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Gravity
Kinds of Gravity Terms modified by Gravity Selected AbstractsChanges in gravitational force cause changes in gene expression in the lens of developing zebrafishDEVELOPMENTAL DYNAMICS, Issue 10 2006Naoko Shimada Abstract Gravity has been a constant physical factor during the evolution and development of life on Earth. We have been studying effects of simulated microgravity on gene expression in transgenic zebrafish embryos expressing gfp under the influence of gene-specific promoters. In this study, we assessed the effect of microgravity on the expression of the heat shock protein 70 (hsp70) gene in lens during development using transgenic zebrafish embryos expressing gfp under the control of hsp70 promoter/enhancer. Hsp70:gfp expression was up-regulated (45%) compared with controls during the developmental period that included the lens differentiation stage. This increase was lens specific, because the entire embryo showed only a 4% increase in gfp expression. Northern blot and in situ hybridization analysis indicated that the hsp70:gfp expression recapitulated endogenous hsp70 mRNA expression. Hypergravity exposure also increased hsp70 expression during the same period. In situ hybridization analysis for two lens-specific crystallin genes revealed that neither micro- nor hypergravity affected the expression level of ,B1 - crystallin, a non-hsp gene used as a marker for lens differentiation. However, hypergravity changed the expression level of ,A - crystallin, a member of the small hsp gene family. Terminal deoxynucleotidyl transferase,mediated deoxyuridinetriphosphate nick end-labeling (TUNEL) assay analysis showed that altered-gravity (,g) decreased apoptosis in lens during the same period and the decrease correlated with the up-regulation of hsp70 expression, suggesting that elimination of nuclei from differentiating lens fiber cells was suppressed probably through hsp70 up-regulation. These results support the idea that ,g influences hsp70 expression and differentiation in lens-specific and developmental period specific manners and that hsp family genes play a specific role in the response to ,g. Developmental Dynamics 235:2686,2694, 2006. © 2006 Wiley-Liss, Inc. [source] Nonlocal quantum gravity and the size of the universeFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 6-7 2004M. Reuter Motivated by the conjecture that the cosmological constant problem is solved by strong quantum effects in the infrared we use the exact flow equation of Quantum Einstein Gravity to determine the renormalization group behavior of a class of nonlocal effective actions. They consist of the Einstein-Hilbert term and a general nonlinear function Fk(V) of the Euclidean spacetime volume V. For the V + V ln V -invariant the renormalization group running enormously suppresses the value of the renormalized curvature which results from Planck-size parameters specified at the Planck scale. One obtains very large, i.e., almost flat universes without finetuning the cosmological constant. A critical infrared fixed point is found where gravity is scale invariant. [source] Influence of inertia, topography and gravity on transient axisymmetric thin-film flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2004Roger E. Khayat Abstract This study examines theoretically the development of early transients for axisymmetric flow of a thin film over a stationary cylindrical substrate of arbitrary shape. The fluid is assumed to emerge from an annular tube as it is driven by a pressure gradient maintained inside the annulus, and/or by gravity in the axial direction. The interplay between inertia, annulus aspect ratio, substrate topography and gravity is particularly emphasized. Initial conditions are found to have a drastic effect on the ensuing flow. The flow is governed by the thin-film equations of the ,boundary-layer' type, which are solved by expanding the flow field in terms of orthonormal modes in the radial direction. The formulation is validated upon comparison with the similarity solution of Watson (J. Fluid Mech 1964; 20:481) leading to an excellent agreement when only 2,3 modes are included. The wave and flow structure are examined for high and low inertia. It is found that low-inertia fluids tend to accumulate near the annulus exit, exhibiting a standing wave that grows with time. This behaviour clearly illustrates the difficulty faced with coating high-viscosity fluids. The annulus aspect is found to be influential only when inertia is significant; there is less flow resistance for a film over a cylinder of smaller diameter. For high inertia, the free surface evolves similarly to two-dimensional flow. The substrate topography is found to have a significant