its primordial

  4. Development of a Mantle Convection Physical Model to Assist with Teaching about Earth's Interior Processes

    Science.gov (United States)

    Glesener, G. B.; Aurnou, J. M.

    2010-12-01

    The Modeling and Educational Demonstrations Laboratory (MEDL) at UCLA is developing a mantle convection physical model to assist educators with the pedagogy of Earth’s interior processes. Our design goal consists of two components to help the learner gain conceptual understanding by means of visual interactions without the burden of distracters, which may promote alternative conceptions. Distracters may be any feature of the conceptual model that causes the learner to use inadequate mental artifact to help him or her understand what the conceptual model is intended to convey. The first component, and most important, is a psychological component that links properties of “everyday things” (Norman, 1988) to the natural phenomenon, mantle convection. Some examples of everyday things may be heat rising out from a freshly popped bag of popcorn, or cold humid air falling from an open freezer. The second component is the scientific accuracy of the conceptual model. We would like to simplify the concepts for the learner without sacrificing key information that is linked to other natural phenomena the learner will come across in future science lessons. By taking into account the learner’s mental artifacts in combination with a simplified, but accurate, representation of what scientists know of the Earth’s interior, we expect the learner to have the ability to create an adequate qualitative mental simulation of mantle convection. We will be presenting some of our prototypes of this mantle convection physical model at this year’s poster session and invite constructive input from our colleagues.

  5. The Earth's mantle in a microwave oven: thermal convection driven by a heterogeneous distribution of heat sources

    Science.gov (United States)

    Fourel, Loïc; Limare, Angela; Jaupart, Claude; Surducan, Emanoil; Farnetani, Cinzia G.; Kaminski, Edouard C.; Neamtu, Camelia; Surducan, Vasile

    2017-08-01

    Convective motions in silicate planets are largely driven by internal heat sources and secular cooling. The exact amount and distribution of heat sources in the Earth are poorly constrained and the latter is likely to change with time due to mixing and to the deformation of boundaries that separate different reservoirs. To improve our understanding of planetary-scale convection in these conditions, we have designed a new laboratory setup allowing a large range of heat source distributions. We illustrate the potential of our new technique with a study of an initially stratified fluid involving two layers with different physical properties and internal heat production rates. A modified microwave oven is used to generate a uniform radiation propagating through the fluids. Experimental fluids are solutions of hydroxyethyl cellulose and salt in water, such that salt increases both the density and the volumetric heating rate. We determine temperature and composition fields in 3D with non-invasive techniques. Two fluorescent dyes are used to determine temperature. A Nd:YAG planar laser beam excites fluorescence, and an optical system, involving a beam splitter and a set of colour filters, captures the fluorescence intensity distribution on two separate spectral bands. The ratio between the two intensities provides an instantaneous determination of temperature with an uncertainty of 5% (typically 1K). We quantify mixing processes by precisely tracking the interfaces separating the two fluids. These novel techniques allow new insights on the generation, morphology and evolution of large-scale heterogeneities in the Earth's lower mantle.

  6. Slow convection of a magnetized plasma and the earth plasma sheet

    International Nuclear Information System (INIS)

    Hruska, A.

    1980-01-01

    Stationary convection of an isotropic, infinitely conducting plasma in a magnetic field with non-trivial geometry is discussed under the assumption that the inertial term in the equation of motion may be ignored. The energy gained or lost by a volume element of plasma per unit time does not vary along the field-lines. Simple relations between the components of the current density, depending on the field-line geometry, exist. Similar relations hold for the components of the plasma velocity. The theoretical analysis is applied to the geomagnetically-quiet plasma sheet and a qualitative physical picture of the sheet is suggested. The observed structure of the sheet is compatible with Axford-Hines type of convection perhaps combined with a low-speed flow from a distant neutral point. The magnetic-field-aligned currents are driven by the deformations of the closed field-lines which are enforced by the solar wind. (orig.)

  7. Archean greenstone-tonalite duality: Thermochemical mantle convection models or plate tectonics in the early Earth global dynamics?

    Science.gov (United States)

    Kerrich, Robert; Polat, Ali

    2006-03-01

    Mantle convection and plate tectonics are one system, because oceanic plates are cold upper thermal boundary layers of the convection cells. As a corollary, Phanerozoic-style of plate tectonics or more likely a different version of it (i.e. a larger number of slowly moving plates, or similar number of faster plates) is expected to have operated in the hotter, vigorously convecting early Earth. Despite the recent advances in understanding the origin of Archean greenstone-granitoid terranes, the question regarding the operation of plate tectonics in the early Earth remains still controversial. Numerical model outputs for the Archean Earth range from predominantly shallow to flat subduction between 4.0 and 2.5 Ga and well-established steep subduction since 2.5 Ga [Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940], to no plate tectonics but rather foundering of 1000 km sectors of basaltic crust, then "resurfaced" by upper asthenospheric mantle basaltic melts that generate the observed duality of basalts and tonalities [van Thienen, P., van den Berg, A.P., Vlaar, N.J., 2004a. Production and recycling of oceanic crust in the early earth. Tectonophysics 386, 41-65; van Thienen, P., Van den Berg, A.P., Vlaar, N.J., 2004b. On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth. Tectonophysics 394, 111-124]. These model outputs can be tested against the geological record. Greenstone belt volcanics are composites of komatiite-basalt plateau sequences erupted from deep mantle plumes and bimodal basalt-dacite sequences having the geochemical signatures of convergent margins; i.e. horizontally imbricated plateau and island arc crust. Greenstone belts from 3.8 to 2.5 Ga include volcanic types reported from Cenozoic convergent margins including: boninites; arc picrites; and the association of adakites-Mg andesites- and Nb-enriched basalts. Archean cratons

  8. Internally heated mantle convection and the thermal and degassing history of the earth

    Science.gov (United States)

    Williams, David R.; Pan, Vivian

    1992-01-01

    An internally heated model of parameterized whole mantle convection with viscosity dependent on temperature and volatile content is examined. The model is run for 4l6 Gyr, and temperature, heat flow, degassing and regassing rates, stress, and viscosity are calculated. A nominal case is established which shows good agreement with accepted mantle values. The effects of changing various parameters are also tested. All cases show rapid cooling early in the planet's history and strong self-regulation of viscosity due to the temperature and volatile-content dependence. The effects of weakly stress-dependent viscosity are examined within the bounds of this model and are found to be small. Mantle water is typically outgassed rapidly to reach an equilibrium concentration on a time scale of less than 200 Myr for almost all models, the main exception being for models which start out with temperatures well below the melting temperature.

  9. The Effect of Thermal Convection on Earth-Atmosphere CO2 Gas Exchange in Aggregated Soil

    Science.gov (United States)

    Ganot, Y.; Weisbrod, N.; Dragila, M. I.

    2011-12-01

    Gas transport in soils and surface-atmosphere gas exchange are important processes that affect different aspects of soil science such as soil aeration, nutrient bio-availability, sorption kinetics, soil and groundwater pollution and soil remediation. Diffusion and convection are the two main mechanisms that affect gas transport, fate and emissions in the soils and in the upper vadose zone. In this work we studied CO2 soil-atmosphere gas exchange under both day-time and night-time conditions, focusing on the impact of thermal convection (TCV) during the night. Experiments were performed in a climate-controlled laboratory. One meter long columns were packed with matrix of different grain size (sand, gravel and soil aggregates). Air with 2000 ppm CO2 was injected into the bottom of the columns and CO2 concentration within the columns was continuously monitored by an Infra Red Gas Analyzer. Two scenarios were compared for each soil: (1) isothermal conditions, representing day time conditions; and (2) thermal gradient conditions, i.e., atmosphere colder than the soil, representing night time conditions. Our results show that under isothermal conditions, diffusion is the major mechanism for surface-atmosphere gas exchange for all grain sizes; while under night time conditions the prevailing mechanism is dependent on the air permeability of the matrix: for sand and gravel it is diffusion, and for soil aggregates it is TCV. Calculated CO2 flux for the soil aggregates column shows that the TCV flux was three orders of magnitude higher than the diffusive flux.

  10. Hotspots and sunspots - Surface tracers of deep mantle convection in the earth and sun

    Science.gov (United States)

    Stothers, Richard B.

    1993-01-01

    The evolution of the hot-spot distribution on earth in time and space is investigated using available age data. The statistics of continental flood basalt eruptions suggests the formation of a total of about 40 hot spots worldwide during the Cenozoic and Mesozoic, with no true antipodal pairs found. It was found that hot spots tend to concentrate mainly in mid-latitudes, but the pattern of new appearances of hot spots may migrate from high to low latitudes in both hemispheres in long cycles, and may also drift in longitude, although much more slowly prograde.

  11. Attentional capture by masked colour singletons.

    Science.gov (United States)

    Ansorge, Ulrich; Horstmann, Gernot; Worschech, Franziska

    2010-09-15

    We tested under which conditions a colour singleton of which an observer is unaware captures attention. To prevent visual awareness of the colour singleton, we used backward masking. We find that a masked colour singleton cue captures attention if it matches the observer's goal to search for target colours but not if it is task-irrelevant. This is also reflected in event-related potentials to the visible target: the masked goal-matching cue elicits an attentional potential (N2pc) in a target search task. By contrast, a non-matching but equally strong masked colour singleton cue failed to elicit a capture effect and an N2pc. Results are discussed with regard to currently pertaining conceptions of attentional capture by colour singletons. Copyright 2010 Elsevier Ltd. All rights reserved.

  12. ISS COLUMBUS laboratory experiment `GeoFlow I and II' -fluid physics research in microgravity environment to study convection phenomena inside deep Earth and mantle

    Science.gov (United States)

    Futterer, Birgit; Egbers, Christoph; Chossat, Pascal; Hollerbach, Rainer; Breuer, Doris; Feudel, Fred; Mutabazi, Innocent; Tuckerman, Laurette

    Overall driving mechanism of flow in inner Earth is convection in its gravitational buoyancy field. A lot of effort has been involved in theoretical prediction and numerical simulation of both the geodynamo, which is maintained by convection, and mantle convection, which is the main cause for plate tectonics. Especially resolution of convective patterns and heat transfer mechanisms has been in focus to reach the real, highly turbulent conditions inside Earth. To study specific phenomena experimentally different approaches has been observed, against the background of magneto-hydrodynamic but also on the pure hydrodynamic physics of fluids. With the experiment `GeoFlow' (Geophysical Flow Simulation) instability and transition of convection in spherical shells under the influence of central-symmetry buoyancy force field are traced for a wide range of rotation regimes within the limits between non-rotating and rapid rotating spheres. The special set-up of high voltage potential between inner and outer sphere and use of a dielectric fluid as working fluid induce an electro-hydrodynamic force, which is comparable to gravitational buoyancy force inside Earth. To reduce overall gravity in a laboratory this technique requires microgravity conditions. The `GeoFlow I' experiment was accomplished on International Space Station's module COLUM-BUS inside Fluid Science Laboratory FSL und supported by EADS Astrium, Friedrichshafen, User Support und Operations Centre E-USOC in Madrid, Microgravity Advanced Research and Support Centre MARS in Naples, as well as COLUMBUS Control Center COL-CC Munich. Running from August 2008 until January 2009 it delivered 100.000 images from FSL's optical diagnostics module; here more precisely the Wollaston shearing interferometry was used. Here we present the experimental alignment with numerical prediction for the non-rotating and rapid rotation case. The non-rotating case is characterized by a co-existence of several stationary supercritical

  13. The role of upper mantle mineral phase transitions on the current structure of large-scale Earth's mantle convection.

    Science.gov (United States)

    Thoraval, C.

    2017-12-01

    Describing the large-scale structures of mantle convection and quantifying the mass transfer between upper and lower mantle request to account for the role played by mineral phase transitions in the transition zone. We build a density distribution within the Earth mantle from velocity anomalies described by global seismic tomographic models. The density distribution includes thermal anomalies and topographies of the phase transitions at depths of 410 and 660 km. We compute the flow driven by this density distribution using a 3D spherical circulation model, which account for depth-dependent viscosity. The dynamic topographies at the surface and at the CMB and the geoid are calculated as well. Within the range of viscosity profiles allowing for a satisfying restitution of the long wavelength geoid, we perform a parametric study to decipher the role of the characteristics of phase diagrams - mainly the Clapeyron's slopes - and of the kinetics of phase transitions, which may modify phase transition topographies. Indeed, when a phase transition is delayed, the boundary between two mineral phases is both dragged by the flow and interfere with it. The results are compared to recent estimations of surface dynamic topography and to the phase transition topographies as revealed by seismic studies. The consequences are then discussed in terms of structure of mantle flow. Comparisons between various tomographic models allow us to enlighten the most robust features. At last, the role played by the phase transitions on the lateral variations of mass transfer between upper and lower mantle are quantified by comparison to cases with no phase transitions and confronted to regional tomographic models, which reflect the variability of the behaviors of the descending slabs in the transition zone.

  14. Feature singletons attract spatial attention independently of feature priming.

    Science.gov (United States)

    Yashar, Amit; White, Alex L; Fang, Wanghaoming; Carrasco, Marisa

    2017-08-01

    People perform better in visual search when the target feature repeats across trials (intertrial feature priming [IFP]). Here, we investigated whether repetition of a feature singleton's color modulates stimulus-driven shifts of spatial attention by presenting a probe stimulus immediately after each singleton display. The task alternated every two trials between a probe discrimination task and a singleton search task. We measured both stimulus-driven spatial attention (via the distance between the probe and singleton) and IFP (via repetition of the singleton's color). Color repetition facilitated search performance (IFP effect) when the set size was small. When the probe appeared at the singleton's location, performance was better than at the opposite location (stimulus-driven attention effect). The magnitude of this attention effect increased with the singleton's set size (which increases its saliency) but did not depend on whether the singleton's color repeated across trials, even when the previous singleton had been attended as a search target. Thus, our findings show that repetition of a salient singleton's color affects performance when the singleton is task relevant and voluntarily attended (as in search trials). However, color repetition does not affect performance when the singleton becomes irrelevant to the current task, even though the singleton does capture attention (as in probe trials). Therefore, color repetition per se does not make a singleton more salient for stimulus-driven attention. Rather, we suggest that IFP requires voluntary selection of color singletons in each consecutive trial.

  15. Maternal Risk Factors for Singleton Preterm Births and Survival at ...

    African Journals Online (AJOL)

    Context: Risk factors for and survival of singleton preterm births may vary ... factors and survival‑to‑discharge rate for singleton preterm births at the University of ... Statistical analysis involved descriptive and inferential statistics at 95% level of ...

  16. The interaction of a magnetic cloud with the Earth - Ionospheric convection in the Northern and Southern Hemispheres for a wide range of quasi-steady interplanetary magnetic field conditions

    Science.gov (United States)

    Freeman, M. P.; Farrugia, C. J.; Burlaga, L. F.; Hairston, M. R.; Greenspan, M. E.; Ruohoniemi, J. M.; Lepping, R. P.

    1993-01-01

    Observations are presented of the ionospheric convection in cross sections of the polar cap and auroral zone as part of the study of the interaction of the Earth's magnetosphere with the magnetic cloud of January 13-15, 1988. For strongly northward IMF, the convection in the Southern Hemisphere is characterized by a two-cell convection pattern comfined to high latitudes with sunward flow over the pole. The strength of the flows is comparable to that later seen under southward IMF. Superimposed on this convection pattern there are clear dawn-dusk asymmetries associated with a one-cell convection component whose sense depends on the polarity of the magnetic cloud's large east-west magnetic field component. When the cloud's magnetic field turns southward, the convection is characterized by a two-cell pattern extending to lower latitude with antisunward flow over the pole. There is no evident interhemispheric difference in the structure and strength of the convection. Superimposed dawn-dusk asymmetries in the flow patterns are observed which are only in part attributable to the east-west component of the magnetic field.

  17. The Earth's magnetosphere is 165 R(sub E) long: Self-consistent currents, convection, magnetospheric structure, and processes for northward interplanetary magnetic field

    Science.gov (United States)

    Fedder, J. A.; Lyon, J. G.

    1995-01-01

    The subject of this paper is a self-consistent, magnetohydrodynamic numerical realization for the Earth's magnetosphere which is in a quasi-steady dynamic equilibrium for a due northward interplanetary magnetic field (IMF). Although a few hours of steady northward IMF are required for this asymptotic state to be set up, it should still be of considerable theoretical interest because it constitutes a 'ground state' for the solar wind-magnetosphere interaction. Moreover, particular features of this ground state magnetosphere should be observable even under less extreme solar wind conditions. Certain characteristics of this magnetosphere, namely, NBZ Birkeland currents, four-cell ionospheric convection, a relatively weak cross-polar potential, and a prominent flow boundary layer, are widely expected. Other characteristics, such as no open tail lobes, no Earth-connected magnetic flux beyond 155 R(sub E) downstream, magnetic merging in a closed topology at the cusps, and a 'tadpole' shaped magnetospheric boundary, might not be expected. In this paper, we will present the evidence for this unusual but interesting magnetospheric equilibrium. We will also discuss our present understanding of this singular state.

  18. Distinguishing among potential mechanisms of singleton suppression.

    Science.gov (United States)

    Gaspelin, Nicholas; Luck, Steven J

    2018-04-01

    Previous research has revealed that people can suppress salient stimuli that might otherwise capture visual attention. The present study tests between 3 possible mechanisms of visual suppression. According to first-order feature suppression models , items are suppressed on the basis of simple feature values. According to second-order feature suppression models , items are suppressed on the basis of local discontinuities within a given feature dimension. According to global-salience suppression models , items are suppressed on the basis of their dimension-independent salience levels. The current study distinguished among these models by varying the predictability of the singleton color value. If items are suppressed by virtue of salience alone, then it should not matter whether the singleton color is predictable. However, evidence from probe processing and eye movements indicated that suppression is possible only when the color values are predictable. Moreover, the ability to suppress salient items developed gradually as participants gained experience with the feature that defined the salient distractor. These results are consistent with first-order feature suppression models, and are inconsistent with the other models of suppression. In other words, people primarily suppress salient distractors on the basis of their simple features and not on the basis of salience per se. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

  19. Attentional control during visual search: The effect of irrelevant singletons

    NARCIS (Netherlands)

    Theeuwes, J.; Burger, R.

    1998-01-01

    Four experiments investigated whether a highly salient color singleton can be ignored during serial search. Observers searched for a target letter among nontarget letters and were instructed to ignore an irrelevant, highly salient color singleton that was either compatible or incompatible with the

  20. Role of Frontal Cortex in Attentional Capture by Singleton Distractors

    Science.gov (United States)

    de Fockert, Jan W.; Theeuwes, Jan

    2012-01-01

    The role of frontal cortex in selective attention to visual distractors was examined in an attentional capture task in which participants searched for a unique shape in the presence or absence of an additional colour singleton distractor. The presence of the additional singleton was associated with slower behavioural responses to the shape target,…

  1. Comparison of academic performance of twins and singletons in adolescence

    DEFF Research Database (Denmark)

    Christensen, Kaare; Petersen, Inge; Skytthe, Axel

    2006-01-01

    deviations for twins and singletons (8.02 v 8.02 and 1.05 v 1.06) despite the twins weighing on average 908 g (95% confidence interval 886 to 930 g) less than the singletons at birth. Controlling for birth weight, gestational age at birth, age at test, and parents' age and education confirmed the similarity......OBJECTIVES: To determine whether twins in recent cohorts show similar academic performance in adolescence to singletons and to test the effect of birth weight on academic performance in twins and singletons. DESIGN: Follow-up study. SETTING: Denmark. PARTICIPANTS: All twins (n=3411) and a 5% random...... sample of singletons (n=7796) born in Denmark during 1986-8. MAIN OUTCOME MEASURES: Test scores in ninth grade (age 15 or 16), birth weight, gestational age at birth, parents' age, and parents' education. RESULTS: Ninth grade test scores were normally distributed, with almost identical mean and standard...

  2. Earth

    CERN Document Server

    Carter, Jason

    2017-01-01

    This curriculum-based, easy-to-follow book teaches young readers about Earth as one of the eight planets in our solar system in astronomical terms. With accessible text, it provides the fundamental information any student needs to begin their studies in astronomy, such as how Earth spins and revolves around the Sun, why it's uniquely suitable for life, its physical features, atmosphere, biosphere, moon, its past, future, and more. To enhance the learning experience, many of the images come directly from NASA. This straightforward title offers the fundamental information any student needs to sp

  3. Vanishing twin syndrome among ART singletons and pregnancy outcomes.

    Science.gov (United States)

    Magnus, Maria C; Ghaderi, Sara; Morken, Nils-Halvdan; Magnus, Per; Bente Romundstad, Liv; Skjærven, Rolv; Wilcox, Allen J; Eldevik Håberg, Siri

    2017-11-01

    Among babies born by ART, do singleton survivors of a vanishing twin have lower birth weight than other singletons? Vanishing twin syndrome (VTS) was associated with lower birth weight among ART singletons; a sibship analysis indicated that the association was not confounded by maternal characteristics that remain stable between deliveries. Previous studies indicate that ART singletons with VTS have increased risk of adverse pregnancy outcomes, compared with other ART singletons. The potential contribution of unmeasured maternal background characteristics has been unclear. This was a Norwegian population-based registry study, including 17 368 mothers with 20 410 ART singleton deliveries between January 1984 and December 2013. The study population included 17 291 ART singletons without VTS, 638 ART singletons with VTS and 2418 ART singletons with uncertain vanishing twin status. We estimated differences in birth weight and gestational age comparing ART singletons with VTS first to all ART singletons without VTS, and subsequently to their ART siblings without VTS, using random- and fixed-effects linear regression, respectively. The corresponding comparisons for the associations with preterm birth and small for gestational age (SGA) were conducted using random-and fixed-effects logistic regression. The sibling analysis of preterm birth included 587 discordant siblings, while the sibling analysis of SGA included 674 discordant siblings. ART singletons with VTS had lower birth weight when compared to all ART singletons without VTS, with an adjusted mean difference (95% CI) of -116 g (-165, -67). When we compared ART singletons with VTS to their ART singletons sibling without VTS, the adjusted mean difference was -112 g (-209, -15). ART singletons with VTS also had increased risk of being born SGA, with an adjusted odds ratio (OR) (95% CI) of 1.48 (1.07, 2.03) compared to all ART singletons without VTS, and 2.79 (1.12, 6.91) in the sibship analyses. ART singletons with

  4. The impact of cloud inhomogeneities on the Earth radiation budget: the 14 October 1989 I.C.E. convective cloud case study

    Directory of Open Access Journals (Sweden)

    F. Parol

    1994-01-01

    Full Text Available Through their multiple interactions with radiation, clouds have an important impact on the climate. Nonetheless, the simulation of clouds in climate models is still coarse. The present evolution of modeling tends to a more realistic representation of the liquid water content; thus the problem of its subgrid scale distribution is crucial. For a convective cloud field observed during ICE 89, Landsat TM data (resolution: 30m have been analyzed in order to quantify the respective influences of both the horizontal distribution of liquid water content and cloud shape on the Earth radiation budget. The cloud field was found to be rather well-represented by a stochastic distribution of hemi-ellipsoidal clouds whose horizontal aspect ratio is close to 2 and whose vertical aspect ratio decreases as the cloud cell area increases. For that particular cloud field, neglecting the influence of the cloud shape leads to an over-estimate of the outgoing longwave flux; in the shortwave, it leads to an over-estimate of the reflected flux for high solar elevations but strongly depends on cloud cell orientations for low elevations. On the other hand, neglecting the influence of cloud size distribution leads to systematic over-estimate of their impact on the shortwave radiation whereas the effect is close to zero in the thermal range. The overall effect of the heterogeneities is estimated to be of the order of 10 W m-2 for the conditions of that Landsat picture (solar zenith angle 65°, cloud cover 70%; it might reach 40 W m-2 for an overhead sun and overcast cloud conditions.

  5. The impact of cloud inhomogeneities on the Earth radiation budget: the 14 October 1989 I.C.E. convective cloud case study

    Directory of Open Access Journals (Sweden)

    F. Parol

    Full Text Available Through their multiple interactions with radiation, clouds have an important impact on the climate. Nonetheless, the simulation of clouds in climate models is still coarse. The present evolution of modeling tends to a more realistic representation of the liquid water content; thus the problem of its subgrid scale distribution is crucial. For a convective cloud field observed during ICE 89, Landsat TM data (resolution: 30m have been analyzed in order to quantify the respective influences of both the horizontal distribution of liquid water content and cloud shape on the Earth radiation budget. The cloud field was found to be rather well-represented by a stochastic distribution of hemi-ellipsoidal clouds whose horizontal aspect ratio is close to 2 and whose vertical aspect ratio decreases as the cloud cell area increases. For that particular cloud field, neglecting the influence of the cloud shape leads to an over-estimate of the outgoing longwave flux; in the shortwave, it leads to an over-estimate of the reflected flux for high solar elevations but strongly depends on cloud cell orientations for low elevations. On the other hand, neglecting the influence of cloud size distribution leads to systematic over-estimate of their impact on the shortwave radiation whereas the effect is close to zero in the thermal range. The overall effect of the heterogeneities is estimated to be of the order of 10 W m-2 for the conditions of that Landsat picture (solar zenith angle 65°, cloud cover 70%; it might reach 40 W m-2 for an overhead sun and overcast cloud conditions.

  6. Concepts of magnetospheric convection

    International Nuclear Information System (INIS)

    Vasyliunas, V.M.

    1975-01-01

    Magnetospheric physics, which grew out of attempts to understand the space environment of the Earth, is becoming increasingly applicable to other systems in the Universe. Among the planets, in addition to the Earth, Jupiter, Mercury, Mars and (in a somewhat different way) Venus are now known to have magnetospheres. The magnetospheres of pulsars have been regarded as an essential part of the pulsar phenomenon. Other astrophysical systems, such as supernova remnant shells or magnetic stars and binary star systems, may be describable as magnetospheres. The major concepts of magnetospheric physics thus need to be formulated in a general way not restricted to the geophysical context in which they may have originated. Magnetospheric convection has been one of the most important and fruitful concepts in the study of the Earth's magnetosphere. This paper describes the basic theoretical notions of convection in a manner applicable to magnetospheres generally and discusses the relative importance of convective corotational motions, with particular reference to the comparison of the Earth and Jupiter. (Auth.)

  7. Deciding Type Equivalence in a Language with Singleton Kinds

    National Research Council Canada - National Science Library

    Stone, Christopher

    1999-01-01

    ...: S(A) is the kind of all types provably equivalent to the type A. Singletons are interesting because they provide a very general form of definitions for type variables and allow fine-grained control of type computations...

  8. Capture by colour: evidence for dimension-specific singleton capture.

    Science.gov (United States)

    Harris, Anthony M; Becker, Stefanie I; Remington, Roger W

    2015-10-01

    Previous work on attentional capture has shown the attentional system to be quite flexible in the stimulus properties it can be set to respond to. Several different attentional "modes" have been identified. Feature search mode allows attention to be set for specific features of a target (e.g., red). Singleton detection mode sets attention to respond to any discrepant item ("singleton") in the display. Relational search sets attention for the relative properties of the target in relation to the distractors (e.g., redder, larger). Recently, a new attentional mode was proposed that sets attention to respond to any singleton within a particular feature dimension (e.g., colour; Folk & Anderson, 2010). We tested this proposal against the predictions of previously established attentional modes. In a spatial cueing paradigm, participants searched for a colour target that was randomly either red or green. The nature of the attentional control setting was probed by presenting an irrelevant singleton cue prior to the target display and assessing whether it attracted attention. In all experiments, the cues were red, green, blue, or a white stimulus rapidly rotated (motion cue). The results of three experiments support the existence of a "colour singleton set," finding that all colour cues captured attention strongly, while motion cues captured attention only weakly or not at all. Notably, we also found that capture by motion cues in search for colour targets was moderated by their frequency; rare motion cues captured attention (weakly), while frequent motion cues did not.

  9. Heat Convection

    Science.gov (United States)

    Jiji, Latif M.

    Professor Jiji's broad teaching experience lead him to select the topics for this book to provide a firm foundation for convection heat transfer with emphasis on fundamentals, physical phenomena, and mathematical modelling of a wide range of engineering applications. Reflecting recent developments, this textbook is the first to include an introduction to the challenging topic of microchannels. The strong pedagogic potential of Heat Convection is enhanced by the follow ing ancillary materials: (1) Power Point lectures, (2) Problem Solutions, (3) Homework Facilitator, and, (4) Summary of Sections and Chapters.

  10. Temperature-Driven Convection

    Science.gov (United States)

    Bohan, Richard J.; Vandegrift, Guy

    2003-02-01

    Warm air aloft is stable. This explains the lack of strong winds in a warm front and how nighttime radiative cooling can lead to motionless air that can trap smog. The stability of stratospheric air can be attributed to the fact that it is heated from above as ultraviolet radiation strikes the ozone layer. On the other hand, fluid heated from below is unstable and can lead to Bernard convection cells. This explains the generally turbulent nature of the troposphere, which receives a significant fraction of its heat directly from the Earth's warmer surface. The instability of cold fluid aloft explains the violent nature of a cold front, as well as the motion of Earth's magma, which is driven by radioactive heating deep within the Earth's mantle. This paper describes how both effects can be demonstrated using four standard beakers, ice, and a bit of food coloring.

  11. Congenital Malformations in Singleton Infants Conceived by Assisted Reproductive Technologies and Singleton Infants by Natural Conception in Tehran, Iran

    Directory of Open Access Journals (Sweden)

    Ramin Mozafari Kermani

    2017-10-01

    Full Text Available Background: Multiple pregnancies occur more frequently in assisted reproductive technology (ART compared to normal conception (NC. It is known that the risk of congenital malformations in a multiple pregnancy are higher than single pregnancy. The aim of this study is to compare congenital malformations in singleton infants conceived by ART to singleton infants conceived naturally. Materials and Methods: In this historical cohort study, we performed a historical cohort study of major congenital malformations (MCM in 820 singleton births from January 2012 to December 2014. The data for this analysis were derived from Tehran’s ART linked data file. The risk of congenital malformations was compared in 164 ART infants and 656 NC infants. We performed multiple logistic regression analyses for the independent association of ART on each outcome. Results: We found 40 infants with MCM 29 (4.4% NC infants and 14 (8.3% ART infants. In comparison with NC infants, ART infants had a significant 2-fold increased risk of MCM (P=0.046. After adjusting individually for maternal age, infant gender, prior stillbirth, mother’s history of spontaneous abortion, and type of delivery, we did not find any difference in risk. In this study the majority (95.1% of all infants were normal but 4.9% of infants had at least one MCM. We found a difference in risk of MCMs between in vitro fertilization (IVF and intracytoplasmic sperm injection (ICSI. We excluded the possible role of genotype and other unknown factors in causing more malformations in ART infants. Conclusion: This study reported a higher risk of MCMs in ART singleton infants than in NC singleton infants. Congenital heart disease, developmental dysplasia of the hip (DDH, and urogenital malformations were the most reported major malformations in singleton ART infants according to organ and system classification.

  12. Construction of a specification from its singleton part

    NARCIS (Netherlands)

    Fernández, R.; Maillard, G.

    2006-01-01

    We state a construction theorem for specications starting from single-site conditional probabilities (singleton part). We consider general single-site spaces and kernels that are absolutely continuous with respect to a chosen product mea- sure (free measure). Under a natural order-consistency

  13. Pregnancy outcome in singleton term breeches from a referral ...

    African Journals Online (AJOL)

    It is recommended that attention should be given to trainee obstetrician in selective external cephalic version at term and also the procedure of AVBD so as to reduce the caesarean section rate and also neonatal morbidity in term breeches in our community. Keywords: Pregnancy outcome, Singleton breech, Vaginal ...

  14. Pulmonary function in advanced uncomplicated singleton and twin pregnancy

    Directory of Open Access Journals (Sweden)

    Anwar Hasan Siddiqui

    2014-06-01

    Full Text Available Objective: Pregnancy brings about significant changes in respiratory function, as evidenced by alterations in lung volumes and capacities, which are attributable to the mechanical impediment caused by the growing foetus. This study was undertaken in order to identify changes in respiratory function during normal pregnancy and to determine whether such changes are more pronounced in twin pregnancy than in singleton pregnancy. Methods: Respiratory function was assessed in 50 women with twin pregnancies and in 50 women with singleton pregnancies (during the third trimester in both groups, as well as in 50 non-pregnant women. We measured the following pulmonary function test parameters: FVC; FEV1; PEF rate; FEV1/FVC ratio; FEF25-75%; and maximal voluntary ventilation. Results: All respiratory parameters except the FEV1/FVC ratio were found to be lower in the pregnant women than in the non-pregnant women. We found no significant differences between women with twin pregnancies and those with singleton pregnancies, in terms of respiratory function. Conclusions: Despite its higher physiological demands, twin pregnancy does not appear to impair respiratory function to any greater degree than does singleton pregnancy.

  15. Pulmonary function in advanced uncomplicated singleton and twin pregnancy.

    Science.gov (United States)

    Siddiqui, Anwar Hasan; Tauheed, Nazia; Ahmad, Aquil; Mohsin, Zehra

    2014-01-01

    Pregnancy brings about significant changes in respiratory function, as evidenced by alterations in lung volumes and capacities, which are attributable to the mechanical impediment caused by the growing foetus. This study was undertaken in order to identify changes in respiratory function during normal pregnancy and to determine whether such changes are more pronounced in twin pregnancy than in singleton pregnancy. Respiratory function was assessed in 50 women with twin pregnancies and in 50 women with singleton pregnancies (during the third trimester in both groups), as well as in 50 non-pregnant women. We measured the following pulmonary function test parameters: FVC; FEV1; PEF rate; FEV1/FVC ratio; FEF25-75%; and maximal voluntary ventilation. All respiratory parameters except the FEV1/FVC ratio were found to be lower in the pregnant women than in the non-pregnant women. We found no significant differences between women with twin pregnancies and those with singleton pregnancies, in terms of respiratory function. Despite its higher physiological demands, twin pregnancy does not appear to impair respiratory function to any greater degree than does singleton pregnancy.

  16. Influences on achieving motor milestones: A twin-singleton study

    NARCIS (Netherlands)

    Brouwer, S.I.; van Beijsterveldt, C.E.M.; Bartels, M.; Hudziak, J.; Boomsma, D.I.

    2006-01-01

    In order to determine if twinning impacted achievement of motor milestones the attainment of early motor milestones in twins was examined and compared to published data from singletons of the same age from the same culture and birth years. We examined the influence of twinning, sex, zygosity and

  17. Auditory Attentional Capture: Effects of Singleton Distractor Sounds

    Science.gov (United States)

    Dalton, Polly; Lavie, Nilli

    2004-01-01

    The phenomenon of attentional capture by a unique yet irrelevant singleton distractor has typically been studied in visual search. In this article, the authors examine whether a similar phenomenon occurs in the auditory domain. Participants searched sequences of sounds for targets defined by frequency, intensity, or duration. The presence of a…

  18. Stress-tensor commutators and Schwinger terms in singleton theories

    International Nuclear Information System (INIS)

    Bergshoeff, E.; Sezgin, E.; Tanii, Y.

    1989-06-01

    We compute the commutators of the regularized quantum stress-tensor of singleton theories formulated on the boundary of a (p + 2)-dimensional anti de Sitter space (AdS p+2 ). (These are superconformal field theories on S p x S 1 ). We find that the algebra is not closed except in the case of AdS 3 . It does contain, however, the finite dimensional AdS p+2 algebra SO(p + 1,2). We also find divergent, field dependent as well as field independent Schwinger terms (i.e. the central extensions), which, however, do not lead to anomalies in the algebra of the AdS charges. We also give a simple derivation of the two-point functions for bosonic and fermionic singletons. (author). 15 refs

  19. Oculomotor capture by colour singletons depends on intertrial priming.

    Science.gov (United States)

    Becker, Stefanie I

    2010-10-12

    In visual search, an irrelevant colour singleton captures attention when the colour of the distractor changes across trials (e.g., from red to green), but not when the colour remains constant (Becker, 2007). The present study shows that intertrial changes of the distractor colour also modulate oculomotor capture: an irrelevant colour singleton distractor was only selected more frequently than the inconspicuous nontargets (1) when its features had switched (compared to the previous trial), or (2) when the distractor had been presented at the same position as the target on the previous trial. These results throw doubt on the notion that colour distractors capture attention and the eyes because of their high feature contrast, which is available at an earlier point in time than information about specific feature values. Instead, attention and eye movements are apparently controlled by a system that operates on feature-specific information, and gauges the informativity of nominally irrelevant features. Copyright © 2010 Elsevier Ltd. All rights reserved.

  20. A note on twin-singleton differences in asthma

    DEFF Research Database (Denmark)

    Thomsen, Simon Francis; Kyvik, Kirsten Ohm; Backer, Vibeke

    2008-01-01

    Twins constitute a valuable resource for genetic studies of asthma. However, critics argue that twins are 'special' in terms of prenatal environment and upbringing and therefore nonrepresentative. In respect to asthma a small range of studies report differential morbidity in twins compared...... with singletons. We review some of the possible explanations for these findings and conclude that results from twin studies of asthma can be extrapolated to the general population....

  1. National Convective Weather Diagnostic

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current convective hazards identified by the National Convective Weather Detection algorithm. The National Convective Weather Diagnostic (NCWD) is an automatically...

  2. Mantle Convection on Modern Supercomputers

    Science.gov (United States)

    Weismüller, J.; Gmeiner, B.; Huber, M.; John, L.; Mohr, M.; Rüde, U.; Wohlmuth, B.; Bunge, H. P.

    2015-12-01

    Mantle convection is the cause for plate tectonics, the formation of mountains and oceans, and the main driving mechanism behind earthquakes. The convection process is modeled by a system of partial differential equations describing the conservation of mass, momentum and energy. Characteristic to mantle flow is the vast disparity of length scales from global to microscopic, turning mantle convection simulations into a challenging application for high-performance computing. As system size and technical complexity of the simulations continue to increase, design and implementation of simulation models for next generation large-scale architectures is handled successfully only in an interdisciplinary context. A new priority program - named SPPEXA - by the German Research Foundation (DFG) addresses this issue, and brings together computer scientists, mathematicians and application scientists around grand challenges in HPC. Here we report from the TERRA-NEO project, which is part of the high visibility SPPEXA program, and a joint effort of four research groups. TERRA-NEO develops algorithms for future HPC infrastructures, focusing on high computational efficiency and resilience in next generation mantle convection models. We present software that can resolve the Earth's mantle with up to 1012 grid points and scales efficiently to massively parallel hardware with more than 50,000 processors. We use our simulations to explore the dynamic regime of mantle convection and assess the impact of small scale processes on global mantle flow.

  3. Free convective boundary layers in variable-viscosity fluids by the method of local nonsimilarity: application to plumes in the earth's mantle

    International Nuclear Information System (INIS)

    Quareni, F.; Yuen, D.A.; Eby, H.E.

    1983-01-01

    The effects due to departures from local similarity in steady-state boundary layers ascending through a fluid with strongly variable viscosity are examined with the local-nonsimilarity method. Both the absolute temperature and the hydrostatic pressure appear in the argument of an exponential in the viscosity function. The fluid-dynamical system studied here is that which characterizes plume structures in the Earth's mantle. By means of an iterative approach, two successive nonlinear boundary value problems are solved simultaneously and the errors incurred in the locally similar solutions are then assessed from a comparison between the first (locally similar) and the second level of a system of truncated equations. Three different sources of nonsimilarity have been considered: 1) localized radiogenic hearting within the plume, 2) ambient thermal stratification, 3) pressure dependence of mantle rheology. Of particular interest is an appraisal of the degree of accuracy of the locally similar solutions as a function of viscosity contrast within the boundary layer. For the range of viscosity contrast examined, up to 10 8 , the velocity and temperature fields between the first- and second-level solutions differ at most by 20 to 30%, for the rheological parameter values relevant to the Earth's mantle

  4. Overweight in Singletons Compared to Children with Siblings

    DEFF Research Database (Denmark)

    Hunsberger, Monica; Formisano, Annarita; Reisch, Lucia

    2012-01-01

    and prevention of Dietary- and lifestyle-induced health EFfects In Children and infantS (IDEFICS). The present analysis is based on measured anthropometry and parent or guardian-reported socio-demographic characteristics. Subjects include 12 720 children aged 2–9 years for whom number of siblings was known......The aim of this study was to compare the prevalence of overweight in only children to those with siblings and to explore potential behavioral mediating factors. This study relies upon cross-sectional data collected at survey centers in eight European countries participating in Identification....... Singletons were more likely (odds ratio 1.52, 95% confidence interval (CI):1.34–1.72) to be overweight than their peers with siblings when controlling for factors related to childhood overweight, including survey country, parental education, parental weight, maternal age, child's age, birth weight and gender...

  5. Singletons, higher spin massless states and the supermembrane

    International Nuclear Information System (INIS)

    Bergshoeff, E.; Salam, A.; Sezgin, E.; Tanii, Yoshiaki.

    1988-01-01

    We analyse the spectrum of the eleven dimensional supermembrane quantized in AdS 4 xS 7 background. The classical membrane lives at the boundary of AdS 4 which is S 2 xS 1 , and has OSp(8,4) symmetry. We find that the spectrum contains, in addition to the N=8 supersymmetric (massive) singletons (which may possibly be the ultimate preons), also massless states of all higher integer and half-integer spin. These states fill the irreducible representations of OSp(8,4) with highest spin s max =2,4,6,... The s max =2 multiplet corresponds to the states of the de Wit-Nicolai's N=8 gauged supergravity in four dimensions. (author). 24 refs

  6. Cord around neck in singleton term pregnancies and its outcome

    International Nuclear Information System (INIS)

    Sajjad, R.; Mustafa, N.

    2014-01-01

    To enlist the complications with nuchal cord in singleton term pregnancies and to determine maternal and fetal outcome in singleton term pregnancies. Design: Descriptive study. Place and duration of study: The study was carried out at Gynaecology and Obstetric department Combined Military Hospital Quetta from Nov 2007 to May 2008. Patients and methods: One hundred women irrespective of parity with healthy, singleton term pregnancy and cephalic presentation, labouring or not labouring, were selected from outpatient department. A total of 41 patients were booked with Doppler ultrasound done in antenatal period. Other 59 were poorly booked and diagnosed with cord around neck by clinical criteria e.g. high head at term, fetal distress, meconium discharge, slow progress in labour leading to prolonged labour. All patients signed well informed written proforma regarding study and its outcome. Vigilant feto maternal monitoring was done during labour. All events during labour were mentioned in proformas which were attached with patients case notes. Data was interperated in term of frequency and percentages. Results: Complications with cord around neck found were still birth 3%, fetal distress 15%, intrauterine death 1%. Prolonged labour was seen in 14%, Meconium discharge in 5%, and high presenting part was found in 11% of cases. Maternal outcome were elective caesarean section in 6%, emergency caesarean-section in 32%, spontaneous vaginal delivery in 54% and instrumental vaginal delivery in 8% of the cases. Different fetal outcomes seen were intrauterine death, stillbirth in 1%, and 3% patients respectively. Regarding neonatal outcome, 31% stayed in neonatal intensive care unit (NICU) for less than 48 hours, 69% stayed in NICU for more than 48 hours out of which 4% had early neonatal deaths (ENND). Fifty nine percent patients detected and suspected during labour were with, high head, slow progress in labour, decreased fetal movements, intra partum fetal distress, meconium

  7. Vanishing twins: a predictor of small-for-gestational age in IVF singletons

    DEFF Research Database (Denmark)

    Pinborg, Anja; Lidegaard, Ojvind; Freiesleben, Nina la Cour

    2007-01-01

    The purpose of this study was to assess the effect of a vanishing twin on the risk of being small-for-gestational age (SGA) in in vitro fertilization (IVF) singletons.......The purpose of this study was to assess the effect of a vanishing twin on the risk of being small-for-gestational age (SGA) in in vitro fertilization (IVF) singletons....

  8. Recurrence risk of low Apgar score among term singletons: a population-based cohort study

    NARCIS (Netherlands)

    Ensing, Sabine; Schaaf, Jelle M.; Abu-Hanna, Ameen; Mol, Ben W. J.; Ravelli, Anita C. J.

    2014-01-01

    To examine the risk of recurrence of low Apgar score in a subsequent term singleton pregnancy. Population-based cohort study. The Netherlands. A total of 190,725 women with two subsequent singleton term live births between 1999 and 2007. We calculated the recurrence risk of low Apgar score after

  9. Recurrence risk of preterm birth in subsequent twin pregnancy after preterm singleton delivery

    NARCIS (Netherlands)

    Schaaf, J. M.; Hof, M. H. P.; Mol, B. W. J.; Abu-Hanna, A.; Ravelli, A. C. J.

    2012-01-01

    Please cite this paper as: Schaaf J, Hof M, Mol B, Abu-Hanna A, Ravelli A. Recurrence risk of preterm birth in subsequent twin pregnancy after preterm singleton delivery.BJOG 2012;119:16241629. Objective To determine the risk of preterm birth in a subsequent twin pregnancy after previous singleton

  10. Irrelevant Singletons in Pop-Out Search: Attentional Capture or Filtering Costs?

    Science.gov (United States)

    Becker, Stefanie I.

    2007-01-01

    The aim of the present study was to investigate whether costs invoked by the presence of an irrelevant singleton distractor in a visual search task are due to attentional capture by the irrelevant singleton or spatially unrelated filtering costs. Measures of spatial effects were based on distance effects, compatibility effects, and differences…

  11. Attentional Capture by an Unannounced Color Singleton Depends on Expectation Discrepancy

    Science.gov (United States)

    Horstmann, Gernot

    2005-01-01

    Eight experiments examined the conditions under which a color singleton that is presented for the 1st time without prior announcement captures attention. The main hypothesis is that an unannounced singleton captures attention to the extent that it deviates from expectations. This hypothesis was tested within a visual-search paradigm in which…

  12. National Convective Weather Forecast

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The NCWF is an automatically generated depiction of: (1) current convection and (2) extrapolated signficant current convection. It is a supplement to, but does NOT...

  13. Southern Ocean Convection and tropical telleconnections

    Science.gov (United States)

    Marinov, I.; Cabre, A.; Gnanadesikan, A.

    2014-12-01

    We show that Southern Ocean (SO) temperatures in the latest generation of Earth System Models exhibit two major modes of variation, one driven by deep convection, the other by tropical variability. We perform a CMIP5 model intercomparison to understand why different climate models represent SO variability so differently in long, control simulations. We show that multiyear variability in Southern Ocean sea surface temperatures (SSTs) can in turn influence oceanic and atmospheric conditions in the tropics on short (atmospheric) time-scales. We argue that the strength and pattern of SO-tropical teleconnections depends on the intensity of SO deep convection. Periodic convection in the SO is a feature of most CMIP5 models under preindustrial forcing (deLavergne et al., 2014). Models show a wide distribution in the spatial extent, periodicity and intensity of their SO convection, with some models convecting most of the time, and some showing very little convection. In a highly convective coupled model, we find that multidecadal variability in SO and global SSTs, as well as SO heat storage are driven by Weddell Sea convective variability, with convective decades relatively warm due to the heat released from the deep southern ocean and non-convective decades cold due to the subsurface storage of heat. Furthermore, pulses of SO convection drive SST and sea ice variations, influencing absorbed shortwave and emitted longwave radiation, wind, cloud and precipitation patterns, with climatic implications for the low latitudes via fast atmospheric teleconnections. We suggest that these high-low latitude teleconnection mechanisms are relevant for understanding hiatus decades. Additionally, Southern Ocean deep convection varied significantly during past, natural climate changes such as during the last deglaciation. Weddell Sea open convection was recently weakened, likely as a consequence of anthropogenic forcing and the resulting surface freshening. Our study opens up the

  14. Modes of convection in the magnetotail

    International Nuclear Information System (INIS)

    Baumjohann, Wolfgang

    2002-01-01

    The flow of plasma in the Earth's magnetotail cannot reach a steady state, since adiabatic convection would lead to exceedingly high pressure of the associated magnetic flux tubes closer to the Earth, the so-called pressure catastrophe. The natural way to avoid the pressure catastrophe is to significantly reduce the flux tube volume by reconnection, and observations show a near-Earth reconnection line typically around 20-25 Earth radii down tail. Earthward flows from this reconnection line are rather bursty and typically seen outside of 10 Earth radii. At this point they are strongly braked by the here dominant dipolar magnetic field. The pressure gradients piled up by the flow lead to the substorm current wedge, and possibly other substorm phenomena observed in the Earth's ionosphere. When more and more flux tubes are piled up, the dipolarization front moves tailward and finally shuts off near-Earth reconnection

  15. Boundary Layer Control of Rotating Convection Systems

    Science.gov (United States)

    King, E. M.; Stellmach, S.; Noir, J.; Hansen, U.; Aurnou, J. M.

    2008-12-01

    Rotating convection is ubiquitous in the natural universe, and is likely responsible for planetary processes such magnetic field generation. Rapidly rotating convection is typically organized by the Coriolis force into tall, thin, coherent convection columns which are aligned with the axis of rotation. This organizational effect of rotation is thought to be responsible for the strength and structure of magnetic fields generated by convecting planetary interiors. As thermal forcing is increased, the relative influence of rotation weakens, and fully three-dimensional convection can exist. It has long been assumed that rotational effects will dominate convection dynamics when the ratio of buoyancy to the Coriolis force, the convective Rossby number, Roc, is less than unity. We investigate the influence of rotation on turbulent Rayleigh-Benard convection via a suite of coupled laboratory and numerical experiments over a broad parameter range: Rayleigh number, 10310; Ekman number, 10-6≤ E ≤ ∞; and Prandtl number, 1≤ Pr ≤ 100. In particular, we measure heat transfer (as characterized by the Nusselt number, Nu) as a function of the Rayleigh number for several different Ekman and Prandtl numbers. Two distinct heat transfer scaling regimes are identified: non-rotating style heat transfer, Nu ~ Ra2/7, and quasigeostrophic style heat transfer, Nu~ Ra6/5. The transition between the non-rotating regime and the rotationally dominant regime is described as a function of the Ekman number, E. We show that the regime transition depends not on the global force balance Roc, but on the relative thicknesses of the thermal and Ekman boundary layers. The transition scaling provides a predictive criterion for the applicability of convection models to natural systems such as Earth's core.

  16. Maternal obesity in singleton versus twin gestations: a population-based matched case-control study.

    Science.gov (United States)

    Lucovnik, Miha; Blickstein, Isaac; Verdenik, Ivan; Trojner-Bregar, Andreja; Tul, Natasa

    2015-04-01

    To examine the impact of pre-pregnancy obesity on adverse outcomes in twin compared to singleton pregnancies. Dichorionic twin gestations with maternal body mass index >30 were matched to three singleton controls. Both obese groups were matched (1:3) with non-obese controls. Rates of preeclampsia, gestational diabetes, cesarean section, and preterm birth were compared. One hundred eighty-nine dichorionic twin pregnancies in obese mothers were matched to 567 twin pregnancies in non-obese mothers, and to 567 singleton pregnancies in obese mothers. The latter were matched to 1701 non-obese mothers with singletons. Preeclampsia was more common in obese mothers with both twins and singletons (odds ratio (OR) 3.95, 95% confidence interval (CI) 2.18-7.16 and OR 6.53, 95% CI 3.75-11.4, respectively) as was gestational diabetes (OR 4.35, 95% CI 2.18-8.69; OR 5.53 95% CI 3.60-8.50). Obese mothers with singletons were more likely to deliver abdominally, but the cesarean rates were obesity independent in twins. Obese mothers were more likely to deliver at Obesity-attributable adverse outcomes are lower in twins compared to singletons. Obesity increases the risk of preterm birth regardless of plurality.

  17. Language Development of Three- to Twelve-Year-Old Twins Compared to Singletons.

    Science.gov (United States)

    Dʼhaeseleer, Evelien; Geenens, Eline; Parmentier, Sarah; Corthals, Paul; Van Lierde, Kristiane

    2016-01-01

    The language development of twins tends to lag behind in comparison to that of singletons. The purpose of this study was to compare expressive and receptive language skills of 3- to 12-year-old twins with singletons. Secondly, correlations between language differences between twins and singletons and age were investigated. Twenty-four twins with a mean age of 5.1 years participated in the study. The control group consisted of 24 singletons who were matched for gender and age. Language development was investigated using the Clinical Evaluation of Language Fundamentals. Twins scored significantly lower for expressive and receptive language skills compared to singletons. Even when excluding preterm-born children, twins still scored significantly lower for expressive language skills. There was no correlation between age and language differences between twins and their matched singletons. Twins score lower for expressive and receptive language skills compared to singletons, and preterm birth cannot be regarded as the main cause for the language delay. The language delay in twins is rather mild but does not seem to decrease with increasing age. © 2016 S. Karger AG, Basel.

  18. What and where in speech recognition: Geminates and singletons in spoken Italian

    NARCIS (Netherlands)

    Tagliapietra, L.; McQueen, J.M.

    2010-01-01

    Four cross-modal repetition priming experiments examined whether consonant duration in Italian provides listeners with information not only for segmental identification ("what" information: whether the consonant is a geminate or a singleton) but also for lexical segmentation ("where" information:

  19. Cesarean Section Rate in Singleton Primiparae and Related Factors in Beijing, China

    Directory of Open Access Journals (Sweden)

    Geng Song

    2017-01-01

    Conclusions: Maternal age, prepregnancy body mass index, gestational weight gain, blood glucose levels, residence, education level, and singleton fetal birth weight are all factors that might significantly affect the CSR.

  20. Large baby syndrome in singletons born after frozen embryo transfer (FET)

    DEFF Research Database (Denmark)

    Pinborg, Anja; Henningsen, AA; Loft, A

    2013-01-01

    Are singletons born after frozen embryo transfer (FET) at increased risk of being born large for gestational age (LGA) and if so, is this caused by intrinsic maternal factors or related to the freezing/thawing procedures?......Are singletons born after frozen embryo transfer (FET) at increased risk of being born large for gestational age (LGA) and if so, is this caused by intrinsic maternal factors or related to the freezing/thawing procedures?...

  1. Twin-singleton differences in cognitive abilities in a sample of Africans in Nigeria.

    Science.gov (United States)

    Hur, Yoon-Mi; Lynn, Richard

    2013-08-01

    Recent studies comparing cognitive abilities between contemporary twins and singletons in developed countries have suggested that twin deficits in cognitive abilities no longer exist. We examined cognitive abilities in a sample of twins and singletons born recently in Nigeria to determine whether recent findings can be replicated in developing countries. Our sample consisted of 413 pairs of twins and 280 singletons collected from over 45 public schools in Abuja and its neighboring states in Nigeria. The ages of twins and singletons ranged from 9 to 20 years with a mean (SD) of 14.6 years (2.2 years) for twins and 16.1 years (1.8 years) for singletons. Zygosity of the same-sex twins was determined by analysis of 16 deoxyribonucleic acid markers. We asked participants to complete a questionnaire booklet that included Standard Progressive Matrices-Plus Version (SPM+), Mill-Hill Vocabulary Scale (MHV), Family Assets Questionnaire, and demographic questions. The data were corrected for sex and age and then analyzed using maximum likelihood model-fitting analysis. Although twins and singletons were comparable in family social class indicators, singletons did better than twins across all the tests (d = 0.10 to 0.35). The average of d for SPM+ total [0.32; equivalent to 4.8 Intelligence Quotient (IQ) points] and d for MHV (0.24; equivalent to 3.6 IQ points) was 0.28 (equivalent to 4.2 IQ points), similar to the twin-singleton gap found in old cohorts in developed countries. We speculate that malnutrition, poor health, and educational systems in Nigeria may explain the persistence of twin deficits in cognitive abilities found in our sample.

  2. Ovarian hyperstimulation syndrome in a spontaneous singleton pregnancy.

    Science.gov (United States)

    Cabar, Fábio Roberto

    2016-05-24

    The ovarian hyperstimulation syndrome is the combination of increased ovarian volume, due to the presence of multiple cysts and vascular hyperpermeability, with subsequent hypovolemia and hemoconcentration. We report a case of spontaneous syndrome in a singleton pregnancy. This was a spontaneous pregnancy with 12 weeks of gestational age. The pregnancy was uneventful until 11 weeks of gestational age. After that, the pregnant woman complained of progressive abdominal distention associated with abdominal discomfort. She did not report other symptoms. In the first trimester, a routine ultrasonography showed enlarged ovaries, multiples cysts and ascites. Upon admission, the patient was hemodynamically stable, her serum β-hCG was 24,487mIU/mL, thyroid-stimulating hormone was 2.2µUI/mL and free T4 was 1.8ng/dL. All results were within normal parameters. However, levels of estradiol were high (10,562pg/mL). During hospitalization, she received albumin, furosemide and prophylactic dose of enoxaparin. The patient was discharged on the sixth hospital day. RESUMO A síndrome de hiperestimulação ovariana é a combinação do aumento dos ovários, devido à presença de múltiplos cistos e de hiperpermeabilidade vascular, com subsequente hipovolemia e hemoconcentração. Relata-se um caso de síndrome espontânea em uma gestação única. Trata-se de gravidez espontânea com 12 semanas de idade gestacional. A gravidez ocorreu sem intercorrências até 11 semanas de idade gestacional. Após, a gestante passou a se queixar de distensão abdominal progressiva, associada com desconforto abdominal. A paciente não relatava outros sintomas. A ultrassonografia de rotina no primeiro trimestre mostrou ovários aumentados com múltiplos cistos e ascite. No momento da internação, a paciente apresentava-se hemodinamicamente estável, com β-hCG sérico de 24.487mUI/mL, hormônio estimulante da tireoide de 2,2µUI/m e T4 livre de 1,8ng/dL, ou seja, valores dentro dos par

  3. Dissociating Compatibility Effects and Distractor Costs in the Additional Singleton Paradigm

    Directory of Open Access Journals (Sweden)

    Charles eFolk

    2013-07-01

    Full Text Available The interpretation of identity compatibility effects associated with irrelevant items outside the nominal focus of attention has fueled much of the debate over early versus late selection and perceptual load theory. However, compatibility effects have also played a role in the debate over the extent to which the involuntary allocation of spatial attention (i.e., attentional capture is completely stimulus-driven or whether it is contingent on top-down control settings. For example, in the context of the additional singleton paradigm, irrelevant color singletons have been found to produce not only an overall cost in search performance but also significant compatibility effects. This combination of search costs and compatibility effects has been taken as evidence that spatial attention is indeed allocated in a bottom-up fashion to the salient but irrelevant singletons. However, it is possible that compatibility effects in the additional singleton paradigm reflect parallel processing of identity associated with low perceptual load rather than an involuntary shift of spatial attention. In the present experiments, manipulations of load were incorporated into the traditional additional singleton paradigm. Under low load conditions, both search costs and compatibility effects were obtained, replicating previous studies. Under high load conditions, search costs were still present, but compatibility effects were eliminated. This dissociation suggests that the costs associated with irrelevant singletons may reflect filtering processes rather than the allocation of spatial attention.

  4. Conformity expectations: Differential effects on IVF twins and singletons' parent-child relationships and adjustment.

    Science.gov (United States)

    Anderson, Kayla N; Rueter, Martha A; Connor, Jennifer J; Chen, Muzi; Damario, Mark

    2015-08-01

    Increased utilization of in vitro fertilization (IVF) to treat infertility has resulted in a growing twin birthrate. Despite early childhood risks, twins have fewer psychosocial problems in middle childhood than singleton children. This study proposes that parents' conformity expectations for children have differential effects on parent-child relationships for twin and singleton children, which indirectly explains twins' more optimum psychosocial adjustment. Parental conformity expectations, parent-child relationship satisfaction, and children's emotional, behavioral, and attention problems were assessed in a sample of 288 6- to 12-year-old IVF-conceived twins and singletons. Overall, parents of twins had higher expectations for child conformity to parent rules than singleton parents. Path models demonstrate that twin status and parental expectations for child conformity interact to influence parent-child relationships, and this interaction indirectly accounted for differences in twins' and singletons' psychosocial adjustment. Findings suggest parenting constructs have differential influences on the association between twin status and parent-child relationships. Parenting research, predominantly conducted with singletons, should be reexamined before applying existing research to twin children and their families. (c) 2015 APA, all rights reserved).

  5. Cervical stitch (cerclage) for preventing preterm birth in singleton pregnancy.

    Science.gov (United States)

    Alfirevic, Zarko; Stampalija, Tamara; Medley, Nancy

    2017-06-06

    Cervical cerclage is a well-known surgical procedure carried out during pregnancy. It involves positioning of a suture (stitch) around the neck of the womb (cervix), aiming to give mechanical support to the cervix and thereby reduce risk of preterm birth. The effectiveness and safety of this procedure remains controversial. This is an update of a review last published in 2012. To assess whether the use of cervical stitch in singleton pregnancy at high risk of pregnancy loss based on woman's history and/or ultrasound finding of 'short cervix' and/or physical exam improves subsequent obstetric care and fetal outcome. We searched Cochrane Pregnancy and Childbirth's Trials Register (30 June 2016) and reference lists of identified studies. We included all randomised trials of cervical suturing in singleton pregnancies. Cervical stitch was carried out when the pregnancy was considered to be of sufficiently high risk due to a woman's history, a finding of short cervix on ultrasound or other indication determined by physical exam. We included any study that compared cerclage with either no treatment or any alternative intervention. We planned to include cluster-randomised studies but not cross-over trials. We excluded quasi-randomised studies. We included studies reported in abstract form only. Three review authors independently assessed trials for inclusion. Two review authors independently assessed risk of bias and extracted data. We resolved discrepancies by discussion. Data were checked for accuracy. The quality of the evidence was assessed using the GRADE approach. This updated review includes a total of 15 trials (3490 women); three trials were added for this update (152 women). Cerclage versus no cerclageOverall, cerclage probably leads to a reduced risk of perinatal death when compared with no cerclage, although the confidence interval (CI) crosses the line of no effect (RR 0.82, 95% CI 0.65 to 1.04; 10 studies, 2927 women; moderate quality evidence). Considering

  6. Modeling of plasma-sheet convection: implications for substorms

    International Nuclear Information System (INIS)

    Erickson, G.M.

    1985-01-01

    An answer is suggested to the question of why plasma and magnetic energy accumulate in the Earth's magnetotail to be released in sporadic events, namely substorms. It is shown that the idea of steady convection is inconsistent with the idea of slow, approximately lossless, plasma convection in a long, closed-field-line region that extends into a long magnetotail, such as occurs during Earthward convection in the Earth's plasma sheet. This inconsistency is argued generally and demonstrated specifically using several quantitative models of the Earth's magnetospheric magnetic field. These results suggest that plasma-sheet convection is necessarily time dependent. If flux tubes are to convect adiabatically earthward, the confining magnetic pressure in the tail lobes must increase with time, and the magnetotail must evolve into a more stretched configuration. Eventually, the magnetosphere must find some way to release plasma from inner-plasma-sheet flux tubes. This suggests an obvious role for the magnetospheric substorm in the convection process. To probe this process further, a two-dimensional, self-consistent, quasi-static convection model was developed. This model self consistently includes a dipole field and can reasonably account for the effects of inner-magnetospheric shielding

  7. Prenatal screening for fetal aneuploidy in singleton pregnancies.

    Science.gov (United States)

    Chitayat, David; Langlois, Sylvie; Douglas Wilson, R

    2011-07-01

    To develop a Canadian consensus document on maternal screening for fetal aneuploidy (e.g., Down syndrome and trisomy 18) in singleton pregnancies. Pregnancy screening for fetal aneuploidy started in the mid 1960s, using maternal age as the screening test. New developments in maternal serum and ultrasound screening have made it possible to offer all pregnant patients a non-invasive screening test to assess their risk of having a fetus with aneuploidy to determine whether invasive prenatal diagnostic testing is necessary. This document reviews the options available for non-invasive screening and makes recommendations for Canadian patients and health care workers. To offer non-invasive screening for fetal aneuploidy (trisomy 13, 18, 21) to all pregnant women. Invasive prenatal diagnosis would be offered to women who screen above a set risk cut-off level on non-invasive screening or to pregnant women whose personal, obstetrical, or family history places them at increased risk. Currently available non-invasive screening options include maternal age combined with one of the following: (1) first trimester screening (nuchal translucency, maternal age, and maternal serum biochemical markers), (2) second trimester serum screening (maternal age and maternal serum biochemical markers), or (3) 2-step integrated screening, which includes first and second trimester serum screening with or without nuchal translucency (integrated prenatal screen, serum integrated prenatal screening, contingent, and sequential). These options are reviewed, and recommendations are made. Studies published between 1982 and 2009 were retrieved through searches of PubMed or Medline and CINAHL and the Cochrane Library, using appropriate controlled vocabulary and key words (aneuploidy, Down syndrome, trisomy, prenatal screening, genetic health risk, genetic health surveillance, prenatal diagnosis). Results were restricted to systematic reviews, randomized controlled trials, and relevant observational

  8. Twin versus singleton pregnancies: the incidence, pregnancy complications, and obstetric outcomes in a Nigerian tertiary hospital.

    Science.gov (United States)

    Obiechina, Nj; Okolie, Ve; Eleje, Gu; Okechukwu, Zc; Anemeje, Oa

    2011-01-01

    Twin pregnancy is associated with more pregnancy complications and poorer pregnancy outcome than singleton pregnancy. Hence periodic review is necessary to improve on the pregnancy outcome. To determine the incidence and compare pregnancy complications and obstetric outcomes of twin pregnancies and singleton pregnancies. The twin pregnancies (study group) that were delivered at Nnamdi Azikiwe University Teaching Hospital (NAUTH), Nnewi, South-East Nigeria from 1st February 2005 to 31st January 2010 were compared with singleton deliveries (control group) that occurred in the same hospital during the same period. A total of 3351 deliveries were conducted during the study period, of which 113 were twin deliveries, giving an incidence of 1:29.6 deliveries. Only 100 case files could be retrieved for analysis. The mean parities for the twins and singletons were 2.7 ± 2.33 weeks and 1.96 ± 1.87 weeks whereas the mean gestational age at delivery for twin and singleton deliveries were 34 ± 5.2 weeks and 38.7 ± 2.4 weeks respectively (P < 0.05). The mean birth weights were 3.14 ± 0.73 kg and 2.3 ± 1.0 kg for singletons and twins respectively (P < 0.05). Hypertensive disorders of pregnancy, cord prolapse, malpresentation, premature rupture of membranes, low Apgar scores, cesarean section rate, and perinatal death were significantly higher in twin pregnancies than in singleton. The incidence of twin pregnancy over the study period was high and was significantly associated with more pregnancy complications and poorer obstetric outcomes. Close antenatal and intrapartum care are needed in order to improve outcome and decrease complications.

  9. Observing Convective Aggregation

    Science.gov (United States)

    Holloway, Christopher E.; Wing, Allison A.; Bony, Sandrine; Muller, Caroline; Masunaga, Hirohiko; L'Ecuyer, Tristan S.; Turner, David D.; Zuidema, Paquita

    2017-11-01

    Convective self-aggregation, the spontaneous organization of initially scattered convection into isolated convective clusters despite spatially homogeneous boundary conditions and forcing, was first recognized and studied in idealized numerical simulations. While there is a rich history of observational work on convective clustering and organization, there have been only a few studies that have analyzed observations to look specifically for processes related to self-aggregation in models. Here we review observational work in both of these categories and motivate the need for more of this work. We acknowledge that self-aggregation may appear to be far-removed from observed convective organization in terms of time scales, initial conditions, initiation processes, and mean state extremes, but we argue that these differences vary greatly across the diverse range of model simulations in the literature and that these comparisons are already offering important insights into real tropical phenomena. Some preliminary new findings are presented, including results showing that a self-aggregation simulation with square geometry has too broad distribution of humidity and is too dry in the driest regions when compared with radiosonde records from Nauru, while an elongated channel simulation has realistic representations of atmospheric humidity and its variability. We discuss recent work increasing our understanding of how organized convection and climate change may interact, and how model discrepancies related to this question are prompting interest in observational comparisons. We also propose possible future directions for observational work related to convective aggregation, including novel satellite approaches and a ground-based observational network.

  10. Physical examination-indicated cerclage in singleton and twin pregnancies: maternal-fetal outcomes.

    Science.gov (United States)

    Bernabeu, Andrea; Goya, Maria; Martra, Miquel; Suy, Anna; Pratcorona, Laia; Merced, Carme; Llurba, Elisa; Casellas, Manel; Carreras, Elena; Cabero, Luis

    2016-01-01

    To study maternal and perinatal outcomes after physical examination-indicated cerclage in both singleton and twin pregnancies and evaluate the possible risk factors associated. Retrospective review of all women undergoing physical examination-indicated cerclage at the Hospital Vall d'Hebro, Barcelona from January 2009 to December 2012 after being diagnosed with cervical incompetence and risk of premature birth. During the study period, 60 cases of women diagnosed with cervical incompetence who were carrying live and morphologically-normal fetuses (53 singleton and 7 twin pregnancies), and who had an imminent risk of premature birth were evaluated. Mean gestational age until birth was 35 weeks in singleton and 32 weeks in twin pregnancies. Four cases (7.5%) of immature births and one case (2.0%) of neonatal death were recorded in singleton pregnancies. No cases of immature births or neonatal deaths were recorded in twin pregnancies. Diagnostic amniocentesis was performed IN all cases to rule out possible chorioamnionitis. Physical examination-indicated cerclage for cervical incompetence in women at risk for immature or preterm birth demonstrates good perinatal prognosis without increasing maternal morbidity in either singleton or twin pregnancies. The increase in gestation time in our study may also have been due to the fact that patients with subclinical chorioamnionitis were excluded by diagnostic amniocentesis.

  11. Attentional Capture to a Singleton Distractor Degrades Visual Marking in Visual Search

    Directory of Open Access Journals (Sweden)

    Kenji Yamauchi

    2017-05-01

    Full Text Available Visual search is easier after observing some distractors in advance; it is as if the previewed distractors were excluded from the search. This effect is referred to as the preview benefit, and a memory template that visually marks the old locations of the distractors is thought to help in prioritizing the locations of newly presented items. One remaining question is whether the presence of a conspicuous item during the sequential shift of attention within the new items reduces this preview benefit. To address this issue, we combined the above preview search and a conventional visual search paradigm using a singleton distractor and examined whether the search performance was affected by the presence of the singleton. The results showed that the slope of reaction time as a function of set size became steeper in the presence of a singleton, indicating that the singleton distractor reduced the preview benefit. Furthermore, this degradation effect was positively correlated with the degree of conventional attentional capture to a singleton measured in a separate experiment with simultaneous search. These findings suggest that the mechanism of visual marking shares common attentional resources with the search process.

  12. Cost analysis of singleton versus twin pregnancies after in vitro fertilization.

    Science.gov (United States)

    Lukassen, H G Marieke; Schönbeck, Yvonne; Adang, Eddy M M; Braat, Didi D M; Zielhuis, Gerhard A; Kremer, Jan A M

    2004-05-01

    To determine the difference in costs between singleton and twin pregnancies after IVF treatment from pregnancy to 6 weeks after delivery from a health care perspective. Retrospective cost analysis. IVF department at the University Medical Center Nijmegen, The Netherlands. A representative sample of singleton and twin pregnancies after IVF treatment between 1995 and 2001 at the University Medical Center Nijmegen. IVF with or without intracytoplasmic sperm injection and with or without cryopreservation. Medical costs per singleton and twin pregnancy after IVF. In patients pregnant with twins, the incidence of hospital antenatal care, complicated vaginal deliveries, and cesarean sections was higher and was associated with more frequent and longer maternal and neonatal hospital admissions. Maternal and neonatal hospital admissions were the major cost drivers. The medical cost per twin pregnancy was found to be more than five times higher than per singleton pregnancy, 13,469 and 2,550, respectively. The medical cost per twin pregnancy was more than 10,000 higher than per singleton pregnancy. A reduction in the number of twin pregnancies by elective single ET will save substantial amounts of money. This money might be used for the additional IVF cycles that will probably be needed to achieve similar success rates between single ET and two-embryo transfer.

  13. Turbulent convection in liquid metal with and without rotation

    OpenAIRE

    King, Eric M.; Aurnou, Jonathan M.

    2013-01-01

    The magnetic fields of Earth and other planets are generated by turbulent, rotating convection in liquid metal. Liquid metals are peculiar in that they diffuse heat more readily than momentum, quantified by their small Prandtl numbers, . Most analog models of planetary dynamos, however, use moderate fluids, and the systematic influence of reducing is not well understood. We perform rotating Rayleigh–Bénard convection experiments in the liquid metal gallium over a range of nondimensional bu...

  14. Stovetop Earth Pecan Pie

    Science.gov (United States)

    Robin, C. M.

    2005-12-01

    Many fluid mechanical experiments with direct applications to Earth Science are performed with sugary syrups using conceptually straightforward procedures. Corn syrup has indeed proven to be a godsend for those studying convection and related non-linear phenomena. In addition, however, it gives experimentalists a deep physical intuition for the interior workings of hot planets. The basic concepts behind plate tectonics and mantle convection are not difficult; indeed, although they may not be aware of it, most students probably have a basic intuitive understanding of fluid mechanics gained in their daily life. However, the large size and long time scale of geophysical processes may be quite intimidating to young students. Even a simple geophysical experiment requires a complicated array of coolers, heaters and measuring and recording equipment. It is of interest to introduce students to the geodynamical concepts that can be visualized in a high-tech lab using familiar processes and equipment. Using a homemade apparatus and grocery store supplies, I propose using a 'Stove-top Earth pecan pie' to introduce simple geodynamic concepts to middle- and high-school students. The initially cold syrup heats up and the pecans begin to float (continent formation), the syrup begins to convect (mantle convection), and convection slows down after the heat is removed (secular cooling). Even Wilson cycles can be simulated by moving the pan to one side or the other of the stovetop or heating element. The activity formally introduces students to convection and its application to the earth, and makes them think about plate motion, heat transfer, scaling, and experimental procedures. As an added bonus, they can eat their experiments after recess!

  15. Changes in the convective population and thermodynamic environments in convection-permitting regional climate simulations over the United States

    Science.gov (United States)

    Rasmussen, K. L.; Prein, A. F.; Rasmussen, R. M.; Ikeda, K.; Liu, C.

    2017-11-01

    Novel high-resolution convection-permitting regional climate simulations over the US employing the pseudo-global warming approach are used to investigate changes in the convective population and thermodynamic environments in a future climate. Two continuous 13-year simulations were conducted using (1) ERA-Interim reanalysis and (2) ERA-Interim reanalysis plus a climate perturbation for the RCP8.5 scenario. The simulations adequately reproduce the observed precipitation diurnal cycle, indicating that they capture organized and propagating convection that most climate models cannot adequately represent. This study shows that weak to moderate convection will decrease and strong convection will increase in frequency in a future climate. Analysis of the thermodynamic environments supporting convection shows that both convective available potential energy (CAPE) and convective inhibition (CIN) increase downstream of the Rockies in a future climate. Previous studies suggest that CAPE will increase in a warming climate, however a corresponding increase in CIN acts as a balancing force to shift the convective population by suppressing weak to moderate convection and provides an environment where CAPE can build to extreme levels that may result in more frequent severe convection. An idealized investigation of fundamental changes in the thermodynamic environment was conducted by shifting a standard atmospheric profile by ± 5 °C. When temperature is increased, both CAPE and CIN increase in magnitude, while the opposite is true for decreased temperatures. Thus, even in the absence of synoptic and mesoscale variations, a warmer climate will provide more CAPE and CIN that will shift the convective population, likely impacting water and energy budgets on Earth.

  16. Observed Mother- and Father-Child Interaction Differences in Families with Medically Assisted Reproduction-Conceived Twins and Singletons.

    Science.gov (United States)

    Anderson, Kayla N; Rueter, Martha A; Connor, Jennifer J; Koh, Bibiana D

    2017-12-01

    Increased medically assisted reproduction (MAR) use to treat infertility has resulted in a growing twin birth rate. Little is known about parent-child relationships for twin relative to singleton children in middle childhood. This study fills this gap by examining parent-child relationships in 57 families with eighty 6- to 12-year-old MAR twin and singleton children using observational data (warm and supportive communication, control, and hostility). Nested ANCOVAs indicate that while mothers exhibit similar interactional behaviors toward twins and singletons, fathers have less optimum behaviors toward twins relative to singletons. Twins displayed less engaged behavior with mothers and fathers relative to singletons. Given the vitality of parent-child relationships for family and child adjustment, future studies should examine determinants and outcomes of twin-singleton relationship differences to bolster twins' and their families' functioning. © 2016 Family Process Institute.

  17. Convective heat transfer

    CERN Document Server

    Kakac, Sadik; Pramuanjaroenkij, Anchasa

    2014-01-01

    Intended for readers who have taken a basic heat transfer course and have a basic knowledge of thermodynamics, heat transfer, fluid mechanics, and differential equations, Convective Heat Transfer, Third Edition provides an overview of phenomenological convective heat transfer. This book combines applications of engineering with the basic concepts of convection. It offers a clear and balanced presentation of essential topics using both traditional and numerical methods. The text addresses emerging science and technology matters, and highlights biomedical applications and energy technologies. What’s New in the Third Edition: Includes updated chapters and two new chapters on heat transfer in microchannels and heat transfer with nanofluids Expands problem sets and introduces new correlations and solved examples Provides more coverage of numerical/computer methods The third edition details the new research areas of heat transfer in microchannels and the enhancement of convective heat transfer with nanofluids....

  18. Risk of Metabolic Syndrome and Diabetes Mellitus Among Young Twins and Singletons in Guinea-Bissau

    DEFF Research Database (Denmark)

    Bjerregaard-Andersen, Morten; Hansen, Lone; da Silva, Leontina I

    2013-01-01

    OBJECTIVETwins in Africa may be at increased risk of metabolic disorders due to strained conditions in utero, including high exposure to infections. We studied metabolic syndrome (MS) and diabetes mellitus (DM) among young twins and singletons in Guinea-Bissau.RESEARCH DESIGN AND METHODSThe study...... was cross-sectional and occurred from October 2009 until August 2011 at the Bandim Health Project, a demographic surveillance site in the capital Bissau. Twins and singleton controls between 5 and 32 years were visited at home. Fasting blood samples for metabolic measurements were collected. Zygosity...... was established genetically for a subset. DM was defined as HbA1c ≥6.5% (48 mmol/mol) and MS by the International Diabetes Federation criteria.RESULTSHbA1c was available for 574 twins and 463 singletons. Mean age was 15.3 years versus 15.8 years, respectively. Eighteen percent of twins were monozygotic...

  19. Chromosomal Aberrations in Monozygotic and Dizygotic Twins Versus Singletons in Denmark During 1968-2009

    DEFF Research Database (Denmark)

    Kristensen, Lone Krøldrup; Larsen, Lisbeth A; Fagerberg, Christina

    2017-01-01

    BACKGROUND: Hall (Embryologic development and monozygotic twinning. Acta Geneticae Medicae et Gemellologiae, Vol. 45, 1996, pp. 53-57) hypothesized that chromosomal aberrations can lead to monozygotic (MZ) twinning. However, twinning and chromosomal aberrations increase prenatal mortality and could...... reduce the prevalence of chromosomal aberrations in live-born twins. We compared prevalence proportion ratios (PPR) of chromosomal aberrations and trisomy 21 (T21) in live-born twins versus singletons born in Denmark during 1968-2009. METHODS: We linked the Danish Twin Registry and a 5% random sample...... of all singletons to the Danish Cytogenetic Central Register and calculated PPR adjusted for maternal age for MZ, dizygotic (DZ), and all twins versus singletons. Zygosity was based on questionnaires or genetic markers. RESULTS: No overall difference in risk of chromosomal aberrations or T21 in twins...

  20. Systematic review of progesterone for the prevention of preterm birth in singleton pregnancies

    DEFF Research Database (Denmark)

    Rode, Line; Langhoff-Roos, Jens; Andersson, Charlotte

    2009-01-01

    . SEARCH STRATEGY: A search in the PubMed, Embase, and Cochrane database was performed using the keywords: pregnancy, progesterone, preterm birth/preterm delivery, preterm labor, controlled trial, and randomized controlled trial. SELECTION CRITERIA: Studies on singleton pregnancies. DATA COLLECTION...... AND ANALYSIS: A meta-analysis was performed on randomized trials including singleton pregnancies with previous preterm birth. MAIN RESULTS: Two new randomized controlled trials of women with previous preterm birth were added to the four analyzed in the Cochrane review, and the meta-analysis of all six studies......BACKGROUND: A Cochrane review in 2006 concluded that further knowledge is required before recommendation can be made with regard to progesterone in the prevention of preterm birth. OBJECTIVE: To provide an update on the preventive effect of progesterone on preterm birth in singleton pregnancies...

  1. Lower marriage and divorce rates among twins than among singletons in Danish birth cohorts 1940-1964

    DEFF Research Database (Denmark)

    Petersen, Inge; Martinussen, Torben; McGue, Matthew

    2011-01-01

    compare rates of marriage and divorce in a sample of 35,975 twins and 81,803 singletons born 1940-1964. Cox-regressions are used in order to control for potential confounders. We find that compared with singletons twins have significantly lower marriage rates: (males: 15-19 years: Hazard Ratio (HR) = 0...... twins compared with singletons (HR=0.87, 95%CI: 0.83-0.90). These differences offset each other, thus 57% of both populations remain in their first marriage until censoring. The interpretation may be that since twins have a partner from birth, they do not have the same need for marriage as singletons...

  2. Simulating deep convection with a shallow convection scheme

    Directory of Open Access Journals (Sweden)

    C. Hohenegger

    2011-10-01

    Full Text Available Convective processes profoundly affect the global water and energy balance of our planet but remain a challenge for global climate modeling. Here we develop and investigate the suitability of a unified convection scheme, capable of handling both shallow and deep convection, to simulate cases of tropical oceanic convection, mid-latitude continental convection, and maritime shallow convection. To that aim, we employ large-eddy simulations (LES as a benchmark to test and refine a unified convection scheme implemented in the Single-column Community Atmosphere Model (SCAM. Our approach is motivated by previous cloud-resolving modeling studies, which have documented the gradual transition between shallow and deep convection and its possible importance for the simulated precipitation diurnal cycle.

    Analysis of the LES reveals that differences between shallow and deep convection, regarding cloud-base properties as well as entrainment/detrainment rates, can be related to the evaporation of precipitation. Parameterizing such effects and accordingly modifying the University of Washington shallow convection scheme, it is found that the new unified scheme can represent both shallow and deep convection as well as tropical and mid-latitude continental convection. Compared to the default SCAM version, the new scheme especially improves relative humidity, cloud cover and mass flux profiles. The new unified scheme also removes the well-known too early onset and peak of convective precipitation over mid-latitude continental areas.

  3. Perinatal outcome in singletons after modified natural cycle IVF and standard IVF with ovarian stimulation

    NARCIS (Netherlands)

    Pelinck, Marie-Jose; Keizer, Marjan H.; Hoek, Annemieke; Simons, Arnold H. M.; Schelling, Karin; Middelburg, Karin; Heineman, Maas Jan

    Objective: Singletons born after IVF treatment are at risk for adverse pregnancy outcome, the cause of which is unknown. The aim of the present study was to investigate the influence of ovarian stimulation on perinatal outcome. Study design: In this single-centre retrospective study, perinatal

  4. Perinatal outcome in singletons after modified natural cycle IVF and standard IVF with ovarian stimulation

    NARCIS (Netherlands)

    Pelinck, Marie-José; Keizer, Marjan H.; Hoek, Annemieke; Simons, Arnold H. M.; Schelling, Karin; Middelburg, Karin; Heineman, Maas Jan

    2010-01-01

    Objective: Singletons born after IVF treatment are at risk for adverse pregnancy outcome, the cause of which is unknown. The aim of the present study was to investigate the influence of ovarian stimulation on perinatal outcome. Study design: In this single-centre retrospective study, perinatal

  5. Why do singletons conceived after assisted reproduction technology have adverse perinatal outcome?

    DEFF Research Database (Denmark)

    Pinborg, A; Wennerholm, U B; Romundstad, L B

    2013-01-01

    Assisted reproduction technology (ART) is used worldwide, at increasing rates, and data show that some adverse outcomes occur more frequently than following spontaneous conception (SC). Possible explanatory factors for the well-known adverse perinatal outcome in ART singletons were evaluated....

  6. Development and health of 5 - 8-year-old singletons born after intracytoplasmic sperm injection

    NARCIS (Netherlands)

    Knoester, Marjolein

    2007-01-01

    This thesis describes the Leiden Artificial Reproductive Techniques Follow-up Project. In this project, the potential long-term effects of intracytoplasmic sperm injection (ICSI) were assessed in 5 – 8-year-old singleton children. ICSI is the method of artificial reproduction in which a sperm cel is

  7. Maternal risk factors for singleton preterm births and survival at the ...

    African Journals Online (AJOL)

    2015-02-24

    Feb 24, 2015 ... The mean age of mothers who delivered singleton preterm babies did not differ significantly from that of mothers .... Classification of preterm babies according to gestational age was ... of admission for preterm babies was 16 ± 5.8 days (range: ..... the etiology of preterm births in the US would be expected.

  8. Child Maltreatment Among Singletons and Multiple Births in Japan: A Population-Based Study.

    Science.gov (United States)

    Yokoyama, Yoshie; Oda, Terumi; Nagai, Noriyo; Sugimoto, Masako; Mizukami, Kenji

    2015-12-01

    The occurrence of multiple births has been recognized as a risk factor for child maltreatment. However, few population-based studies have examined the relationship between multiple births and child maltreatment. This study aimed to evaluate the degree of risk of child maltreatment among singletons and multiple births in Japan and to identify factors associated with increased risk. Using population-based data, we analyzed the database of records on child maltreatment and medical checkups for infants aged 1.5 years filed at Nishinomiya City Public Health Center between April 2007 and March 2011. To protect personal information, the data were transferred to anonymized electronic files for analysis. After adjusting by logistic regression for each associated factor and gestation number, multiples themselves were not associated with the risk of child maltreatment. However, compared with singletons, multiples had a significantly higher rate of risk factors for child maltreatment, including low birth weight and neural abnormality. Moreover, compared with mothers of singleton, mothers of twins had a significantly higher rate of poor health, which is a risk factor of child maltreatment. Multiples were not associated with the risk of child maltreatment. However, compared with singletons, multiples and their mothers had a significantly higher rate of risk factors of child maltreatment.

  9. Trends in preterm birth: singleton and multiple pregnancies in the Netherlands, 2000-2007.

    Science.gov (United States)

    Schaaf, J M; Mol, B W J; Abu-Hanna, A; Ravelli, A C J

    2011-09-01

    Several studies have reported increasing trends in preterm birth in developed countries, mainly attributable to an increase in medically indicated preterm births. Our aim was to describe trends in preterm birth among singleton and multiple pregnancies in the Netherlands. Prospective cohort study. Nationwide study. We studied 1,451,246 pregnant women from 2000 to 2007. We assessed trends in preterm birth. We subdivided preterm birth into spontaneous preterm birth after premature prelabour rupture of membranes (pPROM), medically indicated preterm birth and spontaneous preterm birth without pPROM. We performed analyses separately for singletons and multiples. The primary outcome was preterm birth, defined as birth before 37 weeks of gestation, with very preterm birth (birth was 7.7% and the risk of very preterm birth was 1.3%. In singleton pregnancies, the preterm birth risk decreased significantly from 6.4% to 6.0% (P birth without pPROM (3.6-3.1%, P birth risk increased significantly (47.3-47.7%, P = 0.047), mainly as a result of medically indicated preterm birth, which increased from 15.0% to 17.9% (P birth risk in singleton pregnancies decreased significantly over the years. The trend of increasing preterm birth risk reported in other countries was only observed in (medically indicated) preterm birth in multiple pregnancies. © 2011 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2011 RCOG.

  10. Prediction of neonatal metaboic acidos in women with a singleton term pregnancy in cephalic presentation

    NARCIS (Netherlands)

    Westerhuis, M.E.M.H.; Schuit, E.; Kwee, A.; Zuithoff, N.P.A.; Groenwold, R.H.H.; Akker, van den E.S.A.; Beek, van E.; Dessel, van H.J.H.M.; Drogtrop, A.P.; Geijn, van H.P.; Graziosi, G.C.M.; Lith, van J.M.M.; Nijhuis, J.G.; Oei, S.G.; Oosterbaan, H.P.; Porath, M.M.; Rijnders, R.J.P.; Schuitemaker, N.W.E.; Wijnberger, L.D.E.; Willekes, C.; Wouters, M.G.A.J.; Visser, G.H.A.; Mol, B.W.J.; Moons, K.G.M.

    2012-01-01

    We sought to predict neonatal metabolic acidosis at birth using antepartum obstetric characteristics (model 1) and additional characteristics available during labor (model 2). In 5667 laboring women from a multicenter randomized trial that had a high-risk singleton pregnancy in cephalic presentation

  11. Trends in preterm birth: singleton and multiple pregnancies in the Netherlands, 2000-2007

    NARCIS (Netherlands)

    Schaaf, J. M.; Mol, B. W. J.; Abu-Hanna, A.; Ravelli, A. C. J.

    2011-01-01

    Several studies have reported increasing trends in preterm birth in developed countries, mainly attributable to an increase in medically indicated preterm births. Our aim was to describe trends in preterm birth among singleton and multiple pregnancies in the Netherlands. Prospective cohort study.

  12. A Specific IFIH1 Gain-of-Function Mutation Causes Singleton-Merten Syndrome

    NARCIS (Netherlands)

    Rutsch, Frank; Macdougall, Mary; Lu, Changming; Buers, Insa; Mamaeva, Olga; Nitschke, Yvonne; Rice, Gillian I.; Erlandsen, Heidi; Kehl, Hans Gerd; Thiele, Holger; Nürnberg, Peter; Höhne, Wolfgang; Crow, Yanick J.; Feigenbaum, Annette; Hennekam, Raoul C.

    2015-01-01

    Singleton-Merten syndrome (SMS) is an infrequently described autosomal-dominant disorder characterized by early and extreme aortic and valvular calcification, dental anomalies (early-onset periodontitis and root resorption), osteopenia, and acro-osteolysis. To determine the molecular etiology of

  13. Trends in preterm birth in singleton deliveries in a Hong Kong population

    NARCIS (Netherlands)

    Hui, Annie S. Y.; Lao, Terence T.; Leung, Tak Yeung; Schaaf, Jelle M.; Sahota, Daljit S.

    2014-01-01

    To examine trends in preterm birth and its relationship with perinatal mortality in Hong Kong. In a retrospective cohort study, data were reviewed from singletons delivered between 1995 and 2011 at a university teaching hospital. Trends in preterm birth (between 24 and 36 weeks of pregnancy),

  14. Trends in birth asphyxia, obstetric interventions and perinatal mortality among term singletons: a nationwide cohort study

    NARCIS (Netherlands)

    Ensing, Sabine; Abu-Hanna, Ameen; Schaaf, Jelle M.; Mol, Ben Willem J.; Ravelli, Anita C. J.

    2015-01-01

    The objective of the present study is to investigate trends in birth asphyxia and perinatal mortality in the Netherlands over the last decade. A nationwide cohort study among women with a term singleton pregnancy. We assessed trends in birth asphyxia in relation to obstetric interventions for fetal

  15. Comparison of 24 months neurodevelopmental outcome in twins and singletons ≤ 34 weeks gestation at birth

    Directory of Open Access Journals (Sweden)

    Maria Kyriakidou

    2013-04-01

    Full Text Available The aim of this study was to screen neurodevelopmental impairment of preterm twins born at less than 34 weeks of gestation, compare them with the outcome of preterm singletons, and to determine potential neonatal factors adversely related to motor and cognitive outcome. Twins of 25-34 weeks gestation were included in the study. In total, 46 twins were matched with 46 singletons and were followed prospectively to 24 months corrected age. Obstetrical and neonatal data were recorded. All infants were assessed using the Bayley Scales of Infant and Toddler Development III For all morbidities, a significant difference could not be demonstrated. At 24 month follow up there was no significant difference in the cognitive outcome for the twins compared to singletons [98.6 (± 10.4 vs 97.8 (± 9.7, respectively]. There was also no significant difference in the motor outcome for the twins compared to singletons [94.8 (± 12.4 vs 98.1 (± 9.6., respectively]. For the twins, we found a link between pre-eclampsia and abnormal cognitive (p = 0.012 and motor (p = 0.030 results. With the number of twins steadily increasing, close developmental monitoring and probably early intervention services are needed to determine future directions for research.

  16. Preterm birth in singleton and multiple pregnancies : evaluation of costs and perinatal outcomes

    NARCIS (Netherlands)

    van Baaren, Gert J.; Peelen, Myrthe J. C. S.; Schuit, Ewoud; van der Post, Joris A. M.; Mol, Ben W. J.; Kok, Marjolein; Hajenius, Petra J.

    Objective: To estimate costs of preterm birth in singleton and multiple pregnancies. Study design: Cost analysis based on data from a prospective cohort study and three multicentre randomised controlled trials (2006-2012) in a Dutch nationwide consortium for women's health research. Women with

  17. Is the birthweight of singletons born after IVF reduced by ovarian stimulation or by IVF laboratory procedures?

    NARCIS (Netherlands)

    Pelinck, M. J.; Hadders-Algra, M.; Haadsma, M. L.; Nijhuis, W. L.; Kiewiet, S. M.; Hoek, A.; Heineman, M. J.; Middleburg, K. J.

    Singletons born after IVF are at risk of adverse pregnancy outcome, the cause of which is unknown. The present study investigated the influence of ovarian stimulation and IVF laboratory procedure on birthweight. Birthweight of singleton pregnancies resulting from IVF treatment with (n = 161) and

  18. Is the birthweight of singletons born after IVF reduced by ovarian stimulation or by IVF laboratory procedures?

    NARCIS (Netherlands)

    Pelinck, M. J.; Hadders-Algra, M.; Haadsma, M. L.; Nijhuis, W. L.; Kiewiet, S. M.; Hoek, A.; Heineman, M. J.; Middelburg, K. J.

    2010-01-01

    Singletons born after IVF are at risk of adverse pregnancy outcome, the cause of which is unknown. The present study investigated the influence of ovarian stimulation and IVF laboratory procedure on birthweight. Birthweight of singleton pregnancies resulting from IVF treatment with (n = 161) and

  19. Convection and stellar oscillations

    DEFF Research Database (Denmark)

    Aarslev, Magnus Johan

    2017-01-01

    for asteroseismology, because of the challenges inherent in modelling turbulent convection in 1D stellar models. As a result of oversimplifying the physics near the surface, theoretical calculations systematically overestimate the oscillation frequencies. This has become known as the asteroseismic surface effect. Due...... to lacking better options, this frequency difference is typically corrected for with ad-hoc formulae. The topic of this thesis is the improvement of 1D stellar convection models and the effects this has on asteroseismic properties. The source of improvements is 3D simulations of radiation...... atmospheres to replace the outer layers of stellar models. The additional turbulent pressure and asymmetrical opacity effects in the atmosphere model, compared to convection in stellar evolution models, serve to expand the atmosphere. The enlarged acoustic cavity lowers the pulsation frequencies bringing them...

  20. Active control of convection

    Energy Technology Data Exchange (ETDEWEB)

    Bau, H.H. [Univ. of Pennsylvania, Philadelphia, PA (United States)

    1995-12-31

    Using stability theory, numerical simulations, and in some instances experiments, it is demonstrated that the critical Rayleigh number for the bifurcation (1) from the no-motion (conduction) state to the motion state and (2) from time-independent convection to time-dependent, oscillatory convection in the thermal convection loop and Rayleigh-Benard problems can be significantly increased or decreased. This is accomplished through the use of a feedback controller effectuating small perturbations in the boundary data. The controller consists of sensors which detect deviations in the fluid`s temperature from the motionless, conductive values and then direct actuators to respond to these deviations in such a way as to suppress the naturally occurring flow instabilities. Actuators which modify the boundary`s temperature/heat flux are considered. The feedback controller can also be used to control flow patterns and generate complex dynamic behavior at relatively low Rayleigh numbers.

  1. The placental factor in spontaneous preterm birth in twin vs. singleton pregnancies.

    Science.gov (United States)

    Weiner, Eran; Dekalo, Ann; Feldstein, Ohad; Barber, Elad; Schreiber, Letizia; Bar, Jacob; Kovo, Michal

    2017-07-01

    The association between infection and inflammatory response in singleton preterm birth (PTB) is well established, yet, less is known about PTB in twins. We aimed to compare the placental component and pregnancy outcome in pregnancies complicated with PTB of singletons vs. twin deliveries. We hypothesized that due to different underlying mechanisms, placental inflammatory lesions will be more prevalent in placentas derived from singleton pregnancies than twins. Labor characteristics, neonatal outcome and placental histopathology reports of spontaneous PTB at 24-33 6 / 7 weeks, from 1/2008-12/2015, were reviewed. were compared between dichorionic-diamniotic twin deliveries (twins group) and singleton deliveries (singleton group) matched for gestational age. Excluded from the study medically indicated deliveries, due to preeclampsia or fetal growth restriction, and monochorionic twins. Placental lesions were classified to maternal vascular supply lesions, fetal vascular supply lesions, and maternal (MIR) and fetal (FIR) inflammatory responses. Composite neonatal outcome was defined as one or more of early complications: respiratory distress, necrotizing enterocolitis, sepsis, blood transfusion, ventilation, seizures, intra-ventricular hemorrhage, hypoglycemia, phototherapy, or death. The twins group (n=72) was characterized by higher maternal BMI (p=0.009), and higher rates of assisted reproductive techniques (56.2% vs. 17.8%, pPTBs are characterized by higher rate of inflammatory and malperfusion lesions. The lack of these findings in twins PTBs suggests different factors that participate in the development of preterm birth in twins, such as over-distension of the uterus and up regulation of oxytocin receptors. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. Do very preterm twins and singletons differ in their neurodevelopment at 5 years of age?

    Science.gov (United States)

    Bodeau-Livinec, Florence; Zeitlin, Jennifer; Blondel, Béatrice; Arnaud, Catherine; Fresson, Jeanne; Burguet, Antoine; Subtil, Damien; Marret, Stéphane; Rozé, Jean-Christophe; Marchand-Martin, Laetitia; Ancel, Pierre-Yves; Kaminski, Monique

    2013-11-01

    Twins have inconsistently shown poorer outcomes than singletons. Although a high proportion of twins are born very preterm, data are sparse on the long-term outcomes in very preterm twins. The objective of this study was to compare mortality and neurodevelopmental outcomes of very preterm singletons and twins and to study outcomes in relation to factors specific to twins. Birth cohort study Etude Epidemiologique sur les Petits Ages Gestationnels (EPIPAGE). Nine regions in France. All very preterm live births occurring from 22 to 32 weeks of gestation in all maternity wards of nine French regions in 1997 (n=2773). Neurodevelopmental status, including cerebral palsy, and a cognitive assessment with the Kaufman Assessment Battery for Children, with scores on the Mental Processing Composite (MPC) scale, was available for 1732 and 1473 children at 5 years of age, respectively. Among live births, twins had higher hospital mortality than singletons (adjusted (a)OR: 1.4 (95% CI 1.1 to 1.9)). Among survivors, there was no crude difference at 5 years between twins and singletons in the prevalence of cerebral palsy (8.0% vs 9.1%, respectively), MPC <70 (9.5% vs 11.1%) and mean MPC (94.6 vs 94.4). However, after adjustment for sex, gestational age, intrauterine growth restriction and social factors, twins were more likely to have lower MPC scores (mean difference: -2.4 (95% CI-4.8 to 0.01)). Live born twins had a higher risk of mortality when birth weight discordance was present (aOR:2.9 (95% CI 1.7 to 4.8)), but there were no differences in long-term outcomes. Compared with very preterm singletons, twins had higher mortality, no difference with respect to severe deficiencies, but slightly lower MPC scores at 5 years.

  3. Gestational diabetes mellitus: glycemic control during pregnancy and neonatal outcomes of twin and singleton pregnancies.

    Science.gov (United States)

    Guillén-Sacoto, María Augusta; Barquiel, Beatriz; Hillman, Natalia; Burgos, María Ángeles; Herranz, Lucrecia

    2018-04-20

    To assess the impact of glycemic control in gestational on neonatal weight and metabolic complications of twin and singleton pregnancies. An observational, retrospective study to monitor 120 twin and 240 singleton pregnancies in women with GDM. Maternal glycemic parameters during pregnancy (oral glucose tolerance test results, treatment, insulinization rate, mean HbA1c in the third trimester), and neonatal complications and weight were recorded. A higher infant birth weight ratio (IBWR 1.02±0.12 vs. 0.88±0.12, P<.001) and a lower rate of newborns small for gestational age (severe SGA 2.5% vs. 8.3%, P=.012) were seen after singleton pregnancies as compared to twin pregnancies. The rates of newborns large for gestational age (LGA 12.6% vs. 12.5%, P=.989); macrosomic (6.7% vs. 7.5%, P=.777); or small for gestational age (SGA 6.7% vs. 10.8%, P=.175) were similar in both groups. Neonates from twin pregnancies had a higher risk of hypoglycemia (adjusted OR 4.71; 1.38-16.07, P=.013) and polycythemia (adjusted OR 10.05; 1.82-55.42, P=0.008). A linear relationship was seen between third trimester HbA1c levels and IBWR in singleton (r=.199, P=.003), but not in twin pregnancies (r=0.049, P=0.610). Risk of severe SGA, hypoglycemia, and polycythemia was significantly higher in twin pregnancies of women with GDM. Neonatal weight outcomes and metabolic complications in twin pregnancies of women with GDM were not related to glycemic control. Moreover, in our study population, fasting glucose at diagnosis and mean HbA1c in the third trimester showed a linear relationship with higher birth weights in singleton, but not in twin pregnancies. Copyright © 2018 SEEN y SED. Publicado por Elsevier España, S.L.U. All rights reserved.

  4. Placenta previa and risk of major congenital malformations among singleton births in Finland.

    Science.gov (United States)

    Kancherla, Vijaya; Räisänen, Sari; Gissler, Mika; Kramer, Michael R; Heinonen, Seppo

    2015-06-01

    Placenta previa has been associated with adverse birth outcomes, but its association with congenital malformations is inconclusive. We examined the association between placenta previa and major congenital malformations among singleton births in Finland. We performed a retrospective population register-based study on all singletons born at or after 22+0 weeks of gestation in Finland during 2000 to 2010. We linked three national health registers: the Finnish Medical Birth Register, the Hospital Discharge Register, and the Register of Congenital Malformations, and examined several demographic and clinical characteristics among women with and without placenta previa, in association with major congenital malformations. We estimated adjusted odds ratios and 95% confidence intervals using multivariable logistic regression models. The prevalence of placenta previa was estimated as 2.65 per 1000 singleton births in Finland (95% confidence interval, 2.53-2.79). Overall, 6.2% of women with placenta previa delivered a singleton infant with a major congenital malformation, compared with 3.8% of unaffected women (p ≤ 0.001). Placenta previa was positively associated with almost 1.6-fold increased risk of major congenital malformations in the offspring, after controlling for maternal age, parity, fetal sex, smoking, socio-economic status, chorionic villus biopsy, In vitro fertilization, pre-existing diabetes, depression, preeclampsia, and prior caesarean section (adjusted odds ratio = 1.55; 95% confidence interval, 1.27-1.90). Using a large population-based study, we found that placenta previa was weakly, but significantly associated with an increased risk of major congenital malformations in singleton births. Future studies should examine the association between placenta previa and individual types of congenital malformations, specifically in high-risk pregnancies. © 2015 Wiley Periodicals, Inc.

  5. Convective transport in tokamaks

    International Nuclear Information System (INIS)

    D'Ippolito, D.A.; Myra, J.R.; Russell, D.A.; Krasheninnikov, S.I.; Pigarov, A.Yu.; Yu, G.Q.; Xu, X.Q.; Nevins, W.M.

    2005-01-01

    Scrape-off-layer (SOL) convection in fusion experiments appears to be a universal phenomenon that can 'short-circuit' the divertor in some cases. The theory of 'blob' transport provides a simple and robust physical paradigm for studying convective transport. This paper summarizes recent advances in the theory of blob transport and its comparison with 2D and 3D computer simulations. We also discuss the common physical basis relating radial transport of blobs, pellets, and ELMs and a new blob regime that may lead to a connection between blob transport and the density limit. (author)

  6. Physics of Stellar Convection

    Science.gov (United States)

    Arnett, W. David

    2009-05-01

    We review recent progress using numerical simulations as a testbed for development of a theory of stellar convection, much as envisaged by John von Newmann. Necessary features of the theory, non-locality and fluctuations, are illustrated by computer movies. It is found that the common approximation of convection as a diffusive process presents the wrong physical picture, and improvements are suggested. New observational results discussed at the conference are gratifying in their validation of some of our theoretical ideas, especially the idea that SNIb and SNIc events are related to the explosion of massive star cores which have been stripped by mass loss and binary interactions [1

  7. Parameterizing convective organization

    Directory of Open Access Journals (Sweden)

    Brian Earle Mapes

    2011-06-01

    Full Text Available Lateral mixing parameters in buoyancy-driven deep convection schemes are among the most sensitive and important unknowns in atmosphere models. Unfortunately, there is not a true optimum value for plume mixing rate, but rather a dilemma or tradeoff: Excessive dilution of updrafts leads to unstable stratification bias in the mean state, while inadequate dilution allows deep convection to occur too easily, causing poor space and time distributions and variability. In this too-small parameter space, compromises are made based on competing metrics of model performance. We attempt to escape this “entrainment dilemma” by making bulk plume parameters (chiefly entrainment rate depend on a new prognostic variable (“organization,” org meant to reflect the rectified effects of subgrid-scale structure in meteorological fields. We test an org scheme in the Community Atmosphere Model (CAM5 with a new unified shallow-deep convection scheme (UW-ens, a 2-plume version of the University of Washington scheme. Since buoyant ascent involves natural selection, subgrid structure makes convection systematically deeper and stronger than the pure unorganized case: plumes of average (or randomly sampled air rising in the average environment. To reflect this, org is nonnegative, but we leave it dimensionless. A time scale characterizes its behavior (here ∼3 h for a 2o model. Currently its source is rain evaporation, but other sources can be added easily. We also let org be horizontally transported by advection, as a mass-weighted mean over the convecting layer. Linear coefficients link org to a plume ensemble, which it assists via: 1 plume base warmth above the mean temperature 2 plume radius enhancement (reduced mixing, and 3 increased probability of overlap in a multi-plume scheme, where interactions benefit later generations (this part has only been implemented in an offline toy column model. Since rain evaporation is a source for org, it functions as a time

  8. Mathematical models of convection

    CERN Document Server

    Andreev, Victor K; Goncharova, Olga N; Pukhnachev, Vladislav V

    2012-01-01

    Phenomena of convection are abundant in nature as well as in industry. This volume addresses the subject of convection from the point of view of both, theory and application. While the first three chapters provide a refresher on fluid dynamics and heat transfer theory, the rest of the book describes the modern developments in theory. Thus it brings the reader to the ""front"" of the modern research. This monograph provides the theoretical foundation on a topic relevant to metallurgy, ecology, meteorology, geo-and astrophysics, aerospace industry, chemistry, crystal physics, and many other fiel

  9. Convective aggregation in realistic convective-scale simulations

    OpenAIRE

    Holloway, Christopher E.

    2017-01-01

    To investigate the real-world relevance of idealized-model convective self-aggregation, five 15-day cases of real organized convection in the tropics are simulated. These include multiple simulations of each case to test sensitivities of the convective organization and mean states to interactive radiation, interactive surface fluxes, and evaporation of rain. These simulations are compared to self-aggregation seen in the same model configured to run in idealized radiative-convective equilibriu...

  10. Birthweight distribution in ART singletons resulting from embryo culture in two different culture media compared with the national population

    DEFF Research Database (Denmark)

    Lemmen, Josephine Gabriela; Pinborg, Anja; Rasmussen, S

    2014-01-01

    IS KNOWN ALREADY: Studies on human ART singletons have reported a difference in birthweight in singletons following IVF culture in different culture media. However, other studies comparing different culture media have not shown any significant differences in birthweight. STUDY DESIGN, SIZE, DURATION......: This study was a retrospective comparison of birthweights in IVF/ICSI singletons conceived after fresh embryo transfer following embryo culture in Cook or Medicult medium and in a national cohort of naturally conceived singletons in nulliparous women. The study compares four independent groups consisting...... of singletons in nulliparous women from Cook-d2: 2-day culture in Cook medium at Rigshospitalet (n = 974), Medicult-d2: 2-day culture in Medicult EmbryoAssist medium at Rigshospitalet (n = 147), Medicult-d3: 3-day culture in Medicult EmbryoAssist medium with and without added GM-CSF (n = 204), and DK...

  11. Contingent orienting or contingent capture: a size singleton matching the target-distractor size relation cannot capture attention.

    Science.gov (United States)

    Du, Feng; Yin, Yue; Qi, Yue; Zhang, Kan

    2014-08-01

    In the present study, we examined whether a peripheral size-singleton distractor that matches the target-distractor size relation can capture attention and disrupt central target identification. Three experiments consistently showed that a size singleton that matches the target-distractor size relation cannot capture attention when it appears outside of the attentional window, even though the same size singleton produces a cuing effect. In addition, a color singleton that matches the target color, instead of a size singleton that matches the target-distractor size relation, captures attention when it is outside of the attentional window. Thus, a size-relation-matched distractor is much weaker than a color-matched distractor in capturing attention and cannot capture attention when the distractor appears outside of the attentional window.

  12. Impact of obstetric history on the risk of spontaneous preterm birth in singleton and multiple pregnancies: a systematic review.

    Science.gov (United States)

    Kazemier, B M; Buijs, P E; Mignini, L; Limpens, J; de Groot, C J M; Mol, B W J

    2014-09-01

    Information about the recurrence of spontaneous preterm birth in subsequent twin/singleton pregnancies is scattered. To quantify the risk of recurrence of spontaneous preterm birth in different subtypes of subsequent pregnancies. An electronic literature search in OVID MEDLINE and EMBASE, complemented by PubMed, to find recent studies. Studies comparing the risk of spontaneous preterm birth after a previous preterm and previous term pregnancy. The absolute risk of recurrence with a 95% confidence interval and the absolute risk of preterm birth after a term delivery were calculated. Data from studies were pooled using the Mantel-Haenszel method. We detected 13 relevant studies. The risk of recurrence of preterm birth was significantly increased in all preterm pregnancy subtypes, compared with their term counterparts. Women pregnant with twins after a previous preterm singleton had the highest absolute risk of recurrence (57.0%, 95% CI 51.9-61.9%), and after a previous term singleton their absolute risk was 25% (95% CI 24.3-26.5%). Women pregnant with a singleton after a previous preterm twin pregnancy have an absolute recurrence risk of 10% (95% CI 8.2-12.3%), whereas a singleton pregnancy after delivering a previous twin up to term yields a low absolute risk of only 1.3% (95% CI 0.8-2.2). Women pregnant with a singleton after a previous preterm singleton have an absolute recurrence risk of 20% (95% CI 19.9-20.6). The risk of recurrence of preterm birth is influenced by the singleton/twin order in both pregnancies, and varies between 10% for a singleton after previous preterm twins to 57% for twins after a previous preterm singleton. © 2014 Royal College of Obstetricians and Gynaecologists.

  13. CDM Convective Forecast Planning guidance

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The CDM Convective Forecast Planning (CCFP) guidance product provides a foreast of en-route aviation convective hazards. The forecasts are updated every 2 hours and...

  14. Turbulent convection in liquid metal with and without rotation.

    Science.gov (United States)

    King, Eric M; Aurnou, Jonathan M

    2013-04-23

    The magnetic fields of Earth and other planets are generated by turbulent, rotating convection in liquid metal. Liquid metals are peculiar in that they diffuse heat more readily than momentum, quantified by their small Prandtl numbers, Pr rotating Rayleigh-Bénard convection experiments in the liquid metal gallium (Pr = 0.025) over a range of nondimensional buoyancy forcing (Ra) and rotation periods (E). Our primary diagnostic is the efficiency of convective heat transfer (Nu). In general, we find that the convective behavior of liquid metal differs substantially from that of moderate Pr fluids, such as water. In particular, a transition between rotationally constrained and weakly rotating turbulent states is identified, and this transition differs substantially from that observed in moderate Pr fluids. This difference, we hypothesize, may explain the different classes of magnetic fields observed on the Gas and Ice Giant planets, whose dynamo regions consist of Pr 1 fluids, respectively.

  15. Presentation on Tropical Mesoscale convective Systems and ...

    Indian Academy of Sciences (India)

    IAS Admin

    Shallow convection- 70% of the storm heights are below 6 km. ♢ Deep convection ... Decay convection, the convective top is found at a higher altitude than deep .... Stratospheric Fountain – Two step process. Warm tropopause- preferable for.

  16. Convective overshooting in stars

    NARCIS (Netherlands)

    Andrássy, R.

    2015-01-01

    Numerous observations provide evidence that the standard picture, in which convective mixing is limited to the unstable layers of a star, is incomplete. The mixing layers in real stars are significantly more extended than what the standard models predict. Some of the observations require changing

  17. Earth and planetary sciences

    International Nuclear Information System (INIS)

    Wetherill, G.W.; Drake, C.L.

    1980-01-01

    The earth is a dynamic body. The major surface manifestation of this dynamism has been fragmentation of the earth's outer shell and subsequent relative movement of the pieces on a large scale. Evidence for continental movement came from studies of geomagnetism. As the sea floor spreads and new crust is formed, it is magnetized with the polarity of the field at the time of its formation. The plate tectonics model explains the history, nature, and topography of the oceanic crust. When a lithospheric plate surmounted by continental crust collides with an oceanic lithosphere, it is the denser oceanic lithosphere that is subducted. Hence the ancient oceans have vanished and the knowledge of ancient earth will require deciphering the complex continental geological record. Geochemical investigation shows that the source region of continental rocks is not simply the depleted mantle that is characteristic of the source region of basalts produced at the oceanic ridges. The driving force of plate tectonics is convection within the earth, but much remains to be learned about the convection and interior of the earth. A brief discussion of planetary exploration is given

  18. Perinatal Outcomes Associated With Isolated Velamentous Cord Insertion in Singleton and Twin Pregnancies.

    Science.gov (United States)

    Sinkin, Joshua A; Craig, Wendy Y; Jones, Michael; Pinette, Michael G; Wax, Joseph R

    2018-02-01

    To evaluate perinatal outcomes in singleton and twin pregnancies with pathologically confirmed velamentous cord insertion without vasa previa. This retrospective case-control study included all nonanomalous singleton and twin pregnancies with pathologically confirmed velamentous cord insertion delivered in a single institution between January 1, 2005, and July 1, 2015, and having an ultrasound examination by maternal-fetal medicine. For each case, the next 2 consecutive deliveries matched for gestational age at delivery ± 1 week and, in twins, amnionicity and chorionicity served as controls. Primary outcomes included surgical delivery for a nonreassuring intrapartum fetal heart rate tracing, umbilical arterial cord pH of less than 7.2, 5-minute Apgar score of less than 7, birth weight below the 10th percentile, neonatal intensive care unit admission, fetal or neonatal death, and cord avulsion necessitating manual placental extraction. Outcomes were available for 53 singletons with 103 matched controls and 33 twin pregnancies with 65 matched controls. In singletons, velamentous cord insertion was associated with cord pH of less than 7.2 (odds ratio [OR] 3.5; 95% confidence interval [CI], 1.1-11.2; P = .039), 5-minute Apgar score of less than 7 (OR, 5.3; 95% CI, 0.99-28.1; P = .045), and cord avulsion requiring manual placental extraction (7.5% versus 0%; P = .012). Associations were suggested with increased surgical delivery for a nonreassuring intrapartum fetal heart rate tracing (OR, 2.4; 95% CI, 0.9-6.9; P = .14), birth weight below the 10th percentile (OR, 2.1; 95% CI, 0.8-5.9; P = .21), and fetal or neonatal death (3.8% versus 0%; P = .11). Velamentous cord insertions were also associated with placental abruption in singletons (7.5% versus 0%; P = .013). Among twins, velamentous cord insertion was associated with fetal or neonatal death (9.1% versus 0%; P = .036). Isolated confirmed velamentous cord insertion is associated

  19. Convective Propagation Characteristics Using a Simple Representation of Convective Organization

    Science.gov (United States)

    Neale, R. B.; Mapes, B. E.

    2016-12-01

    Observed equatorial wave propagation is intimately linked to convective organization and it's coupling to features of the larger-scale flow. In this talk we a use simple 4 level model to accommodate vertical modes of a mass flux convection scheme (shallow, mid-level and deep). Two paradigms of convection are used to represent convective processes. One that has only both random (unorganized) diagnosed fluctuations of convective properties and one with organized fluctuations of convective properties that are amplified by previously existing convection and has an explicit moistening impact on the local convecting environment We show a series of model simulations in single-column, 2D and 3D configurations, where the role of convective organization in wave propagation is shown to be fundamental. For the optimal choice of parameters linking organization to local atmospheric state, a broad array of convective wave propagation emerges. Interestingly the key characteristics of propagating modes are the low-level moistening followed by deep convection followed by mature 'large-scale' heating. This organization structure appears to hold firm across timescales from 5-day wave disturbances to MJO-like wave propagation.

  20. Intra-hole fluid convection: High-resolution temperature monitoring

    Czech Academy of Sciences Publication Activity Database

    Čermák, Vladimír; Šafanda, Jan; Krešl, Milan

    2008-01-01

    Roč. 348, č. 3-4 (2008), s. 464-479 ISSN 0022-1694 Institutional research plan: CEZ:AV0Z30120515 Keywords : temperature monitoring * convection * fluid dynamics * borehole logging Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 2.305, year: 2008

  1. HOW TO MAKE A SINGLETON sdB STAR VIA ACCELERATED STELLAR EVOLUTION

    International Nuclear Information System (INIS)

    Clausen, Drew; Wade, Richard A.

    2011-01-01

    Many hot subdwarf B stars (sdBs) are in close binaries, and the favored formation channels for subdwarfs rely on mass transfer in a binary system to strip a core He-burning star of its envelope. However, these channels cannot account for sdBs that have been observed in long-period binaries nor the narrow mass distribution of isolated (or 'singleton') sdBs. We propose a new formation channel involving the merger of a helium white dwarf and a low-mass, hydrogen-burning star, which addresses these issues. Hierarchical triples whose inner binaries merge and form sdBs by this process could explain the observed long-period subdwarf+main-sequence binaries. This process would also naturally explain the observed slow rotational speeds of singleton sdBs. We also briefly discuss the implications of this formation channel for extreme horizontal branch morphology in globular clusters and the UV upturn in elliptical galaxies.

  2. The role of unique color changes and singletons in attention capture.

    Science.gov (United States)

    von Mühlenen, Adrian; Conci, Markus

    2016-10-01

    Previous studies have shown that a sudden color change is typically less salient in capturing attention than the onset of a new object. Von Mühlenen, Rempel, and Enns (Psychological Science 16: 979-986, 2005) showed that a color change can capture attention as effectively as the onset of a new object given that it occurs during a period of temporal calm, where no other display changes happen. The current study presents a series of experiments that further investigate the conditions under which a change in color captures attention, by disentangling the change signal from the onset of a singleton. The results show that the item changing color receives attentional priority irrespective of whether this change goes along with the appearance of a singleton or not.

  3. Assisted Reproductive Technology and Newborn Size in Singletons Resulting from Fresh and Cryopreserved Embryos Transfer

    OpenAIRE

    Levi Dunietz, Galit; Holzman, Claudia; Zhang, Yujia; Talge, Nicole M.; Li, Chenxi; Todem, David; Boulet, Sheree L.; McKane, Patricia; Kissin, Dmitry M.; Copeland, Glenn; Bernson, Dana; Diamond, Michael P.

    2017-01-01

    Objectives and Study Design The aim of this study was two-fold: to investigate the association of Assisted Reproductive Technology (ART) and small newborn size, using standardized measures; and to examine within strata of fresh and cryopreserved embryos transfer, whether this association is influenced by parental infertility diagnoses. We used a population-based retrospective cohort from Michigan (2000?2009), Florida and Massachusetts (2000?2010). Our sample included 28,946 ART singletons con...

  4. Twin-singleton differences in intelligence: a register-based birth cohort study of Norwegian males.

    Science.gov (United States)

    Eriksen, Willy; Sundet, Jon M; Tambs, Kristian

    2012-10-01

    The aim was to determine the difference in intelligence between singletons and twins in young adulthood. Data from the Medical Birth Register of Norway were linked with register data from the Norwegian National Conscript Service. The study base consisted of data on the 445,463 males who were born alive in either single or twin births in Norway during 1967-1984 and who were examined at the time of the mandatory military conscription (age 18-20). Within this study base, there were data on 1,653 sibships of full brothers that included at least one man born in single birth and at least one man born in twin birth (4,307 persons, including 2,378 twins and 1,929 singletons). The intelligence scores of the singletons were 11% (95% confidence interval [CI]: 9-14%) of a standard deviation higher than those of the twins, after adjustment for birth year, birth order, parental ages at delivery, parental education levels, and other factors. The adjusted within-family difference was also 11% (95 % CI: 6-16%) of a standard deviation, indicating that unmeasured factors shared by siblings (e.g., maternal body height) have not influenced the estimate in important ways. When gestational age at birth was added to the model, the estimate for the difference in intelligence score was approximately the same. Including birth weight in the model strongly reduced the estimate. In conclusion, twins born in Norway during 1967-1984 had slightly lower intelligence in early adulthood compared with the singletons.

  5. Shifts of visuospatial attention to invisible (metacontrast-masked) singletons: Clues from reaction times and event-related potential

    OpenAIRE

    Manfred Heumann; Ulrich Ansorge

    2006-01-01

    In the current study, we tested whether a masked and, thus, invisible singleton-cue captures atten-tion in a stimulus-driven manner or in a top-down contingent manner. The manual RT (Reaction Time) capture effect with the invisible singleton--cue decreased substantially when a match between the singleton-cue and the top-down controlled set of searched-for target features was also decreased. By contrast, with the PCN (Posterior Contralateral Negativity), an electrophysiological measure of the ...

  6. Singleton pregnancy outcomes after assisted and non-assisted reproductive technology in infertile patients.

    Science.gov (United States)

    Tsutsumi, Ryo; Fujimoto, Akihisa; Osuga, Yutaka; Ooi, Nagisa; Takemura, Yuri; Koizumi, Minako; Yano, Tetsu; Taketani, Yuji

    2012-07-01

    Singleton pregnancy after assisted reproductive technology (ART) has been associated with higher risks of adverse pregnancy outcome than naturally conceived singleton pregnancy. This study was to elucidate whether the ART procedure is responsible for abnormal pregnancy outcome comparing those after ART and non-ART in infertile patients. We compare the singleton pregnancy outcome of infertile patients in our university hospital between 2000 and 2008 following ART (351 pregnancies) and non-ART (213 pregnancies) procedures. Pregnancy outcome parameters were incidence of pregnancy induced hypertension, placenta previa, placental abruption, cesarean delivery, preterm birth, very preterm birth, stillbirth, low birth weight and very low birth weight. Most of the pregnancy outcome parameters were not significantly different between the ART group and the non-ART group. Only placenta previa was significantly higher in the ART group than in the non-ART group (odds ratio 4.0; 95 % CI 1.2-13.7). ART procedure may itself be a risk factor for the development of placenta previa. Some of the abnormal perinatal outcomes that had been previously attributed to ART, however, may be due to the baseline characteristics of infertile patients.

  7. Convection heat transfer

    CERN Document Server

    Bejan, Adrian

    2013-01-01

    Written by an internationally recognized authority on heat transfer and thermodynamics, this second edition of Convection Heat Transfer contains new and updated problems and examples reflecting real-world research and applications, including heat exchanger design. Teaching not only structure but also technique, the book begins with the simplest problem solving method (scale analysis), and moves on to progressively more advanced and exact methods (integral method, self similarity, asymptotic behavior). A solutions manual is available for all problems and exercises.

  8. Birthweight distribution in ART singletons resulting from embryo culture in two different culture media compared with the national population.

    Science.gov (United States)

    Lemmen, J G; Pinborg, A; Rasmussen, S; Ziebe, S

    2014-10-10

    Is there a difference in birthweight distribution in ART singletons born after IVF culture in two different culture media? There is no effect of culture media on both crude and adjusted birthweight distributions in ART singletons from nulliparous mothers. Studies on human ART singletons have reported a difference in birthweight in singletons following IVF culture in different culture media. However, other studies comparing different culture media have not shown any significant differences in birthweight. This study was a retrospective comparison of birthweights in IVF/ICSI singletons conceived after fresh embryo transfer following embryo culture in Cook or Medicult medium and in a national cohort of naturally conceived singletons in nulliparous women. The study compares four independent groups consisting of singletons in nulliparous women from Cook-d2: 2-day culture in Cook medium at Rigshospitalet (n = 974), Medicult-d2: 2-day culture in Medicult EmbryoAssist medium at Rigshospitalet (n = 147), Medicult-d3: 3-day culture in Medicult EmbryoAssist medium with and without added GM-CSF (n = 204), and DK: pregnancies from the Danish birth registry (n = 106842). The study compares the birthweights of singletons from nulliparous women in the four independent groups mentioned above; Cook-d2: Medicult-d2: Medicult-d3: and DK. In addition, distributions of large and small for gestational age infants were compared between the groups and a multiple linear regression analysis was used to determine which factors determined birthweight. We found no significant difference in the crude birthweight distributions between singletons born after culture in Cook-d2 or Medicult-groups. Singleton girls from the Cook-d2 group weighed 3302 ± 28 g, versus 3252 ± 76 in the Medicult-d2 group (difference 50 g; P = 0.547). Singleton boys from the Cook-d2 group weighed 3430 ± 27 g, versus 3354 ± 56 in the Medicult-d2 group (difference 76 g; P = 0.279). In the background population, mean

  9. Shifts of visuospatial attention to invisible (metacontrast-masked singletons: Clues from reaction times and event-related potential

    Directory of Open Access Journals (Sweden)

    Manfred Heumann

    2006-01-01

    Full Text Available In the current study, we tested whether a masked and, thus, invisible singleton-cue captures atten-tion in a stimulus-driven manner or in a top-down contingent manner. The manual RT (Reaction Time capture effect with the invisible singleton--cue decreased substantially when a match between the singleton-cue and the top-down controlled set of searched-for target features was also decreased. By contrast, with the PCN (Posterior Contralateral Negativity, an electrophysiological measure of the capture of visuospatial attention by the invisible singleton-cue, no significant decrement was observed. Taken together, the results support the assumption that an invisible singleton-cue can capture attention in a stimulus-driven manner, and that different delays in the deallocation of attention (i.e., attention is deallocated more efficiently from acue that does not match the top-down controlled set than from a cue that does match the same set account for the weaker manual RT capture effect with a set- -nonmatching invisible singleton-cue.

  10. Micro-Physical characterisation of Convective & Stratiform Rainfall at Tropics

    Science.gov (United States)

    Sreekanth, T. S.

    Large Micro-Physical characterisation of Convective & Stratiform Rainfall at Tropics begin{center} begin{center} Sreekanth T S*, Suby Symon*, G. Mohan Kumar (1) , and V Sasi Kumar (2) *Centre for Earth Science Studies, Akkulam, Thiruvananthapuram (1) D-330, Swathi Nagar, West Fort, Thiruvananthapuram 695023 (2) 32. NCC Nagar, Peroorkada, Thiruvananthapuram ABSTRACT Micro-physical parameters of rainfall such as rain drop size & fall speed distribution, mass weighted mean diameter, Total no. of rain drops, Normalisation parameters for rain intensity, maximum & minimum drop diameter from different rain intensity ranges, from both stratiform and convective rain events were analysed. Convective -Stratiform classification was done by the method followed by Testud et al (2001) and as an additional information electrical behaviour of clouds from Atmospheric Electric Field Mill was also used. Events which cannot be included in both types are termed as 'mixed precipitation' and identified separately. For the three years 2011, 2012 & 2013, rain events from both convective & stratiform origin are identified from three seasons viz Pre-Monsoon (March-May), Monsoon (June-September) and Post-Monsoon (October-December). Micro-physical characterisation was done for each rain events and analysed. Ground based and radar observations were made and classification of stratiform and convective rainfall was done by the method followed by Testud et al (2001). Radar bright band and non bright band analysis was done for confimation of stratifom and convective rain respectievely. Atmospheric electric field data from electric field mill is also used for confirmation of convection during convective events. Statistical analyses revealed that the standard deviation of rain drop size in higher rain rates are higher than in lower rain rates. Normalised drop size distribution is ploted for selected events from both forms. Inter relations between various precipitation parameters were analysed in three

  11. Bidispersive-inclined convection

    Science.gov (United States)

    Mulone, Giuseppe; Straughan, Brian

    2016-01-01

    A model is presented for thermal convection in an inclined layer of porous material when the medium has a bidispersive structure. Thus, there are the usual macropores which are full of a fluid, but there are also a system of micropores full of the same fluid. The model we employ is a modification of the one proposed by Nield & Kuznetsov (2006 Int. J. Heat Mass Transf. 49, 3068–3074. (doi:10.1016/j.ijheatmasstransfer.2006.02.008)), although we consider a single temperature field only. PMID:27616934

  12. Cesarean Section Rate in Singleton Primiparae and Related Factors in Beijing, China.

    Science.gov (United States)

    Song, Geng; Wei, Yu-Mei; Zhu, Wei-Wei; Yang, Hui-Xia

    2017-10-20

    The cesarean section rate (CSR) has been a main concern worldwide. The present study aimed to investigate the CSR in Beijing, China, and to analyze the related factors of CS delivery. An observational study was conducted in 15 medical centers in Beijing using a systemic cluster sampling method. In total, 15,194 pregnancies were enrolled in the study between June 20, 2013 and November 30, 2013. Independent t-tests and Pearson's Chi-square test were used to examine differences between two groups, and related factors of the CSR were examined by multivariable logistic regression. The CSR was 41.9% (4471/10,671) in singleton primiparae. Women who were more than 35 years old had a 7.4-fold increased risk of CS delivery compared with women level. Neonates weighing 3000-3499 g had the lowest CSR (36.2%). Neonates weighing levels, residence, education level, and singleton fetal birth weight are all factors that might significantly affect the CSR.