effect on transient behaviour, but this effect depends strongly on inertia. It is observed that the flow of a high-inertia fluid over a step-down exhibits the formation of a secondary wave that moves upstream of the primary wave. Gravity is found to help the film (coating) flow by halting or prohibiting the wave growth. The initial film profile and velocity distribution dictate whether the fluid will flow downstream or accumulate near the annulus exit. Copyright © 2004 John Wiley & Sons, Ltd. [source] Gravity is an important determinant of oxygenation during one-lung ventilationACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 6 2010L. L. SZEGEDI Background: The role of gravity in the redistribution of pulmonary blood flow during one-lung ventilation (OLV) has been questioned recently. To address this controversial but clinically important issue, we used an experimental approach that allowed us to differentiate the effects of gravity from the effects of hypoxic pulmonary vasoconstriction (HPV) on arterial oxygenation during OLV in patients scheduled for thoracic surgery. Methods: Forty patients with chronic obstructive pulmonary disease scheduled for right lung tumour resection were randomized to undergo dependent (left) one-lung ventilation (D-OLV; n=20) or non-dependent (right) one-lung ventilation (ND-OLV; n=20) in the supine and left lateral positions. Partial pressure of arterial oxygen (PaO2) was measured as a surrogate for ventilation/perfusion matching. Patients were studied before surgery under closed chest conditions. Results: When compared with bilateral lung ventilation, both D-OLV and ND-OLV caused a significant and equal decrease in PaO2 in the supine position. However, D-OLV in the lateral position was associated with a higher PaO2 as compared with the supine position [274.2 (77.6) vs. 181.9 (68.3) mmHg, P<0.01, analysis of variance (ANOVA)]. In contrast, in patients undergoing ND-OLV, PaO2 was always lower in the lateral as compared with the supine position [105.3 (63.2) vs. 187 (63.1) mmHg, P<0.01, ANOVA]. Conclusion: The relative position of the ventilated vs. the non-ventilated lung markedly affects arterial oxygenation during OLV. These data suggest that gravity affects ventilation,perfusion matching independent of HPV. [source] Fountain flow revisited: The effect of various fluid mechanics parametersAICHE JOURNAL, Issue 5 2010Evan Mitsoulis Abstract Numerical simulations have been undertaken for the benchmark problem of fountain flow present in injection-mold filling. The finite element method (FEM) is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal, steady-state conditions for Newtonian fluids. The effects of inertia, gravity, surface tension, compressibility, slip at the wall, and pressure dependence of the viscosity are all considered individually in parametric studies covering a wide range of the relevant parameters. These results extend previous ones regarding the shape of the front, and in particular the centerline front position, as a function of the dimensionless parameters. The pressures from the simulations have been used to compute the excess pressure losses in the system (front pressure correction or exit correction). Inertia leads to highly extended front positions relative to the inertialess Newtonian values, which are 0.895 for the planar case and 0.835 for the axisymmetric one. Gravity acting in the direction of flow shows the same effect, while gravity opposing the flow gives a reduced bulge of the fountain. Surface tension, slip at the wall, and compressibility, all decrease the shape of the front. Pressure-dependence of the viscosity leads to increased front position as a corresponding dimensionless parameter goes from zero (no effect) to higher values of the pressure-shift factor. The exit correction increases monotonically with inertia, compressibility, and gravity, while it decreases monotonically with slip and pressure-dependence of the viscosity. Contour plots of the primary variables (velocity-pressure) show interesting trends compared with the base case (zero values of the dimensionless parameters and of surface tension). © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Simulation of the dynamics of depth filtration of non-Brownian particlesAICHE JOURNAL, Issue 4 2001V. N. Burganos A new simulator for flow of aqueous suspensions and deposition of non-Brownian particles in granular media can predict the pattern of deposition and concomitant reduction in permeability as functions of depth, time and system parameters. The porous structure of the granular medium represented as a 3-D network of constricted pores considers the converging,diverging character of flow within pores. Using Lagrangian-type simulation the particle deposition