  13. Singleton birth at term: an old alarm or a new debate?

    Science.gov (United States)

    Hughes, Edward G

    2015-10-01

    In 2004, Human Reproduction published a debate series focusing on the rising tide of multiple pregnancy associated with IVF. The premise of the primary report in that debate was that by considering IVF outcomes differently-by focusing on healthy singleton birth at term rather than clinical pregnancy, the standard currency at that time-the necessary shift toward reduced numbers of embryos transferred might be accelerated. The choice of end-point in that debate-Birth Emphasizing a Successful Singleton at Term (BESST)-was not an effort to 'dumb down' the complex equation linking risks and benefits. That balance is a dynamic and various mix of issues that clinicians discuss with patients on a daily basis. And BESST was certainly not proposed as a new primary outcome for application to other treatment modalities in reproductive medicine, such as ovulation induction. It was simply a responsible and brave call for change in the accelerating and competitive world of IVF. © The Author 2015. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  14. Umbilical cord length in singleton gestations: a Finnish population-based retrospective register study.

    Science.gov (United States)

    Georgiadis, L; Keski-Nisula, L; Harju, M; Räisänen, S; Georgiadis, S; Hannila, M-L; Heinonen, S

    2014-04-01

    Many complications of pregnancy and delivery are associated with umbilical cord length. It is important to examine the variation in length, in order to identify normal and abnormal conditions. Moreover, the factors influencing cord growth and development are not precisely known. The main objectives were to provide updated reference charts for umbilical cord length in singleton pregnancies and to evaluate potential factors affecting cord length. Birth register data of 47,284 singleton pregnant women delivering in Kuopio University Hospital, Finland was collected prospectively. Gender-specific centile charts for cord length from 22 to 44 gestational weeks were obtained using generalized additive models for location, scale, and shape (GAMLSS). Gestational, fetal, and maternal factors were studied for their potential influence on cord length with single variable analysis and stepwise multiple linear regression analysis. Cord length increased according to gestational age, while the growth decelerated post-term. Birth weight, placental weight, pregravid maternal body mass index, parity, and maternal age correlated to cord length. Gestational diabetes and previous miscarriages were associated with longer cords, while female gender and placental abruption were associated with shorter cords. Girls had shorter cords throughout gestation although there was substantial variation in length in both genders. Cord length associated significantly with birth weight, placental weight, and gestational age. Significantly shorter cords were found in women with placental abruption. This important finding requires further investigation. Copyright © 2014 Elsevier Ltd. All rights reserved.

  15. Mixing in heterogeneous internally-heated convection

    Science.gov (United States)

    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

  16. Convection in Porous Media

    CERN Document Server

    Nield, Donald A

    2013-01-01

    Convection in Porous Media, 4th Edition, provides a user-friendly introduction to the subject, covering a wide range of topics, such as fibrous insulation, geological strata, and catalytic reactors. The presentation is self-contained, requiring only routine mathematics and the basic elements of fluid mechanics and heat transfer. The book will be of use not only to researchers and practicing engineers as a review and reference, but also to graduate students and others entering the field. The new edition features approximately 1,750 new references and covers current research in nanofluids, cellular porous materials, strong heterogeneity, pulsating flow, and more. Recognized as the standard reference in the field Includes a comprehensive, 250-page reference list Cited over 2300 times to date in its various editions Serves as an introduction for those entering the field and as a comprehensive reference for experienced researchers Features new sections on nanofluids, carbon dioxide sequestration, and applications...

  17. Convection in porous media

    CERN Document Server

    Nield, Donald A

    1992-01-01

    This book provides a user-friendly introduction to the topic of convection in porous media The authors as- sume that the reader is familiar with the basic elements of fluid mechanics and heat transfer, but otherwise the book is self-contained The book will be useful both as a review (for reference) and as a tutorial work, suitable as a textbook in a graduate course or seminar The book brings into perspective the voluminous research that has been performed during the last two decades The field has recently exploded because of worldwide concern with issues such as energy self-sufficiency and pollution of the environment Areas of application include the insulation of buildings and equipment, energy storage and recovery, geothermal reservoirs, nuclear waste disposal, chemical reactor engineering, and the storage of heat-generating materials such as grain and coal Geophysical applications range from the flow of groundwater around hot intrusions to the stability of snow against avalanches

  18. Stellar convection and dynamo theory

    Energy Technology Data Exchange (ETDEWEB)

    Jennings, R L

    1989-10-01

    In considering the large scale stellar convection problem the outer layers of a star are modelled as two co-rotating plane layers coupled at a fluid/fluid interface. Heating from below causes only the upper fluid to convect, although this convection can penetrate into the lower fluid. Stability analysis is then used to find the most unstable mode of convection. With parameters appropriate to the Sun the most unstable mode is steady convection in thin cells (aspect ratio {approx equal} 0.2) filling the convection zone. There is negligible vertical motion in the lower fluid, but considerable thermal penetration, and a large jump in helicity at the interface, which has implications for dynamo theory. An {alpha}{omega} dynamo is investigated in isolation from the convection problem. Complexity is included by allowing both latitudinal and time dependence in the magnetic fields. The nonlinear dynamics of the resulting partial differential equations are analysed in considerable detail. On varying the main control parameter D (the dynamo number), many transitions of behaviour are found involving many forms of time dependence, but not chaos. Further, solutions which break equatorial symmetry are common and provide a theoretical explanation of solar observations which have this symmetry. Overall the behaviour was more complicated than expected. In particular, there were multiple stable solutions at fixed D, meaning that similar stars can have very different magnetic patterns, depending upon their history. (author).

  19. Evaluation of the sensitivity of the Amazonian diurnal cycle to convective intensity in reanalyses

    Science.gov (United States)

    Itterly, Kyle F.; Taylor, Patrick C.

    2017-02-01

    Model parameterizations of tropical deep convection are unable to reproduce the observed diurnal and spatial variability of convection in the Amazon, which contributes to climatological biases in the water cycle and energy budget. Convective intensity regimes are defined using percentiles of daily minimum 3-hourly averaged outgoing longwave radiation (OLR) from Clouds and the Earth's Radiant Energy System (CERES). This study compares the observed spatial variability of convective diurnal cycle statistics for each regime to MERRA-2 and ERA-Interim (ERA) reanalysis data sets. Composite diurnal cycle statistics are computed for daytime hours (06:00-21:00 local time) in the wet season (December-January-February). MERRA-2 matches observations more closely than ERA for domain averaged composite diurnal statistics—specifically precipitation. However, ERA reproduces mesoscale features of OLR and precipitation phase associated with topography and the propagation of the coastal squall line. Both reanalysis models are shown to underestimate extreme convection.

  20. The type of culture medium and the duration of in vitro culture do not influence birthweight of ART singletons.

    Science.gov (United States)

    De Vos, A; Janssens, R; Van de Velde, H; Haentjens, P; Bonduelle, M; Tournaye, H; Verheyen, G

    2015-01-01

    Does the type of in vitro culture medium or the duration of in vitro culture influence singleton birthweight after IVF/ICSI treatment? In a comparison of two culture media, neither the medium nor the duration of culture (Day 3 versus Day 5 blastocyst transfer) had any effect on mean singleton birthweight. Previous studies indicated that in vitro culture of human embryos may affect birthweight of live born singletons. Both the type of culture medium and the duration of culture may be implicated. However, these studies are small and report conflicting results. A large retrospective analysis was performed including all singleton live births after transferring fresh Day 3 or Day 5 embryos. IVF and ICSI cycles performed between April 2004 and December 2009 at a tertiary care centre were included for analysis. A total of 2098 singleton live births resulting from singleton pregnancies were included for analysis. Two different sequential embryo culture media were concurrently used in an alternating way: Medicult (n = 1388) and Vitrolife (n = 710). Maternal age, maternal and paternal BMI, maternal parity, maternal smoking, main cause of infertility, cycle rank, stimulation protocol, method of fertilization (IVF or ICSI), time in culture and number of embryos transferred were taken into account. Embryo transfers were performed either on Day 3 (n = 1234) or on Day 5 (n = 864). Singleton birthweight was the primary outcome parameter. Gestational age and gender of the newborn were accounted for in the multiple regression analysis. No significant differences in mean singleton birthweight were observed between the two culture media: Medicult 3222 g (±15 SE) and Vitrolife 3251 g (±21 SE) (P = 0.264). The mean singleton birthweight was not different between Day 3 embryo transfers (3219 ± 16 g) and Day 5 blastocyst transfers (3250 ± 19 g; P = 0.209). Multiple regression analysis controlling for potential maternal, paternal, treatment and newborn confounders confirmed the non

  1. The convection patterns in microemulsions

    International Nuclear Information System (INIS)

    Korneta, W.; Lopez Quintela, M.A.; Fernandez Novoa, A.

    1991-07-01

    The Rayleigh-Benard convection in the microemulsion consisting of water (7.5%), cyclohexan (oil-61.7%) and diethylenglycolmonobutylether (surfactant-30.8%) is studied from the onset of convection to the phase separation. The five classes of convection patterns are observed and recorded on the video: localized travelling waves, travelling waves, travelling waves and localized steady rolls, steady rolls and steady polygons. The Fourier transforms and histograms of these patterns are presented. The origin of any pattern is discussed. The intermittent behaviour close to the phase separation was observed. Possible applications of the obtained results are suggested. (author). 6 refs, 4 figs

  2. Thermodynamics of the Earth

    International Nuclear Information System (INIS)

    Stacey, Frank D

    2010-01-01

    Applications of elementary thermodynamic principles to the dynamics of the Earth lead to robust, quantitative conclusions about the tectonic effects that arise from convection. The grand pattern of motion conveys deep heat to the surface, generating mechanical energy with a thermodynamic efficiency corresponding to that of a Carnot engine operating over the adiabatic temperature gradient between the heat source and sink. Referred to the total heat flux derived from the Earth's silicate mantle, the efficiency is 24% and the power generated, 7.7 x 10 12 W, causes all the material deformation apparent as plate tectonics and the consequent geological processes. About 3.5% of this is released in seismic zones but little more than 0.2% as seismic waves. Even major earthquakes are only localized hiccups in this motion. Complications that arise from mineral phase transitions can be used to illuminate details of the motion. There are two superimposed patterns of convection, plate subduction and deep mantle plumes, driven by sources of buoyancy, negative and positive respectively, at the top and bottom of the mantle. The patterns of motion are controlled by the viscosity contrasts (>10 4 : 1) at these boundaries and are self-selected as the least dissipative mechanisms of heat transfer for convection in a body with very strong viscosity variation. Both are subjects of the thermodynamic efficiency argument. Convection also drives the motion in the fluid outer core that generates the geomagnetic field, although in that case there is an important energy contribution by compositional separation, as light solute is rejected by the solidifying inner core and mixed into the outer core, a process referred to as compositional convection. Uncertainty persists over the core energy balance because thermal conduction is a drain on core energy that has been a subject of diverse estimates, with attendant debate over the need for radiogenic heat in the core. The geophysical approach to

  3. Effect of natural convection in a horizontally oriented cylinder on NMR imaging of the distribution of diffusivity

    Science.gov (United States)

    Mohoric; Stepisnik

    2000-11-01

    This paper describes the influence of natural convection on NMR measurement of a self-diffusion constant of fluid in the earth's magnetic field. To get an estimation of the effect, the Lorenz model of natural convection in a horizontally oriented cylinder, heated from below, is derived. Since the Lorenz model of natural convection is derived for the free boundary condition, its validity is of a limited value for the natural no-slip boundary condition. We point out that even a slight temperature gradient can cause significant misinterpretation of measurements. The chaotic nature of convection enhances the apparent self-diffusion constant of the liquid.

  4. Perinatal outcomes among singletons after assisted reproductive technology with single-embryo or double-embryo transfer versus no assisted reproductive technology.

    Science.gov (United States)

    Martin, Angela S; Chang, Jeani; Zhang, Yujia; Kawwass, Jennifer F; Boulet, Sheree L; McKane, Patricia; Bernson, Dana; Kissin, Dmitry M; Jamieson, Denise J

    2017-04-01

    To examine outcomes of singleton pregnancies conceived without assisted reproductive technology (non-ART) compared with singletons conceived with ART by elective single-embryo transfer (eSET), nonelective single-embryo transfer (non-eSET), and double-embryo transfer with the establishment of 1 (DET -1) or ≥2 (DET ≥2) early fetal heartbeats. Retrospective cohort using linked ART surveillance data and vital records from Florida, Massachusetts, Michigan, and Connecticut. Not applicable. Singleton live-born infants. None. Preterm birth (PTB score score approach, we found that singletons conceived after eSET were less likely to have a 5-minute Apgar Reproductive Medicine. All rights reserved.

  5. Method of fuzzy inference for one class of MISO-structure systems with non-singleton inputs

    Science.gov (United States)

    Sinuk, V. G.; Panchenko, M. V.

    2018-03-01

    In fuzzy modeling, the inputs of the simulated systems can receive both crisp values and non-Singleton. Computational complexity of fuzzy inference with fuzzy non-Singleton inputs corresponds to an exponential. This paper describes a new method of inference, based on the theorem of decomposition of a multidimensional fuzzy implication and a fuzzy truth value. This method is considered for fuzzy inputs and has a polynomial complexity, which makes it possible to use it for modeling large-dimensional MISO-structure systems.

  6. Perinatal outcomes in 6,338 singletons born after intrauterine insemination in Denmark, 2007 to 2012

    DEFF Research Database (Denmark)

    Malchau, Sara Sofia; Loft, Anne; Henningsen, Anna-Karina Aaris

    2014-01-01

    . INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Preterm birth (PTB), low birth weight (LBW), small for gestational age (SGA). RESULT(S): Children born after IUI-H had higher risks of PTB, LBW, and SGA vs. SC singletons (adjusted odds ratios [aOR] 1.3; 95% confidence interval (CI), 1.1-1.5; 1.4; 95% CI, 1.......2-1.7; and 1.4; 95% CI, 1.2-1.6), respectively. Compared with IVF, risk of SGA was similar, but risks of PTB and LBW were lower (aOR 0.6; 95% CI, 0.5-0.8; and 0.8; 95% CI, 0.6-0.9). Compared with intracytoplasmic sperm injection, no differences were found. For children born after IUI with donor semen, results...

  7. Mothers' marital adaptation following the birth of twins or singletons: empirical evidence and practical insights.

    Science.gov (United States)

    Taubman-Ben-Ari, Orit; Findler, Liora; Bendet, Chaya; Stanger, Varda; Ben-Shlomo, Shirley; Kuint, Jacob

    2008-08-01

    Parenting twins is typically portrayed as more stressful than is parenting single children and, therefore, more of a strain on the marital relationship. With this in mind, the present study examined the contribution of infant characteristics and mother's internal resources (attachment style) and external resources (maternal and paternal grandmothers' perceived support) to their marital adaptation during the first month following delivery, comparing mothers of twins (n = 88) with mothers of singletons (n = 82). The findings indicate that both internal and external resources contribute to the marital adaptation of the two groups, even beyond the contribution of specific circumstances. Thus, it seems that the birth of twins and the birth of a single child are normative life events that have more in common than previously acknowledged. The implications for the focus of social work interventions, particularly in the case of the birth of twins, are discussed.

  8. Analysis of intracranial hemorrhage grade in preterm singleton pregnancies delivered vaginally or by cesarean section

    Directory of Open Access Journals (Sweden)

    Ljuština Saša

    2013-01-01

    Full Text Available Background/Aim. Preterm birth is the leading cause of neonatal mortality. Periventricular hemorrhage-intraventricular hemorrhage (PVH-IVH remains a significant cause of both morbidity and mortality in infants prematurely born. The aim of the study was to evaluate the perinatal outcome regarding IVH of premature babies according to the mode of delivery. Methods. A total of 126 women in preterm singleton pregnancies with vertex presentation and 126 neonates weighted from 750 g to 1,500 g at birth were enrolled. The outcomes of 64 neonates born vaginally were compared to 62 neonates born by cesarean section. Results. There was no significant difference in the incidence of IVH among both groups. Conclusion. Our data is consistent with the hypothesis that the mode of delivery does not influence IVH and consenquently perinatal outcome in preterm neonates.

  9. Convection in the Labrador Sea

    National Research Council Canada - National Science Library

    Davis, R

    1997-01-01

    The long-term goal of this grant was to describe the process of deep oceanic convection well enough to provide critical tests of, and guidance to, models used to predict subsurface ocean conditions...

  10. Excess Mortality in Patients Diagnosed With Hypothyroidism: A Nationwide Cohort Study of Singletons and Twins

    Science.gov (United States)

    Thvilum, Marianne; Brandt, Frans; Almind, Dorthe; Christensen, Kaare; Brix, Thomas Heiberg

    2013-01-01

    Background: Although hypothyroidism is associated with increased morbidity, an association with increased mortality is still debated. Our objective was to investigate, at a nationwide level, whether a diagnosis of hypothyroidism influences mortality. Methods: In an observational cohort study from January 1, 1978 until December 31, 2008 using record-linkage data from nationwide Danish health registers, 3587 singletons and 682 twins diagnosed with hypothyroidism were identified. Hypothyroid individuals were matched 1:4 with nonhypothyroid controls with respect to age and gender and followed over a mean period of 5.6 years (range 0–30 years). The hazard ratio (HR) for mortality was calculated using Cox regression analyses. Comorbidity was evaluated using the Charlson score (CS). Results: In singletons with hypothyroidism, the mortality risk was increased (HR 1.52; 95% confidence interval [CI]: 1.41–1.65). Although the effect attenuated, hypothyroidism remained associated with increased mortality when evaluating subjects with a CS = 0 (HR 1.23; 95% CI: 1.05–1.44). In twin pairs discordant for hypothyroidism, the hypothyroid twin had excess mortality compared with the corresponding euthyroid cotwin (HR 1.40; 95% CI 0.95–2.05). However, after stratifying for zygosity, hypothyroidism was associated with excess mortality in dizygotic twin pairs (HR 1.61; 95% CI 1.00–2.58), whereas the association attenuated in monozygotic pairs (HR 1.06; 95% CI 0.55–2.05). Conclusions: Hypothyroidism is associated with an excess mortality of around 50%, which to some degree is explained by comorbidity. In addition, the finding of an association between hypothyroidism and mortality within disease discordant dizygotic but not monozygotic twin pairs indicates that the association between hypothyroidism and mortality is also influenced by genetic confounding. PMID:23365121

  11. Home cervical ripening with dinoprostone gel in nulliparous women with singleton pregnancies.

    Science.gov (United States)

    Stock, Sarah J; Taylor, Rebecca; Mairs, Rebecca; Azaghdani, Abdulhamid; Hor, Kahyee; Smith, Imogen; Dundas, Kirsty; Kissack, Chris; Norman, Jane E; Denison, Fiona

    2014-08-01

    To evaluate whether home cervical ripening is safe and results in shorter hospital stay. This was a retrospective cohort study of women with singleton pregnancies having induction of labor for postmaturity at a single center between January 2007 and June 2010. Women were offered home cervical ripening with 1 mg dinoprostone gel if they were nulliparous, had uncomplicated singleton pregnancies, and the indication for induction was postmaturity. Nine hundred seven of 1,536 (59.1%) nulliparous women having induction of labor for postmaturity were eligible for home cervical ripening. The median number of hours at home was 11.76 hours (range 0-24.82 hours). There were no cases of birth outside of the hospital, uterine rupture, or significant neonatal morbidity or neonatal death related to home cervical ripening. Eighty-five (5.5%) women who underwent hospital cervical ripening because of maternal preference or social issues formed a hospital cervical ripening comparison group. There was no significant difference in the total number of hours before delivery spent in the hospital between the two groups (26.25; 95% confidence interval [CI] 25.27-27.23 in home cervical ripening group compared with 24.28; 95% CI 22.5-26.0 in the hospital group; P=.26). Clinical outcomes are comparable in nulliparous women who receive a single dose of dinoprostone gel for home cervical ripening compared with those who undergo hospital cervical ripening. However, preadmission home cervical ripening with 1 mg dinoprostone does not decrease the number of hours women spend in the hospital. II.

  12. Convective heat flow probe

    Science.gov (United States)

    Dunn, James C.; Hardee, Harry C.; Striker, Richard P.

    1985-01-01

    A convective heat flow probe device is provided which measures heat flow and fluid flow magnitude in the formation surrounding a borehole. The probe comprises an elongate housing adapted to be lowered down into the borehole; a plurality of heaters extending along the probe for heating the formation surrounding the borehole; a plurality of temperature sensors arranged around the periphery of the probe for measuring the temperature of the surrounding formation after heating thereof by the heater elements. The temperature sensors and heater elements are mounted in a plurality of separate heater pads which are supported by the housing and which are adapted to be radially expanded into firm engagement with the walls of the borehole. The heat supplied by the heater elements and the temperatures measured by the temperature sensors are monitored and used in providing the desired measurements. The outer peripheral surfaces of the heater pads are configured as segments of a cylinder and form a full cylinder when taken together. A plurality of temperature sensors are located on each pad so as to extend along the length and across the width thereof, with a heating element being located in each pad beneath the temperature sensors. An expansion mechanism driven by a clamping motor provides expansion and retraction of the heater pads and expandable packer-type seals are provided along the probe above and below the heater pads.

  13. Convection-enhanced water evaporation

    OpenAIRE

    B. M. Weon; J. H. Je; C. Poulard

    2011-01-01

    Water vapor is lighter than air; this can enhance water evaporation by triggering vapor convection but there is little evidence. We directly visualize evaporation of nanoliter (2 to 700 nL) water droplets resting on silicon wafer in calm air using a high-resolution dual X-ray imaging method. Temporal evolutions of contact radius and contact angle reveal that evaporation rate linearly changes with surface area, indicating convective (instead of diffusive) evaporation in nanoliter water droplet...

  14. Theory of Earth

    Science.gov (United States)

    Anderson, D. L.

    2014-12-01

    Earth is an isolated, cooling planet that obeys the 2nd law. Interior dynamics is driven from the top, by cold sinking slabs. High-resolution broad-band seismology and geodesy has confirmed that mantle flow is characterized by narrow downwellings and ~20 broad slowly rising updrafts. The low-velocity zone (LVZ) consists of a hot melange of sheared peridotite intruded with aligned melt-rich lamellae that are tapped by intraplate volcanoes. The high temperature is a simple consequence of the thermal overshoot common in large bodies of convecting fluids. The transition zone consists of ancient eclogite layers that are displaced upwards by slabs to become broad passive, and cool, ridge feeding updrafts of ambient mantle. The physics that is overlooked in canonical models of mantle dynamics and geochemistry includes; the 2nd law, convective overshoots, subadiabaticity, wave-melt interactions, Archimedes' principle, and kinetics (rapid transitions allow stress-waves to interact with melting and phase changes, creating LVZs; sluggish transitions in cold slabs keep eclogite in the TZ where it warms up by extracting heat from mantle below 650 km, creating the appearance of slab penetration). Canonical chemical geodynamic models are the exact opposite of physics and thermodynamic based models and of the real Earth. A model that results from inverting the assumptions regarding initial and boundary conditions (hot origin, secular cooling, no external power sources, cooling internal boundaries, broad passive upwellings, adiabaticity and whole-mantle convection not imposed, layering and self-organization allowed) results in a thick refractory-yet-fertile surface layer, with ancient xenoliths and cratons at the top and a hot overshoot at the base, and a thin mobile D" layer that is an unlikely plume generation zone. Accounting for the physics that is overlooked, or violated (2nd law), in canonical models, plus modern seismology, undermines the assumptions and conclusions of these

  15. High accuracy mantle convection simulation through modern numerical methods

    KAUST Repository

    Kronbichler, Martin

    2012-08-21

    Numerical simulation of the processes in the Earth\\'s mantle is a key piece in understanding its dynamics, composition, history and interaction with the lithosphere and the Earth\\'s core. However, doing so presents many practical difficulties related to the numerical methods that can accurately represent these processes at relevant scales. This paper presents an overview of the state of the art in algorithms for high-Rayleigh number flows such as those in the Earth\\'s mantle, and discusses their implementation in the Open Source code Aspect (Advanced Solver for Problems in Earth\\'s ConvecTion). Specifically, we show how an interconnected set of methods for adaptive mesh refinement (AMR), higher order spatial and temporal discretizations, advection stabilization and efficient linear solvers can provide high accuracy at a numerical cost unachievable with traditional methods, and how these methods can be designed in a way so that they scale to large numbers of processors on compute clusters. Aspect relies on the numerical software packages deal.II and Trilinos, enabling us to focus on high level code and keeping our implementation compact. We present results from validation tests using widely used benchmarks for our code, as well as scaling results from parallel runs. © 2012 The Authors Geophysical Journal International © 2012 RAS.

  16. Water in geodynamical models of mantle convection and plate tectonics

    Science.gov (United States)

    Rodríguez-González, J.; Van Hunen, J.; Chotalia, K.; Lithgow-Bertelloni, C. R.; Rozel, A.; Tackley, P. J.; Nakagawa, T.

    2017-12-01

    The presence of water in the the mantle has a significant effect in the dynamical and thermal evolution of Earth, which partially explains the differences with other planets and is a key factor for the presence of life on Earth. First, a small amount of water can decrease the mantle viscosity by a several orders of magnitude, thereby changing the convection regime and affecting the thermal evolution. Second, the presence of water significantly changes the solidus curve, with crucial implications for melting. Third, water in the mantle can change the Clapeyron slope of mantle materials, which changes the depth at which phase transitions take place. The thermal and dynamical evolution of Earth under the presence of water in the mantle has been the focus of recent studies, but many questions remain unanswered. In this project we intend to investigate how the maximum water capacity of different mantle regions affects water transport and Earth's convective regime. We will study the effect phase transitions under the presence of water, which can change the buoyancy of slabs in the transition zone. We present preliminary results numerical models of global mantle convection for the whole history of earth using the numerical geodynamics software tool StagYY. We will use a new parametrisation of dehydration processes, obtained from high-resolution numerical simulations, to implement a more accurate description of the water released from the slab as it travels through the mantle. We have integrated recent experimental results of the water capacity of deep mantle minerals to study the water circulation and the total water budget. We use data from the most recent experiments and ab-inito calculations to implement a realistic rheology.

  17. Plasma convection in the magnetotail lobes: statistical results from Cluster EDI measurements

    Directory of Open Access Journals (Sweden)

    S. Haaland

    2008-08-01

    Full Text Available A major part of the plasma in the Earth's magnetotail is populated through transport of plasma from the solar wind via the magnetotail lobes. In this paper, we present a statistical study of plasma convection in the lobes for different directions of the interplanetary magnetic field and for different geomagnetic disturbance levels. The data set used in this study consists of roughly 340 000 one-minute vector measurements of the plasma convection from the Cluster Electron Drift Instrument (EDI obtained during the period February 2001 to June 2007. The results show that both convection magnitude and direction are largely controlled by the interplanetary magnetic field (IMF. For a southward IMF, there is a strong convection towards the central plasma sheet with convection velocities around 10 km s−1. During periods of northward IMF, the lobe convection is almost stagnant. A By dominated IMF causes a rotation of the convection patterns in the tail with an oppositely directed dawn-dusk component of the convection for the northern and southern lobe. Our results also show that there is an overall persistent duskward component, which is most likely a result of conductivity gradients in the footpoints of the magnetic field lines in the ionosphere.

  18. The Oscillatory Nature of Rotating Convection in Liquid Metal

    Science.gov (United States)

    Aurnou, J. M.; Bertin, V. L.; Grannan, A. M.

    2016-12-01

    Earth's magnetic field is assumed to be generated by fluid motions in its liquid metal core. In this fluid, the heat diffuses significantly more than momentum and thus, the ratio of these two diffusivities, the Prandtl number Pr=ν/Κ, is well below unity. The convective flow dynamics of liquid metal is very different from Pr ≈ 1 fluids like water and those used in current dynamo simulations. In order to characterize rapidly rotating thermal convection in low Pr number fluids, we have performed laboratory experiments in a cylinder using liquid gallium (Pr ≈ 0.023) as the working fluid. The Ekman number, which characterizes the effect of rotation, varies from E = 4 10-5 to 4 10-6 and the dimensionless buoyancy forcing (Rayleigh number, Ra) varies from Ra =3 105 to 2 107. Using heat transfer measurements (Nusselt number, Nu) as well as temperature measurements within the fluid, we characterize the different styles of low Pr rotating convective flow. The convection threshold is first overcome in the form of a container scale inertial oscillatory mode. At stronger forcing, wall-localized modes are identified for the first time in liquid metal laboratory experiments. These wall modes coexist with the bulk inertial oscillatory modes. When the strengh of the buoyancy increases, the bulk flow becomes turbulent while the wall modes remain. Our results imply that rotating convective flows in liquid metals do not develop in the form of quasi-steady columns, as in Pr ≈ 1 dynamo models, but in the form of oscillatory motions. Therefore, the flows that drive thermally-driven dynamo action in low Pr geophysical and astrophysical fluids can differ substantively than those occuring in current-day Pr ≈ 1 numerical models. In addition, our results suggest that relatively low wavenumber, wall-attached modes may be dynamically important in rapidly-rotating convection in liquid metals.

  19. Seasonal Scale Convective-Stratiform Pricipitation Variabilities at Tropics

    Science.gov (United States)

    S, Sreekanth T.

    begin{center} Large Seasonal Scale Convective-Stratiform Pricipitation Variabilities at Tropics Sreekanth T S*, Suby Symon*, G. Mohan Kumar (1) and V Sasi Kumar (2) *Centre for Earth Science Studies, Akkulam, Thiruvananthapuram (1) D-330, Swathi Nagar, West Fort, Thiruvananthapuram 695023 (2) 32. NCC Nagar Peroorkada, Thiruvananthapuram ABSTRACT This study investigates the variabilities of convective and stratiform rainfall from 2011 to 2013 at a tropical coastal station in three seasons viz Pre-Monsoon (March-May), Monsoon (June-September) and Post-Monsoon (October-December). Understanding the climatological variability of these two dominant forms of precipitation and their implications in the total rainfall were the main objectives of this investigation. Variabilities in the frequency & duration of events, rain rate & total number of rain drops distribution in different events and the accumulated amount of rain water were analysed. Based on the ground & radar observations from optical & impact disdrometers, Micro Rain Radar and Atmospheric Electric Field Mill, precipitation events were classified into convective and stratiform in three seasons. Classification was done by the method followed by Testud et al (2001) and as an additional information electrical behaviour of clouds from Atmospheric Electric Field Mill is also used. Events which could not be included in both types were termed as 'mixed precipitation' and were included separately. Diurnal variability of the total rainfall in each seasons were also examined. For both convective and stratiform rainfall there exist distinct day-night differences. During nocturnal hours convective rain draged more attention. In all seasons almost 70% of rain duration and 60% of rain events of convective origin were confined to nocturnal hours. But stratiform rain was not affected by diurnal variations greatly because night time occurrences of stratiform duration and events were less than 50%. Also in Monsoon above 35% of

  20. Differences in outcome between twins and singletons born very preterm: results from a population-based European cohort.

    NARCIS (Netherlands)

    Papiernik, E.; Zeitlin, J.; Delmas, D.; Blondel, B.; Kunzel, W.; Cuttini, M.; Weber, T.; Petrou, S.; Gortner, L.; Kollee, L.A.A.; Draper, E.S.

    2010-01-01

    BACKGROUND: About 10% of twins are born before 32 weeks of gestation and very preterm birth rates are increasing. Preterm twins tend to have more favourable outcomes than singletons of the same gestational age, but fewer data are available for very preterm infants. This study aims to determine

  1. Acoustic cue weighting in the singleton vs geminate contrast in Lebanese Arabic: The case of fricative consonants.

    Science.gov (United States)

    Al-Tamimi, Jalal; Khattab, Ghada

    2015-07-01

    This paper is the first reported investigation of the role of non-temporal acoustic cues in the singleton-geminate contrast in Lebanese Arabic, alongside the more frequently reported temporal cues. The aim is to explore the extent to which singleton and geminate consonants show qualitative differences in a language where phonological length is prominent and where moraic structure governs segment timing and syllable weight. Twenty speakers (ten male, ten female) were recorded producing trochaic disyllables with medial singleton and geminate fricatives preceded by phonologically short and long vowels. The following acoustic measures were applied on the medial fricative and surrounding vowels: absolute duration; intensity; fundamental frequency; spectral peak and shape, dynamic amplitude, and voicing patterns of medial fricatives; and vowel quality and voice quality correlates of surrounding vowels. Discriminant analysis and receiver operating characteristics (ROC) curves were used to assess each acoustic cue's contribution to the singleton-geminate contrast. Classification rates of 89% and ROC curves with an area under the curve rate of 96% confirmed the major role played by temporal cues, with non-temporal cues contributing to the contrast but to a much lesser extent. These results confirm that the underlying contrast for gemination in Arabic is temporal, but highlight [+tense] (fortis) as a secondary feature.

  2. A comparison of perinatal outcomes in singletons and multiples born after IVF or ICSI, stratified for neonatal risk criteria

    NARCIS (Netherlands)

    van Heesch, Mirjam M. J.; Evers, Johannes L. H.; Dumoulin, John C. M.; van der Hoeven, Mark A. H. B. M.; van Beijsterveldt, Catharina E. M.; Bonsel, Gouke J.; Dykgraaf, Ramon H. M.; van Goudoever, Johannes B.; Koopman-Esseboom, Corine; Nelen, Willianne L. D. M.; Steiner, Katerina; Tamminga, Pieter; Tonch, Nino; van Zonneveld, Piet; Dirksen, Carmen D.

    2014-01-01

    To compare perinatal singleton and multiple outcomes in a large Dutch in-vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) population and within risk subgroups. Newborns were assigned to a risk category based on gestational age, birthweight, Apgar score and congenital malformation.

  3. Differences in outcome between twins and singletons born very preterm: results from a population-based European cohort

    DEFF Research Database (Denmark)

    Papiernik, Emile; Zeitlin, Jennifer; Delmas, Dominique

    2010-01-01

    About 10% of twins are born before 32 weeks of gestation and very preterm birth rates are increasing. Preterm twins tend to have more favourable outcomes than singletons of the same gestational age, but fewer data are available for very preterm infants. This study aims to determine whether outcom...

  4. Impact of obstetric history on the risk of spontaneous preterm birth in singleton and multiple pregnancies: a systematic review

    NARCIS (Netherlands)

    Kazemier, B. M.; Buijs, P. E.; Mignini, L.; Limpens, J.; de Groot, C. J. M.; Mol, B. W. J.; von Dadelszen, P.; Magee, L.; Sawchuck, D.; Gao, E.; Oude Rengerink, K.; Zamora, J.; Fox, C.; Daniels, J.; Khan, K. S.; Thangaratinam, S.; Meads, C.

    2014-01-01

    Information about the recurrence of spontaneous preterm birth in subsequent twin/singleton pregnancies is scattered. To quantify the risk of recurrence of spontaneous preterm birth in different subtypes of subsequent pregnancies. An electronic literature search in OVID MEDLINE and EMBASE,

  5. An outcome-based approach for the creation of fetal growth standards: do singletons and twins need separate standards?

    Science.gov (United States)

    Joseph, K S; Fahey, John; Platt, Robert W; Liston, Robert M; Lee, Shoo K; Sauve, Reg; Liu, Shiliang; Allen, Alexander C; Kramer, Michael S

    2009-03-01

    Contemporary fetal growth standards are created by using theoretical properties (percentiles) of birth weight (for gestational age) distributions. The authors used a clinically relevant, outcome-based methodology to determine if separate fetal growth standards are required for singletons and twins. All singleton and twin livebirths between 36 and 42 weeks' gestation in the United States (1995-2002) were included, after exclusions for missing information and other factors (n = 17,811,922). A birth weight range was identified, at each gestational age, over which serious neonatal morbidity and neonatal mortality rates were lowest. Among singleton males at 40 weeks, serious neonatal morbidity/mortality rates were lowest between 3,012 g (95% confidence interval (CI): 3,008, 3,018) and 3,978 g (95% CI: 3,976, 3,980). The low end of this optimal birth weight range for females was 37 g (95% CI: 21, 53) less. The low optimal birth weight was 152 g (95% CI: 121, 183) less for twins compared with singletons. No differences were observed in low optimal birth weight by period (1999-2002 vs. 1995-1998), but small differences were observed for maternal education, race, parity, age, and smoking status. Patterns of birth weight-specific serious neonatal morbidity/neonatal mortality support the need for plurality-specific fetal growth standards.

  6. A Static Color Discontinuity Can Capture Spatial Attention when the Target Is an Abrupt-Onset Singleton

    Science.gov (United States)

    Burnham, Bryan R.; Neely, James H.

    2008-01-01

    C. L. Folk, R. W. Remington, and J. C. Johnston's (1992) contingent involuntary orienting hypothesis states that a salient visual feature will involuntarily capture attention only when the observer's attentional set includes similar features. In four experiments, when the target's relevant feature was its being an abruptly onset singleton,…

  7. Melting in super-earths.

    Science.gov (United States)

    Stixrude, Lars

    2014-04-28

    We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

  8. Reference Curve for the Mean Uterine Artery Pulsatility Index in Singleton Pregnancies.

    Science.gov (United States)

    Weichert, Alexander; Hagen, Andreas; Tchirikov, Michael; Fuchs, Ilka B; Henrich, Wolfgang; Entezami, Michael

    2017-05-01

    Doppler sonography of the uterine artery (UA) is done to monitor pregnancies, because the detected flow patterns are useful to draw inferences about possible disorders of trophoblast invasion. Increased resistance in the UA is associated with an increased risk of preeclampsia and/or intrauterine growth restriction (IUGR) and perinatal mortality. In the absence of standardized figures, the normal ranges of the various available reference curves sometimes differ quite substantially from one another. The causes for this are differences in the flow patterns of the UA depending on the position of the pulsed Doppler gates as well as branching of the UA. Because of the discrepancies between the different reference curves and the practical problems this poses for guideline recommendations, we thought it would be useful to create our own reference curves for Doppler measurements of the UA obtained from a singleton cohort under standardized conditions. This retrospective cohort study was carried out in the Department of Obstetrics of the Charité - Universitätsmedizin Berlin, the Department for Obstetrics and Prenatal Medicine of the University Hospital Halle (Saale) and the Center for Prenatal Diagnostics and Human Genetics Kurfürstendamm 199. Available datasets from the three study locations were identified and reference curves were generated using the LMS method. Measured values were correlated with age of gestation, and a cubic model and Box-Cox power transformation (L), the median (M) and the coefficient of variation (S) were used to smooth the curves. 103 720 Doppler examinations of the UA carried out in singleton pregnancies from the 11th week of gestation (10 + 1 GW) were analyzed. The mean pulsatility index (Mean PI) showed a continuous decline over the course of pregnancy, dropping to a plateau of around 0.84 between the 23rd and 27th GW, after which it decreased again. Age of gestation, placental position, position of pulsed Doppler gates and branching of

  9. Influence of convection on eutectic microstructure

    Science.gov (United States)

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

    1985-01-01

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

  10. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science. M Venkat Ratnam. Articles written in Journal of Earth System Science. Volume 120 Issue 5 October 2011 pp 807-823. Long-term variations in outgoing long-wave radiation (OLR), convective available potential energy (CAPE) and temperature in the tropopause region over ...

  11. Tectonic predictions with mantle convection models

    Science.gov (United States)

    Coltice, Nicolas; Shephard, Grace E.

    2018-04-01

    Over the past 15 yr, numerical models of convection in Earth's mantle have made a leap forward: they can now produce self-consistent plate-like behaviour at the surface together with deep mantle circulation. These digital tools provide a new window into the intimate connections between plate tectonics and mantle dynamics, and can therefore be used for tectonic predictions, in principle. This contribution explores this assumption. First, initial conditions at 30, 20, 10 and 0 Ma are generated by driving a convective flow with imposed plate velocities at the surface. We then compute instantaneous mantle flows in response to the guessed temperature fields without imposing any boundary conditions. Plate boundaries self-consistently emerge at correct locations with respect to reconstructions, except for small plates close to subduction zones. As already observed for other types of instantaneous flow calculations, the structure of the top boundary layer and upper-mantle slab is the dominant character that leads to accurate predictions of surface velocities. Perturbations of the rheological parameters have little impact on the resulting surface velocities. We then compute fully dynamic model evolution from 30 and 10 to 0 Ma, without imposing plate boundaries or plate velocities. Contrary to instantaneous calculations, errors in kinematic predictions are substantial, although the plate layout and kinematics in several areas remain consistent with the expectations for the Earth. For these calculations, varying the rheological parameters makes a difference for plate boundary evolution. Also, identified errors in initial conditions contribute to first-order kinematic errors. This experiment shows that the tectonic predictions of dynamic models over 10 My are highly sensitive to uncertainties of rheological parameters and initial temperature field in comparison to instantaneous flow calculations. Indeed, the initial conditions and the rheological parameters can be good enough

  12. Lightning-based propagation of convective rain fields

    Directory of Open Access Journals (Sweden)

    S. Dietrich

    2011-05-01

    Full Text Available This paper describes a new multi-sensor approach for continuously monitoring convective rain cells. It exploits lightning data from surface networks to propagate rain fields estimated from multi-frequency brightness temperature measurements taken by the AMSU/MHS microwave radiometers onboard NOAA/EUMETSAT low Earth orbiting operational satellites. Specifically, the method allows inferring the development (movement, morphology and intensity of convective rain cells from the spatial and temporal distribution of lightning strokes following any observation by a satellite-borne microwave radiometer. Obviously, this is particularly attractive for real-time operational purposes, due to the sporadic nature of the low Earth orbiting satellite measurements and the continuous availability of ground-based lightning measurements – as is the case in most of the Mediterranean region. A preliminary assessment of the lightning-based rainfall propagation algorithm has been successfully made by using two pairs of consecutive AMSU observations, in conjunction with lightning measurements from the ZEUS network, for two convective events. Specifically, we show that the evolving rain fields, which are estimated by applying the algorithm to the satellite-based rainfall estimates for the first AMSU overpass, show an overall agreement with the satellite-based rainfall estimates for the second AMSU overpass.

  13. Application of supercomputers to 3-D mantle convection

    International Nuclear Information System (INIS)

    Baumgardner, J.R.

    1986-01-01

    Current generation vector machines are providing for the first time the computing power needed to treat planetary mantle convection in a fully three-dimensional fashion. A numerical technique known as multigrid has been implemented in spherical geometry using a hierarchy of meshes constructed from the regular icosahedron to yield a highly efficient three-dimensional compressible Eulerian finite element hydrodynamics formulation. The paper describes the numerical method and presents convection solutions for the mantles of both the earth and the Moon. In the case of the Earth, the convection pattern is characterized by upwelling in narrow circular plumes originating at the core-mantle boundary and by downwelling in sheets or slabs derived from the cold upper boundary layer. The preferred number of plumes appears to be on the order of six or seven. For the Moon, the numerical results indicate that development of a predominately L = 2 pattern in later lunar history is a plausible explanation for the present large second-degree non-hydrostatic component in the lunar figure

  14. Convective behaviour in severe accidents

    International Nuclear Information System (INIS)

    Clement, C.F.

    1988-01-01

    The nature and magnitude of the hazard from radioactivity posed by a possible nuclear accident depend strongly on convective behaviour within and immediately adjacent to the plant in question. This behaviour depends upon the nature of the vapour-gas-aerosol mixture concerned, and can show unusual properties such as 'upside-down' convection in which hot mixtures fall and cold mixtures rise. Predictions and criteria as to the types of behaviour which could possibly occur are summarised. Possible applications to present reactors are considered, and ways in which presently expected convection could be drastically modified are described. In some circumstances these could be used to suppress the radioactive source term or to switch its effect between distant dilute contamination and severe local contamination. (author). 8 refs, 2 figs, 2 tabs

  15. True polar wander on convecting planets

    Science.gov (United States)

    Rose, Ian Robert

    Rotating planets are most stable when spinning around their maximum moment of inertia, and will tend to reorient themselves to achieve this configuration. Geological activity redistributes mass in the planet, making the moment of inertia a function of time. As the moment of inertia of the planet changes, the spin axis shifts with respect to a mantle reference frame in order to maintain rotational stability. This process is known as true polar wander (TPW). Of the processes that contribute to a planet's moment of inertia, convection in the mantle generates the largest and longest-period fluctuations, with corresponding shifts in the spin axis. True polar wander has been hypothesized to explain several physiographic features on planets and moons in our solar system. On Earth, TPW events have been invoked in some interpretations of paleomagnetic data. Large swings in the spin axis could have enormous ramifications for paleogeography, paleoclimate, and the history of life. Although the existence of TPW is well-verified, it is not known whether its rate and magnitude have been large enough for it to be an important process in Earth history. If true polar wander has been sluggish compared to plate tectonic speeds, then it would be difficult to detect and its consequences would be minor. I investigate rates of true polar wander on convecting planets using scaling, numerics, and inverse problems. I perform a scaling analysis of TPW on a convecting planet, identifying a minimal set of nondimensional parameters which describe the problem. The primary nondimensional numbers that control the rate of TPW are the ratio of centrifugal to gravitational forces m and the Rayleigh number Ra. The parameter m sets the size of a planet's rotational bulge, which determines the amount of work that needs to be done to move the spin axis. The Rayleigh number controls the size, distribution, and rate of change of moment of inertia anomalies, all of which affect the rate of TPW. I find that

  16. Topology Optimization for Convection Problems

    DEFF Research Database (Denmark)

    Alexandersen, Joe

    2011-01-01

    This report deals with the topology optimization of convection problems.That is, the aim of the project is to develop, implement and examine topology optimization of purely thermal and coupled thermomechanical problems,when the design-dependent eects of convection are taken into consideration.......This is done by the use of a self-programmed FORTRAN-code, which builds on an existing 2D-plane thermomechanical nite element code implementing during the course `41525 FEM-Heavy'. The topology optimizationfeatures have been implemented from scratch, and allows the program to optimize elastostatic mechanical...

  17. Experimental methods in natural convection

    International Nuclear Information System (INIS)

    Koster, J.N.

    1982-11-01

    Some common experimental techniques to determine local velocities and to visualize temperature fields in natural convection research are discussed. First the physics and practice of anemometers are discussed with emphasis put on optical anemometers. In the second and third case the physics and practice of the most developed interferometers are discussed; namely differential interferometry for visualization of temperature gradient fields and holographic interferometry for visualization of temperature fields. At the Institut fuer Reaktorbauelemente these three measuring techniques are applied for convection and pipe flow studies. (orig.) [de

  18. Health policies for the reduction of obstetric interventions in singleton full-term births in Catalonia.

    Science.gov (United States)

    Pueyo, Maria-Jesus; Escuriet, Ramon; Pérez-Botella, M; de Molina, I; Ruíz-Berdun, D; Albert, S; Díaz, S; Torres-Capcha, P; Ortún, V

    2018-04-01

    To explore the effect of hospital's characteristics in the proportion of obstetric interventions (OI) performed in singleton fullterm births (SFTB) in Catalonia (2010-2014), while incentives were employed to reduce C-sections. Data about SFTB assisted at 42 public hospitals were extracted from the dataset of hospital discharges. Hospitals were classified according to the level of complexity, the volume of births attended, and the adoption of a non-medicalized delivery (NMD) strategy. The annual average change in the percentage for OI was calculated based on Poisson regression models. The rate of OI (35% of all SFTB) including C-sections (20.6%) remained stable through the period. Hospitals attending less complex cases had a lower average of OI, while hospitals attending lower volumes had the highest average. Higher levels of complexity increased the use of C-sections (+4% yearly) and forceps (+16%). The adoption of the NMD strategy decreased the rate of C-sections. The proportion of OI, including C-sections, remained stable in spite of public incentives to reduce them. The adoption of the NMD strategy could help in decreasing the rate of OI. To reduce the OI rate, new strategies should be launched as the development of low-risk pregnancies units, alignment of incentives and hospital payment, increased value of incentives and encouragement of a cultural shift towards non-medicalized births. Copyright © 2018 Elsevier B.V. All rights reserved.

  19. RIG-I-Like Receptor Signaling in Singleton-Merten Syndrome

    Directory of Open Access Journals (Sweden)

    Changming Lu

    2017-09-01

    Full Text Available Singleton-Merten syndrome (SMS is an autosomal dominant, multi-system innate immune disorder characterized by early and severe aortic and valvular calcification, dental and skeletal abnormalities, psoriasis, glaucoma, and other varying clinical findings. Recently we identified a specific gain-of-function mutation in IFIH1, interferon induced with helicase C domain 1, segregated with this disease. SMS disease without hallmark dental anomalies, termed atypical SMS, has recently been reported caused by variants in DDX58, DEXD/H-box helicase 58. IFIH1 and DDX58 encode retinoic acid-inducible gene I (RIG-I-like receptors family members melanoma differentiation-associated gene 5 and RIG-I, respectively. These cytosolic pattern recognition receptors function in viral RNA detection initiating an innate immune response through independent pathways that promote type I and type III interferon expression and proinflammatory cytokines. In this review, we focus on SMS as an innate immune disorder summarizing clinical features, molecular aspects of the pathogenetic pathway and discussing underlying mechanisms of the disease.

  20. A stochastic parameterization for deep convection using cellular automata

    Science.gov (United States)

    Bengtsson, L.; Steinheimer, M.; Bechtold, P.; Geleyn, J.

    2012-12-01

    large-scale variables in regions where convective activity is large. A two month extended evaluation of the deterministic behaviour of the scheme indicate a neutral impact on forecast skill. References: Bengtsson, L., H. Körnich, E. Källén, and G. Svensson, 2011: Large-scale dynamical response to sub-grid scale organization provided by cellular automata. Journal of the Atmospheric Sciences, 68, 3132-3144. Frenkel, Y., A. Majda, and B. Khouider, 2011: Using the stochastic multicloud model to improve tropical convective parameterization: A paradigm example. Journal of the Atmospheric Sciences, doi: 10.1175/JAS-D-11-0148.1. Huang, X.-Y., 1988: The organization of moist convection by internal 365 gravity waves. Tellus A, 42, 270-285. Khouider, B., J. Biello, and A. Majda, 2010: A Stochastic Multicloud Model for Tropical Convection. Comm. Math. Sci., 8, 187-216. Palmer, T., 2011: Towards the Probabilistic Earth-System Simulator: A Vision for the Future of Climate and Weather Prediction. Quarterly Journal of the Royal Meteorological Society 138 (2012) 841-861 Plant, R. and G. Craig, 2008: A stochastic parameterization for deep convection based on equilibrium statistics. J. Atmos. Sci., 65, 87-105.

  1. Magnetohydrodynamic Convection in the Outer Core and its Geodynamic Consequences

    Science.gov (United States)

    Kuang, Weijia; Chao, Benjamin F.; Fang, Ming

    2004-01-01

    The Earth's fluid outer core is in vigorous convection through much of the Earth's history. In addition to generating and maintaining Earth s time-varying magnetic field (geodynamo), the core convection also generates mass redistribution in the core and a dynamical pressure field on the core-mantle boundary (CMB). All these shall result in various core-mantle interactions, and contribute to surface geodynamic observables. For example, electromagnetic core-mantle coupling arises from finite electrically conducting lower mantle; gravitational interaction occurs between the cores and the heterogeneous mantle; mechanical coupling may also occur when the CMB topography is aspherical. Besides changing the mantle rotation via the coupling torques, the mass-redistribution in the core shall produce a spatial-temporal gravity anomaly. Numerical modeling of the core dynamical processes contributes in several geophysical disciplines. It helps explain the physical causes of surface geodynamic observables via space geodetic techniques and other means, e.g. Earth's rotation variation on decadal time scales, and secular time-variable gravity. Conversely, identification of the sources of the observables can provide additional insights on the dynamics of the fluid core, leading to better constraints on the physics in the numerical modeling. In the past few years, our core dynamics modeling efforts, with respect to our MoSST model, have made significant progress in understanding individual geophysical consequences. However, integrated studies are desirable, not only because of more mature numerical core dynamics models, but also because of inter-correlation among the geophysical phenomena, e.g. mass redistribution in the outer core produces not only time-variable gravity, but also gravitational core-mantle coupling and thus the Earth's rotation variation. They are expected to further facilitate multidisciplinary studies of core dynamics and interactions of the core with other

  2. Natural convection and dispersion in a tilted fracture

    International Nuclear Information System (INIS)

    Woods, A.W.; Linz, S.J.

    1992-01-01

    In many geophysical situations, fluid is contained in long narrow fractures embedded within an impermeable medium of different thermal conductivity; and there may be a uniform vertical temperature gradient imposed upon the system. We show that whenever the slot is tilted to the vertical, convection develops in the fluid, even if the background temperature increases with height. Using typical values for the physical properties of a water-filled fracture, we show that the Earth's geothermal gradient produces a convective flow in a fracture; this has an associated dispersion coefficient D T ∼10 2 -10 3 D in fractures about a centimetre wide. We show that this shear dispersion could transport radioactive material, of half-life 10 4 years, tens of metres along the fracture within one half-life; without this dispersion, the material would only diffuse a few metres along the fracture within one half-life. (author)

  3. Segregation and convection in dendritic alloys

    Science.gov (United States)

    Poirier, D. R.

    1990-01-01

    Microsegregation in dentritic alloys is discussed, including solidification with and without thermal gradient, the convection of interdendritic liquid. The conservation of momentum, energy, and solute is considered. Directional solidification and thermosolutal convection are discussed.

  4. Boiling Suppression in Convective Flow

    International Nuclear Information System (INIS)

    Aounallah, Y.

    2004-01-01

    The development of convective boiling heat transfer correlations and analytical models has almost exclusively been based on measurements of the total heat flux, and therefore on the overall two-phase heat transfer coefficient, when the well-known heat transfer correlations have often assumed additive mechanisms, one for each mode of heat transfer, convection and boiling. While the global performance of such correlations can readily be assessed, the predictive capability of the individual components of the correlation has usually remained elusive. This becomes important when, for example, developing mechanistic models for subcooled void formation based on the partitioning of the wall heat flux into a boiling and a convective component, or when extending a correlation beyond its original range of applications where the preponderance of the heat transfer mechanisms involved can be significantly different. A new examination of existing experimental heat transfer data obtained under fixed hydrodynamic conditions, whereby the local flow conditions are decoupled from the local heat flux, has allowed the unequivocal isolation of the boiling contribution over a broad range of thermodynamic qualities (0 to 0.8) for water at 7 MPa. Boiling suppression, as the quality increases, has consequently been quantified, thus providing valuable new insights on the functionality and contribution of boiling in convective flows. (author)

  5. Thermal-chemical Mantle Convection Models With Adaptive Mesh Refinement

    Science.gov (United States)

    Leng, W.; Zhong, S.

    2008-12-01

    In numerical modeling of mantle convection, resolution is often crucial for resolving small-scale features. New techniques, adaptive mesh refinement (AMR), allow local mesh refinement wherever high resolution is needed, while leaving other regions with relatively low resolution. Both computational efficiency for large- scale simulation and accuracy for small-scale features can thus be achieved with AMR. Based on the octree data structure [Tu et al. 2005], we implement the AMR techniques into the 2-D mantle convection models. For pure thermal convection models, benchmark tests show that our code can achieve high accuracy with relatively small number of elements both for isoviscous cases (i.e. 7492 AMR elements v.s. 65536 uniform elements) and for temperature-dependent viscosity cases (i.e. 14620 AMR elements v.s. 65536 uniform elements). We further implement tracer-method into the models for simulating thermal-chemical convection. By appropriately adding and removing tracers according to the refinement of the meshes, our code successfully reproduces the benchmark results in van Keken et al. [1997] with much fewer elements and tracers compared with uniform-mesh models (i.e. 7552 AMR elements v.s. 16384 uniform elements, and ~83000 tracers v.s. ~410000 tracers). The boundaries of the chemical piles in our AMR code can be easily refined to the scales of a few kilometers for the Earth's mantle and the tracers are concentrated near the chemical boundaries to precisely trace the evolvement of the boundaries. It is thus very suitable for our AMR code to study the thermal-chemical convection problems which need high resolution to resolve the evolvement of chemical boundaries, such as the entrainment problems [Sleep, 1988].

  6. Hospital costs during the first 5 years of life for multiples compared with singletons born after IVF or ICSI.

    Science.gov (United States)

    van Heesch, M M J; Evers, J L H; van der Hoeven, M A H B M; Dumoulin, J C M; van Beijsterveldt, C E M; Bonsel, G J; Dykgraaf, R H M; van Goudoever, J B; Koopman-Esseboom, C; Nelen, W L D M; Steiner, K; Tamminga, P; Tonch, N; Torrance, H L; Dirksen, C D

    2015-06-01

    Do in vitro fertilization (IVF) multiples generate higher hospital costs than IVF singletons, from birth up to age 5? Hospital costs from birth up to age 5 were significantly higher among IVF/ICSI multiple children compared with IVF/ICSI singletons; however, when excluding the costs incurred during the birth admission period, hospital costs of multiples and singletons were comparable. Concern has risen over the long-term outcome of children born after IVF. The increased incidence of multiple births in IVF as a result of double-embryo transfer predisposes children to a poorer neonatal outcome such as preterm birth and low birthweight. As a consequence, IVF multiples require more medical care. Costs and consequences of poorer neonatal outcomes in multiples may also exist later in life. All 5497 children born from IVF in 2003-2005, whose parents received IVF or ICSI treatment in one of five participating Dutch IVF centers, served as a basis for a retrospective cohort study. Based on gestational age, birthweight, Apgar and congenital malformation, children were assigned to one of three risk strata (low-, moderate- or high-risk). To enhance the efficiency of the data collection, 816 multiples and 584 singletons were selected for 5-year follow-up based on stratified (risk) sampling. Parental informed consent was received of 322 multiples and 293 singletons. Individual-level hospital resource use data (hospitalization, outpatient visits and medical procedures) were retrieved from hospital information systems and patient charts for 302 multiples and 278 singletons. The risk of hospitalization (OR 4.9, 95% CI 3.3-7.0), outpatient visits (OR 2.6, 95% CI 1.8-3.6) and medical procedures (OR 1.7, 95% CI 1.2-2.2) was higher for multiples compared with singletons. The average hospital costs amounted to €10 018 and €2093 during the birth admission period (P IVF/ICSI multiples compared with IVF/ICSI singletons. Single-embryo transfer may result in substantial savings

  7. Costs and effects of screening and treating low risk women with a singleton pregnancy for asymptomatic bacteriuria, the ASB study

    OpenAIRE

    Kazemier, B.M.; Schneeberger, C.; Miranda, de, E.; Wassenaer, van, A.G.; Bossuyt, P.M.; Vogelvang, T.E.; Reijnders, F.J.L.; Delemarre, F.M.C.; Verhoeven, C.J.M.; Oudijk, M.A.; Ven, van der, J.A.; Kuiper, P.N.; Feiertag, N.; Ott, A; Groot, de, C.J.M.

    2012-01-01

    Abstract Background The prevalence of asymptomatic bacteriuria (ASB) in pregnancy is 2-10% and is associated with both maternal and neonatal adverse outcomes as pyelonephritis and preterm delivery. Antibiotic treatment is reported to decrease these adverse outcomes although the existing evidence is of poor quality. Methods/Design We plan a combined screen and treat study in women with a singleton pregnancy. We will screen women between 16 and 22 weeks of gestation for ASB using the urine dips...

  8. False Labor at Term in Singleton Pregnancies: Discharge After a Standardized Assessment and Perinatal Outcomes.

    Science.gov (United States)

    Nelson, David B; McIntire, Donald D; Leveno, Kenneth J

    2017-07-01

    To evaluate perinatal outcomes in women sent home with a diagnosis of false labor at term and assess the time interval to return for delivery. This was a prospective observational cohort study of women at 37 0/7 to 41 6/7 weeks of gestation without pre-existing medical complications who presented to our hospital-based triage unit with symptoms of labor and underwent a standardized evaluation. Women diagnosed as having false labor with a live singleton fetus in cephalic presentation without a prior cesarean delivery and sent home were compared with a group of similar women diagnosed to be in spontaneous labor. Women with hypertension, diabetes, and known fetal malformations were excluded. Using a perinatal composite outcome of respiratory insufficiency, intraventricular hemorrhage, culture-proven sepsis, Apgar score 3 or less at 5 minutes, phototherapy, and perinatal death, we tested the noninferiority of being sent home compared with being admitted for labor. The relationship of cervical dilatation to the time interval from discharge home to delivery was also analyzed. Between October 2012 and March 2016, a total of 3,949 women met inclusion criteria and were diagnosed with false labor, discharged, and returned to deliver, whereas 2,592 similar women were admitted in early labor. The mean interval from discharge to return was 4.9 days. Cesarean delivery rates were not different between the study groups-11% for both (P=.69), and the perinatal composite outcome rates were not significantly different between those sent home and those admitted-3.2% compared with 3.1% (P=.79). Women with more advanced cervical dilatation at discharge returned and delivered significantly earlier than those with less dilatation regardless of parity. Discharge with false labor at term after a standardized assessment in a triage unit was not associated with increased rates of adverse perinatal composite outcomes or cesarean delivery. The time interval to return for delivery was

  9. Infant feeding and mental and motor development at 18 months of age in first born singletons.

    Science.gov (United States)

    Florey, C D; Leech, A M; Blackhall, A

    1995-01-01

    To determine the relationship between type of infant feeding and mental and psychomotor development at age 18 months. A follow-up study of children born to primigravidae living in Dundee and booked into antenatal clinics in the City of Dundee (Local Authority District) from 1 May 1985 to 30 April 1986. The study population was 846 first born singletons, of whom 592 attended for developmental assessment at age 18 months. The main outcome measures were the Bayley Scales of Infant Mental and Motor Development. Higher mental development was significantly related to breast feeding on discharge from hospital and according to the health visitors' notes at about 2 weeks after discharge after allowing for partner's social class, mother's education, height, alcohol and cigarette consumption; placental weight and the child's sex, birth weight and gestational age at birth. After adjustment for statistically significant variables, the difference in Bayley mental development index between breast and bottle fed infants was between 3.7 and 5.7 units depending on the source of feeding data. No differences were found for psychomotor development or behaviour. The study provides further evidence of a robust statistical association between type of feeding and child intelligence. However, the literature is replete with suggestions for potential confounding variables which offer alternative causal explanations. To unravel what is an important clinical and public health question, further research should concentrate on randomized trials of supplemented formula feeds for children of mothers opting for bottle feeding and on epidemiological studies designed to disentangle the relation between method of feeding, parental intelligence and social environment.

  10. Employment trends during preschool years among mothers of term singletons born with low birth weight.

    Science.gov (United States)

    Hauge, Lars Johan; Kornstad, Tom; Nes, Ragnhild Bang; Kristensen, Petter; Irgens, Lorentz M; Landolt, Markus A; Eskedal, Leif T; Vollrath, Margarete E

    2014-11-01

    Children born at term with low birth weight (LBW) are regarded growth restricted and are at particular risk of adverse health outcomes requiring a high degree of parental participation in the day-to-day care. This study examined whether their increased risk of special health care needs compared to other children may influence mothers' opportunities for participation in the labor market at different times after delivery. Data from 32,938 participants in the population-based Norwegian Mother and Child Cohort Study with singleton children born at term in 2004-2006 were linked to national registers in order to investigate the mothers' employment status when their children were 1-3 years in 2007 and 4-6 years in 2010. Children weighing less than two standard deviations below the gender-specific mean were defined as LBW children. Although not significantly different from mothers of children in the normal weight range, mothers of LBW children had the overall highest level of non-employment when the children were 1-3 years. At child age 4-6 years on the other hand, LBW was associated with an increased risk of non-employment (RR 1.39: 95 % CI 1.11-1.75) also after adjustment for factors associated with employment in general. In accordance with employment trends in the general population, our findings show that while mothers of normal birth weight children re-enter the labor market as their children grow older, mothers of LBW children born at term participate to a lesser extent in paid employment and remain at levels similar to those of mothers with younger children.

  11. Development of a prognostic model for predicting spontaneous singleton preterm birth.

    Science.gov (United States)

    Schaaf, Jelle M; Ravelli, Anita C J; Mol, Ben Willem J; Abu-Hanna, Ameen

    2012-10-01

    To develop and validate a prognostic model for prediction of spontaneous preterm birth. Prospective cohort study using data of the nationwide perinatal registry in The Netherlands. We studied 1,524,058 singleton pregnancies between 1999 and 2007. We developed a multiple logistic regression model to estimate the risk of spontaneous preterm birth based on maternal and pregnancy characteristics. We used bootstrapping techniques to internally validate our model. Discrimination (AUC), accuracy (Brier score) and calibration (calibration graphs and Hosmer-Lemeshow C-statistic) were used to assess the model's predictive performance. Our primary outcome measure was spontaneous preterm birth at model included 13 variables for predicting preterm birth. The predicted probabilities ranged from 0.01 to 0.71 (IQR 0.02-0.04). The model had an area under the receiver operator characteristic curve (AUC) of 0.63 (95% CI 0.63-0.63), the Brier score was 0.04 (95% CI 0.04-0.04) and the Hosmer Lemeshow C-statistic was significant (pvalues of predicted probability. The positive predictive value was 26% (95% CI 20-33%) for the 0.4 probability cut-off point. The model's discrimination was fair and it had modest calibration. Previous preterm birth, drug abuse and vaginal bleeding in the first half of pregnancy were the most important predictors for spontaneous preterm birth. Although not applicable in clinical practice yet, this model is a next step towards early prediction of spontaneous preterm birth that enables caregivers to start preventive therapy in women at higher risk. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  12. Reference charts of fetal biometric parameters in 31,476 Brazilian singleton pregnancies.

    Science.gov (United States)

    Araujo Júnior, Edward; Martins Santana, Eduardo Félix; Martins, Wellington P; Júnior, Julio Elito; Ruano, Rodrigo; Pires, Claudio Rodrigues; Filho, Sebastião Marques Zanforlin

    2014-07-01

    The purpose of this study was to establish reference charts of fetal biometric parameters measured by 2-dimensional sonography in a large Brazilian population. A cross-sectional retrospective study was conducted including 31,476 low-risk singleton pregnancies between 18 and 38 weeks' gestation. The following fetal parameters were measured: biparietal diameter, head circumference, abdominal circumference, femur length, and estimated fetal weight. To assess the correlation between the fetal biometric parameters and gestational age, polynomial regression models were created, with adjustments made by the determination coefficient (R(2)). The means ± SDs of the biparietal diameter, head circumference, abdominal circumference, femur length, and estimated fetal weight measurements at 18 and 38 weeks were 4.2 ± 2.34 and 9.1 ± 4.0 cm, 15.3 ± 7.56 and 32.3 ± 11.75 cm, 13.3 ± 10.42 and 33.4 ± 20.06 cm, 2.8 ± 2.17 and 7.2 ± 3.58 cm, and 256.34 ± 34.03 and 3169.55 ± 416.93 g, respectively. Strong correlations were observed between all fetal biometric parameters and gestational age, best represented by second-degree equations, with R(2) values of 0.95, 0.96, 0.95, 0.95, and 0.95 for biparietal diameter, head circumference, abdominal circumference, femur length, and estimated fetal weight. Fetal biometric parameters were determined for a large Brazilian population, and they may serve as reference values in cases with a high risk of intrauterine growth disorders. © 2014 by the American Institute of Ultrasound in Medicine.

  13. [Effect of hyperandrogenism on obstetric complications of singleton pregnancy from in vitro fertilization in women with polycystic ovary syndrome].

    Science.gov (United States)

    Wei, D M; Zhang, Z Z; Wang, Z; Li, P; Wang, J F; Liu, Y J; Zhang, J T; Shi, Y H

    2018-01-25

    Objective: To compare the difference in risks of obstetric complications of singleton pregnancy between women with hyperandrogenic polycystic ovary syndrome (PCOS) and women with normoandrogenic PCOS. Methods: Prospective cohort study. This study was a secondary analysis of data collected during a multicenter randomized controlled clinical trial. Women who got clinical singleton pregnancy were grouped according to whether they were diagnosed with hyperandrogenism at baseline. There were 118 women with hyperandrogenism and 366 women without hyperandrogenism. The incidences of obstetric complications and birth weight were compared between the two groups. Results: Women with hyperandrogenic PCOS had a significantly higher risk of preterm delivery than women with normoandrogenic PCOS [12.7% (15/118) versus 3.6% (13/366); OR= 3.94, 95% CI: 1.82-8.56]. After adjustment of age, duration of infertility, body mass index, and fresh or frozen embryo transfer group, hyperandrogenism was still associated with an increased risk of preterm delivery ( OR= 3.67, 95% CI: 1.67-8.07). Compared with women with normoandrogenic PCOS, women with hyperandrogenic PCOS had similar risks of pregnancy loss, gestational diabetes mellitus, pre-eclampsia, placenta previa, and postpartum hemorrhage (all P> 0.05). Birth weight as well as the risks of being small for gestational age and large for gestational age were also comparable between the two groups (all P> 0.05). Conclusion: In women with PCOS and singleton pregnancy, those with preconceptional hyperandrogenism have a higher risk of preterm delivery than those without hyperandrogenism.

  14. Gestational age and birth weight centiles of singleton babies delivered normally following spontaneous labor, in Southern Sri Lanka

    Science.gov (United States)

    Attanayake, K; Munasinghe, S; Goonewardene, M; Widanapathirana, P; Sandeepani, I; Sanjeewa, L

    2018-03-31

    To estimate the gestational age and birth weight centiles of babies delivered normally, without any obstetric intervention, in women with uncomplicated singleton pregnancies establishing spontaneous onset of labour. Consecutive women with uncomplicated singleton pregnancies, attending the Academic Obstetrics and Gynecology Unit of the Teaching Hospital Mahamodara Galle, Sri Lanka, with confirmed dates and establishing spontaneous onset of labor and delivering vaginally between gestational age of 34 - 41 weeks, without any obstetric intervention , during the period September 2013 to February 2014 were studied. The gestational age at spontaneous onset of labor and vaginal delivery and the birth weights of the babies were recorded. There were 3294 consecutive deliveries during this period, and of them 1602 (48.6%) met the inclusion criteria. Median gestational age at delivery was 275 days (range 238-291 days, IQR 269 to 280 days) and the median birth weight was 3000 g (range1700g - 4350g; IQR 2750-3250g). The 10th, 50th and 90th birth weight centiles of the babies delivered at a gestational age of 275 days were approximately 2570g, 3050g and 3550g respectively. The median gestational age among women with uncomplicated singleton pregnancies who established spontaneous onset of labor and delivered vaginally, without any obstetric intervention, was approximately five days shorter than the traditionally accepted 280 days. At a gestational age of 275 days, the mean birth weight was approximately 3038g and the 50th centile of the birth weight of the babies delivered was approximately 3050g.

  15. A transilient matrix for moist convection

    Energy Technology Data Exchange (ETDEWEB)

    Romps, D.; Kuang, Z.

    2011-08-15

    A method is introduced for diagnosing a transilient matrix for moist convection. This transilient matrix quantifies the nonlocal transport of air by convective eddies: for every height z, it gives the distribution of starting heights z{prime} for the eddies that arrive at z. In a cloud-resolving simulation of deep convection, the transilient matrix shows that two-thirds of the subcloud air convecting into the free troposphere originates from within 100 m of the surface. This finding clarifies which initial height to use when calculating convective available potential energy from soundings of the tropical troposphere.

  16. Rare earths

    Energy Technology Data Exchange (ETDEWEB)

    Cranstone, D A

    1979-01-01

    Rare earth elements are commonly extracted from the minerals monazite, bastnaesite, and xenotine. New uses for these elements are constantly developing; they have found applications in glass polishing, television tube phosphors, high-strength low-alloy steels, magnets, catalysts, refractory ceramics, and hydrogen sponge alloys. In Canada, rare earths have been produced as byproducts of the uranium mining industry, but there was no production of rare earths in 1978 or 1979. The world sources of and markets for the rare earth elements are discussed.

  17. Covariability in the Monthly Mean Convective and Radiative Diurnal Cycles in the Amazon

    Science.gov (United States)

    Dodson, Jason B.; Taylor, Patrick C.

    2015-01-01

    The diurnal cycle of convective clouds greatly influences the radiative energy balance in convectively active regions of Earth, through both direct presence, and the production of anvil and stratiform clouds. Previous studies show that the frequency and properties of convective clouds can vary on monthly timescales as a result of variability in the monthly mean atmospheric state. Furthermore, the radiative budget in convectively active regions also varies by up to 7 Wm-2 in convectively active regions. These facts suggest that convective clouds connect atmospheric state variability and radiation variability beyond clear sky effects alone. Previous research has identified monthly covariability between the diurnal cycle of CERES-observed top-of-atmosphere radiative fluxes and multiple atmospheric state variables from reanalysis over the Amazon region. ASVs that enhance (reduce) deep convection, such as CAPE (LTS), tend to shift the daily OLR and cloud albedo maxima earlier (later) in the day by 2-3 hr. We first test the analysis method using multiple reanalysis products for both the dry and wet seasons to further investigate the robustness of the preliminary results. We then use CloudSat data as an independent cloud observing system to further evaluate the relationships of cloud properties to variability in radiation and atmospheric states. While CERES can decompose OLR variability into clear sky and cloud effects, it cannot determine what variability in cloud properties lead to variability in the radiative cloud effects. Cloud frequency, cloud top height, and cloud microphysics all contribute to the cloud radiative effect, all of which are observable by CloudSat. In addition, CloudSat can also observe the presence and variability of deep convective cores responsible for the production of anvil clouds. We use these capabilities to determine the covariability of convective cloud properties and the radiative diurnal cycle.

  18. Parents' anxiety and depression symptoms after successful infertility treatment and spontaneous conception: does singleton/twin pregnancy matter?

    Science.gov (United States)

    Tendais, I; Figueiredo, B

    2016-10-01

    Does mode of conception [spontaneous/after infertility treatment (IT)], type of pregnancy (singleton/twin) and parent gender have an effect on anxiety and depression levels and trajectories during pregnancy and the post-partum period? Conception after IT was associated with a transitory increase in anxiety during the perinatal period for parents of singletons, while for IT parents of twins higher levels of psychopathological symptoms tended to persist during pregnancy and the post-partum period. Most previous studies have shown that successful IT is not associated with poor psychological well-being during pregnancy and the post-partum period, but there is also some evidence for heightened pregnancy-related anxiety, lower self-esteem and lower self-efficacy. Parents of twins experience increased postnatal anxiety and depression. This prospective longitudinal study assessed 267 couples (N = 534) at each trimester of pregnancy, after childbirth and at 3 months post-partum. The sample comprised 36 couples who had conceived after IT (19 twin pairs and 17 singletons) and 231 couples who had conceived spontaneously (SC; 28 twin pairs and 203 singletons). Couples were recruited at four public hospitals in Portugal, and self-report measures of anxiety and depression symptoms were administered. IT parents reported higher anxiety after childbirth than parents who SC, regardless of pregnancy type. IT parents of twins showed higher anxiety at mid-pregnancy, as well as higher anxiety and depression at 3 months post-partum than IT parents of singletons. Among IT mothers, those who had twins exhibited higher depression after childbirth than those who had singletons. Differences according to mode of conception, pregnancy type and parents gender over time were also noted. During pregnancy, IT parents of twins showed no significant change in depression scores, while the other groups depression scores statistically significantly decreased over time. From pregnancy to the post

  19. Convective aggregation in realistic convective-scale simulations

    Science.gov (United States)

    Holloway, Christopher E.

    2017-06-01

    To investigate the real-world relevance of idealized-model convective self-aggregation, five 15 day cases of real organized convection in the tropics are simulated. These include multiple simulations of each case to test sensitivities of the convective organization and mean states to interactive radiation, interactive surface fluxes, and evaporation of rain. These simulations are compared to self-aggregation seen in the same model configured to run in idealized radiative-convective equilibrium. Analysis of the budget of the spatial variance of column-integrated frozen moist static energy shows that control runs have significant positive contributions to organization from radiation and negative contributions from surface fluxes and transport, similar to idealized runs once they become aggregated. Despite identical lateral boundary conditions for all experiments in each case, systematic differences in mean column water vapor (CWV), CWV distribution shape, and CWV autocorrelation length scale are found between the different sensitivity runs, particularly for those without interactive radiation, showing that there are at least some similarities in sensitivities to these feedbacks in both idealized and realistic simulations (although the organization of precipitation shows less sensitivity to interactive radiation). The magnitudes and signs of these systematic differences are consistent with a rough equilibrium between (1) equalization due to advection from the lateral boundaries and (2) disaggregation due to the absence of interactive radiation, implying disaggregation rates comparable to those in idealized runs with aggregated initial conditions and noninteractive radiation. This points to a plausible similarity in the way that radiation feedbacks maintain aggregated convection in both idealized simulations and the real world.Plain Language SummaryUnderstanding the processes that lead to the organization of tropical rainstorms is an important challenge for weather

  20. CRUCIB: an axisymmetric convection code

    International Nuclear Information System (INIS)

    Bertram, L.A.

    1975-03-01

    The CRUCIB code was written in support of an experimental program aimed at measurement of thermal diffusivities of refractory liquids. Precise values of diffusivity are necessary to realistic analysis of reactor safety problems, nuclear waste disposal procedures, and fundamental metal forming processes. The code calculates the axisymmetric transient convective motions produced in a right circular cylindrical crucible, which is surface heated by an annular heat pulse. Emphasis of this report is placed on the input-output options of the CRUCIB code, which are tailored to assess the importance of the convective heat transfer in determining the surface temperature distribution. Use is limited to Prandtl numbers less than unity; larger values can be accommodated by replacement of a single block of the code, if desired. (U.S.)

  1. Fluid convection, constraint and causation

    Science.gov (United States)

    Bishop, Robert C.

    2012-01-01

    Complexity—nonlinear dynamics for my purposes in this essay—is rich with metaphysical and epistemological implications but is receiving sustained philosophical analysis only recently. I will explore some of the subtleties of causation and constraint in Rayleigh–Bénard convection as an example of a complex phenomenon, and extract some lessons for further philosophical reflection on top-down constraint and causation particularly with respect to causal foundationalism. PMID:23386955

  2. Cryogenic helium gas convection research

    International Nuclear Information System (INIS)

    Donnelly, R.J.

    1994-10-01

    This is a report prepared by a group interested in doing research in thermal convection using the large scale refrigeration facilities available at the SSC Laboratories (SSCL). The group preparing this report consists of Michael McAshan at SSCL, Robert Behringer at Duke University, Katepalli Sreenivasan at Yale University, Xiao-Zhong Wu at Northern Illinois University and Russell Donnelly at the University of Oregon, who served as Editor for this report. This study reports the research and development opportunities in such a project, the technical requirements and feasibility of its construction and operation, and the costs associated with the needed facilities and support activities. The facility will be a unique national resource for studies of high-Reynolds-number and high-Rayleigh-number and high Rayleigh number turbulence phenomena, and is one of the six items determined as suitable for potential funding through a screening of Expressions of Interest. The proposed facility is possible only because of the advanced cryogenic technology available at the SSCL. Typical scientific issues to be addressed in the facility will be discussed. It devolved during our study, that while the main experiment is still considered to be the thermal convection experiment discussed in our original Expression of Interest, there are now a very substantial set of other, important and fundamental experiments which can be done with the large cryostat proposed for the convection experiment. We believe the facility could provide several decades of front-line research in turbulence, and shall describe why this is so

  3. Thermosolutal convection during dendritic solidification

    Science.gov (United States)

    Heinrich, J. C.; Nandapurkar, P.; Poirier, D. R.; Felicelli, S.

    1989-01-01

    This paper presents a mathematical model for directional solidification of a binary alloy including a dendritic region underlying an all-liquid region. It is assumed initially that there exists a nonconvecting state with planar isotherms and isoconcentrates solidifying at a constant velocity. The stability of this system has been analyzed and nonlinear calculations are performed that show the effect of convection in the solidification process when the system is unstable. Results of calculations for various cases defined by the initial temperature gradient at the dendrite tips and varying strength of the gravitational field are presented for systems involving lead-tin alloys. The results show that the systems are stable for a gravitational constant of 0.0001 g(0) and that convection can be suppressed by appropriate choice of the container's size for higher values of the gravitational constant. It is also concluded that for the lead-tin systems considered, convection in the mushy zone is not significant below the upper 20 percent of the dendritic zone, if al all.

  4. Scaling rates of true polar wander in convecting planets and moons

    Science.gov (United States)

    Rose, Ian; Buffett, Bruce

    2017-12-01

    Mass redistribution in the convecting mantle of a planet causes perturbations in its moment of inertia tensor. Conservation of angular momentum dictates that these perturbations change the direction of the rotation vector of the planet, a process known as true polar wander (TPW). Although the existence of TPW on Earth is firmly established, its rate and magnitude over geologic time scales remain controversial. Here we present scaling analyses and numerical simulations of TPW due to mantle convection over a range of parameter space relevant to planetary interiors. For simple rotating convection, we identify a set of dimensionless parameters that fully characterize true polar wander. We use these parameters to define timescales for the growth of moment of inertia perturbations due to convection and for their relaxation due to true polar wander. These timescales, as well as the relative sizes of convective anomalies, control the rate and magnitude of TPW. This analysis also clarifies the nature of so called "inertial interchange" TPW events, and relates them to a broader class of events that enable large and often rapid TPW. We expect these events to have been more frequent in Earth's past.

  5. Assessing the role of slab rheology in coupled plate-mantle convection models

    Science.gov (United States)

    Bello, Léa; Coltice, Nicolas; Tackley, Paul J.; Dietmar Müller, R.; Cannon, John

    2015-11-01

    Reconstructing the 3D structure of the Earth's mantle has been a challenge for geodynamicists for about 40 yr. Although numerical models and computational capabilities have substantially progressed, parameterizations used for modeling convection forced by plate motions are far from being Earth-like. Among the set of parameters, rheology is fundamental because it defines in a non-linear way the dynamics of slabs and plumes, and the organization of lithosphere deformation. In this study, we evaluate the role of the temperature dependence of viscosity (variations up to 6 orders of magnitude) and the importance of pseudo-plasticity on reconstructing slab evolution in 3D spherical models of convection driven by plate history models. Pseudo-plasticity, which produces plate-like behavior in convection models, allows a consistent coupling between imposed plate motions and global convection, which is not possible with temperature-dependent viscosity alone. Using test case models, we show that increasing temperature dependence of viscosity enhances vertical and lateral coherence of slabs, but leads to unrealistic slab morphologies for large viscosity contrasts. Introducing pseudo-plasticity partially solves this issue, producing thin laterally and vertically more continuous slabs, and flat subduction where trench retreat is fast. We evaluate the differences between convection reconstructions employing different viscosity laws to be very large, and similar to the differences between two models with the same rheology but using two different plate histories or initial conditions.

  6. Compressible Convection Experiment using Xenon Gas in a Centrifuge

    Science.gov (United States)

    Menaut, R.; Alboussiere, T.; Corre, Y.; Huguet, L.; Labrosse, S.; Deguen, R.; Moulin, M.

    2017-12-01

    We present here an experiment especially designed to study compressible convection in the lab. For significant compressible convection effects, the parameters of the experiment have to be optimized: we use xenon gaz in a cubic cell. This cell is placed in a centrifuge to artificially increase the apparent gravity and heated from below. With these choices, we are able to reach a dissipation number close to Earth's outer core value. We will present our results for different heating fluxes and rotation rates. We success to observe an adiabatic gradient of 3K/cm in the cell. Studies of pressure and temperature fluctuations lead us to think that the convection takes place under the form of a single roll in the cell for high heating flux. Moreover, these fluctuations show that the flow is geostrophic due to the high rotation speed. This important role of rotation, via Coriolis force effects, in our experimental setup leads us to develop a 2D quasigeostrophic compressible model in the anelastic liquid approximation. We test numerically this model with the finite element solver FreeFem++ and compare its results with our experimental data. In conclusion, we will present our project for the next experiment in which the cubic cell will be replace by a annulus cell. We will discuss the new expected effects due to this geometry as Rossby waves and zonal flows.

  7. MAGNETIC CYCLES IN A DYNAMO SIMULATION OF FULLY CONVECTIVE M-STAR PROXIMA CENTAURI

    Energy Technology Data Exchange (ETDEWEB)

    Yadav, Rakesh K.; Wolk, Scott J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Christensen, Ulrich R. [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Poppenhaeger, Katja, E-mail: rakesh.yadav@cfa.harvard.edu [Astrophysics Research Center, Queen’s University Belfast, Belfast BT7 1NN (United Kingdom)

    2016-12-20

    The recent discovery of an Earth-like exoplanet around Proxima Centauri has shined a spot light on slowly rotating fully convective M-stars. When such stars rotate rapidly (period ≲20 days), they are known to generate very high levels of activity that is powered by a magnetic field much stronger than the solar magnetic field. Recent theoretical efforts are beginning to understand the dynamo process that generates such strong magnetic fields. However, the observational and theoretical landscape remains relatively uncharted for fully convective M-stars that rotate slowly. Here, we present an anelastic dynamo simulation designed to mimic some of the physical characteristics of Proxima Centauri, a representative case for slowly rotating fully convective M-stars. The rotating convection spontaneously generates differential rotation in the convection zone that drives coherent magnetic cycles where the axisymmetric magnetic field repeatedly changes polarity at all latitudes as time progress. The typical length of the “activity” cycle in the simulation is about nine years, in good agreement with the recently proposed activity cycle length of about seven years for Proxima Centauri. Comparing our results with earlier work, we hypothesis that the dynamo mechanism undergoes a fundamental change in nature as fully convective stars spin down with age.

  8. The Grell-Freitas Convective Parameterization: Recent Developments and Applications Within the NASA GEOS Global Model

    Science.gov (United States)

    Freitas, S.; Grell, G. A.; Molod, A.

    2017-12-01

    We implemented and began to evaluate an alternative convection parameterization for the NASA Goddard Earth Observing System (GEOS) global model. The parameterization (Grell and Freitas, 2014) is based on the mass flux approach with several closures, for equilibrium and non-equilibrium convection, and includes scale and aerosol awareness functionalities. Scale dependence for deep convection is implemented either through using the method described by Arakawa et al (2011), or through lateral spreading of the subsidence terms. Aerosol effects are included though the dependence of autoconversion and evaporation on the CCN number concentration.Recently, the scheme has been extended to a tri-modal spectral size approach to simulate the transition from shallow, congestus, and deep convection regimes. In addition, the inclusion of a new closure for non-equilibrium convection resulted in a substantial gain of realism in model simulation of the diurnal cycle of convection over the land. Also, a beta-pdf is employed now to represent the normalized mass flux profile. This opens up an additional venue to apply stochasticism in the scheme.

  9. Tropical teleconnections via the ocean and atmosphere induced by Southern Ocean deep convective events

    Science.gov (United States)

    Marinov, I.; Cabre, A.; Gunn, A.; Gnanadesikan, A.

    2016-12-01

    The current generation (CMIP5) of Earth System Models (ESMs) shows a huge variability in their ability to represent Southern Ocean (SO) deep-ocean convection and Antarctic Bottom Water, with a preference for open-sea convection in the Weddell and Ross gyres. A long control simulation in a coarse 3o resolution ESM (the GFDL CM2Mc model) shows a highly regular multi-decadal oscillation between periods of SO open sea convection and non-convective periods. This process also happens naturally, with different frequencies and durations of convection across most CMIP5 models under preindustrial forcing (deLavergne et al, 2014). Here we assess the impact of SO deep convection and resulting sea surface temperature (SST) anomalies on the tropical atmosphere and ocean via teleconnections, with a focus on interannual to multi-decadal timescales. We combine analysis of our low-resolution coupled model with inter-model analysis across historical CMIP5 simulations. SST cooling south of 60S during non-convective decades triggers a stronger, northward shifted SH Hadley cell, which results in intensified northward cross-equatorial moist heat transport and a poleward shift in the ITCZ. Resulting correlations between the cross-equatorial atmospheric heat transport and ITCZ location are in good agreement with recent theories (e.g. Frierson et al. 2013; Donohoe et al. 2014). Lagged correlations between a SO convective index and cross-equatorial heat transports (in the atmosphere and ocean), as well as various tropical (and ENSO) climate indices are analyzed. In the ocean realm, we find that non-convective decades result in weaker AABW formation and weaker ACC but stronger Antarctic Intermediate Water (AAIW) formation, likely as a result of stronger SO westerlies (more positive SAM). The signals of AABW and AAIW are seen in the tropics on short timescales of years to decades in the temperature, heat storage and heat transport anomalies and also in deep and intermediate ocean oxygen. Most

  10. Rare earths

    International Nuclear Information System (INIS)

    1984-01-01

    The conference was held from September 12 to 13, 1984 in Jetrichovice, Czechoslovakia. The participants heard 16 papers of which 4 were inputted in INIS. These papers dealt with industrial separation processes of rare earths, the use of chemical methods of separation from the concentrate of apatite and bastnesite, the effect of the relative permittivity of solvents in the elution of rare earth elements from a cation exchanger, and the determination of the content of different rare earth elements using X-ray fluorescence analysis and atomic absorption spectroscopy. (E.S.)

  11. Controls on sublithospheric small-scale convection on Curie depths

    Science.gov (United States)

    Likerman, Jeremias; Zlotnik, Sergio; Chun-Feng, Li

    2017-04-01

    As the ocean lithosphere cools and thickens, its bottom layer goes unstable leading to sub-lithospheric small-scale convection (SSC). Since SSC was originally proposed, there have been considerable efforts regarding the understanding of the physics that rules the thermal instabilities of the SSC (e.g. Dumoulin et al, 1999; Solomatov and Moresi, 2000). Over the last several years, it is understood that the interaction between the plate movement and the SSC tends to form longitudinal (LRs or also called 'Richter rolls') and transverse rolls (TRs), of which the axis is parallel and perpendicular to the plate motion, respectively. The geometry of these rolls have been been recently inferred by Li et al (2013) using Curie depths from the North Atlantic as proxies for plates temperatures. They showed that Curie depths have a large oscillating and heterogeneous patterns that could be related to SSC. In the North Atlantic transverse rolls seem predominant. In this work we analyze, by means of 3D dynamical numerical simulations, the influence of SSC on the Curie depths patterns observed in the North Atlantic and Pacific plates. We investigate the behaviour of the Curie isotherms trying to determine if SSC is able to reproduce the observed data, and the influence of several poorly constrained rheological parameters. Our numerical simulations show that: a) using realistic laboratory-constrained rheologies and temperature it is possible to modify temperatures as low as those at Curie depths; b) transverse rolls are generated as well as longitudinal rolls on those isotherms; c) the spreading rate is a first order control on the developing of transverse rolls. References Dumoulin, C., Doin, M. P., & Fleitout, L. (1999). Heat transport in stagnant lid convection with temperature-and pressure-dependent Newtonian or non-Newtonian rheology. Journal of Geophysical Research: Solid Earth, 104(B6), 12759-12777. Li, C. F., Wang, J., Lin, J., & Wang, T. (2013). Thermal evolution of the

  12. Convective overshoot at the solar tachocline

    Science.gov (United States)

    Brown, Benjamin; Oishi, Jeffrey S.; Anders, Evan H.; Lecoanet, Daniel; Burns, Keaton; Vasil, Geoffrey M.

    2017-08-01

    At the base of the solar convection zone lies the solar tachocline. This internal interface is where motions from the unstable convection zone above overshoot and penetrate downward into the stiffly stable radiative zone below, driving gravity waves, mixing, and possibly pumping and storing magnetic fields. Here we study the dynamics of convective overshoot across very stiff interfaces with some properties similar to the internal boundary layer within the Sun. We use the Dedalus pseudospectral framework and study fully compressible dynamics at moderate to high Peclet number and low Mach number, probing a regime where turbulent transport is important, and where the compressible dynamics are similar to those of convective motions in the deep solar interior. We find that the depth of convective overshoot is well described by a simple buoyancy equilibration model, and we consider implications for dynamics at the solar tachocline and for the storage of magnetic fields there by overshooting convection.

  13. The convection electric field in auroral substorms

    DEFF Research Database (Denmark)

    Gjerløv, Jesper Wittendorff; Hoffman, R.A.

    2001-01-01

    Dynamics Explorer 2 (DE 2) electric field and ion drift data are used in a statistical study of the ionospheric convection electric field in bulge-type auroral substorms. Thirty-one individual DE 2 substorm crossings were carefully selected and organized by the use of global auroral images obtained...... this database enabled us to compile a model of the ionospheric convection electric field. The characteristics of the premidnight convection reversal show a pronounced local time dependency. Far west of the surge it is a fairly well defined point reversal or convection shear. Approaching the surge and within...... the surge it is a region of weak electric fields increasing in width toward midnight that separates regions of equatorward and poleward electric fields. Therefore we adopt the term Harang region rather than the Harang discontinuity for the premidnight convection reversal. A relatively narrow convection...

  14. The pattern of convection in the Sun

    International Nuclear Information System (INIS)

    Weiss, N.O.

    1976-01-01

    The structure of solar magnetic fields is dominated by the effects of convection, which should be incorporated in any model of the solar cycle. Although mixing length theory is adequate for calculating the structure of main sequence stars, a better description of convection is needed for any detailed dynamo model. Recent work on nonlinear convection at low Prandt numbers is reviewed. There has been some progress towards a theory of compressible convection, though there is still no firm theoretical evidence for cells with scales less than the depth of the convecting layer. However, it remains likely that the pattern of solar convection is dominated by granules, supergranules and giant cells. The effects of rotation on these cells are briefly considered. (Auth.)

  15. Free surface deformation and heat transfer by thermocapillary convection

    Science.gov (United States)

    Fuhrmann, Eckart; Dreyer, Michael; Basting, Steffen; Bänsch, Eberhard

    2016-04-01

    Knowing the location of the free liquid/gas surface and the heat transfer from the wall towards the fluid is of paramount importance in the design and the optimization of cryogenic upper stage tanks for launchers with ballistic phases, where residual accelerations are smaller by up to four orders of magnitude compared to the gravity acceleration on earth. This changes the driving forces drastically: free surfaces become capillary dominated and natural or free convection is replaced by thermocapillary convection if a non-condensable gas is present. In this paper we report on a sounding rocket experiment that provided data of a liquid free surface with a nonisothermal boundary condition, i.e. a preheated test cell was filled with a cold but storable liquid in low gravity. The corresponding thermocapillary convection (driven by the temperature dependence of the surface tension) created a velocity field directed away from the hot wall towards the colder liquid and then in turn back at the bottom towards the wall. A deformation of the free surface resulting in an apparent contact angle rather different from the microscopic one could be observed. The thermocapillary flow convected the heat from the wall to the liquid and increased the heat transfer compared to pure conduction significantly. The paper presents results of the apparent contact angle as a function of the dimensionless numbers (Weber-Marangoni and Reynolds-Marangoni number) as well as heat transfer data in the form of a Nusselt number. Experimental results are complemented by corresponding numerical simulations with the commercial software Flow3D and the inhouse code Navier.

  16. Continuous reorientation of synchronous terrestrial planets due to mantle convection

    Science.gov (United States)

    Leconte, Jérémy

    2018-02-01

    Many known rocky exoplanets are thought to have been spun down by tidal interactions to a state of synchronous rotation, in which a planet's period of rotation is equal to that of its orbit around its host star. Investigations into atmospheric and surface processes occurring on such exoplanets thus commonly assume that day and night sides are fixed with respect to the surface over geological timescales. Here we use an analytical model to show that true polar wander—where a planetary body's spin axis shifts relative to its surface because of changes in mass distribution—can continuously reorient a synchronous rocky exoplanet. As occurs on Earth, we find that even weak mantle convection in a rocky exoplanet can produce density heterogeneities within the mantle sufficient to reorient the planet. Moreover, we show that this reorientation is made very efficient by the slower rotation rate of a synchronous planet when compared with Earth, which limits the stabilizing effect of rotational and tidal deformations. Furthermore, a relatively weak lithosphere limits its ability to support remnant loads and stabilize against reorientation. Although uncertainties exist regarding the mantle and lithospheric evolution of these worlds, we suggest that the axes of smallest and largest moment of inertia of synchronous exoplanets with active mantle convection change continuously over time, but remain closely aligned with the star-planet and orbital axes, respectively.

  17. Earth Rotation

    Science.gov (United States)

    Dickey, Jean O.

    1995-01-01

    The study of the Earth's rotation in space (encompassing Universal Time (UT1), length of day, polar motion, and the phenomena of precession and nutation) addresses the complex nature of Earth orientation changes, the mechanisms of excitation of these changes and their geophysical implications in a broad variety of areas. In the absence of internal sources of energy or interactions with astronomical objects, the Earth would move as a rigid body with its various parts (the crust, mantle, inner and outer cores, atmosphere and oceans) rotating together at a constant fixed rate. In reality, the world is considerably more complicated, as is schematically illustrated. The rotation rate of the Earth's crust is not constant, but exhibits complicated fluctuations in speed amounting to several parts in 10(exp 8) [corresponding to a variation of several milliseconds (ms) in the Length Of the Day (LOD) and about one part in 10(exp 6) in the orientation of the rotation axis relative to the solid Earth's axis of figure (polar motion). These changes occur over a broad spectrum of time scales, ranging from hours to centuries and longer, reflecting the fact that they are produced by a wide variety of geophysical and astronomical processes. Geodetic observations of Earth rotation changes thus provide insights into the geophysical processes illustrated, which are often difficult to obtain by other means. In addition, these measurements are required for engineering purposes. Theoretical studies of Earth rotation variations are based on the application of Euler's dynamical equations to the problem of finding the response of slightly deformable solid Earth to variety of surface and internal stresses.

  18. Earth's Decelerating Tectonic Plates

    Energy Technology Data Exchange (ETDEWEB)

    Forte, A M; Moucha, R; Rowley, D B; Quere, S; Mitrovica, J X; Simmons, N A; Grand, S P

    2008-08-22

    Space geodetic and oceanic magnetic anomaly constraints on tectonic plate motions are employed to determine a new global map of present-day rates of change of plate velocities. This map shows that Earth's largest plate, the Pacific, is presently decelerating along with several other plates in the Pacific and Indo-Atlantic hemispheres. These plate decelerations contribute to an overall, globally averaged slowdown in tectonic plate speeds. The map of plate decelerations provides new and unique constraints on the dynamics of time-dependent convection in Earth's mantle. We employ a recently developed convection model constrained by seismic, geodynamic and mineral physics data to show that time-dependent changes in mantle buoyancy forces can explain the deceleration of the major plates in the Pacific and Indo-Atlantic hemispheres.

  19. Titan Balloon Convection Model, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — This innovative research effort is directed at determining, quantitatively, the convective heat transfer coefficients applicable to a Montgolfiere balloon operating...

  20. REVERSALS IN THE 6-CELLS CONVECTION DRIVEN

    Directory of Open Access Journals (Sweden)

    G.M. Vodinchar

    2015-12-01

    Full Text Available We describe the large-scale model geodynamo, which based on indirect data of inhomogeneities in the density of the Earth’s core. Convection structure is associated with spherical harmonic Y24 , which defines the basic poloidal component of velocity. Coriolis drift of this mode determines the toroidal component of velocity. Thus, 6 convective cells are formed. The model takes into account the feedback effect of the magnetic field on convection. It was ascertained that the model contains stable regimes of field generation. The velocity of convection and the dipole component of the magnetic field are close to the observed ones.

  1. Scale analysis of convective clouds

    Directory of Open Access Journals (Sweden)

    Micha Gryschka

    2008-12-01

    Full Text Available The size distribution of cumulus clouds due to shallow and deep convection is analyzed using satellite pictures, LES model results and data from the German rain radar network. The size distributions found can be described by simple power laws as has also been proposed for other cloud data in the literature. As the observed precipitation at ground stations is finally determined by cloud numbers in an area and individual sizes and rain rates of single clouds, the cloud size distributions might be used for developing empirical precipitation forecasts or for validating results from cloud resolving models being introduced to routine weather forecasts.

  2. Characterizing Convection in Stellar Atmospheres

    International Nuclear Information System (INIS)

    Tanner, Joel; Basu, Sarbani; Demarque, Pierre; Robinson, Frank

    2011-01-01

    We perform 3D radiative hydrodynamic simulations to study the properties of convection in the superadiabatic layer of stars. The simulations show differences in both the stratification and turbulent quantities for different types of stars. We extract turbulent pressure and eddy sizes, as well as the T-τ relation for different stars and find that they are sensitive to the energy flux and gravity. We also show that contrary to what is usually assumed in the field of stellar atmospheres, the structure and gas dynamics of simulations of turbulent atmospheres cannot be parameterized with T eff and log(g) alone.

  3. Two-dimensional turbulent convection

    Science.gov (United States)

    Mazzino, Andrea

    2017-11-01

    We present an overview of the most relevant, and sometimes contrasting, theoretical approaches to Rayleigh-Taylor and mean-gradient-forced Rayleigh-Bénard two-dimensional turbulence together with numerical and experimental evidences for their support. The main aim of this overview is to emphasize that, despite the different character of these two systems, especially in relation to their steadiness/unsteadiness, turbulent fluctuations are well described by the same scaling relationships originated from the Bolgiano balance. The latter states that inertial terms and buoyancy terms balance at small scales giving rise to an inverse kinetic energy cascade. The main difference with respect to the inverse energy cascade in hydrodynamic turbulence [R. H. Kraichnan, "Inertial ranges in two-dimensional turbulence," Phys. Fluids 10, 1417 (1967)] is that the rate of cascade of kinetic energy here is not constant along the inertial range of scales. Thanks to the absence of physical boundaries, the two systems here investigated turned out to be a natural physical realization of the Kraichnan scaling regime hitherto associated with the elusive "ultimate state of thermal convection" [R. H. Kraichnan, "Turbulent thermal convection at arbitrary Prandtl number," Phys. Fluids 5, 1374-1389 (1962)].

  4. Perception and Production of Singleton and Geminate Stops in Japanese: Implications for the Theory of Acoustic Invariance.

    Science.gov (United States)

    Amano, Shigeaki; Hirata, Y

    2015-01-01

    The theory of relational acoustic invariance claims that there are stable acoustic properties in speech signals that correspond to a phonological feature, and that the perception system utilizes these acoustic properties for stable perception of a phoneme. The present study examines whether such an invariance exists in native listeners' perception of Japanese singleton and geminate stops despite variability in speaking rate and word length, and whether this perception corresponds to production. Native Japanese listeners identified singleton and geminate stops in continua of 3- and 4-mora words spoken at different speaking rates. Results indicated that the perception boundary is well predicted by a linear function with two variables: durations of stop closure and the (C)V(C)CV portion (with the contrasting stops underlined) of the 3- and 4-mora words. In addition, these two variables were in a consistent relationship for both perception and production of words containing 2-4 moras. The results support the relational acoustic invariance theory. © 2015 S. Karger AG, Basel.

  5. Upper Troposphere Lower Stratosphere structure during convective systems using GPS radio occultations

    DEFF Research Database (Denmark)

    Biondi, Riccardo

    The deep convective systems play a fundamental role in atmospheric circulation and climate. Thunderstorms and meso-scale convective systems produce fast vertical transport, redistributing water vapor and trace gases and influencing the thermal structure of the upper troposphere and lower...... stratosphere (UTLS) contributing to the troposphere-stratosphere transport and affecting the Earth global circulation and the climate changes. The Global Positioning System (GPS) Radio Occultation (RO) technique enables measurement of atmospheric density structure in any meteorological condition...... to the analysis of tropical storms for the future mission ACES will also be evaluated. Using data from the past and ongoing GPS RO missions we have defined an algorithm to detect the clouds top of the convective systems and their thermal structure. Other satellite and in-situ measurements co-located with GPS ROs...

  6. New population-based references for birth weight, length, and head circumference in singletons and twins from 23 to 43 gestation weeks.

    Science.gov (United States)

    Sankilampi, Ulla; Hannila, Marja-Leena; Saari, Antti; Gissler, Mika; Dunkel, Leo

    2013-09-01

    Birth size curves are needed for clinical and epidemiological purposes. We constructed birth weight (BW), length (BL), and head circumference (BHC) references, assessed effects of twinness and parity, and defined cut-off points for small, appropriate, and large for gestational age. Birth register data of all 753,036 infants born in 1996-2008 in Finland were cleaned to create references reflecting optimal intrauterine growth. The final data included 533,666 singletons and 15,033 twins (median gestation weeks (gws) 40.0 and 37.1, respectively, 41.6% primiparous). Sex-specific BW, BL, and BHC references were constructed from 23 to 43 gws separately for singletons and twins born to primiparous or multiparous mothers. GAMLSS method was used for modelling. In singletons from 36 gws onwards, increased BW and BL were observed in comparison to previous reference from 1979-1983. Twins diverged from singletons from 30 gws onwards. At 37.0 gws, mean BW was 400 g lower and mean BL 1.2 cm shorter than in singletons. From 30 gws onwards, birth size was larger in infants of multiparous than primiparous mothers. Population-based birth size references are available for the evaluation of birth size. Accounting for plurality and parity improves the accuracy of birth size evaluation.

  7. Benard convection in gaps and cavities

    International Nuclear Information System (INIS)

    Mueller, U.

    1981-04-01

    The article contains two parts. In the first part a condensed review of the most striking phenomena in Benard convection in laterally confined fluid layers is given. In the second part recent experimental and theoretical work on Benard convection in gaps is presented an analysed. (orig.) [de

  8. Convective mixing and accretion in white dwarfs

    International Nuclear Information System (INIS)

    Koester, D.

    1976-01-01

    The evolution of convection zones in cooling white dwarfs with helium envelopes and outer hydrogen layers is calculated with a complete stellar evolution code. It is shown that white dwarfs of spectral type DB cannot be formed from DA stars by convective mixing. However, for cooler temperatures (Tsub(e) [de

  9. The GeoFlow experiment-spherical Rayleigh-Benard convection under the influence of an artificial central force field

    International Nuclear Information System (INIS)

    Gellert, M; Beltrame, P; Egbers, C

    2005-01-01

    Spherical Rayleigh-Benard convection under the influence of an artificial central force field produced by the so-called dielectrophoretic effect is studied as a simplified model of the flow in the outer earth core. The fluid motion there is most probably driving the earth's dynamo and the energy source for the earth's magnetic field. Studying convective flows in earth-like geometry could lead to a deeper understanding of the basics of these processes. This research is a preparatory study for the experiments on the International Space Station (ISS). A bifurcation-theoretical approach shows the existence of heteroclinic cycles between spherical modes (l, l + 1) for the non-rotating system. This behavior depends strong on the radius ratio of the spheres and will be hard to detect in the experiment. For slow rotations interactions of the azimuthal modes (m, m + 1) found in numerical simulations for supercritical states are supposed to be experimentally observable

  10. Topology Optimisation for Coupled Convection Problems

    DEFF Research Database (Denmark)

    Alexandersen, Joe

    This thesis deals with topology optimisation for coupled convection problems. The aim is to extend and apply topology optimisation to steady-state conjugate heat transfer problems, where the heat conduction equation governs the heat transfer in a solid and is coupled to thermal transport...... in a surrounding uid, governed by a convection-diffusion equation, where the convective velocity field is found from solving the isothermal incompressible steady-state Navier-Stokes equations. Topology optimisation is also applied to steady-state natural convection problems. The modelling is done using stabilised...... finite elements, the formulation and implementation of which was done partly during a special course as prepatory work for this thesis. The formulation is extended with a Brinkman friction term in order to facilitate the topology optimisation of fluid flow and convective cooling problems. The derived...

  11. Convective penetration in a young sun

    Science.gov (United States)

    Pratt, Jane; Baraffe, Isabelle; Goffrey, Tom; MUSIC developers group

    2018-01-01

    To interpret the high-quality data produced from recent space-missions it is necessary to study convection under realistic stellar conditions. We describe the multi-dimensional, time implicit, fully compressible, hydrodynamic, implicit large eddy simulation code MUSIC. We use MUSIC to study convection during an early stage in the evolution of our sun where the convection zone covers approximately half of the solar radius. This model of the young sun possesses a realistic stratification in density, temperature, and luminosity. We approach convection in a stellar context using extreme value theory and derive a new model for convective penetration, targeted for one-dimensional stellar evolution calculations. This model provides a scenario that can explain the observed lithium abundance in the sun and in solar-like stars at a range of ages.

  12. Numerical simulations of convectively excited gravity waves

    International Nuclear Information System (INIS)

    Glatzmaier, G.A.

    1983-01-01

    Magneto-convection and gravity waves are numerically simulated with a nonlinear, three-dimensional, time-dependent model of a stratified, rotating, spherical fluid shell heated from below. A Solar-like reference state is specified while global velocity, magnetic field, and thermodynamic perturbations are computed from the anelastic magnetohydrodynamic equations. Convective overshooting from the upper (superadiabatic) part of the shell excites gravity waves in the lower (subadiabatic) part. Due to differential rotation and Coriolis forces, convective cell patterns propagate eastward with a latitudinally dependent phase velocity. The structure of the excited wave motions in the stable region is more time-dependent than that of the convective motions above. The magnetic field tends to be concentrated over giant-cell downdrafts in the convective zone but is affected very little by the wave motion in the stable region

  13. Digital Earth - A sustainable Earth

    Science.gov (United States)

    Mahavir

    2014-02-01

    All life, particularly human, cannot be sustainable, unless complimented with shelter, poverty reduction, provision of basic infrastructure and services, equal opportunities and social justice. Yet, in the context of cities, it is believed that they can accommodate more and more people, endlessly, regardless to their carrying capacity and increasing ecological footprint. The 'inclusion', for bringing more and more people in the purview of development is often limited to social and economic inclusion rather than spatial and ecological inclusion. Economic investment decisions are also not always supported with spatial planning decisions. Most planning for a sustainable Earth, be at a level of rural settlement, city, region, national or Global, fail on the capacity and capability fronts. In India, for example, out of some 8,000 towns and cities, Master Plans exist for only about 1,800. A chapter on sustainability or environment is neither statutorily compulsory nor a norm for these Master Plans. Geospatial technologies including Remote Sensing, GIS, Indian National Spatial Data Infrastructure (NSDI), Indian National Urban Information Systems (NUIS), Indian Environmental Information System (ENVIS), and Indian National GIS (NGIS), etc. have potential to map, analyse, visualize and take sustainable developmental decisions based on participatory social, economic and social inclusion. Sustainable Earth, at all scales, is a logical and natural outcome of a digitally mapped, conceived and planned Earth. Digital Earth, in fact, itself offers a platform to dovetail the ecological, social and economic considerations in transforming it into a sustainable Earth.

  14. Magnetic Fields in the Solar Convection Zone

    Directory of Open Access Journals (Sweden)

    Fan Yuhong

    2004-07-01

    Full Text Available Recent studies of the dynamic evolution of magnetic flux tubes in the solar convection zone are reviewed with focus on emerging flux tubes responsible for the formation of solar active regions. The current prevailing picture is that active regions on the solar surface originate from strong toroidal magnetic fields generated by the solar dynamo mechanism at the thin tachocline layer at the base of the solar convection zone. Thus the magnetic fields need to traverse the entire convection zone before they reach the photosphere to form the observed solar active regions. This review discusses results with regard to the following major topics: 1. the equilibrium properties of the toroidal magnetic fields stored in the stable overshoot region at the base of the convection zone, 2. the buoyancy instability associated with the toroidal magnetic fields and the formation of buoyant magnetic flux tubes, 3. the rise of emerging flux loops through the solar convective envelope as modeled by the thin flux tube calculations which infer that the field strength of the toroidal magnetic fields at the base of the solar convection zone is significantly higher than the value in equipartition with convection, 4. the minimum twist needed for maintaining cohesion of the rising flux tubes, 5. the rise of highly twisted kink unstable flux tubes as a possible origin of d -sunspots, 6. the evolution of buoyant magnetic flux tubes in 3D stratified convection, 7. turbulent pumping of magnetic flux by penetrative compressible convection, 8. an alternative mechanism for intensifying toroidal magnetic fields to significantly super-equipartition field strengths by conversion of the potential energy associated with the superadiabatic stratification of the solar convection zone, and finally 9. a brief overview of our current understanding of flux emergence at the surface and post-emergence evolution of the subsurface magnetic fields.

  15. Actively convected liquid metal divertor

    International Nuclear Information System (INIS)

    Shimada, Michiya; Hirooka, Yoshi

    2014-01-01

    The use of actively convected liquid metals with j × B force is proposed to facilitate heat handling by the divertor, a challenging issue associated with magnetic fusion experiments such as ITER. This issue will be aggravated even more for DEMO and power reactors because the divertor heat load will be significantly higher and yet the use of copper would not be allowed as the heat sink material. Instead, reduced activation ferritic/martensitic steel alloys with heat conductivities substantially lower than that of copper, will be used as the structural materials. The present proposal is to fill the lower part of the vacuum vessel with liquid metals with relatively low melting points and low chemical activities including Ga and Sn. The divertor modules, equipped with electrodes and cooling tubes, are immersed in the liquid metal. The electrode, placed in the middle of the liquid metal, can be biased positively or negatively with respect to the module. The j × B force due to the current between the electrode and the module provides a rotating motion for the liquid metal around the electrodes. The rise in liquid temperature at the separatrix hit point can be maintained at acceptable levels from the operation point of view. As the rotation speed increases, the current in the liquid metal is expected to decrease due to the v × B electromotive force. This rotating motion in the poloidal plane will reduce the divertor heat load significantly. Another important benefit of the convected liquid metal divertor is the fast recovery from unmitigated disruptions. Also, the liquid metal divertor concept eliminates the erosion problem. (letter)

  16. Progestogens in singleton gestations with preterm prelabor rupture of membranes: a systematic review and metaanalysis of randomized controlled trials.

    Science.gov (United States)

    Quist-Nelson, Johanna; Parker, Pamela; Mokhtari, Neggin; Di Sarno, Rossana; Saccone, Gabriele; Berghella, Vincenzo

    2018-03-31

    Preterm prelabor rupture of membranes occurs in 3% of all pregnancies. Neonatal benefit is seen in uninfected women who do not deliver immediately after preterm prelabor rupture of membranes. The purpose of this study was to evaluate whether the administration of progestogens in singleton pregnancies prolongs pregnancy after preterm prelabor rupture of membranes. Searches were performed in MEDLINE, OVID, Scopus, EMBASE, ClinicalTrials.gov, and the Cochrane Central Register of Controlled Trials with the use of a combination of keywords and text words related to "progesterone," "progestogen," "prematurity," and "preterm premature rupture of membranes" from the inception of the databases until January 2018. We included all randomized controlled trials of singleton gestations after preterm prelabor rupture of membranes that were randomized to either progestogens or control (either placebo or no treatment). Exclusion criteria were trials that included women who had contraindications to expectant management after preterm prelabor rupture of membranes (ie, chorioamnionitis, severe preeclampsia, and nonreassuring fetal status) and trials on multiple gestations. We planned to include all progestogens, including but not limited to 17-α hydroxyprogesterone caproate, and natural progesterone. The primary outcome was latency from randomization to delivery. Metaanalysis was performed with the use of the random effects model of DerSimonian and Laird to produce relative risk with 95% confidence interval. Analysis was performed for each mode of progestogen administration separately. Six randomized controlled trials (n=545 participants) were included. Four of the included trials assessed the efficacy of 17-α hydroxyprogesterone caproate; 1 trial assessed rectal progestogen, and 1 trial had 3 arms that compared 17-α hydroxyprogesterone caproate, rectal progestogen, and placebo. The mean gestational age at time randomization was 26.9 weeks in the 17-α hydroxyprogesterone caproate

  17. Non-singleton colors are not attended faster than categories, but they are encoded faster: A combined approach of behavior, modeling and ERPs.

    Science.gov (United States)

    Callahan-Flintoft, Chloe; Wyble, Brad

    2017-11-01

    The visual system is able to detect targets according to a variety of criteria, such as by categorical (letter vs digit) or featural attributes (color). These criteria are often used interchangeably in rapid serial visual presentation (RSVP) studies but little is known about how rapidly they are processed. The aim of this work was to compare the time course of attentional selection and memory encoding for different types of target criteria. We conducted two experiments where participants reported one or two targets (T1, T2) presented in lateral RSVP streams. Targets were marked either by being a singleton color (red letter among black letters), being categorically distinct (digits among letters) or non-singleton color (target color letter among heterogeneously colored letters). Using event related potential (ERPs) associated with attention and memory encoding (the N2pc and the P3 respectively), we compared the relative latency of these two processing stages for these three kinds of targets. In addition to these ERP measures, we obtained convergent behavioral measures for attention and memory encoding by presenting two targets in immediate sequence and comparing their relative accuracy and proportion of temporal order errors. Both behavioral and EEG measures revealed that singleton color targets were attended much more quickly than either non-singleton color or categorical targets, and there was very little difference between attention latencies to non-singleton color and categorical targets. There was however a difference in the speed of memory encoding for non-singleton color and category latencies in both behavioral and EEG measures, which shows that encoding latency differences do not always mirror attention latency differences. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Substorms and polar cap convection: the 10 January 2004 interplanetary CME case

    Directory of Open Access Journals (Sweden)

    Y. Andalsvik

    2012-01-01

    Full Text Available The expansion-contraction model of Dungey cell plasma convection has two different convection sources, i.e. reconnections at the magnetopause and in the magnetotail. The spatial-temporal structure of the nightside source is not yet well understood. In this study we shall identify temporal variations in the winter polar cap convection structure during substorm activity under steady interplanetary conditions. Substorm activity (electrojets and particle precipitations is monitored by excellent ground-satellite DMSP F15 conjunctions in the dusk-premidnight sector. We take advantage of the wide latitudinal coverage of the IMAGE chain of ground magnetometers in Svalbard – Scandinavia – Russia for the purpose of monitoring magnetic deflections associated with polar cap convection and substorm electrojets. These are augmented by direct observations of polar cap convection derived from SuperDARN radars and cross-track ion drift observations during traversals of polar cap along the dusk-dawn meridian by spacecraft DMSP F13. The interval we study is characterized by moderate, stable forcing of the magnetosphere-ionosphere system (EKL = 4.0–4.5 mV m−1; cross polar cap potential (CPCP, Φ (Boyle = 115 kV during Earth passage of an interplanetary CME (ICME, choosing an 4-h interval where the magnetic field pointed continuously south-west (Bz By By polarity of the ICME magnetic field, a clear indication of a nightside source.

  19. Snow precipitation on Mars driven by cloud-induced night-time convection

    Science.gov (United States)

    Spiga, Aymeric; Hinson, David P.; Madeleine, Jean-Baptiste; Navarro, Thomas; Millour, Ehouarn; Forget, François; Montmessin, Franck

    2017-09-01

    Although it contains less water vapour than Earth's atmosphere, the Martian atmosphere hosts clouds. These clouds, composed of water-ice particles, influence the global transport of water vapour and the seasonal variations of ice deposits. However, the influence of water-ice clouds on local weather is unclear: it is thought that Martian clouds are devoid of moist convective motions, and snow precipitation occurs only by the slow sedimentation of individual particles. Here we present numerical simulations of the meteorology in Martian cloudy regions that demonstrate that localized convective snowstorms can occur on Mars. We show that such snowstorms--or ice microbursts--can explain deep night-time mixing layers detected from orbit and precipitation signatures detected below water-ice clouds by the Phoenix lander. In our simulations, convective snowstorms occur only during the Martian night, and result from atmospheric instability due to radiative cooling of water-ice cloud particles. This triggers strong convective plumes within and below clouds, with fast snow precipitation resulting from the vigorous descending currents. Night-time convection in Martian water-ice clouds and the associated snow precipitation lead to transport of water both above and below the mixing layers, and thus would affect Mars' water cycle past and present, especially under the high-obliquity conditions associated with a more intense water cycle.

  20. EarthLabs - Investigating Hurricanes: Earth's Meteorological Monsters

    Science.gov (United States)

    McDaris, J. R.; Dahlman, L.; Barstow, D.

    2007-12-01

    which students investigate the different interactions involved in hurricane generation, steering, and intensification. Students analyze a variety of visualization resources looking for patterns in occurrence and to develop an understanding of hurricane structure. They download archived data about past hurricanes and produce temporal and spatial plots to discover patterns in hurricane life cycles. They investigate the relationship between hurricane wind speed and factors such as barometric pressure and sea surface temperature by conducting spreadsheet analyses on archived data. They also conduct hands-on laboratory experiments in order to understand the physical processes that underpin energy transfer in convection, condensation, and latent heat. These activities highlight Earth science as a vital, rich, invigorating course, employing state-of-the-art technologies and in-depth labs with high relevance for our daily lives and the future.

  1. Plate tectonics, mantle convection and D'' seismic structures

    Science.gov (United States)

    Wen, Lianxing

    This thesis adopts multidisciplinary (geodynamical and seismological) approaches toward understanding dynamics of the Earth's mantle. My geodynamical approach is directed at understanding the relationship between large-scale surface observables (geoid, topography, plate motions) and mantle rheology and convection of the present-day Earth. In chapter 2, I remove shallow mantle structure of various tectonic features to generate "residual tomography." In chapter 3, I show that the pattern, spectrum and amplitude of the "residual topography" are consistent with shallow origin of the "Earth surface dynamic topography;" the long wavelength geoid and topography (l = 2-3) are successfully explained by density models inferred from the "residual tomography," assuming layered mantle convection stratified at the "920 km seismic discontinuity." In chapter 4, I develop a new method to calculate mantle flow with lateral variation of viscosity. The viscosity contrast between continental and oceanic regions is identified to have dominating effects on both the observed poloidal/toroidal ratio and pattern of toroidal motions at long wavelengths. My seismological approach is focused on exploring fine structures near the core-mantle boundary (CMB) and developing new seismic techniques. I discuss the method development and strategies to explore fine structures in the following chapters. In chapter 5, I develop a hybrid method, a combination of analytical and numerical methods, with numerical methods applied in heterogeneous regions only. In chapter 6, I constrain the general structures of the ultra low velocity zones (ULVZ) near the CMB under the south-east Pacific and Iceland. The SKS-SPdKS data are explained by ULVZ with P-velocity reduction of 10%, horizontal length-scales of about 250 km and height of about 40 km. S-velocity reduction of 30% is consistent with the data. In chapter 7, I constrain the detailed structures of the ULVZ near the CMB from observed broadband PKP precursors

  2. A thermodynamically general theory for convective vortices

    Science.gov (United States)

    Renno, Nilton O.

    2008-08-01

    Convective vortices are common features of atmospheres that absorb lower-entropy-energy at higher temperatures than they reject higher-entropy-energy to space. These vortices range from small to large-scale and play an important role in the vertical transport of heat, momentum, and tracer species. Thus, the development of theoretical models for convective vortices is important to our understanding of some of the basic features of planetary atmospheres. The heat engine framework is a useful tool for studying convective vortices. However, current theories assume that convective vortices are reversible heat engines. Since there are questions about how reversible real atmospheric heat engines are, their usefulness for studying real atmospheric vortices is somewhat controversial. In order to reduce this problem, a theory for convective vortices that includes irreversible processes is proposed. The paper's main result is that the proposed theory provides an expression for the pressure drop along streamlines that includes the effects of irreversible processes. It is shown that a simplified version of this expression is a generalization of Bernoulli's equation to convective circulations. It is speculated that the proposed theory not only explains the intensity, but also sheds light on other basic features of convective vortices such as their physical appearance.

  3. Prenatal screening at 11-13+6 weeks in assisted reproductive technology singleton pregnancies and those conceived naturally.

    Science.gov (United States)

    Gong, Meng; Shi, Hua; Zhang, Yu-guo; Ming, Lei

    2015-10-01

    To investigate whether assisted reproductive technology (ART) increases the risk of fetal chromosomal abnormalities. A total of 2034 singleton pregnant women were included in this retrospective study. They were divided into ART (574 fetuses) and control groups (1460 fetuses conceived naturally). All pregnant women received screening according to the Fetal Medicine Foundation, London 2004 Kypros H. Nicolaides guidelines at 11-13+6 weeks of gestation. Accordingly, women with value at risk of chromosomal abnormalities >1:250 underwent chorionic villus sampling or amniocentesis. Mean body mass index was 22.83 ± 3.27 versus 21.29 ± 2.81 kg/m(2) in the ART and control groups, respectively (P fetal chromosomal abnormalities. Additionally, fetus size in the ART group was bigger than that in the natural conception group. © 2015 Japan Society of Obstetrics and Gynecology.

  4. Electromagnetic weather in the near-earth space in dependence on solar wind parameters

    International Nuclear Information System (INIS)

    Belov, B.A.; Burtsev, Yu.A.; Dremukhina, L.A.; Papitashvili, V.O.

    1995-01-01

    Analysis of modern models of electrical and magnetic fields, electrical current and plasma convection is carried out with the purpose of quantitative description of the near-earth electrodynamic parameters. Possibility of utilizing such models simultaneously with radar and geomagnetic observations for continuous real time control of electromagnetic weather in the earth magnetosphere is considered. Refs. 24, refs. 3

  5. A clinically driven variant prioritization framework outperforms purely computational approaches for the diagnostic analysis of singleton WES data.

    Science.gov (United States)

    Stark, Zornitza; Dashnow, Harriet; Lunke, Sebastian; Tan, Tiong Y; Yeung, Alison; Sadedin, Simon; Thorne, Natalie; Macciocca, Ivan; Gaff, Clara; Oshlack, Alicia; White, Susan M; James, Paul A

    2017-11-01

    Rapid identification of clinically significant variants is key to the successful application of next generation sequencing technologies in clinical practice. The Melbourne Genomics Health Alliance (MGHA) variant prioritization framework employs a gene prioritization index based on clinician-generated a priori gene lists, and a variant prioritization index (VPI) based on rarity, conservation and protein effect. We used data from 80 patients who underwent singleton whole exome sequencing (WES) to test the ability of the framework to rank causative variants highly, and compared it against the performance of other gene and variant prioritization tools. Causative variants were identified in 59 of the patients. Using the MGHA prioritization framework the average rank of the causative variant was 2.24, with 76% ranked as the top priority variant, and 90% ranked within the top five. Using clinician-generated gene lists resulted in ranking causative variants an average of 8.2 positions higher than prioritization based on variant properties alone. This clinically driven prioritization approach significantly outperformed purely computational tools, placing a greater proportion of causative variants top or in the top 5 (permutation P-value=0.001). Clinicians included 40 of the 49 WES diagnoses in their a priori list of differential diagnoses (81%). The lists generated by PhenoTips and Phenomizer contained 14 (29%) and 18 (37%) of these diagnoses respectively. These results highlight the benefits of clinically led variant prioritization in increasing the efficiency of singleton WES data analysis and have important implications for developing models for the funding and delivery of genomic services.

  6. Less-Restrictive Food Intake During Labor in Low-Risk Singleton Pregnancies: A Systematic Review and Meta-analysis.

    Science.gov (United States)

    Ciardulli, Andrea; Saccone, Gabriele; Anastasio, Hannah; Berghella, Vincenzo

    2017-03-01

    To evaluate benefits and harms of food intake during labor. Electronic databases such as MEDLINE and ClinicalTrials.gov were searched from their inception until October 2016. We included randomized trials comparing a policy of less-restrictive food intake with a policy of more restrictive food intake during labor. The primary outcome was the mean duration of labor. Meta-analysis was performed using the random-effects model of DerSimonian and Laird to produce summary treatment effects in terms of either a relative risk or a mean difference with 95% confidence interval (CI). Ten trials, including 3,982 laboring women, were included. All the studies involved laboring singletons considered at low risk because they had no obstetric or medical complications that would increase the likelihood of cesarean delivery. In three studies, women were allowed to select from a low-residue diet throughout the course of labor. One study had honey date syrup as the allowed food intake. Five studies had carbohydrate drinks as food intake in labor. The last one was the only trial that allowed unrestrictive food intake. In the included studies, all women in the intervention group were allowed the assigned food intake until delivery, whereas women in a control group were allowed only ice chips, water, or sips of water until delivery. A policy of less-restrictive food intake was associated with a significantly shorter duration of labor (mean difference -16 minutes, 95% CI -25 to -7). No other benefits or harms in obstetric or neonatal outcome were noticed. Regurgitation during general anesthesia and Mendelson syndrome did not occur in either group. Women with low-risk singleton pregnancies who were allowed to eat more freely during labor had a shorter duration of labor. A policy of less-restrictive food intake during labor did not influence other obstetric or neonatal outcomes nor did it increase the incidence of vomiting. Operative delivery rates were similar.

  7. Earth thermics

    Energy Technology Data Exchange (ETDEWEB)

    Ueda, M

    1960-01-01

    The thermodynamics of the Earth are described, including terrestrial heat flow, internal temperatures and thermal history. The value of the geothermal gradient has been considered to be 3/sup 0/C/100 m but measured values are slightly different. The values of terrestrial heat flow are relatively constant and are calculated be about 2.3 x 10 to the minus 6 cal/cm/sup 2/ sec (2.3 HFU). The Earth's internal temperature can be calculated from the adiabatic temperature gradient of adiabatic expansion. Using Simon's equation No. 9, a value of 2100-2500/sup 0/C is obtained, this is much lower than it was previously thought to be. The value of 2.3 HFU can easily be obtained from this internal temperature figure.

  8. Measuring Convective Mass Fluxes Over Tropical Oceans

    Science.gov (United States)

    Raymond, David

    2017-04-01

    Deep convection forms the upward branches of all large-scale circulations in the tropics. Understanding what controls the form and intensity of vertical convective mass fluxes is thus key to understanding tropical weather and climate. These mass fluxes and the corresponding conditions supporting them have been measured by recent field programs (TPARC/TCS08, PREDICT, HS3) in tropical disturbances considered to be possible tropical storm precursors. In reality, this encompasses most strong convection in the tropics. The measurements were made with arrays of dropsondes deployed from high altitude. In some cases Doppler radar provided additional measurements. The results are in some ways surprising. Three factors were found to control the mass flux profiles, the strength of total surface heat fluxes, the column-integrated relative humidity, and the low to mid-tropospheric moist convective instability. The first two act as expected, with larger heat fluxes and higher humidity producing more precipitation and stronger lower tropospheric mass fluxes. However, unexpectedly, smaller (but still positive) convective instability produces more precipitation as well as more bottom-heavy convective mass flux profiles. Furthermore, the column humidity and the convective instability are anti-correlated, at least in the presence of strong convection. On spatial scales of a few hundred kilometers, the virtual temperature structure appears to be in dynamic balance with the pattern of potential vorticity. Since potential vorticity typically evolves on longer time scales than convection, the potential vorticity pattern plus the surface heat fluxes then become the immediate controlling factors for average convective properties. All measurements so far have taken place in regions with relatively flat sea surface temperature (SST) distributions. We are currently seeking funding for a measurement program in the tropical east Pacific, a region that exhibits strong SST gradients and

  9. Transient Mixed Convection Validation for NGNP

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Barton [Utah State Univ., Logan, UT (United States); Schultz, Richard [Idaho National Lab. (INL), Idaho Falls, ID (United States)

    2015-10-19

    The results of this project are best described by the papers and dissertations that resulted from the work. They are included in their entirety in this document. They are: (1) Jeff Harris PhD dissertation (focused mainly on forced convection); (2) Blake Lance PhD dissertation (focused mainly on mixed and transient convection). This dissertation is in multi-paper format and includes the article currently submitted and one to be submitted shortly; and, (3) JFE paper on CFD Validation Benchmark for Forced Convection.

  10. Convective cells and transport in toroidal plasmas

    International Nuclear Information System (INIS)

    Hassam, A.B.; Kulsrud, R.M.

    1978-12-01

    The properties of convective cells and the diffusion resulting from such cells are significantly influenced by an inhomogeneity in the extermal confining magnetic field, such as that in toroidal plasmas. The convective diffusion in the presence of a field inhomogeneity is estimated. For a thermal background, this diffusion is shown to be substantially smaller than classical collisional diffusion. For a model nonthermal background, the diffusion is estimated, for typical parameters, to be at most of the order of collisional diffusion. The model background employed is based on spectra observed in numerical simulations of drift-wave-driven convective cells

  11. Transient Mixed Convection Validation for NGNP

    International Nuclear Information System (INIS)

    Smith, Barton; Schultz, Richard

    2015-01-01

    The results of this project are best described by the papers and dissertations that resulted from the work. They are included in their entirety in this document. They are: (1) Jeff Harris PhD dissertation (focused mainly on forced convection); (2) Blake Lance PhD dissertation (focused mainly on mixed and transient convection). This dissertation is in multi-paper format and includes the article currently submitted and one to be submitted shortly; and, (3) JFE paper on CFD Validation Benchmark for Forced Convection.

  12. Dynamics of a Snowball Earth ocean.

    Science.gov (United States)

    Ashkenazy, Yosef; Gildor, Hezi; Losch, Martin; Macdonald, Francis A; Schrag, Daniel P; Tziperman, Eli

    2013-03-07

    Geological evidence suggests that marine ice extended to the Equator at least twice during the Neoproterozoic era (about 750 to 635 million years ago), inspiring the Snowball Earth hypothesis that the Earth was globally ice-covered. In a possible Snowball Earth climate, ocean circulation and mixing processes would have set the melting and freezing rates that determine ice thickness, would have influenced the survival of photosynthetic life, and may provide important constraints for the interpretation of geochemical and sedimentological observations. Here we show that in a Snowball Earth, the ocean would have been well mixed and characterized by a dynamic circulation, with vigorous equatorial meridional overturning circulation, zonal equatorial jets, a well developed eddy field, strong coastal upwelling and convective mixing. This is in contrast to the sluggish ocean often expected in a Snowball Earth scenario owing to the insulation of the ocean from atmospheric forcing by the thick ice cover. As a result of vigorous convective mixing, the ocean temperature, salinity and density were either uniform in the vertical direction or weakly stratified in a few locations. Our results are based on a model that couples ice flow and ocean circulation, and is driven by a weak geothermal heat flux under a global ice cover about a kilometre thick. Compared with the modern ocean, the Snowball Earth ocean had far larger vertical mixing rates, and comparable horizontal mixing by ocean eddies. The strong circulation and coastal upwelling resulted in melting rates near continents as much as ten times larger than previously estimated. Although we cannot resolve the debate over the existence of global ice cover, we discuss the implications for the nutrient supply of photosynthetic activity and for banded iron formations. Our insights and constraints on ocean dynamics may help resolve the Snowball Earth controversy when combined with future geochemical and geological observations.

  13. Hospital utilization, costs and mortality rates during the first 5 years of life: a population study of ART and non-ART singletons.

    Science.gov (United States)

    Chambers, G M; Lee, E; Hoang, V P; Hansen, M; Bower, C; Sullivan, E A

    2014-03-01

    Do singletons conceived following assisted reproduction technologies (ARTs) have significantly different hospital utilization, and therefore costs, compared with non-ART children during the first 5 years of life? ART singletons have longer hospital birth-admissions and a small increased risk of re-admission during the first 5 years of life resulting in higher costs of hospital care. ART singletons are at greater risk of adverse perinatal outcomes compared with non-ART singletons. Long-term physical and mental health outcomes of ART singletons are generally reassuring. There is a scarcity of information on health service utilization and the health economic impact of ART conceived children. A population cohort study using linked birth, hospital and death records. Perinatal outcomes, hospital utilization and costs, and mortality rates were compared for non-ART and ART singletons to 5 years. Adjustments were made for maternal age, parity, sex, birth year, socioeconomic status and funding source. Australian Diagnosis Related Groups cost-weights were used to derive costs. All costs are reported in 2009/2010 Australian dollars. All babies born in Western Australia between 1994 and 2003 were included; 224 425 non-ART singletons and 2199 ART conceived singletons. Hospital admission and death records in Western Australia linked to 2008 were used. Overall, ART singletons had a significantly longer length of stay during the birth-admission (mean difference 1.8 days, P birth-admission ($1473). The independent residual cost associated with ART conception was $342 during the birth-admission and an additional $548 up to 5 years of age, indicating that being conceived as an ART child predicts not only higher birth-admission costs but excess costs to at least 5 years of age. This study could not investigate the impact of different ART practices and techniques on perinatal outcomes or hospital utilization, nor could it adjust for parental characteristics such as cause of infertility

  14. MODELING OF CONVECTIVE FLOWS IN PNEUMOBASED OBJECTS. Part 1

    Directory of Open Access Journals (Sweden)

    B. M. Khrustalyov

    2014-01-01

    Full Text Available A computer modeling process of three-dimensional forced convection proceeding from computation of thermodynamic parameters of pneumo basic buildings (pneumo supported structures is presented. The mathematical model of numerical computation method of temperature and velocity fields, pressure profile in the object is developed using the package Solid works and is provided by grid methods on specified software. Special Navier–Stokes, Clapeyron–Mendeleev, continuity and thermal-conductivity equations are used to calculate parameters in the building with four supply and exhaust channels. Differential equations are presented by algebraic equation systems, initial-boundary conditions are changed by differential conditions for mesh functions and their solutions are performed by algebraic operations. In this article the following is demonstrated: in pneumo basic buildings convective and heat flows are identical structures near the surfaces in unlimited space, but in single-multiply shells (envelopescirculation lines take place, geometrical sizes of which depend on thermal-physical characteristics of gas(airin envelopes, radiation reaction with heated surfaces of envelopes with  sphere, earth surface, neighboring buildings. Natural surveys of pneumo-basic buildings of different purposes were carried out in Minsk, in different cities of Belarus and Russia, including temperature fields of external and internal surfaces of air envelopes, relative humidity, thermal (heatflows, radiation characteristics and others.The results of research work are illustrated with diagrams of temperature, velocity, density and pressure dependent on coordinates and time.

  15. Convection in complex shaped vessel; Convection dans des enceintes de forme complexe

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2000-07-01

    The 8 november 2000, the SFT (Societe Francaise de Thermique) organized a technical day on the convection in complex shaped vessels. Nine papers have been presented in the domains of the heat transfers, the natural convection, the fluid distribution, the thermosyphon effect, the steam flow in a sterilization cycle and the transformers cooling. Eight papers are analyzed in ETDE and one paper dealing with the natural convection in spent fuels depository is analyzed in INIS. (A.L.B.)

  16. The structure and dynamics of patterns of Benard convection cells

    International Nuclear Information System (INIS)

    Rivier, N.; Imperial Coll. of Science and Technology, London; Lausanne Univ.

    1990-08-01

    Benard-Marangoni convection, in containers with large aspect ratio, exhibits space-filling cellular structures, highly deformable, but crystallized. They contain dislocations and grain boundaries generated and moved by elementary topological transformations, and are subjected to a weak shear stress due to the earth's rotation. The cellular structure and its fluctuations are analyzed from a crystallographic viewpoint, by using two complementary approaches. One is a global analysis of cellular structures in cylindrical symmetry. Their structural stability and defect pattern are obtained as topological mode-locking of a continuous structural parameter. The other, a local, molecular dynamics of the cells, gives a realistic parametrization of the forces and the transformations by generalizing the Voronoi cell construction in one extra dimension. 23 refs., 8 figs

  17. Steady, three-dimensional, internally heated convection

    International Nuclear Information System (INIS)

    Schubert, G.; Glatzmaier, G.A.; Travis, B.

    1993-01-01

    Numerical calculations have been carried out of steady, symmetric, three-dimensional modes of convection in internally heated, infinite Prandtl number, Boussinesq fluids at a Rayleigh number of 1.4x10 4 in a spherical shell with inner/outer radius of 0.55 and in a 3x3x1 rectangular box. Multiple patterns of convection occur in both geometries. In the Cartesian geometry the patterns are dominated by cylindrical cold downflows and a broad hot upwelling. In the spherical geometry the patterns consist of cylindrical cold downwellings centered either at the vertices of a tetrahedron or the centers of the faces of a cube. The cold downflow cylinders are immersed in a background of upwelling within which there are cylindrical hot concentrations (plumes) and hot halos around the downflows. The forced hot upflow return plumes of internally heated spherical convection are fundamentally different from the buoyancy-driven plumes of heated from below convection

  18. Convective Radio Occultations Final Campaign Summary

    Energy Technology Data Exchange (ETDEWEB)

    Biondi, R. [Atmospheric Radiation Measurement, Washington, DC (United States)

    2016-03-01

    Deep convective systems are destructive weather phenomena that annually cause many deaths and injuries as well as much damage, thereby accounting for major economic losses in several countries. The number and intensity of such phenomena have increased over the last decades in some areas of the globe. Damage is mostly caused by strong winds and heavy rain parameters that are strongly connected to the structure of the particular storm. Convection over land is usually stronger and deeper than over the ocean and some convective systems, known as supercells, also develop tornadoes through processes that remain mostly unclear. The intensity forecast and monitoring of convective systems is one of the major challenges for meteorology because in situ measurements during extreme events are too sparse or unreliable and most ongoing satellite missions do not provide suitable time/space coverage.

  19. Ignition in Convective-Diffusive Systems

    National Research Council Canada - National Science Library

    Law, Chung

    1999-01-01

    ... efficiency as well as the knock and emission characteristics. The ignition event is clearly controlled by the chemical reactions of fuel oxidation and the fluid mechanics of convective and diffusive transport...

  20. Understanding and controlling plasmon-induced convection

    Science.gov (United States)

    Roxworthy, Brian J.; Bhuiya, Abdul M.; Vanka, Surya P.; Toussaint, Kimani C.

    2014-01-01

    The heat generation and fluid convection induced by plasmonic nanostructures is attractive for optofluidic applications. However, previously published theoretical studies predict only nanometre per second fluid velocities that are inadequate for microscale mass transport. Here we show both theoretically and experimentally that an array of plasmonic nanoantennas coupled to an optically absorptive indium-tin-oxide (ITO) substrate can generate >micrometre per second fluid convection. Crucially, the ITO distributes thermal energy created by the nanoantennas generating an order of magnitude increase in convection velocities compared with nanoantennas on a SiO2 base layer. In addition, the plasmonic array alters absorption in the ITO, causing a deviation from Beer-Lambert absorption that results in an optimum ITO thickness for a given system. This work elucidates the role of convection in plasmonic optical trapping and particle assembly, and opens up new avenues for controlling fluid and mass transport on the micro- and nanoscale.

  1. What favors convective aggregation and why?

    Science.gov (United States)

    Muller, Caroline; Bony, Sandrine

    2015-07-01

    The organization of convection is ubiquitous, but its physical understanding remains limited. One particular type of organization is the spatial self-aggregation of convection, taking the form of cloud clusters, or tropical cyclones in the presence of rotation. We show that several physical processes can give rise to self-aggregation and highlight the key features responsible for it, using idealized simulations. Longwave radiative feedbacks yield a "radiative aggregation." In that case, sufficient spatial variability of radiative cooling rates yields a low-level circulation, which induces the upgradient energy transport and radiative-convective instability. Not only do vertically integrated radiative budgets matter but the vertical profile of cooling is also crucial. Convective aggregation is facilitated when downdrafts below clouds are weak ("moisture-memory aggregation"), and this is sufficient to trigger aggregation in the absence of longwave radiative feedbacks. These results shed some light on the sensitivity of self-aggregation to various parameters, including resolution or domain size.

  2. Antartic observations of plasma convection

    International Nuclear Information System (INIS)

    Hansen, H.J.

    1983-01-01

    This thesis is concerned with the use of whistler duct tracking as a diagnostic for the behaviour of plasma in the plasmasphere. As a setting for the results given in the thesis, a broad review is presented which embraces pertinent aspects of previous experimental and theoretical studies of the plasmasphere. From a study of 24 hours of continuous whistler data recorded at Sanae, (L = 3,98), it is shown that associated with quiet magnetic conditions (Av Ksub(p)=1), there exists two plasmasphere bulges centred on about 1700 and 0100 UT. There is evidence that these plasmasphere bulge structures are part of a ground-state or reference base drift pattern. Electric field measurements provide some evidence that quiet time plasmasphere drift behaviour is controlled by the internal ionospheric current systems of dynamo origin, rather than being controlled by magnetospheric convection. Finally, this thesis describes an application of the whistler duct tracking technique to whistler data recorded simultaneously at two ground-based stations (Sanae (L = 3,98) and Halley (L = 4,23)). The identification of common whistler components on each station's data set provides a means of estimating the lifetimes of the associated whistler ducts. Duct lifetimes of as little as 30 minutes are found. Such short lived ducts have important implications for current theories of duct formation

  3. Dynamics of acoustic-convective drying of sunflower cake

    Science.gov (United States)

    Zhilin, A. A.

    2017-10-01

    The dynamics of drying sunflower cake by a new acoustic-convective method has been studied. Unlike the conventional (thermal-convective) method, the proposed method allows moisture to be extracted from porous materials without applying heat to the sample to be dried. Kinetic curves of drying by the thermal-convective and acoustic-convective methods were obtained and analyzed. The advantages of the acoustic-convective extraction of moisture over the thermal-convective method are discussed. The relaxation times of drying were determined for both drying methods. An intermittent drying mode which improves the efficiency of acoustic-convective extraction of moisture is considered.

  4. Neonatal and maternal outcomes comparing women undergoing two in vitro fertilization (IVF) singleton pregnancies and women undergoing one IVF twin pregnancy.

    Science.gov (United States)

    Sazonova, Antonina; Källen, Karin; Thurin-Kjellberg, Ann; Wennerholm, Ulla-Britt; Bergh, Christina

    2013-03-01

    To compare outcomes for women undergoing two in vitro fertilization (IVF) pregnancies with singletons and women undergoing one IVF twin pregnancy. The concept of single-embryo transfer in IVF has reduced the risks of both maternal and neonatal complications, but there is still a discussion of whether or not twins are a desired outcome of IVF. Registry study. Not applicable. All reported twins after IVF with double-embryo transfer (n = 1,982) and their mothers (n = 991) and all mothers (n = 921) who gave birth to two IVF singletons (n = 1,842). None. Maternal and neonatal outcomes including severe neonatal morbidity. Preterm birth, very preterm birth, low birth weight, very low birth weight, and small for gestational age were dramatically increased for IVF twins compared with two IVF singletons with the same mother, with adjusted odds ratios from 4 to 16. Significantly higher rates of respiratory complications, sepsis, and jaundice were detected among the IVF twins. Significantly higher rates of preeclampsia, preterm premature rupture of the membranes, and cesarean section were observed for IVF twin pregnancies. The neonatal and maternal outcomes were dramatically better for women undergoing two IVF singleton pregnancies compared with one IVF twin pregnancy after double-embryo transfer. These results support single-embryo transfer to minimize the risks associated with twin pregnancies. Copyright © 2013 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.

  5. Large for gestational age and macrosomia in singletons born after frozen/thawed embryo transfer (FET) in assisted reproductive technology (ART)

    DEFF Research Database (Denmark)

    Berntsen, Sine; Pinborg, Anja

    2018-01-01

    Increase in success rates with frozen embryo transfer (FET) and reduced risk of ovarian hyperstimulation syndrome (OHSS) and multiple pregnancies has lead to a steady rise in FET. Further, FET is associated with lower risk of prematurity and low birth weight in singletons, when compared with fres...

  6. Outcome of Multifetal Pregnancy Reduction in Women with a Dichorionic Triamniotic Triplet Pregnancy to a Singleton Pregnancy: A Retrospective Nationwide Cohort Study

    NARCIS (Netherlands)

    van de Mheen, L.; Everwijn, S. M. P.; Haak, M. C.; Manten, G. T. R.; Zondervan, H. A.; Knapen, M. F. C. M.; Engels, M. A. J.; Erwich, J. J. H. M.; Coumans, A. B.; van Vugt, J. M. G.; Bilardo, C. M.; van Pampus, M. G.; de Groot, C. J. M.; Mol, B. W. J.; Pajkrt, E.

    2016-01-01

    To study the pregnancy outcomes of women with a dichorionic triamniotic triplet pregnancy that was reduced to a singleton pregnancy and to review the literature. We performed a nationwide retrospective cohort study. We compared time to delivery and perinatal mortality in dichorionic triplet

  7. Outcome of Multifetal Pregnancy Reduction in Women with a Dichorionic Triamniotic Triplet Pregnancy to a Singleton Pregnancy : A Retrospective Nationwide Cohort Study

    NARCIS (Netherlands)

    van de Mheen, L.; Everwijn, S. M. P.; Haak, M. C.; Manten, G. T. R.; Zondervan, H. A.; Knapen, M. F. C. M.; Engels, M. A. J.; Erwich, J. J. H. M.; Coumans, A. B.; van Vugt, J. M. G.; Bilardo, C. M.; van Pampus, M. G.; de Groot, C. J. M.; Mol, B. W. J.; Pajkrt, E.

    2016-01-01

    Objective:To study the pregnancy outcomes of women with a dichorionic triamniotic triplet pregnancy that was reduced to a singleton pregnancy and to review the literature. Methods: We performed a nationwide retrospective cohort study. We compared time to delivery and perinatal mortality in

  8. Outcome of Multifetal Pregnancy Reduction in Women with a Dichorionic Triamniotic Triplet Pregnancy to a Singleton Pregnancy : A Retrospective Nationwide Cohort Study

    NARCIS (Netherlands)

    Van De Mheen, L.; Everwijn, S. M P; Haak, M. C.; Manten, G. T R; Zondervan, H. A.; Knapen, M. F C M; Engels, M. A J; Erwich, J. J H M; Coumans, A. B.; Van Vugt, J. M G; Bilardo, C. M.; Van Pampus, M. G.; De Groot, C. J M; Mol, B. W J; Pajkrt, E.

    2016-01-01

    Objective: To study the pregnancy outcomes of women with a dichorionic triamniotic triplet pregnancy that was reduced to a singleton pregnancy and to review the literature. Methods: We performed a nationwide retrospective cohort study. We compared time to delivery and perinatal mortality in

  9. A comparison of perinatal outcomes in singletons and multiples born after in vitro fertilization or intracytoplasmic sperm injection stratified for neonatal risk criteria

    NARCIS (Netherlands)

    van Heesch, M.M.J.; Evers, J.L.H.; Dumoulin, J.C.M.; van der Hoeven, M.A.H.B.; van Beijsterveldt, C.E.M.; Bonsel, G.J.; Dykgraaf, R.H.M.; van Goudoever, J.B.; Koopman-Esseboom, C.; Nelen, W.L.D.M.; Steiner, K.; Tamminga, P.; Tonch, N.; van Zonneveld, P.; Dirksen, C.D.

    2014-01-01

    Objective To compare perinatal singleton and multiple outcomes in a large Dutch in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) population and within risk subgroups. Newborns were assigned to a risk category based on gestational age, birthweight, Apgar score and congenital

  10. A comparison of perinatal outcomes in singletons and multiples born after in vitro fertilization or intracytoplasmic sperm injection stratified for neonatal risk criteria

    NARCIS (Netherlands)

    Heesch, M.M. van; Evers, J.L.H.; Dumoulin, J.C.; Hoeven, M.A. van der; Beijsterveldt, C.E. van; Bonsel, G.J.; Dykgraaf, R.H.; Goudoever, J.B. van; Koopman-Esseboom, C.; Nelen, W.L.D.M.; Steiner, K.; Tamminga, P.; Tonch, N.; Zonneveld, P. van; Dirksen, C.D.

    2014-01-01

    OBJECTIVE: To compare perinatal singleton and multiple outcomes in a large Dutch in vitro fertilization (IVF)/intracytoplasmic sperm injection (ICSI) population and within risk subgroups. Newborns were assigned to a risk category based on gestational age, birthweight, Apgar score and congenital

  11. Loop electrosurgical excision of the cervix and subsequent risk for spontaneous preterm delivery: a population-based study of singleton deliveries during a 9-year period

    DEFF Research Database (Denmark)

    Noehr, Bugge; Jensen, Allan; Frederiksen, Kirsten

    2009-01-01

    OBJECTIVE: Our aim was to assess the association between loop electrosurgical excision procedure (LEEP) and the subsequent risk for spontaneous preterm delivery, with the use of population-based data from various nationwide registries. STUDY DESIGN: The study population consisted of all singleton...

  12. CONVECTION IN CONDENSIBLE-RICH ATMOSPHERES

    Energy Technology Data Exchange (ETDEWEB)

    Ding, F. [Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637 (United States); Pierrehumbert, R. T., E-mail: fding@uchicago.edu [Department of Physics, University of Oxford, Oxford OX1 3PU (United Kingdom)

    2016-05-01

    Condensible substances are nearly ubiquitous in planetary atmospheres. For the most familiar case—water vapor in Earth’s present climate—the condensible gas is dilute, in the sense that its concentration is everywhere small relative to the noncondensible background gases. A wide variety of important planetary climate problems involve nondilute condensible substances. These include planets near or undergoing a water vapor runaway and planets near the outer edge of the conventional habitable zone, for which CO{sub 2} is the condensible. Standard representations of convection in climate models rely on several approximations appropriate only to the dilute limit, while nondilute convection differs in fundamental ways from dilute convection. In this paper, a simple parameterization of convection valid in the nondilute as well as dilute limits is derived and used to discuss the basic character of nondilute convection. The energy conservation properties of the scheme are discussed in detail and are verified in radiative-convective simulations. As a further illustration of the behavior of the scheme, results for a runaway greenhouse atmosphere for both steady instellation and seasonally varying instellation corresponding to a highly eccentric orbit are presented. The latter case illustrates that the high thermal inertia associated with latent heat in nondilute atmospheres can damp out the effects of even extreme seasonal forcing.

  13. Hospital costs of multiple-birth and singleton-birth children during the first 5 years of life and the role of assisted reproductive technology.

    Science.gov (United States)

    Chambers, Georgina M; Hoang, Van Phuong; Lee, Evelyn; Hansen, Michele; Sullivan, Elizabeth A; Bower, Carol; Chapman, Michael

    2014-11-01

    The unprecedented increase in multiple births during the past 3 decades is a major public health concern and parallels the uptake of medically assisted conception. The economic implications of such births are not well understood. To conduct a comprehensive economic and health services assessment of the frequency, duration, and cost of hospital admissions during the first 5 years of life for singleton, twin, and higher-order multiple (HOM) children and to examine the contribution of assisted reproductive technology (ART) to the incidence and cost of multiple births. A retrospective population cohort study using individually linked birth, hospital, and death records among 233,850 infants born in Western Australia between October 1993 and September 2003, and followed up to September 2008. Multiple-gestation delivery and ART conception. Odds of stillbirth, prematurity and low birth weight, frequency and length of hospital admissions, the mean costs by plurality, and the independent effect of prematurity on childhood costs. Of 226,624 singleton, 6941 twin, and 285 HOM infants, 1.0% of singletons, 15.4% of twins, and 34.7% of HOM children were conceived following ART. Compared with singletons, twins and HOMs were 3.4 and 9.6 times, respectively, more likely to be stillborn and were 6.4 and 36.7 times, respectively, more likely to die during the neonatal period. Twins and HOMs were 18.7 and 525.1 times, respectively, more likely to be preterm, and 3.6 and 2.8 times, respectively, more likely to be small for gestational age. The mean hospital costs of a singleton, twin, and HOM child to age 5 years were $2730, $8993, and $24,411 (in 2009-2010 US dollars), respectively, with cost differences concentrated in the neonatal period and during the first year of life. Almost 15% of inpatient costs for multiple births could have been avoided if ART twins and HOMs had been born as singletons. Compared with singletons, multiple-birth infants consume significantly more hospital

  14. Mortality among twins and singletons in sub-Saharan Africa between 1995 and 2014: a pooled analysis of data from 90 Demographic and Health Surveys in 30 countries.

    Science.gov (United States)

    Monden, Christiaan W S; Smits, Jeroen

    2017-07-01

    Sub-Saharan Africa has the world's highest under-5 and neonatal mortality rates as well as the highest naturally occurring twin rates. Twin pregnancies carry high risk for children and mothers. Under-5 mortality has declined in sub-Saharan Africa over the last decades. It is unknown whether twins have shared in this reduction. We pooled data from 90 Demographic and Health Surveys for 30 sub-Saharan Africa countries on births reported between 1995 and 2014. We used information on 1 685 110 singleton and 56 597 twin livebirths to compute trends in mortality rates for singletons and twins. We examined whether the twin-singleton rate ratio can be attributed to biological, socioeconomic, care-related factors, or birth size, and estimated the mortality burden among sub-Saharan African twins. Under-5 mortality among twins has declined from 327·7 (95% CI 312·0-343·5) per 1000 livebirths in 1995-2001 to 213·0 (196·7-229·2) in 2009-14. This decline of 35·0% was much less steep than the 50·6% reduction among singletons (from 128·6 [95% CI 126·4-130·8] per 1000 livebirths in 1995-2001 to 63·5 [61·6-65·3] in 2009-14). Twins account for an increasing share of under-5 deaths in sub-Saharan Africa: currently 10·7% of under-5 mortality and 15·1% of neonatal mortality. We estimated that about 315 000 twins (uncertainty interval 289 000-343 000) die in sub-Saharan African each year. Excess twin mortality cannot be explained by common risk factors for under-5 mortality, including birthweight. The difference with singletons was especially stark for neonatal mortality (rate ratio 5·0, 95% CI 4·5-5·6). 51·7% of women pregnant with twins reported receiving medical assistance at birth. The fate of twins in sub-Saharan Africa is lagging behind that of singletons. An alarming one-fifth of twins in the region dies before age 5 years, three times the mortality rate among singletons. Twins account for a substantial and growing share of under-5 and neonatal

  15. Stirring up a storm: convective climate variability on tidally locked exoplanets

    Science.gov (United States)

    Koll, D. D. B.; Cronin, T.

    2017-12-01

    Earth-sized exoplanets are extremely common in the galaxy and many of them are likely tidally locked, such that they have permanent day- and nightsides. Astronomers have started to probe the atmospheres of such planets, which raises the question: can tidally locked planets support habitable climates and life?Several studies have explored this question using global circulation models (GCMs). Not only did these studies find that tidally locked Earth analogs can indeed sustain habitable climates, their large day-night contrast should also create a distinct cloud structure that could help astronomers identify such planets. These studies, however, relied on GCMs which do not explicitly resolve convection, raising the question of how robust their results are.Here we consider the dynamics of clouds and convection on a tidally locked planet using the System for Atmospheric Modeling (SAM) cloud-resolving model. We simulate a 3d `channel', representing an equatorial strip that covers both day- and nightside of a tidally locked planet. We use interactive radiation and an interactive slab ocean surface and investigate the response to changes in the stellar constant. We find mean climates that are broadly comparable to those produced by a GCM. However, when the slab ocean is shallow, we also find internal variability that is far bigger than in a GCM. Convection in a tidally locked domain can self-organize in a dramatic fashion, with large outbursts of convection followed by periods of relative calm. We show that one of the timescales for this behavior is set by the time it takes for a dry gravity wave to travel between day- and nightside. The quasi-periodic self-organization of clouds can vary the planetary albedo by up to 50%. Changes this large are potentially detectable with future space telescopes, which raises the prospect of using convectively driven variability to identify high priority targets in the search for life around other stars.

  16. Preliminary three-dimensional model of mantle convection with deformable, mobile continental lithosphere

    Science.gov (United States)

    Yoshida, Masaki

    2010-06-01

    Characteristic tectonic structures such as young orogenic belts and suture zones in a continent are expected to be mechanically weaker than the stable part of the continental lithosphere with the cratonic root (or cratonic lithosphere) and yield lateral viscosity variations in the continental lithosphere. In the present-day Earth's lithosphere, the pre-existing, mechanically weak zones emerge as a diffuse plate boundary. However, the dynamic role of a weak (low-viscosity) continental margin (WCM) in the stability of continental lithosphere has not been understood in terms of geophysics. Here, a new numerical simulation model of mantle convection with a compositionally and rheologically heterogeneous, deformable, mobile continental lithosphere is presented for the first time by using three-dimensional regional spherical-shell geometry. A compositionally buoyant and highly viscous continental assemblage with pre-existing WCMs, analogous to the past supercontinent, is modeled and imposed on well-developed mantle convection whose vigor of convection, internal heating rate, and rheological parameters are appropriate for the Earth's mantle. The visco-plastic oceanic lithosphere and the associated subduction of oceanic plates are incorporated. The time integration of the advection of continental materials with zero chemical diffusion is performed by a tracer particle method. The time evolution of mantle convection after setting the model supercontinent is followed over 800 Myr. Earth-like continental drift is successfully reproduced, and the characteristic thermal interaction between the mantle and the continent/supercontinent is observed in my new numerical model. Results reveal that the WCM protects the cratonic lithosphere from being stretched by the convecting mantle and may play a significant role in the stability of the cratonic lithosphere during the geological timescale because it acts as a buffer that prevents the cratonic lithosphere from undergoing global

  17. EFFECTS OF STELLAR FLUX ON TIDALLY LOCKED TERRESTRIAL PLANETS: DEGREE-1 MANTLE CONVECTION AND LOCAL MAGMA PONDS

    International Nuclear Information System (INIS)

    Gelman, S. E.; Elkins-Tanton, L. T.; Seager, S.

    2011-01-01

    We model the geodynamical evolution of super-Earth exoplanets in synchronous rotation about their star. While neglecting the effects of a potential atmosphere, we explore the parameter spaces of both the Rayleigh number and intensity of incoming stellar flux, and identify two main stages of mantle convection evolution. The first is a transient stage in which a lithospheric temperature and thickness dichotomy emerges between the substellar and the antistellar hemispheres, while the style of mantle convection is dictated by the Rayleigh number. The second stage is the development of degree-1 mantle convection. Depending on mantle properties, the timescale of onset of this second stage of mantle evolution varies from order 1 to 100 billion years of simulated planetary evolution. Planets with higher Rayleigh numbers (due to, for instance, larger planetary radii than the Earth) and planets whose incoming stellar flux is high (likely for most detectable exoplanets) will develop degree-1 mantle convection most quickly, on the order of 1 billion years, which is within the age of many planetary systems. Surface temperatures range from 220 K to 830 K, implying the possibility of liquid water in some regions near the surface. These results are discussed in the context of stable molten magma ponds on hotter planets, and the habitability of super-Earths which may lie outside the Habitable Zone.

  18. [Gestational weight gain and optimal ranges in Chinese mothers giving singleton and full-term births in 2013].

    Science.gov (United States)

    Wang, J; Duan, Y F; Pang, X H; Jiang, S; Yin, S A; Yang, Z Y; Lai, J Q

    2018-01-06

    Objective: To analyze the status of gestational weight gain (GWG) among Chinese mothers who gave singleton and full-term births, and to look at optimal GWG ranges. Methods: In 2013, using the multi-stage stratified and population proportional cluster sampling method, we investigated 8 323 mother-child pairs at their 0-24 months postpartum from 55 counties (cities/districts) of 30 provinces (except Tibet) in mainland China. Questionnaire was used to collect data on body weight before pregnancy and delivery, diseases during gestation, hemorrhage or not at postpartum, child birth weight and length, and other information about pregnant outcomes. We measured mother's body weight and height, and child's body weight and length. Based on 'Chinese Adult Body Weight Standard', we divided mothers into four groups according to their body weight before pregnancy: low weight (BMImothers and children, and according to P25-P75 of GWG among mothers who had good pregnant outcomes and good anthropometry, and whose children had good anthropometry. The status of GWG was assessed by the new optimal ranges. Results: P50 (P25-P75) of GWG among the 8 323 mothers was 15.0 (10.0-19.0) kg. According to the proposed optimal GWG ranges of IOM, the proportions of inadequate, optimal and excessive GWG accounted for 27.2% (2 263 mothers), 36.2% (3 016 mothers) and 36.6% (3 044 mothers). The optimal GWG ranges for low weight, normal weight, overweight and obesity were 11.5-18.0, 10.0-15.0, 8.0-14.0 and 5.0-11.5 kg. Based on these optimal GWG ranges established in this study, the rates of inadequate, optimal and excessive GWG were 15.7% (1 303 mothers), 45.0% (3 744 mothers) and 39.3% (3 276 mothers), and these rates were significantly different from that defined by the IOM standards (χ2=345.36, Pmothers is 15.0 kg, which is at a relatively higher level. This study suggests the optimal GWG ranges for Chinese women who give singleton and full-term babies, which appears lower than IOM's.

  19. Sulfur Earth

    Science.gov (United States)

    de Jong, B. H.

    2007-12-01

    Variations in surface tension affect the buoyancy of objects floating in a liquid. Thus an object floating in water will sink deeper in the presence of dishwater fluid. This is a very minor but measurable effect. It causes for instance ducks to drown in aqueous solutions with added surfactant. The surface tension of liquid iron is very strongly affected by the presence of sulfur which acts as a surfactant in this system varying between 1.9 and 0.4 N/m at 10 mass percent Sulfur (Lee & Morita (2002), This last value is inferred to be the maximum value for Sulfur inferred to be present in the liquid outer core. Venting of Sulfur from the liquid core manifests itself on the Earth surface by the 105 to 106 ton of sulfur vented into the atmosphere annually (Wedepohl, 1984). Inspection of surface Sulfur emission indicates that venting is non-homogeneously distributed over the Earth's surface. The implication of such large variation in surface tension in the liquid outer core are that at locally low Sulfur concentration, the liquid outer core does not wet the predominantly MgSiO3 matrix with which it is in contact. However at a local high in Sulfur, the liquid outer core wets this matrix which in the fluid state has a surface tension of 0.4 N/m (Bansal & Doremus, 1986), couples with it, and causes it to sink. This differential and diapiric movement is transmitted through the essentially brittle mantle (1024 Pa.s, Lambeck & Johnson, 1998; the maximum value for ice being about 1030 Pa.s at 0 K, in all likely hood representing an upper bound of viscosity for all materials) and manifests itself on the surface by the roughly 20 km differentiation, about 0.1 % of the total mantle thickness, between topographical heights and lows with concomitant lateral movement in the crust and upper mantle resulting in thin skin tectonics. The brittle nature of the medium though which this movement is transmitted suggests that the extremes in topography of the D" layer are similar in range to

  20. Vertical natural convection: application of the unifying theory of thermal convection

    NARCIS (Netherlands)

    Ng, C.S.; Ooi, A.; Lohse, Detlef; Chung, D.

    2015-01-01

    Results from direct numerical simulations of vertical natural convection at Rayleigh numbers 1.0×10 5 –1.0×10 9 and Prandtl number 0.709 support a generalised applicability of the Grossmann–Lohse (GL) theory, which was originally developed for horizontal natural (Rayleigh–Bénard) convection. In

  1. Electron thermal effect on linear and nonlinear coupled Shukla-Varma and convective cell modes in dust-contaminated magnetoplasma

    Science.gov (United States)

    Masood, W.; Mirza, Arshad M.

    2010-11-01

    Linear and nonlinear properties of coupled Shukla-Varma (SV) and convective cell modes in the presence of electron thermal effects are studied in a nonuniform magnetoplasma composed of electrons, ions, and extremely massive and negatively charged immobile dust grains. In the linear case, the modified dispersion relation is given and, in the nonlinear case, stationary solutions of the nonlinear equations that govern the dynamics of coupled SV and convective cell modes are obtained. It is found that electrostatic dipolar and vortex street type solutions can appear in such a plasma. The relevance of the present investigation with regard to the Earth's mesosphere as well as in ionospheric plasmas is also pointed out.

  2. Electron thermal effect on linear and nonlinear coupled Shukla-Varma and convective cell modes in dust-contaminated magnetoplasma

    International Nuclear Information System (INIS)

    Masood, W.; Mirza, Arshad M.

    2010-01-01

    Linear and nonlinear properties of coupled Shukla-Varma (SV) and convective cell modes in the presence of electron thermal effects are studied in a nonuniform magnetoplasma composed of electrons, ions, and extremely massive and negatively charged immobile dust grains. In the linear case, the modified dispersion relation is given and, in the nonlinear case, stationary solutions of the nonlinear equations that govern the dynamics of coupled SV and convective cell modes are obtained. It is found that electrostatic dipolar and vortex street type solutions can appear in such a plasma. The relevance of the present investigation with regard to the Earth's mesosphere as well as in ionospheric plasmas is also pointed out.

  3. Influence of the Ringwoodite-Perovskite transition on mantle convection in spherical geometry as a function of Clapeyron slope and Rayleigh number

    Directory of Open Access Journals (Sweden)

    M. Wolstencroft

    2011-12-01

    Full Text Available We investigate the influence on mantle convection of the negative Clapeyron slope ringwoodite to perovskite and ferro-periclase mantle phase transition, which is correlated with the seismic discontinuity at 660 km depth. In particular, we focus on understanding the influence of the magnitude of the Clapeyron slope (as measured by the Phase Buoyancy parameter, P and the vigour of convection (as measured by the Rayleigh number, Ra on mantle convection. We have undertaken 76 simulations of isoviscous mantle convection in spherical geometry, varying Ra and P. Three domains of behaviour were found: layered convection for high Ra and more negative P, whole mantle convection for low Ra and less negative P, and transitional behaviour in an intervening domain. The boundary between the layered and transitional domain was fit by a curve P = α Raβ where α = −1.05, and β = −0.1, and the fit for the boundary between the transitional and whole mantle convection domain was α = −4.8, and β = −0.25. These two curves converge at Ra ≈ 2.5 × 104 (well below Earth mantle vigour and P ≈ −0.38. Extrapolating to high Ra, which is likely earlier in Earth history, this work suggests a large transitional domain. It is therefore likely that convection in the Archean would have been influenced by this phase change, with Earth being at least in the transitional domain, if not the layered domain.

  4. Comparison of the Mercury and earth magnetospheres - electron measurements and substorm time scales

    International Nuclear Information System (INIS)

    Christon, S.P.

    1987-01-01

    The present search for similarities between earth and Mercury plasma electron distribution and large-scale dynamics notes that both spectral shapes are similar to a kappa-distribution. A model distribution of this type which incorporates convective flow is used to simulate the observed plasma electron spectral variations near the Mariner 10-Mercury 1 A event; convection appears to be stronger before, rather than during, the A event, in contradiction to the Baker (1986) convective injection model for Mercury's two relativistic electron flux enhancements. Mercury's postmidnight energetic electron B and B-prime events seem to be multiple onsets in the course of a substorm. 65 references

  5. Venus and the Archean Earth: Thermal considerations

    International Nuclear Information System (INIS)

    Sleep, N.H.

    1989-01-01

    The Archean Era of the Earth is not a direct analog of the present tectonics of Venus. In this regard, it is useful to review the state of the Archean Earth. Most significantly, the temperature of the adiabatic interior of the Earth was 200 to 300 C hotter than the current temperature. Preservation biases limit what can be learned from the Archean record. Archean oceanic crust, most of the planetary surface at any one time, has been nearly all subducted. More speculatively, the core of the Earth has probably cooled more slowly than the mantle. Thus the temperature contrast above the core-mantle boundary and the vigor of mantle plumes has increased with time on the Earth. The most obvious difference between Venus and the present Earth is the high surface temperature and hence a low effective viscosity of the lithosphere. In addition, the temperature contrast between the adiabatic interior and the surface, which drives convection, is less on Venus than on the Earth. It appears that the hot lithosphere enhanced tectonics on the early Venus significantly enough that its interior cooled faster than the Earth's. The best evidence for a cool interior of Venus comes from long wavelength gravity anomalies. The low interior temperatures retard seafloor spreading on Venus. The high surface temperatures on Venus enhance crustal deformation. That is, the lower crust may become ductile enough to permit significant flow between the upper crust and the mantle. There is thus some analogy to modern and ancient areas of high heat flow on the Earth. Archean crustal blocks typically remained stable for long intervals and thus overall are not good analogies to the deformation style on Venus

  6. How singleton breech babies at term are born in France: a survey of data from the AUDIPOG network.

    Science.gov (United States)

    Lansac, J; Crenn-Hebert, C; Rivière, O; Vendittelli, F

    2015-05-01

    Based on data from the AUDIPOG sentinel network between 1994 and 2010, we can say that the rate of singleton breech presentation at term is 3% and remains unchanged despite an external cephalic version rate of 35%. The total cesarean section rate is currently 75%. This rate increased by nearly 20% after the Hannah publication in 2000, regardless of the type of breech and type of maternity unit. The rate of planned cesarean sections increased in particular, going from 40% to 60%, and even reaching 67% for footling breech presentations. The rate is higher in type I maternity units than in type II or III. This cesarean section rate has been stable since 2005 and has even decreased for the Frank breech. The average rate of external cephalic version remains stable at around 23%. The episiotomy rate is 28%. The rate of babies transferred to neonatology units is higher for breech babies at term than for babies presenting cephalically (3.9% compared to 2.9%), but the newborns most often transferred are those born by cesarean section (4.1% compared to 3.4%). Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  7. Costs and effects of screening and treating low risk women with a singleton pregnancy for asymptomatic bacteriuria, the ASB study.

    Science.gov (United States)

    Kazemier, Brenda M; Schneeberger, Caroline; De Miranda, Esteriek; Van Wassenaer, Aleid; Bossuyt, Patrick M; Vogelvang, Tatjana E; Reijnders, Frans J L; Delemarre, Friso M C; Verhoeven, Corine J M; Oudijk, Martijn A; Van Der Ven, Jeanine A; Kuiper, Petra N; Feiertag, Nicolette; Ott, Alewijn; De Groot, Christianne J M; Mol, Ben Willem J; Geerlings, Suzanne E

    2012-06-21

    The prevalence of asymptomatic bacteriuria (ASB) in pregnancy is 2-10% and is associated with both maternal and neonatal adverse outcomes as pyelonephritis and preterm delivery. Antibiotic treatment is reported to decrease these adverse outcomes although the existing evidence is of poor quality. We plan a combined screen and treat study in women with a singleton pregnancy. We will screen women between 16 and 22 weeks of gestation for ASB using the urine dipslide technique. The dipslide is considered positive when colony concentration ≥105 colony forming units (CFU)/mL of a single microorganism or two different colonies but one ≥105 CFU/mL is found, or when Group B Streptococcus bacteriuria is found in any colony concentration. Women with a positive dipslide will be randomly allocated to receive nitrofurantoin or placebo 100 mg twice a day for 5 consecutive days (double blind). Primary outcomes of this trial are maternal pyelonephritis and/or preterm delivery before 34 weeks. Secondary outcomes are neonatal and maternal morbidity, neonatal weight, time to delivery, preterm delivery rate before 32 and 37 weeks, days of admission in neonatal intensive care unit, maternal admission days and costs. This trial will provide evidence for the benefit and cost-effectiveness of dipslide screening for ASB among low risk women at 16-22 weeks of pregnancy and subsequent nitrofurantoin treatment. Dutch trial registry: NTR-3068.

  8. Costs and effects of screening and treating low risk women with a singleton pregnancy for asymptomatic bacteriuria, the ASB study

    Directory of Open Access Journals (Sweden)

    Kazemier Brenda M

    2012-06-01

    Full Text Available Abstract Background The prevalence of asymptomatic bacteriuria (ASB in pregnancy is 2-10% and is associated with both maternal and neonatal adverse outcomes as pyelonephritis and preterm delivery. Antibiotic treatment is reported to decrease these adverse outcomes although the existing evidence is of poor quality. Methods/Design We plan a combined screen and treat study in women with a singleton pregnancy. We will screen women between 16 and 22 weeks of gestation for ASB using the urine dipslide technique. The dipslide is considered positive when colony concentration ≥105 colony forming units (CFU/mL of a single microorganism or two different colonies but one ≥105 CFU/mL is found, or when Group B Streptococcus bacteriuria is found in any colony concentration. Women with a positive dipslide will be randomly allocated to receive nitrofurantoin or placebo 100 mg twice a day for 5 consecutive days (double blind. Primary outcomes of this trial are maternal pyelonephritis and/or preterm delivery before 34 weeks. Secondary outcomes are neonatal and maternal morbidity, neonatal weight, time to delivery, preterm delivery rate before 32 and 37 weeks, days of admission in neonatal intensive care unit, maternal admission days and costs. Discussion This trial will provide evidence for the benefit and cost-effectiveness of dipslide screening for ASB among low risk women at 16–22 weeks of pregnancy and subsequent nitrofurantoin treatment. Trial registration Dutch trial registry: NTR-3068

  9. Amnioinfusion for women with a singleton breech presentation and a previous failed external cephalic version: a randomized controlled trial.

    Science.gov (United States)

    Diguisto, Caroline; Winer, Norbert; Descriaud, Celine; Tavernier, Elsa; Weymuller, Victoire; Giraudeau, Bruno; Perrotin, Franck

    2018-04-01

    Our trial aimed to assess the effectiveness of amnioinfusion for a second attempt at external cephalic version (ECV). This open randomized controlled trial was planned with a sequential design. Women at a term ≥36 weeks of gestation with a singleton fetus in breech presentation and a first unsuccessful ECV were recruited in two level-3 maternity units. They were randomly allocated to transabdominal amnioinfusion with a 500-mL saline solution under ultrasound surveillance or no amnioinfusion before the second ECV attempt. Trained senior obstetricians performed all procedures. The primary outcome was the cephalic presentation rate at delivery. Analyses were conducted according to intention to treat (NCT00465712). Recruitment difficulties led to stopping the trial after a 57-month period, 119 women were randomized: 59 allocated to amnioinfusion + ECV and 60 to ECV only. Data were analyzed without applying the sequential feature of the design. The rate of cephalic presentation at delivery did not differ significantly according to whether the second version attempt was or was not preceded by amnioinfusion (20 versus 12%, p = .20). Premature rupture of the membranes occurred for 15% of the women in the amnioinfusion group. Amnioinfusion before a second attempt to external version does not significantly increase the rate of cephalic presentation at delivery.

  10. Delivery of double singleton pregnancies in a woman with a double uterus, double cervix, and complete septate vagina

    Directory of Open Access Journals (Sweden)

    Ming-Jie Yang

    2015-12-01

    Full Text Available Uterine anomalies involving a double uterus, double cervix, also known as didelphys uterus, and complete septate vagina are rarely seen and have an associated fertility problem. However, artificial reproductive technology with embryo transfers can help solve this fertility challenge. Conception in the uterus in just one side is commonly seen for embryos, which are always transferred through the usually used (dilated vagina. We here present a patient with the above uterine anomaly who conceived with the aid of in vitro fertilization and embryo transfer to both uterine cavities under general anesthesia, which resulted in successful double singleton pregnancies with one fetus in each uterus. With intensive prenatal care, the pregnancy course for each fetus was rather uneventful. Although both fetuses were in cephalic presentation, cesarean section was performed at the 39th week of gestation with good outcomes in order to preclude anticipated difficulties if the baby had been delivered through the rarely dilated vagina. However, order of birth between the two fetuses was a crucial decision during the operation.

  11. Spontaneously generated field theories, zero-center modules, colored singletons and the virtues of N = 6 supergravity

    International Nuclear Information System (INIS)

    Flato, M.; Fronsdal, C.

    1986-01-01

    Attention is called to an interesting property of the space of one-particle states in some especially important massless field theories: the appearance of a one-particle ghost with zero energy. It appears in conformal as well as de Sitter electrodynamics, in the physical sectors of the field mode representations of the respective symmetry groups. It appears again in super de Sitter electrodynamics based on the superalgebra osp(4/1) and in super conformal electrodynamics based on su(2,2/1). The authors next construct two families of extended super QED, incorporating this property, based on osp(4/N) and on su(2,2/N). There is precisely one osp(4/N) theory and one su(2,2/N) theory of this type for each value of N. The osp(4/6) theory is the same as N = 6 extended supergravity, this is the only one among this family of osp(4/N) theories in which the highest spin is 2. All the one particle states are massless, and in the osp(4/N) theories they can be interpreted as states of two colored singletons. The authors also critically examine the concept of the Witten index in flat space as well as in de Sitter supersymmetric field theories. (Auth.)

  12. References of birth weights for gestational age and sex from a large cohort of singleton births in cameroon.

    Science.gov (United States)

    Kemfang Ngowa, Jean Dupont; Domkam, Irénée; Ngassam, Anny; Nguefack-Tsague, Georges; Dobgima Pisoh, Walter; Noa, Cyrille; Kasia, Jean Marie

    2014-01-01

    Objective. To establish the percentile charts of birth weights for gestational age and sex within the Cameroonian population. Methods. A review of medical records of infants born between January 2007 and December 2011 at the maternities of two hospitals in Cameroon, Central Africa. Multiple pregnancies, births of HIV infected women, stillbirths, and births with major fetal malformations were excluded. The smooth curves of birth weight for gestational age and sex were created using the Gamlss package under R.3.0.1 software. Results. The birth weights of 12837 live birth singleton infants born to HIV negative women between 28 and 42 weeks of gestation were analyzed to construct the birth weight curves for gestational age and sex. The smoothed percentile curves of birth weights for gestational age and sex of Cameroonian infants have demonstrated an increasing slope until 40 weeks and then a plateau. There was a varied difference of distribution in birth weights for gestational age between Cameroonian, Botswanan, American, and French infants. Conclusion. We established the reference curves of birth weights for gestational age and sex for Cameroonians. The difference in birth weight curves noted between Cameroonian, Botswanan, American, and French infants suggests the importance of establishing the regional birth weight norms.

  13. References of Birth Weights for Gestational Age and Sex from a Large Cohort of Singleton Births in Cameroon

    Directory of Open Access Journals (Sweden)

    Jean Dupont Kemfang Ngowa

    2014-01-01

    Full Text Available Objective. To establish the percentile charts of birth weights for gestational age and sex within the Cameroonian population. Methods. A review of medical records of infants born between January 2007 and December 2011 at the maternities of two hospitals in Cameroon, Central Africa. Multiple pregnancies, births of HIV infected women, stillbirths, and births with major fetal malformations were excluded. The smooth curves of birth weight for gestational age and sex were created using the Gamlss package under R.3.0.1 software. Results. The birth weights of 12837 live birth singleton infants born to HIV negative women between 28 and 42 weeks of gestation were analyzed to construct the birth weight curves for gestational age and sex. The smoothed percentile curves of birth weights for gestational age and sex of Cameroonian infants have demonstrated an increasing slope until 40 weeks and then a plateau. There was a varied difference of distribution in birth weights for gestational age between Cameroonian, Botswanan, American, and French infants. Conclusion. We established the reference curves of birth weights for gestational age and sex for Cameroonians. The difference in birth weight curves noted between Cameroonian, Botswanan, American, and French infants suggests the importance of establishing the regional birth weight norms.

  14. Limitations of the equivalence between spatial and ensemble estimators in the case of a single-tone excitation.

    Science.gov (United States)

    Monsef, Florian; Cozza, Andrea

    2011-10-01

    The ensemble-average value of the mean-square pressure is often assessed by using the spatial-average technique, underlying an equivalence principle between spatial and ensemble estimators. Using the ideal-diffuse-field model, the accuracy of the spatial-average method has been studied theoretically forty years ago in the case of a single-tone excitation. This study is revisited in the present work on the basis of a more realistic description of the sound field accounting for a finite number of plane waves. The analysis of the spatial-average estimator is based on the study of its convergence rate. Using experimental data from practical examples, it is shown that the classical expression underestimates the estimator uncertainty even for frequencies greater than Schroeder's frequency, and that the number of plane waves may act as lower bound on the spatial-average estimator accuracy. The comparison of the convergence rate with an ensemble-estimator shows that the two statistics cannot be regarded as equivalent in a general case. © 2011 Acoustical Society of America

  15. A systematic review and meta-analysis of velamentous cord insertion among singleton pregnancies and the risk of preterm delivery.

    Science.gov (United States)

    de Los Reyes, Samantha; Henderson, Janice; Eke, Ahizechukwu C

    2018-03-23

    Observational studies have reported varying results about the association of velamentous cord insertion (VCI) with adverse pregnancy outcomes. To evaluate the risk of preterm delivery among singleton pregnancies complicated by VCI. Various databases were searched for English-language articles published up to February, 28, 2017, using keywords including VCI; abnormal placentation; abnormal cord insertions; adverse perinatal outcomes; and preterm birth. Outcome measures included preterm delivery; pre-eclampsia; cesarean delivery; fetal demise in utero (FDIU); and small for gestational age (SGA). Only studies involving VCI were included in the meta-analysis. Analyses were performed using RevMan version 5.3.5 (The Nordic Cochrane Centre, Copenhagen, Denmark). There were six studies included in the analysis. The VCI and control groups comprised 16 295 and 1 366 485 women, respectively. An increased incidence of preterm delivery was found for the VCI group compared with the control group (11.8% vs 7.0%; adjusted odds ratio [aOR] 1.95, 95% confidence interval [CI] 1.85-2.04). A diagnosis of VCI was also associated with cesarean delivery (aOR 1.17, 95% CI 1.12-1.23), SGA (aOR 1.93, 95% CI 1.83-2.04), and FDIU (aOR 3.96, 95% CI 3.21-4.89). The presence of VCI was associated with adverse pregnancy outcomes. © 2018 International Federation of Gynecology and Obstetrics.

  16. Economic Conditions During Pregnancy and Adverse Birth Outcomes Among Singleton Live Births in the United States, 1990-2013.

    Science.gov (United States)

    Margerison-Zilko, Claire E; Li, Yu; Luo, Zhehui

    2017-11-15

    We know little about the relationship between the macroeconomy and birth outcomes, in part due to the methodological challenge of distinguishing effects of economic conditions on fetal health from effects of economic conditions on selection into live birth. We examined associations between state-level unemployment rates in the first 2 trimesters of pregnancy and adverse birth outcomes, using natality data on singleton live births in the United States during 1990-2013. We used fixed-effect logistic regression models and accounted for selection by adjusting for state-level unemployment before conception and maternal characteristics associated with both selection and birth outcomes. We also tested whether associations between macroeconomic conditions and birth outcomes differed during and after (compared with before) the Great Recession (2007-2009). Each 1-percentage-point increase in the first-trimester unemployment rate was associated with a 5% increase in odds of preterm birth, while second-trimester unemployment was associated with a 3% decrease in preterm birth odds. During the Great Recession, however, first-trimester unemployment was associated with a 16% increase in odds of preterm birth. These findings increase our understanding of the effects of the Great Recession on health and add to growing literature suggesting that macro-level social and economic factors contribute to perinatal health. © The Author(s) 2017. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  17. Singleton Pregnancy Outcomes after In Vitro Fertilization with Fresh or Frozen-Thawed Embryo Transfer and Incidence of Placenta Praevia

    Directory of Open Access Journals (Sweden)

    Sara Korosec

    2014-01-01

    Full Text Available The aim of the study was to compare the single pregnancy and neonate outcome after fresh and frozen-thawed embryo transfer in the in vitro fertilization programme (IVF. The study focused on clinical and laboratory factors affecting the abnormal placentation, especially placenta praevia, in patients conceiving in the IVF programme. The results confirm that neonates born after frozen-thawed embryo transfer had significantly higher mean birth weight than after fresh embryo transfer (ET. Moreover, the birth weight distribution in singletons was found to shift towards “large for gestation” (LGA after frozen-thawed ET. On the other hand, the pregnancies after fresh ET were characterized by a higher incidence of placenta praevia and 3rd trimester bleeding. Placenta praevia was more common in IVF patients with fresh ET in a stimulated cycle than in patients with ET in a spontaneous cycle. It occurred more frequently in patients with transfer of 2 embryos. From this point of view, single ET and ET in a spontaneous cycle should be encouraged in good prognosis patients in the future with more than two good quality embryos developed. An important issue arose of how the ovarian hormonal stimulation relates to abnormal placentation and if the serum hormone levels interfere with in the IVF treatment results.

  18. Convective transport resistance in the vitreous humor

    Science.gov (United States)

    Penkova, Anita; Sadhal, Satwindar; Ratanakijsuntorn, Komsan; Moats, Rex; Tang, Yang; Hughes, Patrick; Robinson, Michael; Lee, Susan

    2012-11-01

    It has been established by MRI visualization experiments that the convection of nanoparticles and large molecules with high rate of water flow in the vitreous humor will experience resistance, depending on the respective permeabilities of the injected solute. A set of experiments conducted with Gd-DTPA (Magnevist, Bayer AG, Leverkusen, Germany) and 30 nm gadolinium-based particles (Gado CELLTrackTM, Biopal, Worcester, MA) as MRI contrast agents showed that the degree of convective transport in this Darcy-type porous medium varies between the two solutes. These experiments consisted of injecting a mixture of the two (a 30 μl solution of 2% Magnevist and 1% nanoparticles) at the middle of the vitreous of an ex vivo whole bovine eye and subjecting the vitreous to water flow rate of 100 μl/min. The water (0.9% saline solution) was injected at the top of the eye, and was allowed to drain through small slits cut at the bottom of the eyeball. After 50 minutes of pumping, MRI images showed that the water flow carried the Gd-DTPA farther than the nanoparticles, even though the two solutes, being mixed, were subjected to the same convective flow conditions. We find that the convected solute lags the water flow, depending on the solute permeability. The usual convection term needs to be adjusted to allow for the filtration effect on the larger particles in the form (1- σ) u . ∇ c with important implications for the modeling of such systems.

  19. Classification of Clouds and Deep Convection from GEOS-5 Using Satellite Observations

    Science.gov (United States)

    Putman, William; Suarez, Max

    2010-01-01

    With the increased resolution of global atmospheric models and the push toward global cloud resolving models, the resemblance of model output to satellite observations has become strikingly similar. As we progress with our adaptation of the Goddard Earth Observing System Model, Version 5 (GEOS-5) as a high resolution cloud system resolving model, evaluation of cloud properties and deep convection require in-depth analysis beyond a visual comparison. Outgoing long-wave radiation (OLR) provides a sufficient comparison with infrared (IR) satellite imagery to isolate areas of deep convection. We have adopted a binning technique to generate a series of histograms for OLR which classify the presence and fraction of clear sky versus deep convection in the tropics that can be compared with a similar analyses of IR imagery from composite Geostationary Operational Environmental Satellite (GOES) observations. We will present initial results that have been used to evaluate the amount of deep convective parameterization required within the model as we move toward cloud system resolving resolutions of 10- to 1-km globally.

  20. Simple model for polar cap convection patterns and generation of theta auroras

    International Nuclear Information System (INIS)

    Lyons, L.R.

    1985-01-01

    The simple addition of a uniform interplanetary magnetic field and the Earth's dipole magnetic field is used to evaluate electric field convection patterns over the polar caps that result from solar wind flow across open geomagnetic field lines. This model is found to account for observed polar-cap convection patterns as a function of the interplanetary magnetic field components B/sub y/ and B/sub z/. In particular, the model offers an explanation for sunward and antisunward convection over the polar caps for B/sub z/>0. Observed field-aligned current patterns within the polar cap and observed auroral arcs across the polar cap are also explained by the model. In addition, the model gives several predictions concerning the polar cap that should be testable. Effects of solar wind pressure and magnetospheric currents on magnetospheric electric and magnetic fields are neglected. That observed polar cap features are reproduced suggests that the neglected effects do not modify the large-scale topology of magnetospheric electric and magnetic fields along open polar cap field lines. Of course, the neglected effects significantly modify the magnetic geometry, so that the results of this paper are not quantitatively realistic and many details may be incorrect. Nevertheless, the model provides a simple explanation for many qualitative features of polar cap convection

  1. Background Noises Versus Intraseasonal Variation Signals: Small vs. Large Convective Cloud Objects From CERES Aqua Observations

    Science.gov (United States)

    Xu, Kuan-Man

    2015-01-01

    During inactive phases of Madden-Julian Oscillation (MJO), there are plenty of deep but small convective systems and far fewer deep and large ones. During active phases of MJO, a manifestation of an increase in the occurrence of large and deep cloud clusters results from an amplification of large-scale motions by stronger convective heating. This study is designed to quantitatively examine the roles of small and large cloud clusters during the MJO life cycle. We analyze the cloud object data from Aqua CERES (Clouds and the Earth's Radiant Energy System) observations between July 2006 and June 2010 for tropical deep convective (DC) and cirrostratus (CS) cloud object types according to the real-time multivariate MJO index, which assigns the tropics to one of the eight MJO phases each day. The cloud object is a contiguous region of the earth with a single dominant cloud-system type. The criteria for defining these cloud types are overcast footprints and cloud top pressures less than 400 hPa, but DC has higher cloud optical depths (=10) than those of CS (background noises resulting from various types of the tropical waves with different wavenumbers and propagation speeds/directions.

  2. Where does subduction initiate and die? Insights from global convection models with continental drift

    Science.gov (United States)

    Ulvrova, Martina; Williams, Simon; Coltice, Nicolas; Tackley, Paul

    2017-04-01

    Plate tectonics is a prominent feature on Earth. Together with the underlying convecting mantle, plates form a self-organized system. In order to understand the dynamics of the coupled system, subduction of the lithospheric plates plays the key role since it links the exterior with the interior of the planet. In this work we study subduction initiation and death with respect to the position of the continental rafts. Using thermo-mechanical numerical calculations we investigate global convection models featuring self-consistent plate tectonics and continental drifting employing a pseudo-plastic rheology and testing the effect of a free surface. We consider uncompressible mantle convection in Boussinesq approximation that is basaly and internaly heated. Our calculations indicate that the presence of the continents alterns stress distribution within a certain distance from the margins. Intra-oceanic subudction initiation is favorable during super-continent cycles while the initiation at passive continental margin prevails when continents are dispersed. The location of subduction initiation is additionally controlled by the lithospheric strength. Very weak lithosphere results in domination of intra-oceanic subduction initiation. The subduction zones die more easily in the vicinity of the continent due to the strong rheological contrast between the oceanic and continental lithosphere. In order to compare our findings with subduction positions through time recorded on Earth, we analyse subduction birth in global plate reconstruction back to 410 My.

  3. Convection and magnetic field generation in the interior of planets (August Love Medal Lecture)

    Science.gov (United States)

    Christensen, U. R.

    2009-04-01

    Thermal convection driven by internal energy plays a role of paramount importance in planetary bodies. Its numerical modeling has been an essential tool for understanding how the internal engine of a planet works. Solid state convection in the silicate or icy mantles is the cause of endogenic tectonic activity, volcanism and, in the case of Earth, of plate motion. It also regulates the energy budget of the entire planet, including that of its core, and controls the presence or absence of a dynamo. The complex rheology of solid minerals, effects of phase transitions, and chemical heterogeneity are important issues in mantle convection. Examples discussed here are the convection pattern in Mars and the complex morphology of subducted slabs that are observed by seismic tomography in the Earth's mantle. Internally driven convection in the deep gas envelopes of the giant planets is possibly the cause for the strong jet streams at the surfaces that give rise to their banded appearance. Modeling of the magnetohydrodynamic flow in the conducting liquid core of the Earth has been remarkably successful in reproducing the primary properties of the geomagnetic field. As an examplefor attempts to explain also secondary properties, I will discuss dynamo models that account for the thermal coupling to the mantle. The understanding of the somewhat enigmatic magnetic fields of some other planets is less advanced. Here I will show that dynamos that operate below a stable conducting layer in the upper part of the planetary core can explain the unusual magnetic field properties of Mercury and Saturn. The question what determines the strength of a dynamo-generated magnetic field has been a matter of debate. From a large set of numerical dynamo simulations that cover a fair range of control parameters, we find a rule that relates magnetic field strength to the part of the energy flux that is thermodynamically available to be transformed into other forms of energy. This rules predicts

  4. Convective mixing in helium white dwarfs

    International Nuclear Information System (INIS)

    Vauclair, G.; Fontaine, G.

    1979-01-01

    The conditions under which convective mixing episodes take place between the helium envelopes and the underlying carbon layers in helium-rich white dwarfs are investigated. It is found that, for essentially any value of the initial helium content less than the maximum mass a helium convection zone can have, mixing does occur, and leads, in the vast majority of cases, to an almost pure carbon superficial composition. Mixing products that show only traces of carbon while retaining helium-dominated envelopes are possible only if the initial helium content is quite close to the maximum possible mass of the helium convection zone. In the presence of turbulence, this restriction could be relaxed, however, and the helium-rich lambda4670 stars may possibly be explained in this fashion

  5. Plate Like Convection with Viscous Strain Weakening and Corresponding Surface Deformation Pattern

    Science.gov (United States)

    Fuchs, L.; Becker, T. W.

    2017-12-01

    How plate tectonic surface motions are generated by mantle convection on Earth and possibly other terrestrial type planets has recently become more readily accessible with fully dynamic convection computations. However, it remains debated how plate-like the behavior in such models truly is, and in particular how the well plate boundary dynamics are captured in models which typically exclude the effects of deformation history and memory. Here, we analyze some of the effects of viscous strain weakening on plate behavior and the interactions between interior convection dynamics and surface deformation patterns. We use the finite element code CitcomCU to model convection in a 3D Cartesian model setup. The models are internally heated, with an Arrhenius-type temperature dependent viscosity including plastic yielding and viscous strain weakening (VSW) and healing (VSWH). VSW can mimic first order features of more complex damage mechanisms such as grain-size dependent rheology. Besides plate diagnostic parameters (Plateness, Mobility, and Toroidal: Poloidal ratio) to analyze the tectonic behavior our models, we also explore how "plate boundaries" link to convective patterns. In a first model series, we analyze general surface deformation patterns without VSW. In the early stages, deformation patterns are clearly co-located with up- and downwelling limbs of convection. Along downwellings strain-rates are high and localized, whereas upwellings tend to lead to broad zones of high deformation. At a more advanced stage, however, the plates' interior is highly deformed due to continuous strain accumulation and resurfaced inherited strain. Including only VSW leads to more localized deformation along downwellings. However, at a more advanced stage plate-like convection fails due an overall weakening of the material. This is prevented including strain healing. Deformation pattern at the surface more closely coincide with the internal convection patterns. The average surface

  6. Solutal convection induced by dissolution. Influence on erosion dynamics and interface shaping.

    Science.gov (United States)

    Berhanu, Michael; Philippi, Julien; Cohen, Caroline; Derr, Julien; Courrech du Pont, Sylvain

    2017-04-01

    dissolution patterns can be related to the characteristic of the convective flow. C. Oltéan, F. Golfier and M.A. Buès, Numerical and experimental investigation of buoyancy-driven dissolution in vertical fracture, J. Geophys. Res. Solid Earth, 118(5), 2038-2048 (2013) C. Cohen, M. Berhanu, J. Derr and S. Courrech du Pont, Erosion patterns on dissolving and melting bodies (2015 Gallery of Fluid motion), Phys. Rev. Fluids, 1, 050508 (2016) T. S. Sullivan, Y. Liu, and R. E. Ecke, Turbulent solutal convection and surface patterning in solid dissolution, Phys. Rev. E 54, 486 (1996)

  7. Biodigester Feasibility and Design for Space & Earth

    Science.gov (United States)

    Shutts, Stacy; Ewert, Mike; Bacon, Jack

    2016-01-01

    Anaerobic digestion converts organic waste into methane gas and fertilizer effluent. The ICA-developed prototype system is designed for planetary surface operation. It uses passive hydrostatic control for reliability, and is modular and redundant. The serpentine configuration accommodates tight geometric constraints similar to the ISS ECLSS rack architectures. Its shallow, low-tilt design enables (variable) lower-g convection than standard Earth (1 g) digesters. This technology will reuse and recycle materials including human waste, excess food, as well as packaging (if biodegradable bags are used).

  8. Annual review of earth and planetary sciences. Volume 16

    International Nuclear Information System (INIS)

    Wetherill, G.W.; Albee, A.L.; Stehli, F.G.

    1988-01-01

    Various papers on earth and planetary science topics are presented. The subjects addressed include: role and status of earth science field work; phase relations of prealuminous granitic rocks and their petrogenetic implications; chondritic meteorites and the solar nebula; volcanic winters; mass wasting on continental margins; earthquake ground motions; ore deposits as guides to geologic history of the earth; geology of high-level nuclear waste disposal; and tectonic evolution of the Caribbean. Also discussed are: the earth's rotation; the geophysics of a restless caldera (Long Valley, California); observations of cometary nuclei; geology of Venus; seismic stratigraphy; in situ-produced cosmogenic isotopes in terrestrial rocks; time variations of the earth's magnetic field; deep slabs, geochemical heterogeneity, and the large-scale structure of mantle convection; early proterozoic assembly and growth of Laurentia; concepts and methods of high-resolution event stratigraphy

  9. Natural Convective Heat Transfer from Narrow Plates

    CERN Document Server

    Oosthuizen, Patrick H

    2013-01-01

    Natural Convective Heat Transfer from Narrow Plates deals with a heat transfer situation that is of significant practical importance but which is not adequately dealt with in any existing textbooks or in any widely available review papers. The aim of the book is to introduce the reader to recent studies of natural convection from narrow plates including the effects of plate edge conditions, plate inclination, thermal conditions at the plate surface and interaction of the flows over adjacent plates. Both numerical and experimental studies are discussed and correlation equations based on the results of these studies are reviewed.

  10. Introductory analysis of Benard-Marangoni convection

    International Nuclear Information System (INIS)

    Maroto, J A; Perez-Munuzuri, V; Romero-Cano, M S

    2007-01-01

    We describe experiments on Benard-Marangoni convection which permit a useful understanding of the main concepts involved in this phenomenon such as, for example, Benard cells, aspect ratio, Rayleigh and Marangoni numbers, Crispation number and critical conditions. In spite of the complexity of convection theory, we carry out a simple and introductory analysis which has the additional advantage of providing very suggestive experiments. As a consequence, we recommend our device for use as a laboratory experiment for undergraduate students of the thermodynamics of nonlinear and fluid physics

  11. Introductory analysis of Benard-Marangoni convection

    Energy Technology Data Exchange (ETDEWEB)

    Maroto, J A [Group of Physics and Chemistry of Linares, Escuela Politecnica Superior, St Alfonso X El Sabio, 28, University of Jaen, E-23700 Linares, Jaen (Spain); Perez-Munuzuri, V [Group of Nonlinear Physics, University of Santiago de Compostela, E-15782 Santiago de Compostela (Spain); Romero-Cano, M S [Group of Complex Fluids Physics, Department of Applied Physics, University of Almeria, E-04120 Almeria (Spain)

    2007-03-15

    We describe experiments on Benard-Marangoni convection which permit a useful understanding of the main concepts involved in this phenomenon such as, for example, Benard cells, aspect ratio, Rayleigh and Marangoni numbers, Crispation number and critical conditions. In spite of the complexity of convection theory, we carry out a simple and introductory analysis which has the additional advantage of providing very suggestive experiments. As a consequence, we recommend our device for use as a laboratory experiment for undergraduate students of the thermodynamics of nonlinear and fluid physics.

  12. Topology Optimisation for Coupled Convection Problems

    DEFF Research Database (Denmark)

    Alexandersen, Joe; Andreasen, Casper Schousboe; Aage, Niels

    stabilised finite elements implemented in a parallel multiphysics analysis and optimisation framework DFEM [1], developed and maintained in house. Focus is put on control of the temperature field within the solid structure and the problems can therefore be seen as conjugate heat transfer problems, where heat...... conduction governs in the solid parts of the design domain and couples to convection-dominated heat transfer to a surrounding fluid. Both loosely coupled and tightly coupled problems are considered. The loosely coupled problems are convection-diffusion problems, based on an advective velocity field from...

  13. Lattice BGK simulation of natural convection

    International Nuclear Information System (INIS)

    Chen, Yu; Ohashi, Hirotada; Akiyama, Mamoru

    1995-01-01

    Recently a new thermal lattice Bhatnagar-Gross-Krook fluid model was suggested by the authors. In this study, this new model was applied into the numerical simulation of natural convection, namely the Rayleigh Benard flow. The critical number for the onset of convective phenomenon was numerically measured and compared with that of theoretical prediction. A gravity dependent deviation was found in the numerical simulation, which is explained as an unavoidable consequence of the incorporation of gravity force in the lattice BGK system. (author)

  14. Comparing convective heat fluxes derived from thermodynamics to a radiative-convective model and GCMs

    Science.gov (United States)

    Dhara, Chirag; Renner, Maik; Kleidon, Axel

    2015-04-01

    The convective transport of heat and moisture plays a key role in the climate system, but the transport is typically parameterized in models. Here, we aim at the simplest possible physical representation and treat convective heat fluxes as the result of a heat engine. We combine the well-known Carnot limit of this heat engine with the energy balances of the surface-atmosphere system that describe how the temperature difference is affected by convective heat transport, yielding a maximum power limit of convection. This results in a simple analytic expression for convective strength that depends primarily on surface solar absorption. We compare this expression with an idealized grey atmosphere radiative-convective (RC) model as well as Global Circulation Model (GCM) simulations at the grid scale. We find that our simple expression as well as the RC model can explain much of the geographic variation of the GCM output, resulting in strong linear correlations among the three approaches. The RC model, however, shows a lower bias than our simple expression. We identify the use of the prescribed convective adjustment in RC-like models as the reason for the lower bias. The strength of our model lies in its ability to capture the geographic variation of convective strength with a parameter-free expression. On the other hand, the comparison with the RC model indicates a method for improving the formulation of radiative transfer in our simple approach. We also find that the latent heat fluxes compare very well among the approaches, as well as their sensitivity to surface warming. What our comparison suggests is that the strength of convection and their sensitivity in the climatic mean can be estimated relatively robustly by rather simple approaches.

  15. Effects of convective ice evaporation on interannual variability of tropical tropopause layer water vapor

    Science.gov (United States)

    Ye, Hao; Dessler, Andrew E.; Yu, Wandi

    2018-04-01

    Water vapor interannual variability in the tropical tropopause layer (TTL) is investigated using satellite observations and model simulations. We break down the influences of the Brewer-Dobson circulation (BDC), the quasi-biennial oscillation (QBO), and the tropospheric temperature (ΔT) on TTL water vapor as a function of latitude and longitude using a two-dimensional multivariate linear regression. This allows us to examine the spatial distribution of the impact of each process on TTL water vapor. In agreement with expectations, we find that the impacts from the BDC and QBO act on TTL water vapor by changing TTL temperature. For ΔT, we find that TTL temperatures alone cannot explain the influence. We hypothesize a moistening role for the evaporation of convective ice from increased deep convection as the troposphere warms. Tests using a chemistry-climate model, the Goddard Earth Observing System Chemistry Climate Model (GEOSCCM), support this hypothesis.

  16. Inferring convective responses to El Niño with atmospheric electricity measurements at Shetland

    International Nuclear Information System (INIS)

    Harrison, R G; Pascoe, K; Joshi, M

    2011-01-01

    Pacific ocean temperature anomalies associated with the El Niño–Southern Oscillation (ENSO) modulate atmospheric convection and hence thunderstorm electrification. The generated current flows globally via the atmospheric electric circuit, which can be monitored anywhere on Earth. Atmospheric electricity measurements made at Shetland (in Scotland) display a mean global circuit response to ENSO that is characterized by strengthening during ‘El Niño’ conditions, and weakening during ‘La Niña’ conditions. Examining the hourly varying response indicates that a potential gradient (PG) increase around noon UT is likely to be associated with a change in atmospheric convection and resultant lightning activity over equatorial Africa and Eastern Asia. A secondary increase in PG just after midnight UT can be attributed to more shower clouds in the central Pacific ocean during an ‘El Niño’.

  17. How Many Convective Zones Are There in the Atmosphere of Venus?

    Science.gov (United States)

    Moroz, V. I.; Rodin, A. V.

    2002-11-01

    The qualitative characteristics of the vertical structure of the atmospheres of Venus and the Earth essentially differ. For instance, there are at least two, instead of one, zones with normal (thermal) convection on Venus. The first one is near the surface (a boundary layer); the second is at the altitudes of the lower part of the main cloud layer between 49 and 55 km. Contrary to the hypotheses proposed by Izakov (2001, 2002), the upper convective zone prevents energy transfer from the upper clouds to the subcloud atmosphere by ``anomalous turbulent heat conductivity.'' It is possible, however, that the anomalous turbulent heat conductivity takes part in the redistribution of the heat fluxes within the lower (subcloud) atmosphere.

  18. High Ra, high Pr convection with viscosity gradients

    Indian Academy of Sciences (India)

    First page Back Continue Last page Overview Graphics. High Ra, high Pr convection with viscosity gradients. Weak upward flow through mesh. Top fluid more viscous. Unstable layer Instability Convection.

  19. Stretched flow of Carreau nanofluid with convective boundary ...

    Indian Academy of Sciences (India)

    journal of. January 2016 physics pp. 3–17. Stretched flow of Carreau nanofluid with ... fluid over a flat plate subjected to convective surface condition. ... the steady laminar boundary layer flow over a permeable plate with a convective boundary.

  20. Predictors of successful outcomes after external cephalic version in singleton term breech pregnancies: a nine-year historical cohort study.

    Science.gov (United States)

    Cho, L Y; Lau, W L; Lo, T K; Tang, Helen H T; Leung, W C

    2012-02-01

    To study the success rate, predictors for success, and pregnancy outcomes after external cephalic version. Historical cohort study. Regional hospital, Hong Kong. All women who had singleton term breech pregnancies at term and opted for external cephalic version during 2001 and 2009. Their demographic data, clinical and ultrasound findings, procedure details, complications, and delivery outcomes were analysed. Predictive factors for successful external cephalic version. A total of 209 external cephalic versions were performed during the 9-year period. The success rate was 63% (75% for multiparous and 53% for nulliparous women). There was no significant complication. On univariate analysis, predictors of successful external cephalic version were: multiparity, unengaged presenting part, higher amniotic fluid index (≥ 10 cm), thin abdominal wall, low uterine tone, and easily palpable fetal head (subjective assessment by practitioners before external cephalic version). On multivariate analysis, only multiparity, non-engagement of the fetal buttock and thin maternal abdomen were associated with successful external cephalic version. In all, 69% of those who had successful external cephalic version succeeded in the first roll (Pexternal cephalic versions had vaginal deliveries (93% in multiparous and 69% in nulliparous women). Uptake rate of external cephalic version was studied in the latter part of the study period (2006-2009). Whilst 735 women were eligible for external cephalic version, 131 women chose to have the procedure resulting in an uptake rate of 18%. External cephalic version was effective in reducing breech presentations at term and corresponding caesarean section rates, but the uptake rate was low. Further work should address the barriers to the low acceptance of external cephalic version. The results of this study could encourage women to opt for external cephalic version.

  1. Gestational age, gender and parity specific centile charts for placental weight for singleton deliveries in Aberdeen, UK.

    Science.gov (United States)

    Wallace, J M; Bhattacharya, S; Horgan, G W

    2013-03-01

    The weight of the placenta is a crude but useful proxy for its function in vivo. Accordingly extremes of placental weight are associated with adverse pregnancy outcomes while even normal variations in placental size may impact lifelong health. Centile charts of placental weight for gestational age and gender are used to identify placental weight extremes but none report the effect of parity. Thus the objective was to produce gender and gestational age specific centile charts for placental weight in nulliparous and multiparous women. Data was extracted from the Aberdeen Maternity and Neonatal Databank for all women delivering singleton babies in Aberdeen city and district after 24 weeks gestation. Gestational age specific centile charts for placental weight by gender and parity grouping (n = 88,649 deliveries over a 30 year period) were constructed using the LMS method after exclusion of outliers (0.63% of deliveries meeting study inclusion criteria). Tables and figures are presented for placental weight centiles according to gestational age, gender and parity grouping. Tables are additionally presented for the birth weight to placental weight ratio by gender. Placental weight and the fetal:placental weight ratio were higher in male versus female deliveries. Placental weight was greater in multiparous compared with nulliparous women. We present strong evidence that both gender and parity grouping influence placental weight centiles. The differences at any given gestational age are small and the effects of parity are greater overall than those of gender. In contrast the birth weight to placental weight ratio differs by gender only. These UK population specific centile charts may be useful in studies investigating the role of the placenta in mediating pregnancy outcome and lifelong health. Copyright © 2012 Elsevier Ltd. All rights reserved.

  2. The impact of gestational diabetes mellitus on postpartum urinary incontinence: a longitudinal cohort study on singleton pregnancies.

    Science.gov (United States)

    Chuang, C-M; Lin, I-F; Horng, H-C; Hsiao, Y-H; Shyu, I-L; Chou, P

    2012-10-01

    To determine whether gestational diabetes mellitus (GDM) is an independent risk factor for postpartum urinary incontinence in singleton pregnancies. A longitudinal cohort study. A single tertiary-care hospital in Taiwan. Pregnant women with term deliveries between 2002 and 2007 (n = 6653) were consecutively recruited. Logistic regression models were fitted based on generalised estimating equation methods to derive odds ratios for occurrences of type-specific urinary incontinence in the third trimester and at four time-points over 2 years during the postpartum period. Evaluation of whether GDM is an independent risk factor for postpartum urinary incontinence. The full model analysis revealed that GDM was an independent risk factor for all type-specific urinary incontinence (odds ratio [95% confidence interval]: 1.97 [1.56-2.51], 3.11 [2.18-4.43] and 2.73 [1.70-4.40] for stress, urge and mixed incontinence, respectively]. Compared with women without GDM, women with GDM tended to exhibit more severe symptoms of stress incontinence for up to 2 years postpartum, whereas for urge or mixed incontinence, more severe symptoms were found only for 6 months postpartum. Evaluation of quality of life using the Incontinence Impact Questionnaire 7 suggested that women with GDM requiring insulin treatment had a higher likelihood of functional impairment than women with GDM requiring conservative treatment only or women without GDM (P risk factor for postpartum urinary incontinence and had a significant impact on quality of life. Women with GDM should be provided with timely consultation and support once urinary incontinence occurs. © 2012 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2012 RCOG.

  3. Use of multiple linear regression and logistic regression models to investigate changes in birthweight for term singleton infants in Scotland.

    Science.gov (United States)

    Bonellie, Sandra R

    2012-10-01

    To illustrate the use of regression and logistic regression models to investigate changes over time in size of babies particularly in relation to social deprivation, age of the mother and smoking. Mean birthweight has been found to be increasing in many countries in recent years, but there are still a group of babies who are born with low birthweights. Population-based retrospective cohort study. Multiple linear regression and logistic regression models are used to analyse data on term 'singleton births' from Scottish hospitals between 1994-2003. Mothers who smoke are shown to give birth to lighter babies on average, a difference of approximately 0.57 Standard deviations lower (95% confidence interval. 0.55-0.58) when adjusted for sex and parity. These mothers are also more likely to have babies that are low birthweight (odds ratio 3.46, 95% confidence interval 3.30-3.63) compared with non-smokers. Low birthweight is 30% more likely where the mother lives in the most deprived areas compared with the least deprived, (odds ratio 1.30, 95% confidence interval 1.21-1.40). Smoking during pregnancy is shown to have a detrimental effect on the size of infants at birth. This effect explains some, though not all, of the observed socioeconomic birthweight. It also explains much of the observed birthweight differences by the age of the mother.   Identifying mothers at greater risk of having a low birthweight baby as important implications for the care and advice this group receives. © 2012 Blackwell Publishing Ltd.

  4. Underlying causes of neonatal deaths in term singleton pregnancies: home births versus hospital births in the United States.

    Science.gov (United States)

    Grünebaum, Amos; McCullough, Laurence B; Arabin, Birgit; Dudenhausen, Joachim; Orosz, Brooke; Chervenak, Frank A

    2017-04-01

    The objective of this study was to evaluate the underlying causes of neonatal mortality (NNM) in midwife-attended home births and compare them to hospital births attended by a midwife or a physician in the United States (US). A retrospective cohort study of the Centers for Disease Control (CDC) linked birth/infant death data set (linked files) for 2008 through 2012 of singleton, term (≥37 weeks) births and normal newborn weights (≥2500 grams). Midwife-attended home births had the highest rate of neonatal deaths [122/95,657 neonatal mortality (NNM) 12.75/10,000; relative risk (RR): 3.6, 95% confidence interval (CI) 3-4.4], followed by hospital physician births (8695/14,447,355 NNM 6.02/10,000; RR: 1.7 95% CI 1.6-1.9) and hospital midwife births (480/1,363,199 NNM 3.52/10,000 RR: 1). Among midwife-assisted home births, underlying causes attributed to labor and delivery caused 39.3% (48/122) of neonatal deaths (RR: 13.4; 95% CI 9-19.9) followed by 29.5% due to congenital anomalies (RR: 2.5; 95% CI 1.8-3.6), and 12.3% due to infections (RR: 4.5; 95% CI 2.5-8.1). There are significantly increased risks of neonatal deaths among midwife-attended home births associated with three underlying causes: labor and delivery issues, infections, and fetal malformations. This analysis of the causes of neonatal death in planned home birth shows that it is consistently riskier for newborns to deliver at home than at the hospital. Physicians, midwives, and other health care providers have a professional responsibility to share information about the clinical benefits and risks of clinical management.

  5. Perinatal outcome of singleton siblings born after assisted reproductive technology and spontaneous conception: Danish national sibling-cohort study.

    Science.gov (United States)

    Henningsen, Anna-Karina Aaris; Pinborg, Anja; Lidegaard, Øjvind; Vestergaard, Christina; Forman, Julie Lyng; Andersen, Anders Nyboe

    2011-03-01

    To compare the perinatal outcome of singleton siblings conceived differently. National population-based registry study. Denmark, from 1994 to 2008. Pairs of siblings (13,692 pairs; n = 27,384 children) conceived after IVF, intracytoplasmatic sperm injection (ICSI), frozen embryo replacement (FER), or spontaneous conception subcategorized into five groups according to succession: [1] IVF-ICSI vs. spontaneous conception (n = 7,758), [2] IVF-ICSI vs. FER (n = 716), [3] FER vs. FER (n = 34), [4] IVF-ICSI vs. IVF-ICSI (n = 2,876), and [5] spontaneous conception vs. spontaneous conception (n = 16,000). Observations were obtained from national registries. Birth weight, gestational age, low birth weight (children compared with their spontaneously conceived siblings. FER children were 167 g (95% CI, 90-244] heavier than siblings born after replacement of fresh embryos. The difference in birth weight between firstborn and second born sibling depended on order of conception method. Higher risk of low birth weight with (odds ratio [OR], 1.4; 95%CI, 1.1-1.7] and preterm birth (OR, 1.3; 95% CI, 1.1-1.6] was observed in IVF/ICSI compared with spontaneous conception. When differentiating between order and mode of conception, it seems that assisted reproductive technology plays a role in mean birth weight and risk of low birth weight and preterm birth. Birth weight was higher in siblings born after FER compared with fresh embryos replacement. Copyright © 2011 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.

  6. Convection flow structure in the central polar cap

    Science.gov (United States)

    Bristow, W. A.

    2017-12-01

    A previous study of spatially averaged flow velocity in the central polar cap [Bristow et al., 2015] observed under steady IMF conditions found that it was extremely rare for the average to exceed 850 m/s (less than 0.2 % of the time). Anecdotally, however it is not uncommon to observe line-of-sight velocities in excess of 100 m/s in the McMurdo radar field of view directly over the magnetic pole. This discrepancy motivated this study, which examines the conditions under which high-velocity flows are observed at latitudes greater than 80° magnetic latitude. It was found that highly structured flows are common in the central polar cap, which leads to the flow within regions to have significant deviation from the average. In addition, the high-speed flow regions are usually directed away from the earth-sun line. No specific set of driving conditions was identified to be associated with high-speed flows. The study did conclude that 1)Polar cap velocities are generally highly structured. 2)Flow patterns typically illustrate narrow channels, vortical flow regions, and propagating features. 3) Persistent waves are a regular occurrence. 3)Features are observed to propagate from day side to night side, and from night side to day side.. 4)Convection often exhibits significant difference between the two hemispheres. And 5)About 10% of the time the velocity somewhere in the cap exceeds 1 Km/s The presentation will conclude with a discussion of the physical reasons for the flow structure. Bristow, W. A., E. Amata, J. Spaleta, and M. F. Marcucci (2015), Observations of the relationship between ionospheric central polar cap and dayside throat convection velocities, and solar wind/IMF driving, J. Geophys. Res. Space Physics, 120, doi:10.1002/2015JA021199.

  7. Seismic Wave Velocity in Earth's Shallow Core

    Science.gov (United States)

    Alexandrakis, C.; Eaton, D. W.

    2008-12-01

    Studies of the outer core indicate that it is composed of liquid Fe and Ni alloyed with a ~10% fraction of light elements such as O, S or Si. Recently, unusual features, such as sediment accumulation, immiscible fluid layers or stagnant convection, have been predicted in the shallow core region. Secular cooling and compositional buoyancy drive vigorous convection that sustains the geodynamo, although critical details of light-element composition and thermal regime remain uncertain. Seismic velocity models can provide important constraints on the light element composition, however global reference models, such as Preliminary Reference Earth Model (PREM), IASP91 and AK135 vary significantly in the 200 km below the core-mantle boundary. Past studies of the outermost core velocity structure have been hampered by traveltime uncertainties due to lowermost mantle heterogeneities. The recently published Empirical Transfer Function (ETF) method has been shown to reduce the uncertainty using a waveform stacking approach to improve global observations of SmKS teleseismic waves. Here, we apply the ETF method to achieve a precise top-of-core velocity measurement of 8.05 ± 0.03 km/s. This new model accords well with PREM. Since PREM is based on the adiabatic form of the Adams-Williamson equation, it assumes a well mixed (i.e. homogeneous) composition. This result suggests a lack of heterogeneity in the outermost core due to layering or stagnant convection.

  8. An infinite-dimensional model of free convection

    Energy Technology Data Exchange (ETDEWEB)

    Iudovich, V.I. (Rostovskii Gosudarstvennyi Universitet, Rostov-on-Don (USSR))

    1990-12-01

    An infinite-dimensional model is derived from the equations of free convection in the Boussinesq-Oberbeck approximation. The velocity field is approximated by a single mode, while the heat-conduction equation is conserved fully. It is shown that, for all supercritical Rayleigh numbers, there exist exactly two secondary convective regimes. The case of ideal convection with zero viscosity and thermal conductivity is examined. The averaging method is used to study convection regimes at high Reynolds numbers. 10 refs.

  9. Education: DNA replication using microscale natural convection.

    Science.gov (United States)

    Priye, Aashish; Hassan, Yassin A; Ugaz, Victor M

    2012-12-07

    There is a need for innovative educational experiences that unify and reinforce fundamental principles at the interface between the physical, chemical, and life sciences. These experiences empower and excite students by helping them recognize how interdisciplinary knowledge can be applied to develop new products and technologies that benefit society. Microfluidics offers an incredibly versatile tool to address this need. Here we describe our efforts to create innovative hands-on activities that introduce chemical engineering students to molecular biology by challenging them to harness microscale natural convection phenomena to perform DNA replication via the polymerase chain reaction (PCR). Experimentally, we have constructed convective PCR stations incorporating a simple design for loading and mounting cylindrical microfluidic reactors between independently controlled thermal plates. A portable motion analysis microscope enables flow patterns inside the convective reactors to be directly visualized using fluorescent bead tracers. We have also developed a hands-on computational fluid dynamics (CFD) exercise based on modeling microscale thermal convection to identify optimal geometries for DNA replication. A cognitive assessment reveals that these activities strongly impact student learning in a positive way.

  10. Evolution of Excited Convective Cells in Plasmas

    DEFF Research Database (Denmark)

    Pécseli, Hans; Juul Rasmussen, Jens; Sugai, H.

    1984-01-01

    Convective cells are excited externally in a fully ionized magnetized plasma and their space-time evolution is investigated by two-dimensional potential measurements. A positive cell is excited externally by control of the end losses in the 'scrape off' layer of a plasma column produced by surface...

  11. Free convection film flows and heat transfer

    CERN Document Server

    Shang, Deyi

    2010-01-01

    Presents development of systematic studies for hydrodynamics and heat and mass transfer in laminar free convection, accelerating film boiling and condensation of Newtonian fluids, and accelerating film flow of non-Newtonian power-law fluids. This book provides a system of analysis models with a developed velocity component method.

  12. Penetrative convection at high Rayleigh numbers

    Science.gov (United States)

    Toppaladoddi, Srikanth; Wettlaufer, John S.

    2018-04-01

    We study penetrative convection of a fluid confined between two horizontal plates, the temperatures of which are such that a temperature of maximum density lies between them. The range of Rayleigh numbers studied is Ra=[0.01 ,4 ]106,108 and the Prandtl numbers are Pr=1 and 11.6. An evolution equation for the growth of the convecting region is obtained through an integral energy balance. We identify a new nondimensional parameter, Λ , which is the ratio of temperature difference between the stable and unstable regions of the flow; larger values of Λ denote increased stability of the upper stable layer. We study the effects of Λ on the flow field using well-resolved lattice Boltzmann simulations and show that the characteristics of the flow depend sensitively upon it. For the range Λ = , we find that for a fixed Ra the Nusselt number, Nu, increases with decreasing Λ . We also investigate the effects of Λ on the vertical variation of convective heat flux and the Brunt-Väisälä frequency. Our results clearly indicate that in the limit Λ →0 the problem reduces to that of the classical Rayleigh-Bénard convection.

  13. Radiative-convective equilibrium model intercomparison project

    Science.gov (United States)

    Wing, Allison A.; Reed, Kevin A.; Satoh, Masaki; Stevens, Bjorn; Bony, Sandrine; Ohno, Tomoki

    2018-03-01

    RCEMIP, an intercomparison of multiple types of models configured in radiative-convective equilibrium (RCE), is proposed. RCE is an idealization of the climate system in which there is a balance between radiative cooling of the atmosphere and heating by convection. The scientific objectives of RCEMIP are three-fold. First, clouds and climate sensitivity will be investigated in the RCE setting. This includes determining how cloud fraction changes with warming and the role of self-aggregation of convection in climate sensitivity. Second, RCEMIP will quantify the dependence of the degree of convective aggregation and tropical circulation regimes on temperature. Finally, by providing a common baseline, RCEMIP will allow the robustness of the RCE state across the spectrum of models to be assessed, which is essential for interpreting the results found regarding clouds, climate sensitivity, and aggregation, and more generally, determining which features of tropical climate a RCE framework is useful for. A novel aspect and major advantage of RCEMIP is the accessibility of the RCE framework to a variety of models, including cloud-resolving models, general circulation models, global cloud-resolving models, single-column models, and large-eddy simulation models.

  14. Vortex statistics in turbulent rotating convection

    NARCIS (Netherlands)

    Kunnen, R.P.J.; Clercx, H.J.H.; Geurts, B.J.

    2010-01-01

    The vortices emerging in rotating turbulent Rayleigh-Bénard convection in water at Rayleigh number Ra=6.0×108 are investigated using stereoscopic particle image velocimetry and by direct numerical simulation. The so-called Q criterion is used to detect the vortices from velocity fields. This

  15. Phenomenology of convection-parameterization closure

    Directory of Open Access Journals (Sweden)

    J.-I. Yano

    2013-04-01

    Full Text Available Closure is a problem of defining the convective intensity in a given parameterization. In spite of many years of efforts and progress, it is still considered an overall unresolved problem. The present article reviews this problem from phenomenological perspectives. The physical variables that may contribute in defining the convective intensity are listed, and their statistical significances identified by observational data analyses are reviewed. A possibility is discussed for identifying a correct closure hypothesis by performing a linear stability analysis of tropical convectively coupled waves with various different closure hypotheses. Various individual theoretical issues are considered from various different perspectives. The review also emphasizes that the dominant physical factors controlling convection differ between the tropics and extra-tropics, as well as between oceanic and land areas. Both observational as well as theoretical analyses, often focused on the tropics, do not necessarily lead to conclusions consistent with our operational experiences focused on midlatitudes. Though we emphasize the importance of the interplays between these observational, theoretical and operational perspectives, we also face challenges for establishing a solid research framework that is universally applicable. An energy cycle framework is suggested as such a candidate.

  16. Oscillatory Convection in Rotating Liquid Metals

    Science.gov (United States)

    Bertin, Vincent; Grannan, Alex; Aurnou, Jonathan

    2016-11-01

    We have performed laboratory experiments in a aspect ratio Γ = 2 cylinder using liquid gallium (Pr = 0 . 023) as the working fluid. The Ekman number varies from E = 4 ×10-5 to 4 ×10-6 and the Rayleigh number varies from Ra = 3 ×105 to 2 ×107 . Using heat transfer and temperature measurements within the fluid, we characterize the different styles of low Pr rotating convective flow. The convection threshold is first overcome in the form of a container scale inertial oscillatory mode. At stronger forcing, wall-localized modes develop, coexisting with the inertial oscillatory modes in the bulk. When the strength of the buoyancy increases further, the bulk flow becomes turbulent while the wall modes remain. Our results imply that rotating convective flows in liquid metals do not develop in the form of quasi-steady columns, as in Pr = 1 planetary and stellar dynamo models, but in the form of oscillatory motions. Therefore, convection driven dynamo action in low Pr fluids can differ substantively than that occurring in typical Pr = 1 numerical models. Our results also suggest that low wavenumber, wall modes may be dynamically and observationally important in liquid metal dynamo systems. We thank the NSF Geophysics Program for support of this project.

  17. Natural convection in horizontal fluid layers

    International Nuclear Information System (INIS)

    Suo-Antilla, A.J.

    1977-02-01

    The experimental work includes developing and using a thermal convection cell to obtain measurements of the heat flux and turbulent core temperature of a horizontal layer of fluid heated internally and subject to both stabilizing and destabilizing temperature differences. The ranges of Rayleigh numbers tested were 10 7 equal to or less than R/sub I/ equal to or less than 10 13 and -10 10 equal to or less than R/sub E/ equal to or less than 10 10 . Power integral methods were found to be adequate for interpolating and extrapolating the data. The theoretical work consists of the derivation, solution and use of the mean field equations for study of thermally driven convection in horizontal layers of infinite extent. The equations were derived by a separation of variables technique where the horizontal directions were described by periodic structures and the vertical being some function of z. The derivation resulted in a coupled set of momentum and energy equations. The equations were simplified by using the infinite Prandtl number limit and neglecting direct intermodal interaction. Solutions to these equations are used to predict the existence of multi-wavenumber flows at all supercritical Rayleigh numbers. Subsequent inspection of existing experimental photographs of convecting fluids confirms their existence. The onset of time dependence is found to coincide with the onset of the second convective mode. Each mode is found to consist of two wavenumbers and typically the velocity and temperature fields of the right modal branch are found to be out of phase

  18. Unstable mixed convective transport in groundwater

    International Nuclear Information System (INIS)

    Schincariol, R.A.; Schwartz, F.W.

    1990-01-01

    This study is an experimental investigation of variable density groundwater flow in homogeneous and lenticular porous media. A solution of 500 mg/l Rhodamine WT dye served as the carrier for various concentrations of solute (NaCl) introduced into a two-dimensional flow tank at concentrations ranging from 1000 to 100,000 mg/l. At the scale of the experiments, mass transport depends upon both forced and free convection. In addition, density differences as low as 0.008 g/cm 3 (1000 mg/l NaCl) between a plume of dense water and ambient groundwater in homogeneous medium produces gravitational instabilities at realistic groundwater velocities. These instabilities are manifest by lobe-shaped protuberances that formed first along the bottom edge of the plume and later within the plume. As the density difference increases to 0.0015 g/cm 3 (2000 mg/l NaCl), 0.0037 g/cm 3 (5000 mg/l NaCl) or higher, this unstable mixing due to convective dispersion significantly alters the spreading process, resulting in a large degree of vertical spreading of the plume. In a lenticular medium the combination of convective dispersion and nonuniform flow due to heterogeneities results in relatively large dispersion. Scale considerations indicate that convective dispersion may provide an important component of mixing at the field scale. (Author) (30 refs., 12 figs., 3 tabs.)

  19. Solar Hot Water Heating by Natural Convection.

    Science.gov (United States)

    Noble, Richard D.

    1983-01-01

    Presents an undergraduate laboratory experiment in which a solar collector is used to heat water for domestic use. The working fluid is moved by natural convection so no pumps are required. Experimental apparatus is simple in design and operation so that data can be collected quickly and easily. (Author/JN)

  20. A 'backward' free-convective boundary layer

    NARCIS (Netherlands)

    Kuiken, H.K.

    1981-01-01

    In this paper the cooling of a low-heat-resistance sheet that moves downwards is considered. The free-convective velocities are assumed to be much larger than the velocity of the sheet. As a result the motion of the fluid is mainly towards the point where the sheet enters the system and a ‘backward’

  1. Natural convection inside an irregular porous cavity

    International Nuclear Information System (INIS)

    Beltran, Jorge I. LLagostera; Trevisan, Osvair Vidal

    1990-01-01

    Natural convection flow induced by heating from below in a irregular porous cavity is investigated numerically. The influence of the modified Rayleigh number and geometric ratios on heat transfer and fluid flow is studied. Global and local Nusselt for Rayleigh numbers covering the range 0 - 1600 and for several geometric ratios. The fluid flow and the temperature field are illustrated by contour maps. (author)

  2. Convection in Slab and Spheroidal Geometries

    Science.gov (United States)

    Porter, David H.; Woodward, Paul R.; Jacobs, Michael L.

    2000-01-01

    Three-dimensional numerical simulations of compressible turbulent thermally driven convection, in both slab and spheroidal geometries, are reviewed and analyzed in terms of velocity spectra and mixing-length theory. The same ideal gas model is used in both geometries, and resulting flows are compared. The piecewise-parabolic method (PPM), with either thermal conductivity or photospheric boundary conditions, is used to solve the fluid equations of motion. Fluid motions in both geometries exhibit a Kolmogorov-like k(sup -5/3) range in their velocity spectra. The longest wavelength modes are energetically dominant in both geometries, typically leading to one convection cell dominating the flow. In spheroidal geometry, a dipolar flow dominates the largest scale convective motions. Downflows are intensely turbulent and up drafts are relatively laminar in both geometries. In slab geometry, correlations between temperature and velocity fluctuations, which lead to the enthalpy flux, are fairly independent of depth. In spheroidal geometry this same correlation increases linearly with radius over the inner 70 percent by radius, in which the local pressure scale heights are a sizable fraction of the radius. The effects from the impenetrable boundary conditions in the slab geometry models are confused with the effects from non-local convection. In spheroidal geometry nonlocal effects, due to coherent plumes, are seen as far as several pressure scale heights from the lower boundary and are clearly distinguishable from boundary effects.

  3. Preserving Symmetry in Convection-Diffusion Schemes

    NARCIS (Netherlands)

    Verstappen, R.W.C.P.; Veldman, A.E.P.; Drikakis, D.; Geurts, B.J.

    2002-01-01

    We propose to perform turbulent flow simulations in such manner that the difference operators do have the same symmetry properties as the corresponding differential operators. That is, the convective operator is represented by a skew-symmetric difference operator and the diffusive operator is

  4. Theories for convection in stellar atmospheres

    International Nuclear Information System (INIS)

    Nordlund, Aa.

    1976-02-01

    A discussion of the fundamental differences between laboratory convection in a stellar atmosphere is presented. The shortcomings of laterally homogeneous model atmospheres are analysed, and the extent to which these shortcoming are avoided in the two-component representation is discussed. Finally a qualitative discussion on the scaling properties of stellar granulation is presented. (Auth.)

  5. Terminal project heat convection in thin cylinders

    International Nuclear Information System (INIS)

    Morales Corona, J.

    1992-01-01

    Heat convection in thin cylinders and analysis about natural convection for straight vertical plates, and straight vertical cylinders submersed in a fluid are presented some works carry out by different authors in the field of heat transfer. In the part of conduction, deduction of the equation of heat conduction in cylindrical coordinates by means of energy balance in a control volume is presented. Enthalpy and internal energy are used for the outlining of the equation and finally the equation in its vectorial form is obtained. In the convection part development to calculate the Nusselt number for a straight vertical plate by a forces analysis, an energy balance and mass conservation over a control volume is outlined. Several empiric correlations to calculate the Nusselt number and its relations with other dimensionless numbers are presented. In the experimental part the way in which a prototype rode is assembled is presented measurements of temperatures attained in steady state and in free convection for working fluids as air and water are showed in tables. Also graphs of Nusselt numbers obtained in the experimental way through some empiric correlations are showed (Author)

  6. Influence of convective conditions on three dimensional mixed convective hydromagnetic boundary layer flow of Casson nanofluid

    Energy Technology Data Exchange (ETDEWEB)

    Rauf, A., E-mail: raufamar@ciitsahiwal.edu.pk [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Siddiq, M.K. [Centre for Advanced Studies in Pure and Applied Mathematics, Department of Mathematics, Bahauddin Zakariya University, Multan 63000 (Pakistan); Abbasi, F.M. [Department of Mathematics, Comsats Institute of Information Technology, Islamabad 44000 (Pakistan); Meraj, M.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan); Ashraf, M. [Centre for Advanced Studies in Pure and Applied Mathematics, Department of Mathematics, Bahauddin Zakariya University, Multan 63000 (Pakistan); Shehzad, S.A. [Department of Mathematics, Comsats Institute of Information Technology, Sahiwal 57000 (Pakistan)

    2016-10-15

    The present work deals with the steady laminar three-dimensional mixed convective magnetohydrodynamic (MHD) boundary layer flow of Casson nanofluid over a bidirectional stretching surface. A uniform magnetic field is applied normal to the flow direction. Similarity variables are implemented to convert the non-linear partial differential equations into ordinary ones. Convective boundary conditions are utilized at surface of the sheet. A numerical technique of Runge–Kutta–Fehlberg (RFK45) is used to obtain the results of velocity, temperature and concentration fields. The physical dimensionless parameters are discussed through tables and graphs. - Highlights: • Mixed convective boundary layer flow of Casson nanofluid is taken into account. • Impact of magnetic field is examined. • Convective heat and mass conditions are imposed. • Numerical solutions are presented and discussed.

  7. Testing particle filters on convective scale dynamics

    Science.gov (United States)

    Haslehner, Mylene; Craig, George. C.; Janjic, Tijana

    2014-05-01

    Particle filters have been developed in recent years to deal with highly nonlinear dynamics and non Gaussian error statistics that also characterize data assimilation on convective scales. In this work we explore the use of the efficient particle filter (P.v. Leeuwen, 2011) for convective scale data assimilation application. The method is tested in idealized setting, on two stochastic models. The models were designed to reproduce some of the properties of convection, for example the rapid development and decay of convective clouds. The first model is a simple one-dimensional, discrete state birth-death model of clouds (Craig and Würsch, 2012). For this model, the efficient particle filter that includes nudging the variables shows significant improvement compared to Ensemble Kalman Filter and Sequential Importance Resampling (SIR) particle filter. The success of the combination of nudging and resampling, measured as RMS error with respect to the 'true state', is proportional to the nudging intensity. Significantly, even a very weak nudging intensity brings notable improvement over SIR. The second model is a modified version of a stochastic shallow water model (Würsch and Craig 2013), which contains more realistic dynamical characteristics of convective scale phenomena. Using the efficient particle filter and different combination of observations of the three field variables (wind, water 'height' and rain) allows the particle filter to be evaluated in comparison to a regime where only nudging is used. Sensitivity to the properties of the model error covariance is also considered. Finally, criteria are identified under which the efficient particle filter outperforms nudging alone. References: Craig, G. C. and M. Würsch, 2012: The impact of localization and observation averaging for convective-scale data assimilation in a simple stochastic model. Q. J. R. Meteorol. Soc.,139, 515-523. Van Leeuwen, P. J., 2011: Efficient non-linear data assimilation in geophysical

  8. Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years.

    Science.gov (United States)

    Thornalley, David J R; Oppo, Delia W; Ortega, Pablo; Robson, Jon I; Brierley, Chris M; Davis, Renee; Hall, Ian R; Moffa-Sanchez, Paola; Rose, Neil L; Spooner, Peter T; Yashayaev, Igor; Keigwin, Lloyd D

    2018-04-01

    The Atlantic meridional overturning circulation (AMOC) is a system of ocean currents that has an essential role in Earth's climate, redistributing heat and influencing the carbon cycle 1, 2 . The AMOC has been shown to be weakening in recent years 1 ; this decline may reflect decadal-scale variability in convection in the Labrador Sea, but short observational datasets preclude a longer-term perspective on the modern state and variability of Labrador Sea convection and the AMOC 1, 3-5 . Here we provide several lines of palaeo-oceanographic evidence that Labrador Sea deep convection and the AMOC have been anomalously weak over the past 150 years or so (since the end of the Little Ice Age, LIA, approximately AD 1850) compared with the preceding 1,500 years. Our palaeoclimate reconstructions indicate that the transition occurred either as a predominantly abrupt shift towards the end of the LIA, or as a more gradual, continued decline over the past 150 years; this ambiguity probably arises from non-AMOC influences on the various proxies or from the different sensitivities of these proxies to individual components of the AMOC. We suggest that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA-sourced from melting glaciers and thickened sea ice that developed earlier in the LIA-weakened Labrador Sea convection and the AMOC. The lack of a subsequent recovery may have resulted from hysteresis or from twentieth-century melting of the Greenland Ice Sheet 6 . Our results suggest that recent decadal variability in Labrador Sea convection and the AMOC has occurred during an atypical, weak background state. Future work should aim to constrain the roles of internal climate variability and early anthropogenic forcing in the AMOC weakening described here.

  9. Identification of dominant flow structures in rapidly rotating convection of liquid metals using Dynamic Mode Decomposition

    Science.gov (United States)

    Horn, S.; Schmid, P. J.; Aurnou, J. M.

    2016-12-01

    The Earth's metal core acts as a dynamo whose efficiency in generating and maintaining the magnetic field is essentially determined by the rotation rate and the convective motions occurring in its outer liquid part. For the description of the primary physics in the outer core the idealized system of rotating Rayleigh-Bénard convection is often invoked, with the majority of studies considering only working fluids with Prandtl numbers of Pr ≳ 1. However, liquid metals are characterized by distinctly smaller Prandtl numbers which in turn result in an inherently different type of convection. Here, we will present results from direct numerical simulations of rapidly rotating convection in a fluid with Pr ≈ 0.025 in cylindrical containers and Ekman numbers as low as 5 × 10-6. In this system, the Coriolis force is the source of two types of inertial modes, the so-called wall modes, that also exist at moderate Prandtl numbers, and cylinder-filling oscillatory modes, that are a unique feature of small Prandtl number convection. The obtained flow fields were analyzed using the Dynamic Mode Decomposition (DMD). This technique allows to extract and identify the structures that govern the dynamics of the system as well as their corresponding frequencies. We have investigated both the regime where the flow is purely oscillatory and the regime where wall modes and oscillatory modes co-exist. In the purely oscillatory regime, high and low frequency oscillatory modes characterize the flow. When both types of modes are present, the DMD reveals that the wall-attached modes dominate the flow dynamics. They precess with a relatively low frequency in retrograde direction. Nonetheless, also in this case, high frequency oscillations have a significant contribution.

  10. Numerical simulation of convective generated gravity waves in the stratosphere and MLT regions.

    Science.gov (United States)

    Heale, C. J.; Snively, J. B.

    2017-12-01

    Convection is an important source of gravity wave generation, especially in the summer tropics and midlatitudes, and coherent wave fields above convection are now routinely measured in the stratosphere and mesosphere [e.g. Hoffmann et al., JGR, 118, 2013; Gong et al., JGR, 120, 2015; Perwitasari et al., GRL, 42, 22, 2016]. Numerical studies have been performed to investigate the generation mechanisms, source spectra, and their effects on the middle and upper atmosphere [e.g. Fovell et al., AMS, 49,16, 1992; Alexander and Holton, Atmos. Chem. Phys., 4 2004; Vincent et al., JGR, 1118, 2013], however there is still considerable work needed to fully describe these parameters. GCMs currently lack the resolution to explicitly simulate convection generation and rely on simplified parameterizations while full cloud resolving models are computationally expensive and often only extend into the stratosphere. More recent studies have improved the realism of these simulations by using radar derived precipitation rates to drive latent heating in models that simulate convection [Grimsdell et al., AMS, 67, 2010; Stephan and Alexander., J. Adv. Model. Earth. Syst, 7, 2015], however they too only consider wave propagation in the troposphere and stratosphere. We use a 2D nonlinear, fully compressible model [Snively and Pasko., JGR, 113, 2008] to excite convectively generated waves, based on NEXRAD radar data, using the Stephan and Alexander [2015] algorithms. We study the propagation, and spectral evolution of the generated waves up into the MLT region. Ambient atmosphere parameters are derived from observations and MERRA-2 reanalysis data, and stratospheric (AIRS) and mesospheric (Lidar, OH airglow) observations enable comparisons with simulation results.

  11. Novel Natural Convection Heat Sink Design Concepts From First Principles

    Science.gov (United States)

    2016-06-01

    CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES by Derek E. Fletcher June 2016 Thesis Advisor: Garth Hobson Second Reader...COVERED Master’s Thesis 4. TITLE AND SUBTITLE NOVEL NATURAL CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES 5. FUNDING NUMBERS 6...CONVECTION HEAT SINK DESIGN CONCEPTS FROM FIRST PRINCIPLES Derek E. Fletcher Lieutenant Commander, United States Navy B.S., Southwestern

  12. International symposium on transient convective heat transfer: book of abstracts

    International Nuclear Information System (INIS)

    1996-01-01

    The international symposium on convective heat transfer was held on 19-23 August 1996, in Cesme, Izmir, Turkey. The spesialists discussed forced convection, heat exchangers, free convection and multiphase media and phase change at the meeting. Almost 53 papers were presented in the meeting

  13. Edible Earth and Space Science Activities

    Science.gov (United States)

    Lubowich, D.; Shupla, C.

    2014-07-01

    In this workshop we describe using Earth and Space Science demonstrations with edible ingredients to increase student interest. We show how to use chocolate, candy, cookies, popcorn, bagels, pastries, Pringles, marshmallows, whipped cream, and Starburst candy for activities such as: plate tectonics, the interior structure of the Earth and Mars, radioactivity/radioactive dating of rocks and stars, formation of the planets, lunar phases, convection, comets, black holes, curvature of space, dark energy, and the expansion of the Universe. In addition to creating an experience that will help students remember specific concepts, edible activities can be used as a formative assessment, providing students with the opportunity to create something that demonstrates their understanding of the model. The students often eat the demonstrations. These demonstrations are an effective teaching tool for all ages, and can be adapted for cultural, culinary, and ethnic differences among the students.

  14. Basal melting driven by turbulent thermal convection

    Science.gov (United States)

    Rabbanipour Esfahani, Babak; Hirata, Silvia C.; Berti, Stefano; Calzavarini, Enrico

    2018-05-01

    Melting and, conversely, solidification processes in the presence of convection are key to many geophysical problems. An essential question related to these phenomena concerns the estimation of the (time-evolving) melting rate, which is tightly connected to the turbulent convective dynamics in the bulk of the melt fluid and the heat transfer at the liquid-solid interface. In this work, we consider a convective-melting model, constructed as a generalization of the Rayleigh-Bénard system, accounting for the basal melting of a solid. As the change of phase proceeds, a fluid layer grows at the heated bottom of the system and eventually reaches a turbulent convection state. By means of extensive lattice-Boltzmann numerical simulations employing an enthalpy formulation of the governing equations, we explore the model dynamics in two- and three-dimensional configurations. The focus of the analysis is on the scaling of global quantities like the heat flux and the kinetic energy with the Rayleigh number, as well as on the interface morphology and the effects of space dimensionality. Independently of dimensionality, we find that the convective-melting system behavior shares strong resemblances with that of the Rayleigh-Bénard one, and that the heat flux is only weakly enhanced with respect to that case. Such similarities are understood, at least to some extent, considering the resulting slow motion of the melting front (with respect to the turbulent fluid velocity fluctuations) and its generally little roughness (compared to the height of the fluid layer). Varying the Stefan number, accounting for the thermodynamical properties of the material, also seems to have only a mild effect, which implies the possibility of extrapolating results in numerically delicate low-Stefan setups from more convenient high-Stefan ones. Finally, we discuss the implications of our findings for the geophysically relevant problem of modeling Arctic ice melt ponds.

  15. Convective mass transfer around a dissolving bubble

    Science.gov (United States)

    Duplat, Jerome; Grandemange, Mathieu; Poulain, Cedric

    2017-11-01

    Heat or mass transfer around an evaporating drop or condensing vapor bubble is a complex issue due to the interplay between the substrate properties, diffusion- and convection-driven mass transfer, and Marangoni effects, to mention but a few. In order to disentangle these mechanisms, we focus here mainly on the convective mass transfer contribution in an isothermal mass transfer problem. For this, we study the case of a millimetric carbon dioxide bubble which is suspended under a substrate and dissolved into pure liquid water. The high solubility of CO2 in water makes the liquid denser and promotes a buoyant-driven flow at a high (solutal) Rayleigh number (Ra˜104 ). The alteration of p H allows the concentration field in the liquid to be imaged by laser fluorescence enabling us to measure both the global mass flux (bubble volume, contact angle) and local mass flux around the bubble along time. After a short period of mass diffusion, where the boundary layer thickens like the square root of time, convection starts and the CO2 is carried by a plume falling at constant velocity. The boundary layer thickness then reaches a plateau which depends on the bubble cross section. Meanwhile the plume velocity scales like (dV /d t )1 /2 with V being the volume of the bubble. As for the rate of volume loss, we recover a constant mass flux in the diffusion-driven regime followed by a decrease in the volume V like V2 /3 after convection has started. We present a model which agrees well with the bubble dynamics and discuss our results in the context of droplet evaporation, as well as high Rayleigh convection.

  16. Little Earth Experiment: An instrument to model planetary cores.

    Science.gov (United States)

    Aujogue, Kélig; Pothérat, Alban; Bates, Ian; Debray, François; Sreenivasan, Binod

    2016-08-01

    In this paper, we present a new experimental facility, Little Earth Experiment, designed to study the hydrodynamics of liquid planetary cores. The main novelty of this apparatus is that a transparent electrically conducting electrolyte is subject to extremely high magnetic fields (up to 10 T) to produce electromagnetic effects comparable to those produced by moderate magnetic fields in planetary cores. This technique makes it possible to visualise for the first time the coupling between the principal forces in a convection-driven dynamo by means of Particle Image Velocimetry (PIV) in a geometry relevant to planets. We first present the technology that enables us to generate these forces and implement PIV in a high magnetic field environment. We then show that the magnetic field drastically changes the structure of convective plumes in a configuration relevant to the tangent cylinder region of the Earth's core.

  17. Convection Effects During Bulk Transparent Alloy Solidification in DECLIC-DSI and Phase-Field Simulations in Diffusive Conditions

    Science.gov (United States)

    Mota, F. L.; Song, Y.; Pereda, J.; Billia, B.; Tourret, D.; Debierre, J.-M.; Trivedi, R.; Karma, A.; Bergeon, N.

    2017-08-01

    To study the dynamical formation and evolution of cellular and dendritic arrays under diffusive growth conditions, three-dimensional (3D) directional solidification experiments were conducted in microgravity on a model transparent alloy onboard the International Space Station using the Directional Solidification Insert in the DEvice for the study of Critical LIquids and Crystallization. Selected experiments were repeated on Earth under gravity-driven fluid flow to evidence convection effects. Both radial and axial macrosegregation resulting from convection are observed in ground experiments, and primary spacings measured on Earth and microgravity experiments are noticeably different. The microgravity experiments provide unique benchmark data for numerical simulations of spatially extended pattern formation under diffusive growth conditions. The results of 3D phase-field simulations highlight the importance of accurately modeling thermal conditions that strongly influence the front recoil of the interface and the selection of the primary spacing. The modeling predictions are in good quantitative agreements with the microgravity experiments.

  18. Hydrothermal, multiphase convection of H2O-NaCl fluids from ambient to magmatic temperatures : A new numerical scheme and benchmarks for code comparison

    NARCIS (Netherlands)

    Weis, P.; Driesner, T.; Coumou, D.; Geiger, S.

    2014-01-01

    Thermohaline convection of subsurface fluids strongly influences heat and mass fluxes within the Earth's crust. The most effective hydrothermal systems develop in the vicinity of magmatic activity and can be important for geothermal energy production and ore formation. As most parts of these systems

  19. A continuous and prognostic convection scheme based on buoyancy, PCMT

    Science.gov (United States)

    Guérémy, Jean-François; Piriou, Jean-Marcel

    2016-04-01

    A new and consistent convection scheme (PCMT: Prognostic Condensates Microphysics and Transport), providing a continuous and prognostic treatment of this atmospheric process, is described. The main concept ensuring the consistency of the whole system is the buoyancy, key element of any vertical motion. The buoyancy constitutes the forcing term of the convective vertical velocity, which is then used to define the triggering condition, the mass flux, and the rates of entrainment-detrainment. The buoyancy is also used in its vertically integrated form (CAPE) to determine the closure condition. The continuous treatment of convection, from dry thermals to deep precipitating convection, is achieved with the help of a continuous formulation of the entrainment-detrainment rates (depending on the convective vertical velocity) and of the CAPE relaxation time (depending on the convective over-turning time). The convective tendencies are directly expressed in terms of condensation and transport. Finally, the convective vertical velocity and condensates are fully prognostic, the latter being treated using the same microphysics scheme as for the resolved condensates but considering the convective environment. A Single Column Model (SCM) validation of this scheme is shown, allowing detailed comparisons with observed and explicitly simulated data. Four cases covering the convective spectrum are considered: over ocean, sensitivity to environmental moisture (S. Derbyshire) non precipitating shallow convection to deep precipitating convection, trade wind shallow convection (BOMEX) and strato-cumulus (FIRE), together with an entire continental diurnal cycle of convection (ARM). The emphasis is put on the characteristics of the scheme which enable a continuous treatment of convection. Then, a 3D LAM validation is presented considering an AMMA case with both observations and a CRM simulation using the same initial and lateral conditions as for the parameterized one. Finally, global

  20. Intraseasonal variability of organized convective systems in the Central Andes: Relationship to Regional Dynamical Features

    Science.gov (United States)

    Mohr, K. I.; Slayback, D. A.; Nicholls, S.; Yager, K.

    2013-12-01

    The Andes extend from the west coast of Colombia (10N) to the southern tip of Chile (53S). In southern Peru and Bolivia, the Central Andes is split into separate eastern and western cordilleras, with a high plateau (≥ 3000 m), the Altiplano, between them. Because 90% of the Earth's tropical mountain glaciers are located in the Central Andes, our study focuses on this region, defining its zonal extent as 7S-21S and the meridional extent as the terrain 1000 m and greater. Although intense convection occurs during the wet season in the Altiplano, it is not included in the lists of regions with frequent or the most intense convection. The scarcity of in-situ observations with sufficient density and temporal resolution to resolve individual storms or even mesoscale-organized cloud systems and documented biases in microwave-based rainfall products in poorly gauged mountainous regions have impeded the development of an extensive literature on convection and convective systems in this region. With the tropical glaciers receding at unprecedented rates, leaving seasonal precipitation as an increasingly important input to the water balance in alpine valley ecosystems and streams, understanding the nature and characteristics of the seasonal precipitation becomes increasingly important for the rural economies in this region. Previous work in analyzing precipitation in the Central Andes has emphasized interannual variability with respect to ENSO, this is the first study to focus on shorter scale variability with respect to organized convection. The present study took advantage of the University of Utah's Precipitation Features database compiled from 14 years of TRMM observations (1998-2012), supplemented by field observations of rainfall and streamflow, historical gauge data, and long-term WRF-simulations, to analyze the intraseasonal variability of precipitating systems and their relationship regional dynamical features such as the Bolivian High. Through time series and

  1. Earth mortars and earth-lime renders

    Directory of Open Access Journals (Sweden)

    Maria Fernandes

    2008-01-01

    Full Text Available Earth surface coatings play a decorative architectural role, apart from their function as wall protection. In Portuguese vernacular architecture, earth mortars were usually applied on stone masonry, while earth renders and plasters were used on indoors surface coatings. Limestone exists only in certain areas of the country and consequently lime was not easily available everywhere, especially on granite and schist regions where stone masonry was a current building technique. In the central west coast of Portugal, the lime slaking procedure entailed slaking the quicklime mixed with earth (sandy soil, in a pit; the resulting mixture would then be combined in a mortar or plaster. This was also the procedure for manufactured adobes stabilized with lime. Adobe buildings with earth-lime renderings and plasters were also traditional in the same region, using lime putty and lime wash for final coat and decoration. Classic decoration on earth architecture from the 18th-19th century was in many countries a consequence of the François Cointeraux (1740-1830 manuals - Les Cahiers d'Architecture Rurale" (1793 - a French guide for earth architecture and building construction. This manual arrived to Portugal in the beginning of XIX century, but was never translated to Portuguese. References about decoration for earth houses were explained on this manual, as well as procedures about earth-lime renders and ornamentation of earth walls; in fact, these procedures are exactly the same as the ones used in adobe buildings in this Portuguese region. The specific purpose of the present paper is to show some cases of earth mortars, renders and plasters on stone buildings in Portugal and to explain the methods of producing earth-lime renders, and also to show some examples of rendering and coating with earth-lime in Portuguese adobe vernacular architecture.

  2. Fertility treatment and child intelligence, attention, and executive functions in 5-year-old singletons: a cohort study.

    Science.gov (United States)

    Bay, B; Mortensen, E L; Kesmodel, U S

    2014-12-01

    To assess the association of fertility treatment and subfertility with offspring intelligence, attention, and executive functions in 5-year-old singletons. Follow-up study. Denmark 2003-2008. A cohort of 1782 children sampled from the Danish National Birth Cohort. The children were tested with a neuropsychological battery at age five. In addition to tests of intelligence, attention and executive functions, the follow up included extensive information on important covariates. The analyses were conducted using multiple linear regression and adjusted for parental educational level, maternal intelligence, age, parity, body mass index, smoking in pregnancy, alcohol consumption in pregnancy and child gender, child age, and examiner. Wechsler Preschool and Primary Scale of Intelligence-Revised, the Test of Everyday Attention for Children at Five, and the Behavior Rating Inventory of Executive Functions scores. A consistent pattern of nonsignificantly lower scores were only observed for intelligence and executive functions in children born after fertility treatment or by subfertile parents when the results were unadjusted for maternal intelligence and parental educational level. When adjusted for these and other covariates, there were no significant mean differences in intelligence (mean difference -2.8, 95% CI -7.8, 2.2), overall attention (-0.1, 95% CI -0.6, 0.3), or parent-rated executive functions (-0.1, 95% CI -3.0, 2.9) between children born after spontaneous conception and children born to parents conceiving after fertility treatment. Similarly, there were no significant mean differences in intelligence (mean difference 0.6, 95% CI -2.2, 3.4), overall attention (0.1, 95% CI -0.2, 0.4), or parent-rated executive functions (1.0, 95% CI -1.8, 3.7) between children born after spontaneous conception and children born to subfertile parents waiting more than 12 months before conceiving naturally. This study suggests that parental subfertility and fertility treatment are

  3. Why Earth Science?

    Science.gov (United States)

    Smith, Michael J.

    2004-01-01

    This article briefly describes Earth science. The study of Earth science provides the foundation for an understanding of the Earth, its processes, its resources, and its environment. Earth science is the study of the planet in its entirety, how its lithosphere, atmosphere, hydrosphere, and biosphere work together as systems and how they affect…

  4. A numerical model of mantle convection with deformable, mobile continental lithosphere within three-dimensional spherical geometry

    Science.gov (United States)

    Yoshida, M.

    2010-12-01

    A new numerical simulation model of mantle convection with a compositionally and rheologically heterogeneous, deformable, mobile continental lithosphere is presented for the first time by using three-dimensional regional spherical-shell geometry (Yoshida, 2010, Earth Planet. Sci. Lett.). The numerical results revealed that one of major factor that realizes the supercontinental breakup and subsequent continental drift is a pre-existing, weak (low-viscosity) continental margin (WCM) in the supercontinent. Characteristic tectonic structures such as young orogenic belts and suture zones in a continent are expected to be mechanically weaker than the stable part of the continental lithosphere with the cratonic root (or cratonic lithosphere) and yield lateral viscosity variations in the continental lithosphere. In the present-day Earth's lithosphere, the pre-existing, mechanically weak zones emerge as a diffuse plate boundary. However, the dynamic role of the WCM in the stability of continental lithosphere has not been understood in terms of geophysics. In my numerical model, a compositionally buoyant and highly viscous continental assemblage with pre-existing WCMs, analogous to the past supercontinent, is modeled and imposed on well-developed mantle convection whose vigor of convection, internal heating rate, and rheological parameters are appropriate for the Earth's mantle. The visco-plastic oceanic lithosphere and the associated subduction of oceanic plates are incorporated. The time integration of the advection of continental materials with zero chemical diffusion is performed by a tracer particle method. The time evolution of mantle convection after setting the model supercontinent is followed over 800 Myr. Earth-like continental drift is successfully reproduced, and the characteristic thermal interaction between the mantle and the continent/supercontinent is observed in my new numerical model. Results reveal that the WCM protects the cratonic lithosphere from being

  5. Behaviors and transitions along the path to magnetostrophic convection

    Science.gov (United States)

    Grannan, A. M.; Vogt, T.; Horn, S.; Hawkins, E. K.; Aggarwal, A.; Aurnou, J. M.

    2017-12-01

    The generation of magnetic fields in planetary and stellar interiors are believed to be controlled primarily by turbulent convection constrained by Coriolis and Lorentz forces in their electrically conducting fluid layers. Yet relatively few laboratory experiments are capable of investigating the different regimes of turbulent magnetohydrodynamic convection. In this work, we perform one laboratory experiment in a cylinder at a fixed heat flux using the liquid metal gallium in order to investigate, sequentially: Rayleigh-Bènard convection without any imposed constraints, magnetoconvection with a Lorentz constraint imposed by vertical magnetic field, rotating convection with a Coriolis constraint imposed by rotation, and finally the magnetostrophic convective regime where both Coriolis and Lorentz are imposed and equal. Using an array of internal and external temperature probes, we show that each regime along the path to magnetostrophic convection is unique. The behaviors and transitions in the dominant modes of convection as well as their fundamental frequencies and wavenumbers are investigated.

  6. Convective equilibrium and mixing-length theory for stellarator reactors

    International Nuclear Information System (INIS)

    Ho, D.D.M.; Kulsrud, R.M.

    1985-09-01

    In high β stellarator and tokamak reactors, the plasma pressure gradient in some regions of the plasma may exceed the critical pressure gradient set by ballooning instabilities. In these regions, convective cells break out to enhance the transport. As a result, the pressure gradient can rise only slightly above the critical gradient and the plasma is in another state of equilibrium - ''convective equilibrium'' - in these regions. Although the convective transport cannot be calculated precisely, it is shown that the density and temperature profiles in the convective region can still be estimated. A simple mixing-length theory, similar to that used for convection in stellar interiors, is introduced in this paper to provide a qualitative description of the convective cells and to show that the convective transport is highly efficient. A numerical example for obtaining the density and temperature profiles in a stellarator reactor is given

  7. Moisture Vertical Structure, Deep Convective Organization, and Convective Transition in the Amazon

    Science.gov (United States)

    Schiro, K. A.; Neelin, J. D.

    2017-12-01

    Constraining precipitation processes in climate models with observations is crucial to accurately simulating current climate and reducing uncertainties in future projections. Results from the Green Ocean Amazon (GOAmazon) field campaign (2014-2015) provide evidence that deep convection is strongly controlled by the availability of moisture in the free troposphere over the Amazon, much like over tropical oceans. Entraining plume buoyancy calculations confirm that CWV is a good proxy for the conditional instability of the environment, yet differences in convective onset as a function of CWV exist over land and ocean, as well as seasonally and diurnally over land. This is largely due to variability in the contribution of lower tropospheric humidity to the total column moisture. Boundary layer moisture shows a strong relationship to the onset during the day, which largely disappears during nighttime. Using S-Band radar, these transition statistics are examined separately for unorganized and mesoscale-organized convection, which exhibit sharp increases in probability of occurrence with increasing moisture throughout the column, particularly in the lower free troposphere. Retrievals of vertical velocity from a radar wind profiler indicate updraft velocity and mass flux increasing with height through the lower troposphere. A deep-inflow mixing scheme motivated by this — corresponding to deep inflow of environmental air into a plume that grows with height — provides a weighting of boundary layer and free tropospheric air that yields buoyancies consistent with the observed onset of deep convection across seasons and times of day, across land and ocean sites, and for all convection types. This provides a substantial improvement relative to more traditional constant mixing assumptions, and a dramatic improvement relative to no mixing. Furthermore, it provides relationships that are as strong or stronger for mesoscale-organized convection as for unorganized convection.

  8. The first 800 million years of earth's history

    Science.gov (United States)

    Smith, J. V.

    1981-01-01

    It is pointed out that there is no direct geological information on the first 750 Ma of earth history. Consequently the reported study is based on controversial inferences drawn from the moon, other planets and meteorites, coupled with backward extrapolation from surviving terrestrial rocks, especially those of Archaean age. Aspects of accretion are considered, taking into account cosmochemical and cosmophysical evidence, a new earth model, and convection systems. Attention is given to phase-equilibrium constraints, estimates of heat production, the bombardment history of the moon and implications for the earth, and the nature of the early crust. From a combination of physical, chemical, and petrological arguments, it is concluded that the earth's surface underwent intense volcanism in the pre-Archaean era, and that the rock types were chemically similar to those found in the early Archaean era.

  9. Coupling of convection and circulation at various resolutions

    Directory of Open Access Journals (Sweden)

    Cathy Hohenegger

    2015-03-01

    Full Text Available A correct representation of the coupling between convection and circulation constitutes a prerequisite for a correct representation of precipitation at all scales. In this study, the coupling between convection and a sea breeze is investigated across three main resolutions: large-eddy resolution where convection is fully explicit, convection-permitting resolution where convection is partly explicit and coarse resolution where convection is parameterised. The considered models are the UCLA-LES, COSMO and ICON. Despite the use of prescribed surface fluxes, comparison of the simulations reveals that typical biases associated with a misrepresentation of convection at convection-permitting and coarser resolutions significantly alter the characteristics of the sea breeze. The coarse-resolution simulations integrated without convective parameterisation and the convection-permitting simulations simulate a too slow propagation of the breeze front as compared to the large-eddy simulations. From the various factors affecting the propagation, a delayed onset and intensification of cold pools primarily explains the differences. This is a direct consequence of a delayed development of convection when the grid spacing is coarsened. Scaling the time the sea breeze reaches the centre of the land patch by the time precipitation exceeds 2 mm day−1, used as a measure for significant evaporation, yields a collapse of the simulations onto a simple linear relationship although subtle differences remain due to the use of different turbulence and microphysical schemes. Turning on the convection scheme significantly disrupts the propagation of the sea breeze due to a misrepresented timing (too early triggering and magnitude (too strong precipitation evaporation in one of the tested convection schemes of the convective processes.

  10. Natural convection in heat-generating fluids

    International Nuclear Information System (INIS)

    Bol'shov, Leonid A; Kondratenko, Petr S; Strizhov, Valerii F

    2001-01-01

    Experimental and theoretical studies of convective heat transfer from a heat-generating fluid confined to a closed volume are reviewed. Theoretical results are inferred from analytical estimates based on the relevant conservation laws and the current understanding of the convective heat-transfer processes. Four basic and one asymptotic regime of heat transfer are identified depending on the heat generation rate. Limiting heat-transfer distribution patterns are found for the lower boundary. Heat transfer in a quasi-two-dimensional geometry is analyzed. Quasi-steady-state heat transfer from a cooling-down fluid without internal heat sources is studied separately. Experimental results and theoretical predictions are compared. (reviews of topical problems)

  11. Topology optimisation of natural convection problems

    DEFF Research Database (Denmark)

    Alexandersen, Joe; Aage, Niels; Andreasen, Casper Schousboe

    2014-01-01

    This paper demonstrates the application of the density-based topology optimisation approach for the design of heat sinks and micropumps based on natural convection effects. The problems are modelled under the assumptions of steady-state laminar flow using the incompressible Navier-Stokes equations...... coupled to the convection-diffusion equation through the Boussinesq approximation. In order to facilitate topology optimisation, the Brinkman approach is taken to penalise velocities inside the solid domain and the effective thermal conductivity is interpolated in order to accommodate differences...... in thermal conductivity of the solid and fluid phases. The governing equations are discretised using stabilised finite elements and topology optimisation is performed for two different problems using discrete adjoint sensitivity analysis. The study shows that topology optimisation is a viable approach...

  12. Convective instabilities in SN 1987A

    Science.gov (United States)

    Benz, Willy; Thielemann, Friedrich-Karl

    1990-01-01

    Following Bandiera (1984), it is shown that the relevant criterion to determine the stability of a blast wave, propagating through the layers of a massive star in a supernova explosion, is the Schwarzschild (or Ledoux) criterion rather than the Rayleigh-Taylor criterion. Both criteria coincide only in the incompressible limit. Results of a linear stability analysis are presented for a one-dimensional (spherical) explosion in a realistic model for the progenitor of SN 1987A. When applying the Schwarzschild criterion, unstable regions get extended considerably. Convection is found to develop behind the shock, with a characteristic growth rate corresponding to a time scale much smaller than the shock traversal time. This ensures that efficient mixing will take place. Since the entire ejected mass is found to be convectively unstable, Ni can be transported outward, even into the hydrogen envelope, while hydrogen can be mixed deep into the helium core.

  13. Natural convection heat transfer in SIGMA experiment

    International Nuclear Information System (INIS)

    Lee, Seung Dong; Lee, Gang Hee; Suh, Kune Yull

    2004-01-01

    A loss-of-coolant accident (LOCA) results in core melt formation and relocation at various locations within the reactor core over a considerable period of time. If there is no effective cooling mechanism, the core debris may heat up and commence natural circulation. The high temperature pool of molten core material will threaten the structural integrity of the reactor vessel. The extent and urgency of this threat depend primarily upon the intensity of the internal heat sources and upon the consequent distribution of the heat fluxes on the vessel walls in contact with the molten core material pools. In such a steady molten pool convection state, the thermal loads against the vessel would be determined by the in-vessel heat transfer distribution involving convective and conductive heat transfer from the decay-heated core material pool to the lower head wall in contact with the core material. In this study, upward and downward heat transfer fraction ratio is focused on

  14. An experimental study of mixed convection

    International Nuclear Information System (INIS)

    Saez, Manuel

    1998-01-01

    The aim of our study is to establish a reliable data base for improving thermal-hydraulic codes, in the field of turbulent flows with buoyancy forces. The flow considered is mixed convection in the Reynolds and Richardson number range: Re=10"3 to 6*10"4 and Ri=10"-"4 to 1. Experiments are carried out in an upward turbulent flow between vertical parallel plates at different wall temperatures. Part 1 gives a detailed data base of turbulent mixed flow of free and forced convection. Part II presents the installation and the calibration system intended for probes calibration. Part III describes the measurement technique (constant-temperature probe and cold-wire probe) and the method for measuring the position of the hot-wire anemometer from the wall surface. The measurement accuracy is within 0.001 mm in the present system. Part IV relates the development of a method for near wall measurements. This correction procedure for hot-wire anemometer close to wall has been derived on the basis of a two-dimensional numerical study. The method permits to obtain a quantitative correction of the wall influence on hot-wires and takes into account the velocity profile and the effects the wall material has on the heat loss. Part V presents the experimental data obtained in the channel in forced and mixed convection. Results obtained in the forced convection regime serve as a verification of the measurement technique close to the wall and give the conditions at the entrance of the test section. The effects of the buoyancy force on the mean velocity and temperature profiles are confirmed. The buoyancy strongly affects the flow structure and deforms the distribution of mean velocity. The velocity profiles are asymmetric. The second section of part V gives an approach of analytical wall functions with buoyancy forces, on the basis of the experimental data obtained in the test section. (author) [fr

  15. Convection and crystal settling in sills

    Science.gov (United States)

    Gibb, Fergus G. F.; Henderson, C. Michael B.

    1992-02-01

    It has been advocated that convective and crystal settling processes play significant, and perhaps crucial, roles in magmatic differentiation. The fluid dynamics of magma chambers have been extensively studied in recent years, both theoretically and experimentally, but there is disagreement over the nature and scale of the convection, over its bearing on fractionation and possibly over whether it occurs at all. The differential distribution of modal olivine with height in differentiated alkaline basic sills provides critical evidence to resolve this controversy, at least for small to medium-large magma chambers. Our own and others' published data for such sills show that, irrespective of overall olivine content, modal olivine contents tend to increase in a roughly symmetrical manner inwards from the upper and lower margins of the sill, i.e. the distribution patterns are more often approximately D-shaped rather than the classic S-shape generally ascribed to gravity settling. We concur with the majority of other authors that this is an original feature of the filling process which has survived more or less unchanged since emplacement. We therefore conclude that the magmas have not undergone turbulent convection and that gravity settling has usually played only a minor modifying role since the intrusion of these sills. We offer a possible explanation for the apparent contradiction between fluid dynamical theory and the petrological evidence by suggesting that such sills rarely fill by the rapid injection of a single pulse of magma. Rather, they form from a series of pulses or a continuous pulsed influx over a protracted interval during which marginal cooling severely limits the potential for thermal convection.

  16. Nonlinear Convective Models of RR Lyrae Stars

    Science.gov (United States)

    Feuchtinger, M.; Dorfi, E. A.

    The nonlinear behavior of RR Lyrae pulsations is investigated using a state-of-the-art numerical technique solving the full time-dependent system of radiation hydrodynamics. Grey radiative transfer is included by a variable Eddington-factor method and we use the time-dependent turbulent convection model according to Kuhfuss (1986, A&A 160, 116) in the version of Wuchterl (1995, Comp. Phys. Comm. 89, 19). OPAL opacities extended by the Alexander molecule opacities at temperatures below 6000 K and an equation of state according to Wuchterl (1990, A&A 238, 83) close the system. The resulting nonlinear system is discretized on an adaptive mesh developed by Dorfi & Drury (1987, J. Comp. Phys. 69, 175), which is important to provide the necessary spatial resolution in critical regions like ionization zones and shock waves. Additionally, we employ a second order advection scheme, a time centered temporal discretizaton and an artificial tensor viscosity in order to treat discontinuities. We compute fundamental as well first overtone models of RR Lyrae stars for a grid of stellar parameters both with and without convective energy transport in order to give a detailed picture of the pulsation-convection interaction. In order to investigate the influence of the different features of the convection model calculations with and without overshooting, turbulent pressure and turbulent viscosity are performed and compared with each other. A standard Fourier decomposition is used to confront the resulting light and radial velocity variations with recent observations and we show that the well known RR Lyrae phase discrepancy problem (Simon 1985, ApJ 299, 723) can be resolved with these stellar pulsation computations.

  17. Natural convective heat transfer from square cylinder

    Energy Technology Data Exchange (ETDEWEB)

    Novomestský, Marcel, E-mail: marcel.novomestsky@fstroj.uniza.sk; Smatanová, Helena, E-mail: helena.smatanova@fstroj.uniza.sk; Kapjor, Andrej, E-mail: andrej.kapjor@fstroj.uniza.sk [University of Žilina, Faculty of Mechanical Engineering, Department of Power Engineering, Univerzitná 1, 010 26 Žilina (Slovakia)

    2016-06-30

    This article is concerned with natural convective heat transfer from square cylinder mounted on a plane adiabatic base, the cylinders having an exposed cylinder surface according to different horizontal angle. The cylinder receives heat from a radiating heater which results in a buoyant flow. There are many industrial applications, including refrigeration, ventilation and the cooling of electrical components, for which the present study may be applicable.

  18. Study of mixed convection in sodium pool

    International Nuclear Information System (INIS)

    Wang Zhou; Chen Yan

    1995-01-01

    The mixed convection phenomena in the sodium pool of fast reactor have been studied systematically by the two dimensional modeling method. A generalized concept of circumferential line in the cylindrical coordinates was proposed to overcome the three dimensional effect induced by the pool geometry in an analysis of two dimensional modeling. A method of sub-step in time was developed for solving the turbulent equations. The treatments on the boundary condition for the auxiliary velocity field have been proposed, and the explanation of allowing the flow function method to be used in the flow field in presence of a mass source term was given. As examples of verification, the experiments were conducted with water flow in a rectangular cavity. The results from theoretical analysis were applied to the numerical computation for the mixed convection in the cavity. The mechanism of stratified flow in the cavity was studied. A numerical calculation was carried out for the mixed convection in hot plenum of a typical fast reactor

  19. Heat transport in bubbling turbulent convection.

    Science.gov (United States)

    Lakkaraju, Rajaram; Stevens, Richard J A M; Oresta, Paolo; Verzicco, Roberto; Lohse, Detlef; Prosperetti, Andrea

    2013-06-04

    Boiling is an extremely effective way to promote heat transfer from a hot surface to a liquid due to numerous mechanisms, many of which are not understood in quantitative detail. An important component of the overall process is that the buoyancy of the bubble compounds with that of the liquid to give rise to a much-enhanced natural convection. In this article, we focus specifically on this enhancement and present a numerical study of the resulting two-phase Rayleigh-Bénard convection process in a cylindrical cell with a diameter equal to its height. We make no attempt to model other aspects of the boiling process such as bubble nucleation and detachment. The cell base and top are held at temperatures above and below the boiling point of the liquid, respectively. By keeping this difference constant, we study the effect of the liquid superheat in a Rayleigh number range that, in the absence of boiling, would be between 2 × 10(6) and 5 × 10(9). We find a considerable enhancement of the heat transfer and study its dependence on the number of bubbles, the degree of superheat of the hot cell bottom, and the Rayleigh number. The increased buoyancy provided by the bubbles leads to more energetic hot plumes detaching from the cell bottom, and the strength of the circulation in the cell is significantly increased. Our results are in general agreement with recent experiments on boiling Rayleigh-Bénard convection.

  20. Modeling mantle convection in the spherical annulus

    Science.gov (United States)

    Hernlund, John W.; Tackley, Paul J.

    2008-12-01

    Most methods for modeling mantle convection in a two-dimensional (2D) circular annular domain suffer from innate shortcomings in their ability to capture several characteristics of the spherical shell geometry of planetary mantles. While methods such as rescaling the inner and outer radius to reduce anomalous effects in a 2D polar cylindrical coordinate system have been introduced and widely implemented, such fixes may have other drawbacks that adversely affect the outcome of some kinds of mantle convection studies. Here we propose a new approach that we term the "spherical annulus," which is a 2D slice that bisects the spherical shell and is quantitatively formulated at the equator of a spherical polar coordinate system after neglecting terms in the governing equations related to variations in latitude. Spherical scaling is retained in this approximation since the Jacobian function remains proportional to the square of the radius. We present example calculations to show that the behavior of convection in the spherical annulus compares favorably against calculations performed in other 2D annular domains when measured relative to those in a fully three-dimensional (3D) spherical shell.

  1. Natural convection of nanofluids over a convectively heated vertical plate embedded in a porous medium

    Energy Technology Data Exchange (ETDEWEB)

    Ghalambaz, M.; Noghrehabadi, A.; Ghanbarzadeh, A., E-mail: m.ghalambaz@gmail.com, E-mail: ghanbarzadeh.a@scu.ac.ir [Department of Mechanical Engineering, Shahid Chamran University of Ahvaz, Ahvaz (Iran, Islamic Republic of)

    2014-04-15

    In this paper, the natural convective flow of nanofluids over a convectively heated vertical plate in a saturated Darcy porous medium is studied numerically. The governing equations are transformed into a set of ordinary differential equations by using appropriate similarity variables, and they are numerically solved using the fourth-order Runge-Kutta method associated with the Gauss-Newton method. The effects of parametric variation of the Brownian motion parameter (Nb), thermophoresis parameter (Nt) and the convective heating parameter (Nc) on the boundary layer profiles are investigated. Furthermore, the variation of the reduced Nusselt number and reduced Sherwood number, as important parameters of heat and mass transfer, as a function of the Brownian motion, thermophoresis and convective heating parameters is discussed in detail. The results show that the thickness of the concentration profiles is much lower than the temperature and velocity profiles. For low values of the convective heating parameter (Nc), as the Brownian motion parameter increases, the non-dimensional wall temperature increases. However, for high values of Nc, the effect of the Brownian motion parameter on the non-dimensional wall temperature is not significant. As the Brownian motion parameter increases, the reduced Sherwood number increases and the reduced Nusselt number decreases. (author)

  2. Analysis of the convective timescale during the major floods in the NE Iberian Peninsula since 1871

    Science.gov (United States)

    Pino, David; Reynés, Artur; Mazon, Jordi; Carles Balasch, Josep; Lluis Ruiz-Bellet, Josep; Tuset, Jordi; Barriendos, Mariano; Castelltort, Xavier

    2016-04-01

    most recent episodes rainfall rate estimation from the convective timescale is compared with the observations. Balasch, J. C., Ruiz-Bellet, J. L., Tuset, J., Barriendos, M., Mazón, J., Pino, D. and Castelltort, X.: Transdisciplinary and multiscale reconstruction of the major flash floods in NE Iberian Peninsula. EGU General Assembly, 2015. Barriendos, M., Ruiz--Bellet, J. L., Tuset, J., Mazon, J., Balasch, J. C., Pino, D., Ayala, J. L.: The "Prediflood" database of historical floods in Catalonia (NE Iberian Peninsula) AD 1035--2013, and its potential applications in flood analysis, Hydrol. Earth Syst. Sci., 18, 4807-4823, 2014. Done, J. M., Craig, G. C., Gray, S. L., Clark, P. A., and Gray, M. E. B.: Mesoscale simulations of organized convection: Importance of convective equilibrium, Q. J. Roy. Meteor. Soc., 132, 737-756, 2006. Molini, L., Parodi, A., Rebora, N. and Craig, G. C.: Classifying severe rainfall events over Italy by hydrometeorological and dynamical criteria, Q. J. Roy. Meteor. Soc., 137, 148-154, 2011.

  3. Magnetism, planetary rotation and convection in the solar system

    CERN Document Server

    1985-01-01

    On the 6th, 7th' and 8th April 1983, a conference entitled "Magnetism, planetary rotation and convection in the Solar System" was held in the School of Physics at the University of Newcastle upon Tyne. The purpose of the meeting was to celebrate the 60th birthday of Prof. Stanley Keith Runcorn and his, and his students' and associates', several decades of scientific achievement. The social programme, which consisted of excursions in Northumberland and Durham with visits to ancient castles and churches, to Hexham Abbey and Durham Cathedral, and dinners in Newcastle and Durham, was greatly enjoyed by those attending the meeting and by their guests. The success ofthe scientific programme can be judged by this special edition of Geophysical Surveys which is derived mainly from the papers given at the meeting. The story starts in the late 1940s when the question of the origin of the magnetic field of the Earth and such other heavenly bodies as had at that time been discovered as having a magnetic field, was exerci...

  4. Ground level air convection produces frost damage patterns in turfgrass.

    Science.gov (United States)

    Ackerson, Bruce J; Beier, Richard A; Martin, Dennis L

    2015-11-01

    Frost injury patterns are commonly observed on the warm-season turfgrass species bermudagrass (Cynodon species Rich.), zoysiagrass (Zoysia species Willd.), and buffalograss [Bouteloua dactyloides (Nutt.) J.T. Columbus] in cool-temperate and subtropical zones. Qualitative observations of these injury patterns are presented and discussed. A model for the formation of such patterns based on thermal instability and convection of air is presented. The characteristic length scale of the observed frost pattern injury requires a temperature profile that decreases with height from the soil to the turfgrass canopy surface followed by an increase in temperature with height above the turfgrass canopy. This is justified by extending the earth temperature theory to include a turf layer with atmosphere above it. Then the theory for a thermally unstable layer beneath a stable region by Ogura and Kondo is adapted to a turf layer to include different parameter values for pure air, as well as for turf, which is treated as a porous medium. The earlier porous medium model of Thompson and Daniels proposed to explain frost injury patterns is modified to give reasonable agreement with observed patterns.

  5. Magnetosphere of Uranus: plasma sources, convection, and field configuration

    International Nuclear Information System (INIS)

    Voigt, G.; Hill, T.W.; Dessler, A.J.

    1983-01-01

    At the time of the Voyager 2 flyby of Uranus, the planetary rotational axis will be roughly antiparallel to the solar wind flow. If Uranus has a magnetic dipole moment that is approximately aligned with its spin axis, and if the heliospheric shock has not been encountered, we will have the rare opportunity to observe a ''pole-on'' magnetosphere as discussed qualitatively by Siscoe. Qualitative arguments based on analogy with Earth, Jupiter, and Saturn suggest that the magnetosphere of Uranus may lack a source of plasma adequate to produce significant internal currents, internal convection, and associated effects. In order to provide a test of this hypothesis with the forthcoming Voyager measurements, we have constructed a class of approximately self-consistent quantitative magnetohydrostatic equilibrium configurations for a pole-on magnetosphere with variable plasma pressure parameters. Given a few simplifying assumptions, the geometries of the magnetic field and of the tail current sheet can be computed for a given distribution of trapped plasma pressure. The configurations have a single funnel-shaped polar cusp that points directly into the solar wind and a cylindrical tail plasma sheet whose currents close within the tail rather than on the tail magnetopause, and whose length depends on the rate of decrease of thermal plasma pressure down the tail. Interconnection between magnetospheric and interplanetary fields results in a highly asymmetric tail-field configuration. These features were predicted qualtitatively by Siscoe; the quantitative models presented here may be useful in the interpretation of Voyager encounter results

  6. Ground level air convection produces frost damage patterns in turfgrass

    Science.gov (United States)

    Ackerson, Bruce J.; Beier, Richard A.; Martin, Dennis L.

    2015-11-01

    Frost injury patterns are commonly observed on the warm-season turfgrass species bermudagrass ( Cynodon species Rich.), zoysiagrass ( Zoysia species Willd.), and buffalograss [ Bouteloua dactyloides (Nutt.) J.T. Columbus] in cool-temperate and subtropical zones. Qualitative observations of these injury patterns are presented and discussed. A model for the formation of such patterns based on thermal instability and convection of air is presented. The characteristic length scale of the observed frost pattern injury requires a temperature profile that decreases with height from the soil to the turfgrass canopy surface followed by an increase in temperature with height above the turfgrass canopy. This is justified by extending the earth temperature theory to include a turf layer with atmosphere above it. Then the theory for a thermally unstable layer beneath a stable region by Ogura and Kondo is adapted to a turf layer to include different parameter values for pure air, as well as for turf, which is treated as a porous medium. The earlier porous medium model of Thompson and Daniels proposed to explain frost injury patterns is modified to give reasonable agreement with observed patterns.

  7. THE INFLUENCE OF PRESSURE-DEPENDENT VISCOSITY ON THE THERMAL EVOLUTION OF SUPER-EARTHS

    Energy Technology Data Exchange (ETDEWEB)

    Stamenkovic, Vlada; Noack, Lena; Spohn, Tilman [Institute of Planetology, Westfaelische Wilhelms-Universitaet Muenster, Wilhelm-Klemm-Str. 10, 48149 Muenster (Germany); Breuer, Doris, E-mail: Vlada.Stamenkovic@dlr.de, E-mail: Lena.Noack@dlr.de, E-mail: Doris.Breuer@dlr.de, E-mail: Tilman.Spohn@dlr.de [Institute of Planetary Research, German Aerospace Center DLR, Rutherfordstrasse 2, 12489 Berlin (Germany)

    2012-03-20

    We study the thermal evolution of super-Earths with a one-dimensional (1D) parameterized convection model that has been adopted to account for a strong pressure dependence of the viscosity. A comparison with a 2D spherical convection model shows that the derived parameterization satisfactorily represents the main characteristics of the thermal evolution of massive rocky planets. We find that the pressure dependence of the viscosity strongly influences the thermal evolution of super-Earths-resulting in a highly sluggish convection regime in the lower mantles of those planets. Depending on the effective activation volume and for cooler initial conditions, we observe with growing planetary mass even the formation of a conductive lid above the core-mantle boundary (CMB), a so-called CMB-lid. For initially molten planets our results suggest no CMB-lids but instead a hot lower mantle and core as well as sluggish lower mantle convection. This implies that the initial interior temperatures, especially in the lower mantle, become crucial for the thermal evolution-the thermostat effect suggested to regulate the interior temperatures in terrestrial planets does not work for massive planets if the viscosity is strongly pressure dependent. The sluggish convection and the potential formation of the CMB-lid reduce the convective vigor throughout the mantle, thereby affecting convective stresses, lithospheric thicknesses, and heat fluxes. The pressure dependence of the viscosity may therefore also strongly affect the propensity of plate tectonics, volcanic activity, and the generation of a magnetic field of super-Earths.

  8. Assessing long-run economic benefits attributed to an IVF-conceived singleton based on projected lifetime net tax contributions in the UK.

    Science.gov (United States)

    Connolly, M; Gallo, F; Hoorens, S; Ledger, W

    2009-03-01

    Over the past decade, demand for fertility treatments has increased as a result of delaying time to first pregnancy and growing awareness and acceptance of available treatment options. Despite increasing demand, health authorities often view infertility as a low health priority and consequently limit access to treatments by rationing and limiting funds. To assess the long-term economic benefits attributed to in vitro fertilization (IVF)-conceived children, we developed a health investment model to evaluate whether state-funded IVF programmes in the UK represent sound fiscal policies. Based on the average investment cost to conceive an IVF singleton, we describe the present value of net taxes derived from gross taxes paid minus direct government transfers received (e.g. education, health, pension) over the lifetime of the child. To establish the present value of investing in IVF, we have discounted all costs from benefits (i.e. lifetime taxes paid) using UK Treasury department rates based on a singleton delivery with similar characteristics for education, earnings, health and life expectancy to a naturally conceived child. The lifetime discounted value of net taxes from an IVF-conceived child with mother aged 35 is pound 109,939 compared with pound 122,127 for a naturally conceived child. The lifetime undiscounted net tax contribution for the IVF-conceived child and naturally conceived child are pound 603,000 and pound 616,000, respectively. An investment of pound 12,931 to achieve an IVF singleton is actually worth 8.5-times this amount to the UK Treasury in discounted future tax revenue. The analysis underscores that costs to the health sector are actually investments when a broader government perspective is considered over a longer period of time.

  9. Increased risk of large-for-gestational age birthweight in singleton siblings conceived with in vitro fertilization in frozen versus fresh cycles.

    Science.gov (United States)

    Luke, Barbara; Brown, Morton B; Wantman, Ethan; Stern, Judy E; Toner, James P; Coddington, Charles C

    2017-02-01

    Children born from fresh in vitro fertilization (IVF) cycles are at greater risk of being born smaller and earlier, even when limited to singletons; those born from frozen cycles have an increased risk of large-for-gestational age (LGA) birthweight (z-score ≥1.28). This analysis sought to overcome limitations in other studies by using pairs of siblings, and accounting for prior cycle outcomes, maternal characteristics, and embryo state and stage. Pairs of singleton births conceived with IVF and born between 2004 and 2013 were identified from the Society for Assisted Reproductive Technology Clinic Outcome Reporting System database, matched for embryo stage (blastocyst versus non-blastocyst) and infant gender, categorized by embryo state (fresh versus frozen) in 1st and 2nd births (four groups). The data included 7795 singleton pairs. Birthweight z-scores were 0.00-0.04 and 0.24-0.26 in 1st and 2nd births in fresh cycles, and 0.25-0.34 and 0.50-0.55 in frozen cycles, respectively. LGA was 9.2-9.8 and 14.2-15.4% in 1st and 2nd births in fresh cycles, and 13.1-15.8 and 20.8-21.0% in 1st and 2nd births in frozen cycles. The risk of LGA was increased in frozen cycles (1st births, adjusted odds ratios (AOR) 1.74, 95% CI 1.45, 2.08; and in 2nd births when the 1st birth was not LGA, AOR 1.70, 95% CI 1.46, 1.98 for fresh/frozen and 1.40, 1.11, 1.78 for frozen/frozen). Our results with siblings indicate that frozen embryo state is associated with an increased risk for LGA. The implications of these findings for childhood health and risk of obesity are unclear, and warrant further investigation.

  10. A Single Mode Study of a Quasi-Geostrophic Convection-Driven Dynamo Model

    Science.gov (United States)

    Plumley, M.; Calkins, M. A.; Julien, K. A.; Tobias, S.

    2017-12-01

    Planetary magnetic fields are thought to be the product of hydromagnetic dynamo action. For Earth, this process occurs within the convecting, turbulent and rapidly rotating outer core, where the dynamics are characterized by low Rossby, low magnetic Prandtl and high Rayleigh numbers. Progress in studying dynamos has been limited by current computing capabilities and the difficulties in replicating the extreme values that define this setting. Asymptotic models that embrace these extreme parameter values and enforce the dominant balance of geostrophy provide an option for the study of convective flows with actual relevance to geophysics. The quasi-geostrophic dynamo model (QGDM) is a multiscale, fully-nonlinear Cartesian dynamo model that is valid in the asymptotic limit of low Rossby number. We investigate the QGDM using a simplified class of solutions that consist of a single horizontal wavenumber which enforces a horizontal structure on the solutions. This single mode study is used to explore multiscale time stepping techniques and analyze the influence of the magnetic field on convection.

  11. EUREC4A: A Field Campaign to Elucidate the Couplings Between Clouds, Convection and Circulation

    Science.gov (United States)

    Bony, Sandrine; Stevens, Bjorn; Ament, Felix; Bigorre, Sebastien; Chazette, Patrick; Crewell, Susanne; Delanoë, Julien; Emanuel, Kerry; Farrell, David; Flamant, Cyrille; Gross, Silke; Hirsch, Lutz; Karstensen, Johannes; Mayer, Bernhard; Nuijens, Louise; Ruppert, James H.; Sandu, Irina; Siebesma, Pier; Speich, Sabrina; Szczap, Frédéric; Totems, Julien; Vogel, Raphaela; Wendisch, Manfred; Wirth, Martin

    2017-11-01

    Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. Numerical models represent this interplay in diverse ways, which translates into different responses of trade-cumuli to climate perturbations. Climate models predict that the area covered by shallow cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of trade-cumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air-sea interactions and convective organization.

  12. Self-consistent theory of three-dimensional convection in the geomagnetic tail

    International Nuclear Information System (INIS)

    Birn, J.; Schindler, K.

    1983-01-01

    The self-consistent theory of time-dependent convection in the earth's magnetotail of Schindler and Birn (1982) is extended to three dimensions to include more realistic tail geometry and three-dimensional flow. We confirm that a steady state solution implies unrealistic tail geometry or large particle or energy losses that are unrealistic during quiet times and conclude therefore that as in the 2-dimensional case the magnetotail becomes time-dependent for typical convection electric fields. Explicit solutions are derived, even analytically, for the three-dimensional flow and the electric and magnetic field in a realistic tail geometry, and quantitative examples are presented. Consequences of time-dependent convection are demonstrated considering two idealized cases of magnetosphere response to solar wind changes: (1) uniform compression as the likely consequence of increasing (static, dynamic or magnetic) solar wind pressure; and (2) compression only in the z direction perpendicular to the plasma sheet as the probable consequence of a dawn to dusk external electric field (E/sub y/>0), corresponding to a southward interplanetary magnetic field component (B/sub z/ 0 with geomagnetic activity. Several other features, already present in the 2-dimensional theory, are confirmed

  13. EUREC4A: A Field Campaign to Elucidate the Couplings Between Clouds, Convection and Circulation

    Science.gov (United States)

    Bony, Sandrine; Stevens, Bjorn; Ament, Felix; Bigorre, Sebastien; Chazette, Patrick; Crewell, Susanne; Delanoë, Julien; Emanuel, Kerry; Farrell, David; Flamant, Cyrille; Gross, Silke; Hirsch, Lutz; Karstensen, Johannes; Mayer, Bernhard; Nuijens, Louise; Ruppert, James H.; Sandu, Irina; Siebesma, Pier; Speich, Sabrina; Szczap, Frédéric; Totems, Julien; Vogel, Raphaela; Wendisch, Manfred; Wirth, Martin

    Trade-wind cumuli constitute the cloud type with the highest frequency of occurrence on Earth, and it has been shown that their sensitivity to changing environmental conditions will critically influence the magnitude and pace of future global warming. Research over the last decade has pointed out the importance of the interplay between clouds, convection and circulation in controling this sensitivity. Numerical models represent this interplay in diverse ways, which translates into different responses of tradecumuli to climate perturbations. Climate models predict that the area covered by shallow cumuli at cloud base is very sensitive to changes in environmental conditions, while process models suggest the opposite. To understand and resolve this contradiction, we propose to organize a field campaign aimed at quantifying the physical properties of tradecumuli (e.g., cloud fraction and water content) as a function of the large-scale environment. Beyond a better understanding of clouds-circulation coupling processes, the campaign will provide a reference data set that may be used as a benchmark for advancing the modelling and the satellite remote sensing of clouds and circulation. It will also be an opportunity for complementary investigations such as evaluating model convective parameterizations or studying the role of ocean mesoscale eddies in air-sea interactions and convective organization.

  14. Spontaneous generation and reversals of mean flows in a convectively-generated internal gravity wave field

    Science.gov (United States)

    Couston, Louis-Alexandre; Lecoanet, Daniel; Favier, Benjamin; Le Bars, Michael

    2017-11-01

    We investigate via direct numerical simulations the spontaneous generation and reversals of mean zonal flows in a stably-stratified fluid layer lying above a turbulent convective fluid. Contrary to the leading idealized theories of mean flow generation by self-interacting internal waves, the emergence of a mean flow in a convectively-generated internal gravity wave field is not always possible because nonlinear interactions of waves of different frequencies can disrupt the mean flow generation mechanism. Strong mean flows thus emerge when the divergence of the Reynolds stress resulting from the nonlinear interactions of internal waves produces a strong enough anti-diffusive acceleration for the mean flow, which, as we will demonstrate, is the case when the Prandtl number is sufficiently low, or when the energy input into the internal wavefield by the convection and density stratification are sufficiently large. Implications for mean zonal flow production as observed in the equatorial stratospheres of the Earth, Saturn and Jupiter, and possibly occurring in other geophysical systems such as planetary and stellar interiors will be briefly discussed. Funding provided by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program through Grant Agreement No. 681835-FLUDYCO-ERC-2015-CoG.

  15. Convective Heat Transfer Coefficients of the Human Body under Forced Convection from Ceiling

    DEFF Research Database (Denmark)

    Kurazumi, Yoshihito; Rezgals, Lauris; Melikov, Arsen Krikor

    2014-01-01

    The average convective heat transfer coefficient for a seated human body exposed to downward flow from above was determined. Thermal manikin with complex body shape and size of an average Scandinavian female was used. The surface temperature distribution of the manikin’s body was as the skin...... of the convective heat transfer coefficient of the whole body (hc [W/(m2•K)]) was proposed: hc=4.088+6.592V1.715 for a seated naked body at 20ºC and hc=2.874+7.427V1.345 for a seated naked body at 26ºC. Differences in the convective heat transfer coefficient of the whole body in low air velocity range, V

  16. The Lifeworld Earth and a Modelled Earth

    Science.gov (United States)

    Juuti, Kalle

    2014-01-01

    The goal of this paper is to study the question of whether a phenomenological view of the Earth could be empirically endorsed. The phenomenological way of thinking considers the Earth as a material entity, but not as an object as viewed in science. In the learning science tradition, tracking the process of the conceptual change of the shape of the…

  17. Rare earth sulfates

    International Nuclear Information System (INIS)

    Komissarova, L.N.; Shatskij, V.M.; Pokrovskij, A.N.; Chizhov, S.M.; Bal'kina, T.I.; Suponitskij, Yu.L.

    1986-01-01

    Results of experimental works on the study of synthesis conditions, structure and physico-chemical properties of rare earth, scandium and yttrium sulfates, have been generalized. Phase diagrams of solubility and fusibility, thermodynamic and crystallochemical characteristics, thermal stability of hydrates and anhydrous sulfates of rare earths, including normal, double (with cations of alkali and alkaline-earth metals), ternary and anion-mixed sulfates of rare earths, as well as their adducts, are considered. The state of ions of rare earths, scandium and yttrium in aqueous sulfuric acid solutions is discussed. Data on the use of rare earth sulfates are given

  18. Rare earth germanates

    International Nuclear Information System (INIS)

    Bondar', I.A.; Vinogradova, N.V.; Dem'yanets, L.N.

    1983-01-01

    Rare earth germanates attract close attention both as an independent class of compounds and analogues of a widely spread class of natural and synthetic minerals. The methods of rare earth germanate synthesis (solid-phase, hydrothermal) are considered. Systems on the basis of germanium and rare earth oxides, phase diagrams, phase transformations are studied. Using different chemical analysese the processes of rare earth germanate formation are investigated. IR spectra of alkali and rare earth metal germanates are presented, their comparative analysis being carried out. Crystal structures of the compounds, lattice parameters are studied. Fields of possible application of rare earth germanates are shown

  19. Global imaging of the Earth's deep interior: seismic constraints on (an)isotropy, density and attenuation

    NARCIS (Netherlands)

    Trampert, J.; Fichtner, A.

    2013-01-01

    Seismic tomography is the principal tool to probe the deep interior of the Earth. Models of seismic anisotropy induced by crystal alignment provide insight into the underlying convective motion, and variations of density allow us to discriminate between thermal and compositional heterogeneities.

  20. Convergence behavior of idealized convection-resolving simulations of summertime deep moist convection over land

    Science.gov (United States)

    Panosetti, Davide; Schlemmer, Linda; Schär, Christoph

    2018-05-01

    Convection-resolving models (CRMs) can explicitly simulate deep convection and resolve interactions between convective updrafts. They are thus increasingly used in numerous weather and climate applications. However, the truncation of the continuous energy cascade at scales of O (1 km) poses a serious challenge, as in kilometer-scale simulations the size and properties of the simulated convective cells are often determined by the horizontal grid spacing (Δ x ).In this study, idealized simulations of deep moist convection over land are performed to assess the convergence behavior of a CRM at Δ x = 8, 4, 2, 1 km and 500 m. Two types of convergence estimates are investigated: bulk convergence addressing domain-averaged and integrated variables related to the water and energy budgets, and structural convergence addressing the statistics and scales of individual clouds and updrafts. Results show that bulk convergence generally begins at Δ x =4 km, while structural convergence is not yet fully achieved at the kilometer scale, despite some evidence that the resolution sensitivity of updraft velocities and convective mass fluxes decreases at finer resolution. In particular, at finer grid spacings the maximum updraft velocity generally increases, and the size of the smallest clouds is mostly determined by Δ x . A number of different experiments are conducted, and it is found that the presence of orography and environmental vertical wind shear yields more energetic structures at scales much larger than Δ x , sometimes reducing the resolution sensitivity. Overall the results lend support to the use of kilometer-scale resolutions in CRMs, despite the inability of these models to fully resolve the associated cloud field.

  1. The MJO Transition from Shallow to Deep Convection in CloudSat/CALIPSO Data and GISS GCM Simulations

    Science.gov (United States)

    DelGenio, Anthony G.; Chen, Yonghua; Kim, Daehyun; Yao, Mao-Sung

    2013-01-01

    The relationship between convective penetration depth and tropospheric humidity is central to recent theories of the Madden-Julian oscillation (MJO). It has been suggested that general circulation models (GCMs) poorly simulate the MJO because they fail to gradually moisten the troposphere by shallow convection and simulate a slow transition to deep convection. CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) data are analyzed to document the variability of convection depth and its relation to water vapor during the MJO transition from shallow to deep convection and to constrain GCM cumulus parameterizations. Composites of cloud occurrence for 10MJO events show the following anticipatedMJO cloud structure: shallow and congestus clouds in advance of the peak, deep clouds near the peak, and upper-level anvils after the peak. Cirrus clouds are also frequent in advance of the peak. The Advanced Microwave Scanning Radiometer for EarthObserving System (EOS) (AMSR-E) columnwater vapor (CWV) increases by;5 mmduring the shallow- deep transition phase, consistent with the idea of moisture preconditioning. Echo-top height of clouds rooted in the boundary layer increases sharply with CWV, with large variability in depth when CWV is between;46 and 68 mm. International Satellite Cloud Climatology Project cloud classifications reproduce these climatological relationships but correctly identify congestus-dominated scenes only about half the time. A version of the Goddard Institute for Space Studies Model E2 (GISS-E2) GCM with strengthened entrainment and rain evaporation that produces MJO-like variability also reproduces the shallow-deep convection transition, including the large variability of cloud-top height at intermediate CWV values. The variability is due to small grid-scale relative humidity and lapse rate anomalies for similar values of CWV. 1.

  2. Vorticity imbalance and stability in relation to convection

    Science.gov (United States)

    Read, W. L.; Scoggins, J. R.

    1977-01-01

    A complete synoptic-scale vorticity budget was related to convection storm development in the eastern two-thirds of the United States. The 3-h sounding interval permitted a study of time changes of the vorticity budget in areas of convective storms. Results of analyses revealed significant changes in values of terms in the vorticity equation at different stages of squall line development. Average budgets for all areas of convection indicate systematic imbalance in the terms in the vorticity equation. This imbalance resulted primarily from sub-grid scale processes. Potential instability in the lower troposphere was analyzed in relation to the development of convective activity. Instability was related to areas of convection; however, instability alone was inadequate for forecast purposes. Combinations of stability and terms in the vorticity equation in the form of indices succeeded in depicting areas of convection better than any one item separately.

  3. A Thermodynamically General Theory for Convective Circulations and Vortices

    Science.gov (United States)

    Renno, N. O.

    2007-12-01

    Convective circulations and vortices are common features of atmospheres that absorb low-entropy-energy at higher temperatures than they reject high-entropy-energy to space. These circulations range from small to planetary-scale and play an important role in the vertical transport of heat, momentum, and tracer species. Thus, the development of theoretical models for convective phenomena is important to our understanding of many basic features of planetary atmospheres. A thermodynamically general theory for convective circulations and vortices is proposed. The theory includes irreversible processes and quantifies the pressure drop between the environment and any point in a convective updraft. The article's main result is that the proposed theory provides an expression for the pressure drop along streamlines or streamtubes that is a generalization of Bernoulli's equation to convective circulations. We speculate that the proposed theory not only explains the intensity, but also shed light on other basic features of convective circulations and vortices.

  4. Thermo-electro-hydrodynamic convection under microgravity: a review

    Energy Technology Data Exchange (ETDEWEB)

    Mutabazi, Innocent; Yoshikawa, Harunori N; Fogaing, Mireille Tadie; Travnikov, Vadim; Crumeyrolle, Olivier [Laboratoire Ondes et Milieux Complexes, UMR 6294, CNRS-Université du Havre, CS 80450, F-76058 Le Havre Cedex (France); Futterer, Birgit; Egbers, Christoph, E-mail: Innocent.Mutabazi@univ-lehavre.fr [Department of Aerodynamics and Fluid Mechanics, Brandenburg University of Technology Cottbus-Senftenberg, Cottbus (Germany)

    2016-12-15

    Recent studies on thermo-electro-hydrodynamic (TEHD) convection are reviewed with focus on investigations motivated by the analogy with natural convection. TEHD convection originates in the action of the dielectrophoretic force generated by an alternating electric voltage applied to a dielectric fluid with a temperature gradient. This electrohydrodynamic force is analogous to Archimedean thermal buoyancy and can be regarded as a thermal buoyancy force in electric effective gravity. The review is concerned with TEHD convection in plane, cylindrical, and spherical capacitors under microgravity conditions, where the electric gravity can induce convection without any complexities arising from geometry or the buoyancy force due to the Earth’s gravity. We will highlight the convection in spherical geometry, comparing developed theories and numerical simulations with the GEOFLOW experiments performed on board the International Space Station (ISS). (paper)

  5. Convective boundary layer heights over mountainous terrain - A review of concepts -

    Science.gov (United States)

    De Wekker, Stephan; Kossmann, Meinolf

    2015-12-01

    Mountainous terrain exerts an important influence on the Earth's atmosphere and affects atmospheric transport and mixing at a wide range of temporal and spatial scales. The vertical scale of this transport and mixing is determined by the height of the atmospheric boundary layer, which is therefore an important parameter in air pollution studies, weather forecasting, climate modeling, and many other applications. It is recognized that the spatio-temporal structure of the daytime convective boundary layer (CBL) height is strongly modified and more complex in hilly and mountainous terrain compared to flat terrain. While the CBL over flat terrain is mostly dominated by turbulent convection, advection from multi-scale thermally driven flows plays an important role for the CBL evolution over mountainous terrain. However, detailed observations of the CBL structure and understanding of the underlying processes are still limited. Characteristics of CBL heights in mountainous terrain are reviewed for dry, convective conditions. CBLs in valleys and basins, where hazardous accumulation of pollutants is of particular concern, are relatively well-understood compared to CBLs over slopes, ridges, or mountain peaks. Interests in the initiation of shallow and deep convection, and of budgets and long-range transport of air pollutants and trace gases, have triggered some recent studies on terrain induced exchange processes between the CBL and the overlying atmosphere. These studies have helped to gain more insight into CBL structure over complex mountainous terrain, but also show that the universal definition of CBL height over mountains remains an unresolved issue. The review summarizes the progress that has been made in documenting and understanding spatio-temporal behavior of CBL heights in mountainous terrain and concludes with a discussion of open research questions and opportunities for future research.

  6. NASA Earth Exchange (NEX)

    Data.gov (United States)

    National Aeronautics and Space Administration — The NASA Earth Exchange (NEX) represents a new platform for the Earth science community that provides a mechanism for scientific collaboration and knowledge sharing....

  7. Primary Issues of Mixed Convection Heat Transfer Phenomena

    Energy Technology Data Exchange (ETDEWEB)

    Chae, Myeong-Seon; Chung, Bum-Jin [Kyung Hee University, Yongin (Korea, Republic of)

    2015-10-15

    The computer code analyzing the system operating and transient behavior must distinguish flow conditions involved with convective heat transfer flow regimes. And the proper correlations must be supplied to those flow regimes. However the existing safety analysis codes are focused on the Light Water Reactor and they are skeptical to be applied to the GCRs (Gas Cooled Reactors). One of the technical issues raise by the development of the VHTR is the mixed convection, which occur when the driving forces of both forced and natural convection are of comparable magnitudes. It can be encountered as in channel of the stacked with fuel elements and a decay heat removal system and in VHTR. The mixed convection is not intermediate phenomena with natural convection and forced convection but independent complicated phenomena. Therefore, many researchers have been studied and some primary issues were propounded for phenomena mixed convection. This paper is to discuss some problems identified through reviewing the papers for mixed convection phenomena. And primary issues of mixed convection heat transfer were proposed respect to thermal hydraulic problems for VHTR. The VHTR thermal hydraulic study requires an indepth study of the mixed convection phenomena. In this study we reviewed the classical flow regime map of Metais and Eckert and derived further issues to be considered. The following issues were raised: (1) Buoyancy aided an opposed flows were not differentiated and plotted in a map. (2) Experimental results for UWT and UHF condition were also plotted in the same map without differentiation. (3) The buoyancy coefficient was not generalized for correlating with buoyancy coefficient. (4) The phenomenon analysis for laminarization and returbulization as buoyancy effects in turbulent mixed convection was not established. (5) The defining to transition in mixed convection regime was difficult.

  8. Some problems of free convection in a macrocapillary

    Energy Technology Data Exchange (ETDEWEB)

    Luikov, A V; Berkovsky, B M; Kolpashchikov, V L

    1971-01-01

    Solution is given to a number of problems of free convection in incompressible viscous fluid in elementary macrocapillaries with nonuniform temperature distribution at the boundary. The fluid flow structure and effect of a magnetic field on convection in the case of conducting fluid has been studied in detail. The influence of macrocapillary properties on the flow structure, rate of convection, and temperature distribution has been estimated.

  9. Convective Cold Pool Structure and Boundary Layer Recovery in DYNAMO

    Science.gov (United States)

    Savarin, A.; Chen, S. S.; Kerns, B. W.; Lee, C.; Jorgensen, D. P.

    2012-12-01

    One of the key factors controlling convective cloud systems in the Madden-Julian Oscillation (MJO) over the tropical Indian Ocean is the property of the atmospheric boundary layer. Convective downdrafts and precipitation from the cloud systems produce cold pools in the boundary layer, which can inhibit subsequent development of convection. The recovery time is the time it takes for the boundary layer to return to pre convective conditions. It may affect the variability of the convection on various time scales during the initiation of MJO. This study examines the convective cold pool structure and boundary layer recovery using the NOAA WP-3D aircraft observations, include the flight-level, Doppler radar, and GPS dropsonde data, collected during the Dynamics of MJO (DYNAMO) field campaign from November-December 2011. The depth and strength of convective cold pools are defined by the negative buoyancy, which can be computed from the dropsonde data. Convective downdraft can be affected by environmental water vapor due to entrainment. Mid-level dry air observed during the convectively suppressed phase of MJO seems to enhance convective downdraft, making the cold pools stronger and deeper. Recovery of the cold pools in the boundary layer is determined by the strength and depth of the cold pools and also the air-sea heat and moisture fluxes. Given that the water vapor and surface winds are distinct for the convectively active and suppressed phases of MJO over the Indian Ocean, the aircraft data are stratified by the two different large-scale regimes of MJO. Preliminary results show that the strength and depth of the cold pools are inversely correlated with the surrounding mid-level moisture. During the convectively suppressed phase, the recovery time is ~5-20 hours in relative weak wind condition with small air-sea fluxes. The recovery time is generally less than 6 hours during the active phase of MJO with moist mid-levels and stronger surface wind and air-sea fluxes.

  10. Strategic Repositioning for Convection Business Case Study: AR Vendor

    OpenAIRE

    Anindita, Pratisara Satwika; Toha, Mohamad

    2013-01-01

    The study aims to determine suitable position and strategy in order to reach superiority in convection business based on the company strengths and weaknesses. A study conducted in late 2012 at AR Vendor, a home-based convection company which focus on the t-shirt screen printing service. In response to the issue of the below average profit margin, the company has to rethink their position and strategy in handling the convection business environment. While AR Vendor business may growth in accor...

  11. Convection Cells in the Atmospheric Boundary Layer

    Science.gov (United States)

    Fodor, Katherine; Mellado, Juan-Pedro

    2017-04-01

    In dry, shear-free convective boundary layers (CBLs), the turbulent flow of air is known to organise itself on large scales into coherent, cellular patterns, or superstructures, consisting of fast, narrow updraughts and slow, wide downdraughts which together form circulations. Superstructures act as transport mechanisms from the surface to the top of the boundary layer and vice-versa, as opposed to small-scale turbulence, which only modifies conditions locally. This suggests that a thorough investigation into superstructure properties may help us better understand transport across the atmospheric boundary layer as a whole. Whilst their existence has been noted, detailed studies into superstructures in the CBL have been scarce. By applying methods which are known to successfully isolate similar large-scale patterns in turbulent Rayleigh-Bénard convection, we can assess the efficacy of those detection techniques in the CBL. In addition, through non-dimensional analysis, we can systematically compare superstructures in various convective regimes. We use direct numerical simulation of four different cases for intercomparison: Rayleigh-Bénard convection (steady), Rayleigh-Bénard convection with an adiabatic top lid (quasi-steady), a stably-stratified CBL (quasi-steady) and a neutrally-stratified CBL (unsteady). The first two are non-penetrative and the latter two penetrative. We find that although superstructures clearly emerge from the time-mean flow in the non-penetrative cases, they become obscured by temporal averaging in the CBL. This is because a rigid lid acts to direct the flow into counter-rotating circulation cells whose axis of rotation remains stationary, whereas a boundary layer that grows in time and is able to entrain fluid from above causes the circulations to not only grow in vertical extent, but also to move horizontally and merge with neighbouring circulations. Spatial filtering is a useful comparative technique as it can be performed on boundary

  12. Fully determined scaling laws for volumetrically heated convective systems, a tool for assessing habitability of exoplanets

    Science.gov (United States)

    Vilella, Kenny; Kaminski, Edouard

    2017-05-01

    The long-term habitability of a planet rises from its ability to generate and maintain an atmosphere through partial melting and volcanism. This question has been mainly addressed in the framework of plate tectonics, which may be too specific to apply to the wide range of internal dynamics expected for exoplanets, and even to the thermal evolution of the early Earth. Here we propose a more general theoretical approach of convection to build a regime diagram giving the conditions for partial melting to occur, in planetary bodies, as a function of key parameters that can be estimated for exoplanets, their size and internal heating rate. To that aim, we introduce a refined view of the Thermal Boundary Layer (TBL) in a convective system heated from within, that focuses on the temperature and thickness of the TBL at the top of the hottest temperature profiles, along which partial melting shall first occur. This ;Hottest Thermal Boundary Layer; (HotTBL) is first characterized using fully theoretical scaling laws based on the dynamics of thermal boundary layers. These laws are the first ones proposed in the literature that do not rely on empirical determinations of dimensionless constants and that apply to both low Rayleigh and high Rayleigh convective regimes. We show that the scaling laws can be successfully applied to planetary bodies by comparing their predictions to full numerical simulations of the Moon. We then use the scaling laws to build a regime diagram for exoplanets. Combined with estimates of internal heating in exoplanets, the regime diagram predicts that in the habitable zone partial melting occurs in planets younger than the Earth.

  13. Hyperthyroidism is associated with work disability and loss of labour market income. A Danish register-based study in singletons and disease-discordant twin pairs.

    Science.gov (United States)

    Brandt, Frans; Thvilum, Marianne; Hegedüs, Laszlo; Brix, Thomas Heiberg

    2015-11-01

    To examine the risk of disability pension and changes in labour market income in patients with hyperthyroidism. From a 5% random sample of the Danish population and twins from the Danish Twin Registry we identified 1942 hyperthyroid singletons and 7768 non-hyperthyroid (matched 1:4) controls as well as 584 same-sex twin pairs discordant for hyperthyroidism. Singletons and twins were followed for a mean of 9 years (range 1-20). Cox regression analysis was used to examine the risk of disability pension and a difference-in-differences model was used to evaluate changes in labour market income. Hyperthyroid individuals had an increased risk of receiving disability pension: hazard ratio (HR) was 1.88, (95% CI: 1.57-2.24). Subdividing as to the cause of hyperthyroidism did not change this finding: Graves' disease (GD) HR was 1.51 (95% CI: 0.87-2.63) and toxic nodular goitre (TNG) HR was 2.10 (95% CI: 1.02-4.36). With respect to labour market income, the income of hyperthyroid individuals increased on average 1189 € less than their controls (Phyperthyroidism. Hyperthyroidism is associated with severe work disability as reflected by an 88% increased risk of receiving disability pension and a significant loss of labour market income. Similar results in monozygotic twins discordant for hyperthyroidism suggest that genetic confounding is unlikely. © 2015 European Society of Endocrinology.

  14. Outcome of singleton preterm small for gestational age infants born to mothers with pregnancy-induced hypertension. A population-based study.

    Science.gov (United States)

    Regev, Rivka H; Arnon, Shmuel; Litmanovitz, Ita; Bauer-Rusek, Sofia; Boyko, Valentina; Lerner-Geva, Liat; Reichman, Brian

    2015-04-01

    Pregnancy-induced hypertension (PIH) has been associated with a decreased risk of infant mortality in small for gestational age (SGA) preterm infants. To evaluate the influence of PIH on mortality and major neonatal morbidities in singleton preterm SGA infants, in the presence and absence of acute pregnancy complications. Population-based observational study of singleton SGA infants, born at 24 to 32 weeks gestation in the period 1995-2010 (n = 2139). Multivariable logistic regression analyses were used to assess the independent effect of PIH on mortality and neonatal morbidities. Acute pregnancy complications comprised premature labor, premature rupture of membranes >6 h, antepartum hemorrhage and clinical chorioamnionitis. In the absence of pregnancy complications, the odds ratio (95% confidence interval) for mortality (0.77; 0.50-1.16), survival without severe neurological morbidity (1.14; 0.79-1.65) and survival without bronchopulmonary dysplasia (BPD) (0.85; 0.59-1.21) were similar in the PIH versus no-PIH groups. In the presence of pregnancy complications, mortality (0.76; 0.40-1.44), survival without severe neurological morbidity (1.16; 0.64-2.12) and survival without BPD (1.04; 0.58-1.86) were also similar in the PIH versus no-PIH groups. PIH was not associated with improved outcome in preterm SGA infants, both in the presence and absence of acute pregnancy complications.

  15. Transitions in rapidly rotating convection dynamos

    Science.gov (United States)

    Tilgner, A.

    2013-12-01

    It is commonly assumed that buoyancy in the fluid core powers the geodynamo. We study here the minimal model of a convection driven dynamo, which is a horizontal plane layer in a gravity field, filled with electrically conducting fluid, heated from below and cooled from above, and rotating about a vertical axis. Such a plane layer may be viewed as a local approximation to the geophysically more relevant spherical geometry. The numerical simulations have been run on graphics processing units with at least 960 cores. If the convection is driven stronger and stronger at fixed rotation rate, the flow behaves at some point as if it was not rotating. This transition shows in the scaling of the heat transport which can be used to distinguish slow from rapid rotation. One expects dynamos to behave differently in these two flow regimes. But even within the convection flows which are rapidly rotating according to this criterion, it will be shown that different types of dynamos exist. In one state, the magnetic field strength obeys a scaling indicative of a magnetostrophic balance, in which the Lorentz force is in equilibrium with the Coriolis force. The flow in this case is helical. A different state exists at higher magnetic Reynolds numbers, in which the magnetic energy obeys a different scaling law and the helicity of the flow is much reduced. As one increases the Rayleigh number, all other parameters kept constant, one may find both types of dynamos separated by an interval of Rayleigh numbers in which there are no dynamos at all. The effect of these transitions on energy dissipation and mean field generation have also been studied.

  16. What Determines Upscale Growth of Oceanic Convection into MCSs?

    Science.gov (United States)

    Zipser, E. J.

    2017-12-01

    Over tropical oceans, widely scattered convection of various depths may or may not grow upscale into mesoscale convective systems (MCSs). But what distinguishes the large-scale environment that favors such upscale growth from that favoring "unorganized", scattered convection? Is it some combination of large-scale low-level convergence and ascending motion, combined with sufficient instability? We recently put this to a test with ERA-I reanalysis data, with disappointing results. The "usual suspects" of total column water vapor, large-scale ascent, and CAPE may all be required to some extent, but their differences between large MCSs and scattered convection are small. The main positive results from this work (already published) demonstrate that the strength of convection is well correlated with the size and perhaps "organization" of convective features over tropical oceans, in contrast to tropical land, where strong convection is common for large or small convective features. So, important questions remain: Over tropical oceans, how should we define "organized" convection? By size of the precipitation area? And what environmental conditions lead to larger and better organized MCSs? Some recent attempts to answer these questions will be described, but good answers may require more data, and more insights.

  17. Natural convection in superposed fluid-porous layers

    CERN Document Server

    Bagchi, Aniruddha

    2013-01-01

    Natural Convection in Composite Fluid-Porous Domains provides a timely overview of the current state of understanding on the phenomenon of convection in composite fluid-porous layers. Natural convection in horizontal fluid-porous layers has received renewed attention because of engineering problems such as post-accident cooling of nuclear reactors, contaminant transport in groundwater, and convection in fibrous insulation systems. Because applications of the problem span many scientific domains, the book serves as a valuable resource for a wide audience.

  18. Urban Influences on Convection and Lightning Over Houston

    National Research Council Canada - National Science Library

    Gauthier, Michael L

    2006-01-01

    The research presented in this dissertation addresses a fundamental question regarding urban, ultimately anthropogenic, influences on convection as it relates to lightning production and precipitation structure...

  19. Effects of variable thermal diffusivity on the structure of convection

    Science.gov (United States)

    Shcheritsa, O. V.; Getling, A. V.; Mazhorova, O. S.

    2018-03-01

    The structure of multiscale convection in a thermally stratified plane horizontal fluid layer is investigated by means of numerical simulations. The thermal diffusivity is assumed to produce a thin boundary sublayer convectively much more unstable than the bulk of the layer. The simulated flow is a superposition of cellular structures with three different characteristic scales. In contrast to the largest convection cells, the smaller ones are localised in the upper portion of the layer. The smallest cells are advected by the larger-scale convective flows. The simulated flow pattern qualitatively resembles that observed on the Sun.

  20. Cumulus convection and the terrestrial water-vapor distribution

    Science.gov (United States)

    Donner, Leo J.

    1988-01-01

    Cumulus convection plays a significant role in determining the structure of the terrestrial water vapor field. Cumulus convection acts directly on the moisture field by condensing and precipitating water vapor and by redistributing water vapor through cumulus induced eddy circulations. The mechanisms by which cumulus convection influences the terrestrial water vapor distribution is outlined. Calculations using a theory due to Kuo is used to illustrate the mechanisms by which cumulus convection works. Understanding of these processes greatly aids the ability of researchers to interpret the seasonal and spatial distribution of atmospheric water vapor by providing information on the nature of sources and sinks and the global circulation.

  1. Natural convection between two concentric spheres

    International Nuclear Information System (INIS)

    Blondel-Roux, Marie

    1983-01-01

    After an overview of researches on natural convection in a confined or semi-confined environment, this research thesis reports the use of the Caltagirone and Mojtabi numerical model and the study of its validity for different values of the Rayleigh and Prandtl numbers. Results obtained with this model are compared with experimental ones. Thermal transfer curves are presented and discussed, as well as the different temperature fields numerically obtained, flow function fields, velocities in the fluid layer, and temperature profiles with respect to the Rayleigh number [fr

  2. Measurement of natural convection by speckle photography

    International Nuclear Information System (INIS)

    Wernekinck, U.; Merzkirch, W.

    1986-01-01

    The principle of speckle photography can be applied to the measurement of density variations in fluids. A modification of existing experimental arrangements allows for the measurement of large values of the light deflection angles as they may occur in heat and mass transfer situations. The method is demonstrated for the case of a helium jet exhausting into still air and the natural convective flow along a heated plate. The obtained data are compared with results measured with classical optical interferometers, and good agreement is found. The advantages of the new technique over the classical optical methods are briefly discussed. 11 references

  3. Hamiltonian Description of Convective-cell Generation

    International Nuclear Information System (INIS)

    Krommes, J.A.; Kolesnikov, R.A.

    2004-01-01

    The nonlinear statistical growth rate eq for convective cells driven by drift-wave (DW) interactions is studied with the aid of a covariant Hamiltonian formalism for the gyrofluid nonlinearities. A statistical energy theorem is proven that relates eq to a second functional tensor derivative of the DW energy. This generalizes to a wide class of systems of coupled partial differential equations a previous result for scalar dynamics. Applications to (i) electrostatic ion-temperature-gradient-driven modes at small ion temperature, and (ii) weakly electromagnetic collisional DW's are noted

  4. Sunspots and the physics of magnetic flux tubes. VI - Convective propulsion. VII - Heat flow in a convective downdraft

    Science.gov (United States)

    Parker, E. N.

    1979-01-01

    The effect of negative aerodynamic drag in an ideal fluid subject to convective instability is considered. It is shown that a cylinder moving in such a fluid is propelled forward in its motion by the convective forces and that the characteristic acceleration time is comparable to the onset time of convective motions in the fluid. It is suggested that convective propulsion plays an important role in the dynamics of flux tubes extending through the surface of the sun. The suppression of the upward heat flow in a Boussinesq convective cell with free upper and lower boundaries by a downdraft is then analyzed. Application to the solar convection zone indicates that downdrafts of 1 to 2 km/s at depths of 1000 to 4000 km beneath the visible surface of the sun are sufficient to reduce the upward heat flux to a small fraction of the ambient value.

  5. Convectively coupled Kelvin waves in aquachannel simulations: 2. Life cycle and dynamical-convective coupling

    Science.gov (United States)

    Blanco, Joaquín. E.; Nolan, David S.; Mapes, Brian E.

    2016-10-01

    This second part of a two-part study uses Weather Research and Forecasting simulations with aquachannel and aquapatch domains to investigate the time evolution of convectively coupled Kelvin waves (CCKWs). Power spectra, filtering, and compositing are combined with object-tracking methods to assess the structure and phase speed propagation of CCKWs during their strengthening, mature, and decaying phases. In this regard, we introduce an innovative approach to more closely investigate the wave (Kelvin) versus entity (super cloud cluster or "SCC") dualism. In general, the composite CCKW structures represent a dynamical response to the organized convective activity. However, pressure and thermodynamic fields in the boundary layer behave differently. Further analysis of the time evolution of pressure and low-level moist static energy finds that these fields propagate eastward as a "moist" Kelvin wave (MKW), faster than the envelope of organized convection or SCC. When the separation is sufficiently large the SCC dissipates, and a new SCC generates to the east, in the region of strongest negative pressure perturbations. We revisit the concept itself of the "coupling" between convection and dynamics, and we also propose a conceptual model for CCKWs, with a clear distinction between the SCC and the MKW components.

  6. An application of the unifying theory of thermal convection in vertical natural convection

    Science.gov (United States)

    Ng, Chong Shen; Ooi, Andrew; Lohse, Detlef; Chung, Daniel

    2014-11-01

    Using direct numerical simulations of vertical natural convection (VNC) at Rayleigh numbers 1 . 0 ×105 - 1 . 0 ×109 and Prandtl number 0 . 709 , we provide support for a generalised applicability of the Grossmann-Lohse (GL) theory, originally developed for horizontal natural (Rayleigh-Bénard) convection. In accordance with the theory, the boundary-layer thicknesses of the velocity and temperature fields in VNC obey laminar-like scaling, whereas away from the walls, the dissipation of the turbulent fluctuations obey the scaling for fully developed turbulence. In contrast to Rayleigh-Bénard convection, the direction of gravity in VNC is parallel to the mean flow. Thus, there no longer exists an exact relation linking the normalised global dissipations to the Nusselt, Rayleigh and Prandtl numbers. Nevertheless, we show that the unclosed term, namely the global-averaged buoyancy flux, also exhibits laminar and turbulent scaling, consistent with the GL theory. The findings suggest that, similar to Rayleigh-Bénard convection, a pure power-law relationship between the Nusselt, Rayleigh and Prandtl numbers is not the best description for VNC and existing empirical power-law relationships should be recalibrated to better reflect the underlying physics.

  7. THE EFFECT OF SOLAR RADIATION ON AUTOMOBILE ENVIRONMENT THROUGH NATURAL CONVECTION AND MIXED CONVECTION

    Directory of Open Access Journals (Sweden)

    MD. FAISAL KADER

    2012-10-01

    Full Text Available In the present paper, the effect of solar radiation on automobiles has been studied by both experimentally and numerically. The numerical solution is done by an operation friendly and fast CFD code – SC/Tetra with a full scale model of a SM3 car and turbulence is modeled by the standard k-ε equation. Numerical analysis of the three-dimensional model predicts a detailed description of fluid flow and temperature distribution in the passenger compartment during both the natural convection due to the incoming solar radiation and mixed convection due to the flow from defrost nozzle and radiation. It can be seen that solar radiation is an important parameter to raise the compartment temperature above the ambient temperature during summer. During natural convection, the rate of heat transfer is fast at the initial period. In the mixed convection analyses, it is found that the temperature drops down to a comfortable range almost linearly at the initial stage. Experimental investigations are performed to determine the temperature contour on the windshield and the local temperature at a particular point for further validation of the numerical results.

  8. From convection rolls to finger convection in double-diffusive turbulence

    NARCIS (Netherlands)

    Yang, Yantao; Verzicco, Roberto; Lohse, Detlef

    2015-01-01

    Double-diffusive convection (DDC), which is the buoyancy-driven flow with fluid density depending on two scalar components, is ubiquitous in many natural and engineering environments. Of great interests are scalars’ transfer rate and flow structures. Here we systematically investigate DDC flow

  9. Upscale Impact of Mesoscale Disturbances of Tropical Convection on Convectively Coupled Kelvin Waves

    Science.gov (United States)

    Yang, Q.; Majda, A.

    2017-12-01

    Tropical convection associated with convectively coupled Kelvin waves (CCKWs) is typically organized by an eastward-moving synoptic-scale convective envelope with numerous embedded westward-moving mesoscale disturbances. It is of central importance to assess upscale impact of mesoscale disturbances on CCKWs as mesoscale disturbances propagate at various tilt angles and speeds. Here a simple multi-scale model is used to capture this multi-scale structure, where mesoscale fluctuations are directly driven by mesoscale heating and synoptic-scale circulation is forced by mean heating and eddy transfer of momentum and temperature. The two-dimensional version of the multi-scale model drives the synoptic-scale circulation, successfully reproduces key features of flow fields with a front-to-rear tilt and compares well with results from a cloud resolving model. In the scenario with an elevated upright mean heating, the tilted vertical structure of synoptic-scale circulation is still induced by the upscale impact of mesoscale disturbances. In a faster propagation scenario, the upscale impact becomes less important, while the synoptic-scale circulation response to mean heating dominates. In the unrealistic scenario with upward/westward tilted mesoscale heating, positive potential temperature anomalies are induced in the leading edge, which will suppress shallow convection in a moist environment. In its three-dimensional version, results show that upscale impact of mesoscale disturbances that propagate at tilt angles (110o 250o) induces negative lower-tropospheric potential temperature anomalies in the leading edge, providing favorable conditions for shallow convection in a moist environment, while the remaining tilt angle cases have opposite effects. Even in the presence of upright mean heating, the front-to-rear tilted synoptic-scale circulation can still be induced by eddy terms at tilt angles (120o 240o). In the case with fast propagating mesoscale heating, positive

  10. The effect of convection and semi-convection on the C/O yield of massive stars

    International Nuclear Information System (INIS)

    Dearborn, D.S.

    1979-01-01

    The C/O ratio produced during core helium burning affects the future evolution and nucleosynthetic yield of massive stars. This ratio is shown to be sensitive to the treatment of convection as well as uncertainties in nuclear rates. By minimizing the effect of semi-convection and reducing the size of the convective core, mass loss in OB stars increases the C/O ratio. (Author)

  11. Mission to Planet Earth

    Science.gov (United States)

    Tilford, Shelby G.; Asrar, Ghassem; Backlund, Peter W.

    1994-01-01

    Mission to Planet Earth (MTPE) is NASA's concept for an international science program to produce the understanding needed to predict changes in the Earth's environment. NASA and its interagency and international partners will place satellites carrying advanced sensors in strategic Earth orbits to gather multidisciplinary data. A sophisticated data system will process and archive an unprecedented amount of information about the Earth and how it works as a system. Increased understanding of the Earth system is a basic human responsibility, a prerequisite to informed management of the planet's resources and to the preservation of the global environment.

  12. Mission to Planet Earth

    International Nuclear Information System (INIS)

    Wilson, G.S.; Backlund, P.W.

    1992-01-01

    Mission to Planet Earth (MTPE) is NASA's concept for an international science program to produce the understanding needed to predict changes in the earth's environment. NASA and its interagency and international partners will place satellites carrying advanced sensors in strategic earth orbits to gather multidisciplinary data. A sophisticated data system will process and archive an unprecedented amount of information about the earth and how it works as a system. Increased understanding of the earth system is a basic human responsibility, a prerequisite to informed management of the planet's resources and to the preservation of the global environment. 8 refs

  13. Simulating the convective precipitation diurnal cycle in a North American scale convection-permitting model

    Science.gov (United States)

    Scaff, L.; Li, Y.; Prein, A. F.; Liu, C.; Rasmussen, R.; Ikeda, K.

    2017-12-01

    A better representation of the diurnal cycle of convective precipitation is essential for the analysis of the energy balance and the water budget components such as runoff, evaporation and infiltration. Convection-permitting regional climate modeling (CPM) has been shown to improve the models' performance of summer precipitation, allowing to: (1) simulate the mesoscale processes in more detail and (2) to provide more insights in future changes in convective precipitation under climate change. In this work we investigate the skill of the Weather Research and Forecast model (WRF) in simulating the summer precipitation diurnal cycle over most of North America. We use 4 km horizontal grid spacing in a 13-years long current and future period. The future scenario is assuming no significant changes in large-scale weather patterns and aims to answer how the weather of the current climate would change if it would reoccur at the end of the century under a high-end emission scenario (Pseudo Global Warming). We emphasize on a region centered on the lee side of the Canadian Rocky Mountains, where the summer precipitation amount shows a regional maximum. The historical simulations are capable to correctly represent the diurnal cycle. At the lee-side of the Canadian Rockies the increase in the convective available potential energy as well as pronounced low-level moisture flux from the southeast Prairies explains the local maximum in summer precipitation. The PGW scenario shows an increase in summer precipitation amount and intensity in this region, consistently with a stronger source of moisture and convective energy.

  14. Biomass Smoke Influences on Deep Convection during the 2011 Midlatitude Continental Convective Clouds Experiment (MC3E)

    Science.gov (United States)

    Dong, X.; Logan, T.; Xi, B.

    2015-12-01

    Three deep convective cloud cases were selected during the 2011 Mid-Latitude Continental Convective Clouds Experiment (MC3E). Although biomass burning smoke advected from Mexico and Central America was the dominant source of cloud condensation nuclei (CCN) for deep convective cloud formation, the 11 May, 20 May, and 23 May cases exhibited different convective characteristics. The convection in the 11 May and 23 May cases formed in smoke laden environments in the presence of convective available potential energy (CAPE) values exceeding 1000 m2 s-2 and 3000 m2 s-2 along with low-level (0-1 km) shear of 10.3 m s-1 and 5.1 m s-1, respectively. The 11 May case had linear convection while the 23 May case featured discrete supercells. The 20 May case featured elevated linear convection that formed in a more moist environment with cleaner aerosol conditions, weak CAPE (9 km) suggesting a warm rain suppression mechanism caused by a combination of strong aerosol loading, large CAPE, and weak low-level wind shear. The observed results for the 20 May and 23 May cases agree well with recent modeling studies that simulated the convection and precipitation in these cases. Furthermore, the modeling of the 11 May case is suggested since the abundant amount of smoke CCN did not greatly enhance the overall precipitation amount and could be a possible aerosol-induced precipitation suppression case.

  15. Forced convection heat transfer in He II

    International Nuclear Information System (INIS)

    Kashani, A.

    1986-01-01

    An investigation of forced convection heat transfer in He II is conducted. The study includes both experimental and theoretical treatments of the problem. The experiment consists of a hydraulic pump and a copper flow tube, 3 mm in ID and 2m long. The system allows measurements of one-dimensional heat and mass transfer in He II. The heat transfer experiments are performed by applying heat at the midpoint along the length of the flow tube. Two modes of heat input are employed, i.e., step function heat input and square pulse heat input. The heat transfer results are discussed in terms of temperature distribution in the tube. The experimental temperature profiles are compared with numerical solutions of an analytical model developed from the He II energy equation. The bath temperature is set at three different values of 1.65, 1.80, and 1.95 K. The He II flow velocity is varied up to 90 cm/s. Pressure is monitored at each end of the flow tube, and the He II pressure drop is obtained for different flow velocities. Results indicate that He II heat transfer by forced convention is considerably higher than that by internal convection. The theoretical model is in close agreement with the experiment. He II pressure drop and friction factor are very similar to those of an ordinary fluid

  16. Vertical Slot Convection: A linear study

    International Nuclear Information System (INIS)

    McAllister, A.; Steinolfson, R.; Tajima, T.

    1992-11-01

    The linear stability properties of fluid convection in a vertical slot were studied. We use a Fourier-Chebychev decomposition was used to set up the linear eigenvalue problems for the Vertical Slot Convection and Benard problems. The eigenvalues, neutral stability curves, and critical point values of the Grashof number, G, and the wavenumber were determined. Plots of the real and imaginary parts of the eigenvalues as functions of G and α are given for a wide range of the Prandtl number, Pr, and special note is made of the complex mode that becomes linearly unstable above Pr ∼ 12.5. A discussion comparing different special cases facilitates the physical understanding of the VSC equations, especially the interaction of the shear-flow and buoyancy induced physics. Making use of the real and imaginary eigenvalues and the phase properties of the eigenmodes, the eigenmodes were characterized. One finds that the mode structure becomes progressively simpler with increasing Pr, with the greatest complexity in the mid ranges where the terms in the heat equation are of roughly the same size

  17. Land surface sensitivity of mesoscale convective systems

    Science.gov (United States)

    Tournay, Robert C.

    Mesoscale convective systems (MCSs) are important contributors to the hydrologic cycle in many regions of the world as well as major sources of severe weather. MCSs continue to challenge forecasters and researchers alike, arising from difficulties in understanding system initiation, propagation, and demise. One distinct type of MCS is that formed from individual convective cells initiated primarily by daytime heating over high terrain. This work is aimed at improving our understanding of the land surface sensitivity of this class of MCS in the contiguous United States. First, a climatology of mesoscale convective systems originating in the Rocky Mountains and adjacent high plains from Wyoming southward to New Mexico is developed through a combination of objective and subjective methods. This class of MCS is most important, in terms of total warm season precipitation, in the 500 to 1300m elevations of the Great Plains (GP) to the east in eastern Colorado to central Nebraska and northwest Kansas. Examining MCSs by longevity, short lasting MCSs (15 hrs) reveals that longer lasting systems tend to form further south and have a longer track with a more southerly track. The environment into which the MCS is moving showed differences across commonly used variables in convection forecasting, with some variables showing more favorable conditions throughout (convective inhibition, 0-6 km shear and 250 hPa wind speed) ahead of longer lasting MCSs. Other variables, such as convective available potential energy, showed improving conditions through time for longer lasting MCSs. Some variables showed no difference across longevity of MCS (precipitable water and large-scale vertical motion). From subsets of this MCS climatology, three regions of origin were chosen based on the presence of ridgelines extending eastward from the Rocky Mountains known to be foci for convection initiation and subsequent MCS formation: Southern Wyoming (Cheyenne Ridge), Colorado (Palmer divide) and

  18. Solutocapillary Convection Effects on Polymeric Membrane Morphology

    Science.gov (United States)

    Krantz, William B.; Todd, Paul W.; Kinagurthu, Sanjay

    1996-01-01

    Macro voids are undesirable large pores in membranes used for purification. They form when membranes are cast as thin films on a smooth surface by evaporating solvent (acetone) from a polymer solution. There are two un-tested hypotheses explaining the growth of macro voids. One states that diffusion of the non-solvent (water) is solely responsible, while the other states that solutocapillary convection is the primary cause of macro void growth. Solutocapillary convection is flow-caused by a concentration induced surface-tension gradient. Macrovoid growth in the former hypothesis is gravity independent, while in the latter it is opposed by gravity. To distinguish between these two hypotheses, experiments were designed to cast membranes in zero-gravity. A semi-automated apparatus was designed and built for casting membranes during the 20 secs of zero-g time available in parabolic aircraft flight such as NASA's KC-135. The phase changes were monitored optically, and membrane morphology was evaluated by scanning electron microscopy (SEM). These studies appear to be the first quantitative studies of membrane casting in micro-gravity which incorporate real-time data acquisition. Morphological studies of membranes cast at 0, 1, and 1.8 g revealed the presence of numerous, sparse and no macrovoids respectively. These results are consistent with the predictions of the solutocapillary hypothesis of macrovoid growth.

  19. Conjugate Problems in Convective Heat Transfer: Review

    Directory of Open Access Journals (Sweden)

    Abram Dorfman

    2009-01-01

    Full Text Available A review of conjugate convective heat transfer problems solved during the early and current time of development of this modern approach is presented. The discussion is based on analytical solutions of selected typical relatively simple conjugate problems including steady-state and transient processes, thermal material treatment, and heat and mass transfer in drying. This brief survey is accompanied by the list of almost two hundred publications considering application of different more and less complex analytical and numerical conjugate models for simulating technology processes and industrial devices from aerospace systems to food production. The references are combined in the groups of works studying similar problems so that each of the groups corresponds to one of selected analytical solutions considered in detail. Such structure of review gives the reader the understanding of early and current situation in conjugate convective heat transfer modeling and makes possible to use the information presented as an introduction to this area on the one hand, and to find more complicated publications of interest on the other hand.

  20. Mass transport in propagating patterns of convection

    International Nuclear Information System (INIS)

    Moses, E.; Steinberg, V.

    1988-01-01

    Recent studies of propagating waves in an oscillatory convection of binary mixtures arise questions about transport properties of this flow. Optical visualization of a field of refraction index due to a shadowgraph technique gives information on the temperature and concentration fields. However, experimental observation of rolls propagating along the cell as travelling waves (TW) does not necessarily imply that mass is transferred hydrodynamically by the convective motion along the cell. One of the possibilities discussed, e.g., is that TW observed is only a phase propagation. The traditional examples of such situations come from the domain of linear, superposition-oriented physics. Acoustic waves transfer momentum and energy, but do not cause the mass to make excursions for their equilibrium point that are larger than the oscillation amplitude. In the case of nonlinear physics we were aware that small amplitude surface waves cause only small oscillatory motion round the equilibrium point, while larger amplitudes can cause the mass to start moving in the direction of the TW. This paper discussed the different possibilities of mass transfer by TW. 27 refs., 20 figs

  1. Benard convection in liquid sodium layers

    International Nuclear Information System (INIS)

    Kek, V.

    1989-08-01

    In a sodium layer heated from below and cooled from above, the integral Nusselt numbers are determined in a range of Rayleigh numbers 1.5x10 3 5 . The experiments are performed in containers with dimensions of 500 mm in diameter and 15 mm and 45 mm in height. The relevant quantities are evaluated from measured temperature and heating power data. The experiments show that the heat transfer across the layer is determined mainly by heat conduction up to Rayleigh number Ra ≅ 10 4 . Beyond this value a significant increase of the convective heat transport is observed. At a Rayleigh number of 4x10 4 the Nusselt number achieves the value Nu = 1.7. This result differs from values given by Nusselt-Rayleigh number correlations reported in the literature for liquids with higher Prandtl number. A regression analysis of the experimental data results empirical correlations for the Nusselt number. A time series analysis of the time dependent temperature signals shows that the measured temperature fluctuations exhibit predominantly stochastic features. However, in the lower range of Rayleigh numbers 1.5x10 3 4 certain regular frequencies can be identified from peaks in broadband power density spectra. These frequencies correspond to fluctuations of a period of 80 to 200 seconds. These regular frequencies are explained by instabilities of the cellular pattern in the convection layer reported in the literature. (orig./HP) [de

  2. Effective diffusion in laminar convective flows

    International Nuclear Information System (INIS)

    Rosenbluth, M.N.; Berk, H.L.; Doxas, I.; Horton, W.

    1987-03-01

    The effective diffusion coefficient D* of a passive component, such as test particles, dye, temperature, magnetic flux, etc., is derived for motion in periodic two-dimensional incompressible convective flow with characteristic velocity v and size d in the presence of an intrinsic local diffusivity D. Asymptotic solutions for effective diffusivity D*(P) in the large P limit, with P ∼ vd/D, is shown to be of the form D* = cDP/sup 1/2/ with c being a coefficient that is determined analytically. The constant c depends on the geometry of the convective cell and on an average of the flow speed along the separatrix. The asymptotic method of evaluation applies to both free boundary and rough boundary flow patterns and it is shown that the method can be extended to more complicated patterns such as the flows generated by rotating cylinders, as in the problem considered by Nadim, Cox, and Brenner [J. Fluid Mech., 164: 185 (1986)]. The diffusivity D* is readily calculated for small P, but the evaluation for arbitrary P requires numerical methods. Monte Carlo particle simulation codes are used to evaluate D* at arbitrary P, and thereby describe the transition for D* between the large and small P limits

  3. The Earth’s mantle before convection: Effects of magma oceans and the Moon (Invited)

    Science.gov (United States)

    Elkins-Tanton, L. T.; Smrekar, S. E.; Tobie, G.

    2009-12-01

    Studies of magma oceans indicate that planets obtain a gravitationally stable, compositionally differentiated mantle following solidification. This stable mantle results primarily from iron-magnesium partitioning during solidification, producing progressively iron-enriched mantle phases as solidification proceeds. Near the end of solidification, the dense solids will overturn to a stable configuration. The resulting differentiated mantle is stable from compositional density gradients that are significant enough to suppress thermal convection for up to hundreds of millions of years or longer, a scenario that proceeds self-consistently from physical and chemical principals, but is in contradiction with a previous image of a hot, turbulently convecting earliest terrestrial mantle. The isotopic range found in Martian meteorites indicates that its mantle differentiated in the first tens of millions of years of the solar system and has not been thoroughly remixed since. The specific isotopic range found on Mars is consistent with formation in a magma ocean. Based on the isotopic compositions of magmas, the Earth’s mantle is well mixed in comparison with the mantle of Mars. If the terrestrial planets experienced partial or whole magma oceans and thus began with stable mantles, resisting the onset of thermal convection and subsequent remixing, then why is Earth’s mantle well mixed? Two processes predicted to occur on the Earth, but not on the smaller Mars, may explain the divergent evolutions of these bodies. Here we will present model calculations for these two processes. First, we hypothesize that in the brief period that the Moon was very close to the Earth, it may have tidally heated Earth’s interior sufficiently to overcome its initial compositionally stable mantle, initiate active convection, and set the stage for the well-mixed mantle sampled today. Mars, conversely, may have cooled significantly before thermal convection began, allowing the formation of a

  4. THE INFLUENCE OF PRESSURE-DEPENDENT VISCOSITY ON THE THERMAL EVOLUTION OF SUPER-EARTHS

    International Nuclear Information System (INIS)

    Stamenković, Vlada; Noack, Lena; Spohn, Tilman; Breuer, Doris

    2012-01-01

    We study the thermal evolution of super-Earths with a one-dimensional (1D) parameterized convection model that has been adopted to account for a strong pressure dependence of the viscosity. A comparison with a 2D spherical convection model shows that the derived parameterization satisfactorily represents the main characteristics of the thermal evolution of massive rocky planets. We find that the pressure dependence of the viscosity strongly influences the thermal evolution of super-Earths—resulting in a highly sluggish convection regime in the lower mantles of those planets. Depending on the effective activation volume and for cooler initial conditions, we observe with growing planetary mass even the formation of a conductive lid above the core-mantle boundary (CMB), a so-called CMB-lid. For initially molten planets our results suggest no CMB-lids but instead a hot lower mantle and core as well as sluggish lower mantle convection. This implies that the initial interior temperatures, especially in the lower mantle, become crucial for the thermal evolution—the thermostat effect suggested to regulate the interior temperatures in terrestrial planets does not work for massive planets if the viscosity is strongly pressure dependent. The sluggish convection and the potential formation of the CMB-lid reduce the convective vigor throughout the mantle, thereby affecting convective stresses, lithospheric thicknesses, and heat fluxes. The pressure dependence of the viscosity may therefore also strongly affect the propensity of plate tectonics, volcanic activity, and the generation of a magnetic field of super-Earths.

  5. Risk of placenta praevia is linked to endometrial thickness in a retrospective cohort study of 4537 singleton assisted reproduction technology births.

    Science.gov (United States)

    Rombauts, L; Motteram, C; Berkowitz, E; Fernando, S

    2014-12-01

    Is endometrial thickness measured prior to embryo transfer associated with placenta praevia? Following IVF, the risk of placenta praevia is increased 4-fold in women with an endometrial thickness of >12 mm compared with women with an endometrial thickness of IVF treatment but it remains unknown what factors contribute to that increased risk. Retrospective cohort study involving 4007 women who had 4537 singleton assisted reproduction technology (ART) births occurring between January 2006 and June 2012 with no loss to follow-up. The primary outcome measure was the diagnosis of placenta praevia, made by the treating obstetrician on a transvaginal ultrasound in the third trimester. Women who had singleton births following single embryo transfer performed at Monash IVF in Melbourne, Australia were included. Of the 4537 cycles leading to a singleton ART birth, 2951 were stimulated cycles with fresh embryo transfers; 355 were hormone replacement therapy frozen embryo transfers and 1231 were natural cycles with frozen embryo transfers. The dataset was analysed using binary logistic general estimating equations to calculate odds ratios for placenta praevia adjusted (aOR) for known confounders. The study groups did not differ significantly in age, BMI and aetiologies of infertility prior to IVF treatment. When compared with stimulated cycles, placenta praevia was less common in women undergoing natural cycles with frozen embryo transfers (OR 0.44, 95% confidence interval (CI) 0.27-0.70, P 12 mm had an aOR of 3.74 (95% CI 1.90-7.34, P IVF patients and their offspring. The fact that the observed increased risk is not linked to the type of embryo transfer (fresh/frozen) but to the type of endometrial preparation, suggests that the risk of placenta praevia in ART can be reduced by considering an elective frozen embryo transfer in a natural cycle, especially given the growing evidence that this strategy also provides a number of other maternal and neonatal benefits. No funding

  6. Convective losses through an air-filled gap

    Energy Technology Data Exchange (ETDEWEB)

    Baum, V A; Ovezsakhatov, N

    1976-01-01

    Simplified formulas for the heat fluxes with given parameters of the air are used to calculate the specific heat losses by convection in a number of solar-energy systems (water heater, thermal generator, double-glazed window, and still). Heat losses by convection and radiation are compared.

  7. Unravelling convective heat transfer in the Rotated Arc Mixer

    NARCIS (Netherlands)

    Speetjens, M.F.M.; Baskan, O.; Metcalfe, G.; Clercx, H.J.H.

    2014-01-01

    Thermal homogenization is essentially a transient problem and convective heat transfer by (chaotic) advection is known to accelerate this process. Convective heat transfer traditionally is examined in terms of heat-transfer coefficients at domain walls and characterised by Nusselt relations.

  8. Solar wind effects on ionospheric convection: a review

    DEFF Research Database (Denmark)

    Lu, G.; Cowley, S.W.H.; Milan, S.E.

    2002-01-01

    ), and travelling convection vortices (TCVs). Furthermore, the large-scale ionospheric convection configuration has also demonstrated a strong correspondence to variations in the interplanetary medium and substorm activity. This report briefly discusses the progress made over the past decade in studies...

  9. Modulated convection at high frequencies and large modulation amplitudes

    International Nuclear Information System (INIS)

    Swift, J.B.; Hohenberg, P.C.

    1987-01-01

    Modulated Rayleigh-Benard convection is analyzed for high frequencies and large modulation amplitudes. The linear theory of Gershuni and Zhukhovitskii is generalized to the nonlinear domain, and a subcritical bifurcation to convection is found in agreement with the experiments of Niemela and Donnelly. The crossover between the high-frequency (''Stokes layer'') regime and the low-frequency regime studied previously is analyzed

  10. Measurements of convective and radiative heating in wildland fires

    Science.gov (United States)

    David Frankman; Brent W. Webb; Bret W. Butler; Daniel Jimenez; Jason M. Forthofer; Paul Sopko; Kyle S. Shannon; J. Kevin Hiers; Roger D. Ottmar

    2012-01-01

    Time-resolved irradiance and convective heating and cooling of fast-response thermopile sensors were measured in 13 natural and prescribed wildland fires under a variety of fuel and ambient conditions. It was shown that a sensor exposed to the fire environment was subject to rapid fluctuations of convective transfer whereas irradiance measured by a windowed sensor was...

  11. Natural convection and vapor loss during underground waste storage

    International Nuclear Information System (INIS)

    Plys, M.G.; Epstein, M.; Turner, D.

    1996-01-01

    Natural convection and vapor loss from underground waste storage tanks is examined here. Stability criteria are provided for the onset of natural convection flow within the headspace of a tank, and between tanks and the environment. The flowrate is quantified and used to predict vapor losses during storage

  12. Heat removal by natural convection in a RPR reactor

    International Nuclear Information System (INIS)

    Sampaio, P.A.B. de

    1987-01-01

    In this paper natural convection in RPR reactor is analysed. The effect of natural convection valves size on cladding temperature is studied. The reactor channel heat transfer problem is solved using finite elements in a two-dimensional analysis. Results show that two valves with Φ = 0.16 m are suited to keep coolant and cladding temperatures below 73 0 C. (author) [pt

  13. Interaction of externally-driven acoustic waves with compressible convection

    International Nuclear Information System (INIS)

    Jones, P.; Merryfield, W.

    1992-01-01

    Two-dimensional numerical simulations are used to examine the interaction of acoustic waves with a compressible convecting fluid. Acoustic waves are forced at the lower boundary of the computational domain and propagate through a three-layer system undergoing vigorous penetrative convection. Energy exchange between the wave and the fluid is analyzed using a work integral formulation

  14. Efficiency of Heat Transfer in Turbulent Rayleigh-Benard Convection

    Czech Academy of Sciences Publication Activity Database

    Urban, Pavel; Musilová, Věra; Skrbek, L.

    2011-01-01

    Roč. 107, č. 1 (2011), 014302:1-4 ISSN 0031-9007 R&D Projects: GA AV ČR KJB200650902 Institutional research plan: CEZ:AV0Z20650511 Keywords : natural convection * thermal convection Subject RIV: BK - Fluid Dynamics Impact factor: 7.370, year: 2011

  15. Boundary-modulated Thermal Convection Model in the Mantle

    Science.gov (United States)

    Kurita, K.; Kumagai, I.

    2008-12-01

    Analog experiments have played an important role in the constructing ideas of mantle dynamics. The series of experiments by H. Ramberg is one of the successful examples. Recently, however the realm of the analog experiments seems to be overwhelmed by steady progress of computer simulations. Is there still room for the analog experiments? This might be a main and hidden subject of this session. Here we propose a working hypothesis how the convecting mantle behaves based on the analog experiments in the system of viscous fluid and particles. The essential part is the interaction of convecting flow with heterogeneities existing in the boundaries. It is proposed the preexisting topographical heterogeneity in the boundary could control the flow pattern of convecting fluid. If this kind of heterogeneity can be formed as a consequence of convective motion and mobilized by the flow, the convection also can control the heterogeneity. We can expect interactions in two ways, by which the system behaves in a self-organize fashion. To explore the mutual interactions between convection flow and heterogeneity the system of viscous fluid and particles with slightly higher density is selected as 2D Rayleigh-Benard type convection. The basic structure consists of a basal particulate layer where permeable convection transports heat and an upper viscous fluid layer. By reducing the magnitude of the density difference the convective flow can mobilize the particles and can erode the basal layer. The condition of this erosion can be identified in the phase diagram of the particle Shields"f and the Rayleigh numbers. At Ra greater than 107 the convection style drastically changed before and after the erosion. Before the erosion where the flat interface of the boundary is maintained small scaled turbulent convection pattern is dominant. After the erosion where the interface becomes bumpy the large scale convective motion is observed. The structure is coherent to that of the boundary. This

  16. High resolution geodynamo simulations with strongly-driven convection and low viscosity

    Science.gov (United States)

    Schaeffer, Nathanael; Fournier, Alexandre; Jault, Dominique; Aubert, Julien

    2015-04-01

    Numerical simulations have been successful at explaining the magnetic field of the Earth for 20 years. However, the regime in which these simulations operate is in many respect very far from what is expected in the Earth's core. By reviewing previous work, we find that it appears difficult to have both low viscosity (low magnetic Prandtl number) and strong magnetic fields in numerical models (large ratio of magnetic over kinetic energy, a.k.a inverse squared Alfvén number). In order to understand better the dynamics and turbulence of the core, we have run a series of 3 simulations, with increasingly demanding parameters. The last simulation is at the limit of what nowadays codes can do on current super computers, with a resolution of 2688 grid points in longitude, 1344 in latitude, and 1024 radial levels. We will show various features of these numerical simulations, including what appears as trends when pushing the parameters toward the one of the Earth. The dynamics is very rich. From short time scales to large time scales, we observe at large scales: Inertial Waves, Torsional Alfvén Waves, columnar convective overturn dynamics and long-term thermal winds. In addition, the dynamics inside and outside the tangent cylinder seem to follow different routes. We find that the ohmic dissipation largely dominates the viscous one and that the magnetic energy dominates the kinetic energy. The magnetic field seems to play an ambiguous role. Despite the large magnetic field, which has an important impact on the flow, we find that the force balance for the mean flow is a thermal wind balance, and that the scale of convective cells is still dominated by viscous effects.

  17. Passive margins getting squeezed in the mantle convection vice

    Science.gov (United States)

    Yamato, Philippe; Husson, Laurent; Becker, Thorsten W.; Pedoja, Kevin

    2014-05-01

    Passive margins often exhibit uplift, exhumation and tectonic inversion. We speculate that the compression in the lithosphere gradually increased during the Cenozoic. In the same time, the many mountain belts at active margins that accompany this event seem readily witness this increase. However, how that compression increase affects passive margins remains unclear. In order to address this issue, we design a 2D viscous numerical model wherein a lithospheric plate rests above a weaker mantle. It is driven by a mantle conveyor belt, alternatively excited by a lateral downwelling on one side, an upwelling on the other side, or both simultaneously. The lateral edges of the plate are either free or fixed, representing the cases of free convergence, and collision or slab anchoring, respectively. This distinction changes the upper boundary condition for mantle circulation and, as a consequence, the stress field. Our results show that between these two regimes, the flow pattern transiently evolves from a free-slip convection mode towards a no-slip boundary condition above the upper mantle. In the second case, the lithosphere is highly stressed horizontally and deforms. For an equivalent bulk driving force, compression increases drastically at passive margins provided that upwellings are active. Conversely, if downwellings alone are activated, compression occurs at short distances from the trench and extension prevails elsewhere. These results are supported by Earth-like 3D spherical models that reveal the same pattern, where active upwellings are required to excite passive margins compression. These results support the idea that compression at passive margins, is the response to the underlying mantle flow, that is increasingly resisted by the Cenozoic collisions.

  18. Do tropical wetland plants possess a convective gas flow mechanism?

    DEFF Research Database (Denmark)

    Jensen, Dennis Konnerup; Sorrell, Brian Keith; Brix, Hans

    2011-01-01

    Internal pressurization and convective gas flow, which can aerate wetland plants more efficiently than diffusion, are common in temperate species. Here, we present the first survey of convective flow in a range of tropical plants. The occurrence of pressurization and convective flow was determined...... in 20 common wetland plants from the Mekong Delta in Vietnam. The diel variation in pressurization in culms and the convective flow and gas composition from stubbles were examined for Eleocharis dulcis, Phragmites vallatoria and Hymenachne acutigluma, and related to light, humidity and air temperature....... Nine of the 20 species studied were able to build up a static pressure of >50Pa, and eight species had convective flow rates higher than 1mlmin-1. There was a clear diel variation, with higher pressures and flows during the day than during the night, when pressures and flows were close to zero...

  19. Heat transfer of laminar mixed convection of liquid

    CERN Document Server

    Shang, De-Yi

    2016-01-01

    This book presents a new algorithm to calculate fluid flow and heat transfer of laminar mixed convection. It provides step-by-step tutorial help to learn quickly how to set up the theoretical and numerical models of laminar mixed convection, to consider the variable physical properties of fluids, to obtain the system of numerical solutions, to create a series of formalization equations for the convection heat transfer by using a curve-fitting approach combined with theoretical analysis and derivation. It presents the governing ordinary differential equations of laminar mixed convection, equivalently transformed by an innovative similarity transformation with the description of the related transformation process. A system of numerical calculations of the governing ordinary differential equations is presented for the water laminar mixed convection. A polynomial model is induced for convenient and reliable treatment of variable physical properties of liquids. The developed formalization equations of mixed convec...

  20. Natural Convection Analysis with Various Turbulent Models Using FLUENT

    International Nuclear Information System (INIS)

    Park, Yu Sun

    2007-01-01

    The buoyancy driven convective flow fields are steady circulatory flows which were made between surfaces maintained at two fixed temperatures. They are ubiquitous in nature and play an important role in many engineering applications. Especially, in last decades, natural convection in a close loop or cavity becomes the main issue in the molecular biology for the polymerase chain reaction (PCR). Application of a natural convection can reduce the costs and efforts remarkably. This paper focuses on the sensitivity study of turbulence analysis using CFD for a natural convection in a closed rectangular cavity. Using commercial CFD code, FLUENT, various turbulent models were applied to the turbulent flow. Results from each CFD model will be compared each other in the viewpoints of flow characteristics. This work will suggest the best turbulent model of CFD for analyzing turbulent flows of the natural convection in an enclosure system

  1. The influence of convective current generator on the global current

    Directory of Open Access Journals (Sweden)

    V. N. Morozov

    2006-01-01

    Full Text Available The mathematical generalization of classical model of the global circuit with taking into account the convective current generator, working in the planetary boundary layer was considered. Convective current generator may be interpreted as generator, in which the electromotive force is generated by processes, of the turbulent transport of electrical charge. It is shown that the average potential of ionosphere is defined not only by the thunderstorm current generators, working at the present moment, but by the convective current generator also. The influence of the convective processes in the boundary layer on the electrical parameters of the atmosphere is not only local, but has global character as well. The numerical estimations, made for the case of the convective-unstable boundary layer demonstrate that the increase of the average potential of ionosphere may be of the order of 10% to 40%.

  2. Neutral beam injection and plasma convection in a magnetic field

    International Nuclear Information System (INIS)

    Okuda, H.; Hiroe, S.

    1988-06-01

    Injection of a neutral beam into a plasma in a magnetic field has been studied by means of numerical plasma simulations. It is found that, in the absence of a rotational transform, the convection electric field arising from the polarization charges at the edges of the beam is dissipated by turbulent plasma convection, leading to anomalous plasma diffusion across the magnetic field. The convection electric field increases with the beam density and beam energy. In the presence of a rotational transform, polarization charges can be neutralized by the electron motion along the magnetic field. Even in the presence of a rotational transform, a steady-state convection electric field and, hence, anomalous plasma diffusion can develop when a neutral beam is constantly injected into a plasma. Theoretical investigations on the convection electric field are described for a plasma in the presence of rotational transform. 11 refs., 19 figs

  3. Digital Earth – A sustainable Earth

    International Nuclear Information System (INIS)

    Mahavir

    2014-01-01

    All life, particularly human, cannot be sustainable, unless complimented with shelter, poverty reduction, provision of basic infrastructure and services, equal opportunities and social justice. Yet, in the context of cities, it is believed that they can accommodate more and more people, endlessly, regardless to their carrying capacity and increasing ecological footprint. The 'inclusion', for bringing more and more people in the purview of development is often limited to social and economic inclusion rather than spatial and ecological inclusion. Economic investment decisions are also not always supported with spatial planning decisions. Most planning for a sustainable Earth, be at a level of rural settlement, city, region, national or Global, fail on the capacity and capability fronts. In India, for example, out of some 8,000 towns and cities, Master Plans exist for only about 1,800. A chapter on sustainability or environment is neither statutorily compulsory nor a norm for these Master Plans. Geospatial technologies including Remote Sensing, GIS, Indian National Spatial Data Infrastructure (NSDI), Indian National Urban Information Systems (NUIS), Indian Environmental Information System (ENVIS), and Indian National GIS (NGIS), etc. have potential to map, analyse, visualize and take sustainable developmental decisions based on participatory social, economic and social inclusion. Sustainable Earth, at all scales, is a logical and natural outcome of a digitally mapped, conceived and planned Earth. Digital Earth, in fact, itself offers a platform to dovetail the ecological, social and economic considerations in transforming it into a sustainable Earth

  4. The sensitivity of Alpine summer convection to surrogate climate change: an intercomparison between convection-parameterizing and convection-resolving models

    Directory of Open Access Journals (Sweden)

    M. Keller

    2018-04-01

    Full Text Available Climate models project an increase in heavy precipitation events in response to greenhouse gas forcing. Important elements of such events are rain showers and thunderstorms, which are poorly represented in models with parameterized convection. In this study, simulations with 12 km horizontal grid spacing (convection-parameterizing model, CPM and 2 km grid spacing (convection-resolving model, CRM are employed to investigate the change in the diurnal cycle of convection with warmer climate. For this purpose, simulations of 11 days in June 2007 with a pronounced diurnal cycle of convection are compared with surrogate simulations from the same period. The surrogate climate simulations mimic a future climate with increased temperatures but unchanged relative humidity and similar synoptic-scale circulation. Two temperature scenarios are compared: one with homogeneous warming (HW using a vertically uniform warming and the other with vertically dependent warming (VW that enables changes in lapse rate.The two sets of simulations with parameterized and explicit convection exhibit substantial differences, some of which are well known from the literature. These include differences in the timing and amplitude of the diurnal cycle of convection, and the frequency of precipitation with low intensities. The response to climate change is much less studied. We can show that stratification changes have a strong influence on the changes in convection. Precipitation is strongly increasing for HW but decreasing for the VW simulations. For cloud type frequencies, virtually no changes are found for HW, but a substantial reduction in high clouds is found for VW. Further, we can show that the climate change signal strongly depends upon the horizontal resolution. In particular, significant differences between CPM and CRM are found in terms of the radiative feedbacks, with CRM exhibiting a stronger negative feedback in the top-of-the-atmosphere energy budget.

  5. The sensitivity of Alpine summer convection to surrogate climate change: an intercomparison between convection-parameterizing and convection-resolving models

    Science.gov (United States)

    Keller, Michael; Kröner, Nico; Fuhrer, Oliver; Lüthi, Daniel; Schmidli, Juerg; Stengel, Martin; Stöckli, Reto; Schär, Christoph

    2018-04-01

    Climate models project an increase in heavy precipitation events in response to greenhouse gas forcing. Important elements of such events are rain showers and thunderstorms, which are poorly represented in models with parameterized convection. In this study, simulations with 12 km horizontal grid spacing (convection-parameterizing model, CPM) and 2 km grid spacing (convection-resolving model, CRM) are employed to investigate the change in the diurnal cycle of convection with warmer climate. For this purpose, simulations of 11 days in June 2007 with a pronounced diurnal cycle of convection are compared with surrogate simulations from the same period. The surrogate climate simulations mimic a future climate with increased temperatures but unchanged relative humidity and similar synoptic-scale circulation. Two temperature scenarios are compared: one with homogeneous warming (HW) using a vertically uniform warming and the other with vertically dependent warming (VW) that enables changes in lapse rate. The two sets of simulations with parameterized and explicit convection exhibit substantial differences, some of which are well known from the literature. These include differences in the timing and amplitude of the diurnal cycle of convection, and the frequency of precipitation with low intensities. The response to climate change is much less studied. We can show that stratification changes have a strong influence on the changes in convection. Precipitation is strongly increasing for HW but decreasing for the VW simulations. For cloud type frequencies, virtually no changes are found for HW, but a substantial reduction in high clouds is found for VW. Further, we can show that the climate change signal strongly depends upon the horizontal resolution. In particular, significant differences between CPM and CRM are found in terms of the radiative feedbacks, with CRM exhibiting a stronger negative feedback in the top-of-the-atmosphere energy budget.

  6. Laminar Mixed Convection Heat Transfer Correlation for Horizontal Pipes

    International Nuclear Information System (INIS)

    Chae, Myeong Seon; Chung, Bum Jin

    2013-01-01

    This study aimed at producing experimental results and developing a new heat transfer correlation based upon a semi-empirical buoyancy coefficient. Mixed convection mass transfers inside horizontal pipe were investigated for the pipe of various length-to-diameters with varying Re. Forced convection correlation was developed using a very short cathode. With the length of cathode increase and Re decrease, the heat transfer rates were enhanced and becomes higher than that of forced convection. An empirical buoyancy coefficient was derived from correlation of natural convection and forced convection with the addition of L/D. And the heat transfer correlation for laminar mixed convection was developed using the buoyancy coefficient, it describes not only current results, but also results of other studies. Mixed convection occurs when the driving forces of both forced and natural convections are of comparable magnitude (Gr/Re 2 ∼1). It is classical problem but is still an active area of research for various thermal applications such as flat plate solar collectors, nuclear reactors and heat exchangers. The effect of buoyancy on heat transfer in a forced flow is varied by the direction of the buoyancy force. In a horizontal pipe the direction of the forced and buoyancy forces are perpendicular. The studies on the mixed convections of the horizontal pipes were not investigated very much due to the lack of practical uses compared to those of vertical pipes. Even the definitions on the buoyancy coefficient that presents the relative influence of the forced and the natural convections, are different by scholars. And the proposed heat transfer correlations do not agree

  7. Swimming Behavior of Roach (Rutilus rutilus) and Three-spined Stickleback (Gasterosteus aculeatus) in Response to Wind Power Noise and Single-tone Frequencies

    Energy Technology Data Exchange (ETDEWEB)

    Andersson, Mathias H.; Dock-Aakerman, Emily; Ubral-Hedenberg, Ramona; Oehman, Marcus C. (Dept. of Zoology, Stockholm Univ., Stockholm (Sweden)); Sigray, Peter (Dept. of Underwater Research, Swedish Defense Research Agency, Stockholm (Sweden))

    2007-12-15

    There is an environmental concern of how fish may be influenced by the developments of wind power offshore installations (20-23). In this study, two different species of fish were exposed to single-tone frequencies and sound generated by an offshore wind power plant. Both species reacted to the wind power noise which indicate that the noise may cause stress. However, fish have been noticed to habituate to sound and to associate with windmills at sea. This study was a small scale experiment. For a comprehensive understanding on how fish respond to wind power noise, additional studies are needed involving more species and large scale laboratory and field experiments based on detailed measurements of the noise generated from wind power plants

  8. A model of the solar cycle driven by the dynamo action of the global convection in the solar convection zone

    International Nuclear Information System (INIS)

    Yoshimura, H.

    1976-01-01

    Extensive numerical studies of the dynamo equations due to the global convection are presented to simulate the solar cycle and to open the way to study general stellar magnetic cycles. The dynamo equations which represent the longitudinally-averaged magnetohydrodynamical action (mean magnetohydrodynamics) of the global convection under the influence of the rotation in the solar convection zone are considered here as an initial boundary-value problem. The latitudinal and radial structure of the dynamo action consisting of a generation action due to the differential rotation and a regeneration action due to the global convection is parameterized in accordance with the structure of the rotation and of the global convection. This is done especially in such a way as to represent the presence of the two cells of the regeneration action in the radial direction in which the action has opposite signs, which is typical of the regeneration action of the global convection. The effects of the dynamics of the global convection (e.g., the effects of the stratification of the physical conditions in the solar convection zone) are presumed to be all included in those parameters used in the model and they are presumed not to alter the results drastically since these effects are only to change the structure of the regeneration action topologically. (Auth.)

  9. A dendritic solidification experiment under large gravity - implications for the Earth's inner core solidification regime.

    Science.gov (United States)

    Deguen, R.; Alboussière, T.; Brito, D.; La Rizza, P.; Masson, J.

    2009-05-01

    The Earth's inner core solidification regime is usually thought to be dendritic, which should results in the formation of a mushy layer at the inner core boundary, possibly extending deep in the inner core. The release of latent heat and solute associated with crystallization provides an important boyancy source to drive thermo- chemical convection in the core. In the laboratory, two modes of convection associated with the crystallization of mushy layers have been observed. One is a boundary layer mode originating from the destabilisation of the chemical boundary layer present at the mush-liquid interface; the second is the so-called 'mushy layer mode' which involves the whole mushy layer. In the mushy layer mode, convection usually takes the form of narrow plumes rising through crystal free conduits called chimneys. One particularity of inner core crystallization is its extremely small solidification rate compared to typical outer core convective timescales. We have designed and build an experiment devoted to the study of crystallization under a large gravity field, using a centrifuge, of an aqueous solution of ammonium chloride, which is a good analogue to metallic alloys. The large gravity field allows to reach Rayleigh numbers much larger than in typical solidification experiments. Under large gravity fields, we observe the disappearance of chimney convection and show that the large gravity field promotes the boundary layer convection mode at the expent of the mushy layer mode. As the gravitationnal forcing is increased, convective heat and solute transport are significantly enhanced, which results in larger solid fraction directly below the mush-liquid interface. The increase in solid fraction results in a dramatic decrease of the permeability in the mushy layer, which eventually becomes subcritical in respect to the mushy layer mode. Because of the very slow solidification rate of the inner core, convective transport of heat and solute from the ICB is

  10. Mixed convection flow past a horizontal plate

    Directory of Open Access Journals (Sweden)

    Savić Lj.

    2005-01-01

    Full Text Available The mixed convection flow past a horizontal plate being aligned through a small angle of attack to a uniform free stream will be considered in the limit of large Reynolds number and small Richardson number. Even a small angle of inclination of the wake is sufficient for the buoyancy force to accelerate the flow in the wake which causes a velocity overshoot in the wake. Moreover a hydrostatic pressure difference across the wake induces a correction to the potential flow which influences the inclination of the wake. Thus the wake and the correction of the potential flow have to be determined simultaneously. However, it turns out that solutions exist only if the angle of attack is sufficiently large. Solutions are computed numerically and the influence of the buoyancy on the lift coefficient is determined.

  11. Imaging convection and magnetism in the sun

    CERN Document Server

    Hanasoge, Shravan

    2015-01-01

    This book reviews the field of helioseismology and its outstanding challenges and also offers a detailed discussion of the latest computational methodologies. The focus is on the development and implementation of techniques to create 3-D images of convection and magnetism in the solar interior and to introduce the latest computational and theoretical methods to the interested reader. With the increasing availability of computational resources, demand for greater accuracy in the interpretation of helioseismic measurements and the advent of billion-dollar instruments taking high-quality observations, computational methods of helioseismology that enable probing the 3-D structure of the Sun have increasingly become central. This book will benefit students and researchers with proficiency in basic numerical methods, differential equations and linear algebra who are interested in helioseismology.

  12. Design Aspects of the Rayleigh Convection Code

    Science.gov (United States)

    Featherstone, N. A.

    2017-12-01

    Understanding the long-term generation of planetary or stellar magnetic field requires complementary knowledge of the large-scale fluid dynamics pervading large fractions of the object's interior. Such large-scale motions are sensitive to the system's geometry which, in planets and stars, is spherical to a good approximation. As a result, computational models designed to study such systems often solve the MHD equations in spherical geometry, frequently employing a spectral approach involving spherical harmonics. We present computational and user-interface design aspects of one such modeling tool, the Rayleigh convection code, which is suitable for deployment on desktop and petascale-hpc architectures alike. In this poster, we will present an overview of this code's parallel design and its built-in diagnostics-output package. Rayleigh has been developed with NSF support through the Computational Infrastructure for Geodynamics and is expected to be released as open-source software in winter 2017/2018.

  13. Prediction of flow instability during natural convection

    International Nuclear Information System (INIS)

    Farhadi, Kazem

    2005-01-01

    The occurrence of flow excursion instability during passive heat removal for Tehran Research Reactor (TRR) has been analyzed at low-pressure and low-mass rate of flow conditions without boiling taking place. Pressure drop-flow rate characteristics in the general case are determined upon a developed code for this purpose. The code takes into account variations of different pressure drop components caused by different powers as well as different core inlet temperatures. The analysis revealed the fact that the instability can actually occur in the natural convection mode for a range of powers per fuel plates at a predetermined inlet temperature with fixed geometry of the core. Low mass rate of flow and high sub-cooling are the two important conditions for the occurrence of static instability in the TRR. The calculated results are compared with the existing data in the literature. (author)

  14. Mixed convection in fluid superposed porous layers

    CERN Document Server

    Dixon, John M

    2017-01-01

    This Brief describes and analyzes flow and heat transport over a liquid-saturated porous bed. The porous bed is saturated by a liquid layer and heating takes place from a section of the bottom. The effect on flow patterns of heating from the bottom is shown by calculation, and when the heating is sufficiently strong, the flow is affected through the porous and upper liquid layers. Measurements of the heat transfer rate from the heated section confirm calculations. General heat transfer laws are developed for varying porous bed depths for applications to process industry needs, environmental sciences, and materials processing. Addressing a topic of considerable interest to the research community, the brief features an up-to-date literature review of mixed convection energy transport in fluid superposed porous layers.

  15. Convective heat transfer and infrared thermography.

    Science.gov (United States)

    Carlomagno, Giovanni M; Astarita, Tommaso; Cardone, Gennaro

    2002-10-01

    Infrared (IR) thermography, because of its two-dimensional and non-intrusive nature, can be exploited in industrial applications as well as in research. This paper deals with measurement of convective heat transfer coefficients (h) in three complex fluid flow configurations that concern the main aspects of both internal and external cooling of turbine engine components: (1) flow in ribbed, or smooth, channels connected by a 180 degrees sharp turn, (2) a jet in cross-flow, and (3) a jet impinging on a wall. The aim of this study was to acquire detailed measurements of h distribution in complex flow configurations related to both internal and external cooling of turbine components. The heated thin foil technique, which involves the detection of surface temperature by means of an IR scanning radiometer, was exploited to measure h. Particle image velocimetry was also used in one of the configurations to precisely determine the velocity field.

  16. Optimal fetal growth for the Caucasian singleton and assessment of appropriateness of fetal growth: an analysis of a total population perinatal database

    Directory of Open Access Journals (Sweden)

    Lawrence David M

    2005-05-01

    Full Text Available Abstract Background The appropriateness of an individual's intra uterine growth is now considered an important determinant of both short and long term outcomes, yet currently used measures have several shortcomings. This study demonstrates a method of assessing appropriateness of intrauterine growth based on the estimation of each individual's optimal newborn dimensions from routinely available perinatal data. Appropriateness of growth can then be inferred from the ratio of the value of the observed dimension to that of the optimal dimension. Methods Fractional polynomial regression models including terms for non-pathological determinants of fetal size (gestational duration, fetal gender and maternal height, age and parity were used to predict birth weight, birth length and head circumference from a population without any major risk factors for sub-optimal intra-uterine growth. This population was selected from a total population of all singleton, Caucasian births in Western Australia 1998–2002. Births were excluded if the pregnancy was exposed to factors known to influence fetal growth pathologically. The values predicted by these models were treated as the optimal values, given infant gender, gestational age, maternal height, parity, and age. Results The selected sample (N = 62,746 comprised 60.5% of the total Caucasian singleton birth cohort. Equations are presented that predict optimal birth weight, birth length and head circumference given gestational duration, fetal gender, maternal height, age and parity. The best fitting models explained 40.5% of variance for birth weight, 32.2% for birth length, and 25.2% for head circumference at birth. Conclusion Proportion of optimal birth weight (length or head circumference provides a method of assessing appropriateness of intrauterine growth that is less dependent on the health of the reference population or the quality of their morphometric data than is percentile position on a birth weight

  17. Excess Mortality in Hyperthyroidism: The Influence of Preexisting Comorbidity and Genetic Confounding: A Danish Nationwide Register-Based Cohort Study of Twins and Singletons

    Science.gov (United States)

    Brandt, Frans; Almind, Dorthe; Christensen, Kaare; Green, Anders; Brix, Thomas Heiberg

    2012-01-01

    Context: Hyperthyroidism is associated with severe comorbidity, such as stroke, and seems to confer increased mortality. However, it is unknown whether this increased mortality is explained by hyperthyroidism per se, comorbidity, and/or genetic confounding. Objective: The objective of the study was to investigate whether hyperthyroidism is associated with an increased mortality and, if so, whether the association is influenced by comorbidity and/or genetic confounding. Methods: This was an observational cohort study using record-linkage data from nationwide Danish health registers. We identified 4850 singletons and 926 twins from same-sex pairs diagnosed with hyperthyroidism. Each case was matched with four controls for age and gender. The Charlson score was calculated from discharge diagnoses on an individual level to measure comorbidity. Cases and controls were followed up for a mean of 10 yr (range 0–31 yr), and the hazard ratio (HR) for mortality was calculated using Cox regression analyses. Results: In singletons there was a significantly higher mortality in individuals diagnosed with hyperthyroidism than in controls [HR 1.37; 95% confidence interval (CI) 1.30–1.46]. This persisted after adjustment for preexisting comorbidity (HR 1,28; 95% CI 1.21–1.36). In twin pairs discordant for hyperthyroidism (625 pairs), the twin with hyperthyroidism had an increased mortality compared with the corresponding cotwin (HR 1.43; 95% CI 1.09–1.88). However, this was found only in dizygotic pairs (HR 1.80; 95% CI 1.27–2.55) but not in monozygotic pairs (HR 0.95; 95% CI 0.60–1.50). Conclusions: Hyperthyroidism is associated with an increased mortality independent of preexisting comorbidity. The study of twin pairs discordant for hyperthyroidism suggests that genetic confounding influences the association between hyperthyroidism and mortality. PMID:22930783

  18. The earth's gravitational field

    Digital Repository Service at National Institute of Oceanography (India)

    Ramprasad, T.

    . But to say that gravity acts downwards is not correct. Gravity acts down, no matter where you stand on the Earth. It is better to say that on Earth gravity pulls objects towards the centre of the Earth. So no matter where you are on Earth all objects fall... pull than objects at the poles. In combination, the equatorial bulge and the effects of centrifugal force mean that sea-level gravitational acceleration increases from about 9.780 m/s² at the equator to about 9.832 m/s² at the poles, so an object...

  19. Geomagnetic field of earth

    International Nuclear Information System (INIS)

    Delipetrev, Marjan; Delipetrev, Blagoj; Panovska, Sanja

    2008-01-01

    In this paper is introduced the theory of geomagnetic field of the Earth. A homogenous and isotropic sphere is taken for a model of Earth with a bar magnet at its center as a magnetic potential. The understanding of the real origin of geomagnetic field produced from differential rotation of inner core with respect to the outer core of Earth is here presented. Special attention is given to the latest observed data of the established net of geomagnetic repeat stations in the Republic of Macedonia. Finally, the maps of elements of geomagnetic field and the equation for calculation of normal magnetic field of Earth are provided. (Author)

  20. Rare earth octacyanomolybdates(4)

    International Nuclear Information System (INIS)

    Zubritskaya, D.I.; Sergeeva, A.N.; Pisak, Yu.V.

    1980-01-01

    Optimal conditions for synthesis of rare-earth octacyanomolybdates(4) of the Ln 4 [Mo(CN) 8 ] 3 xnH 2 O composition (where Ln is a rare-earth element, other than Pr, Pm, Lu, Tb) have been worked out. The synthesis has been accomplished by neutralization with octacianomolybdic acid with rare-earth carbonates. The composition and structure of the compounds synthesized have been studied by infrared-spectroscopy. It has been established that rare-earth octacyanomolybdates(4) form three isostructural groups