rate was calculated. Gravity and drag, as well as hydrodynamic and physicochemical interactions between suspended particles and pore walls, were considered in calculating 3-D particle trajectories. Deposit configurations were computed, and the evolution of the pore structure was simulated at discrete time steps. Changes in the pore geometry and nature of the collector surface affect flow and trajectory computations directly. Clusters of deposited particles were allowed to become reentrained if exposed to shear stress higher than a critical value. Reentrained clusters, which moved through downstream pores, might redeposit downstream at suitable sites and cause clogging of sufficiently narrow pores. Particle clusters clogging pores have a finite permeability, which significantly affects the system's transient behavior. Clogged pores act as collectors of solitary particles and of reentrained clusters, and substantially affect the transient behavior of the filter. The loss of permeability was monitored by calculating pore and network hydraulic conductance at each time step. Numerical results for the loss of permeability, temporal evolution of filter efficiency, and specific deposit profiles are based on suspension flow simulations in a typical granular porous medium. [source] Fabrication of an Al2O3/YAG/ZrO2 Ternary Eutectic by Combustion Synthesis Melt Casting Under Ultra-High GravityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009Rui Liang This work presents a novel method for preparing an Al2O3/YAG/ZrO2 ternary eutectic whereby combustion synthesis melt casting has been combined with the ultra-high gravity (UHG) technique. The fabricated product had a relative density of 99.3% of the theoretical one. Phase composition and microstructure analyses indicated that the application of UHG resulted in a metal-free ceramic microstructure with no porosity or microcracks. The microstructure comprises ZrO2 rods dispersed in Al2O3. The product had 17.82 GPa Vickers hardness and 5.51 MPa·m1/2 fracture toughness. [source] Regional ventilation distribution in non-sedated spontaneously breathing newborns and adults is not differentPEDIATRIC PULMONOLOGY, Issue 9 2009Andreas Schibler MD Abstract Background: In adults, ventilation is preferentially distributed towards the dependent lung. A reversal of the adult pattern has been observed in infants using radionuclide ventilation scanning. But these results have been obtained in infants and children with lung disease. In this study we investigate whether healthy infants have a similar reverse pattern of ventilation distribution. Study Design: Measurement of regional ventilation distribution in healthy newborn infants during non-REM sleep in comparison to adults. Methods: Twenty-four healthy newborns and 13 adults were investigated with electrical impedance tomography (EIT) in supine and prone position. Regional ventilation distribution was assessed with profiles of relative impedance change. The phase lag between dependent and non-dependent ventilation was calculated as a measure of asynchronous ventilation. Results: In newborns and adults the geometric center of ventilation was centrally located in the lung at 52.2,±,6.2% from anterior to posterior and at 50.5,±,14.7%, respectively. Using impedance profiles, ventilation was equally distributed to the dependent and non-dependent lung regions in newborns. Ventilation distribution in adults was similar. Phase lag characteristics of the impedance signal showed that infants had slower emptying of the dependent lung than adults. Conclusion: The speculated reverse pattern of regional ventilation distribution in healthy infants compared to adults could not be demonstrated. Gravity had little effect on ventilation distribution in both infants and adults measured in supine and prone position. Pediatr Pulmonol. 2009; 44:851,858. © 2009 Wiley-Liss, Inc. [source] Damping Behavior of the Free Liquid Interface Oscillation upon Step Reduction in GravityPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003M. Michaelis Dipl.-Ing. Experiments were carried out to investigate the damping behavior of the reorientation of a free liquid interface in a right circular cylinder, partly filled with a liquid and suddenly exposed to a step reduction in gravity. The damping behavior basically depends on the Ohnesorge number and the static contact angle. This study shows the strong influence of the contact point for low static contact angles. [source] Gravity and the quantum vacuum inertia hypothesisANNALEN DER PHYSIK, Issue 8 2005A. Rueda Abstract In previous work it has been shown that the electromagnetic quantum vacuum, or electromagnetic zero-point field, makes a contribution to the inertial reaction force on an accelerated object. We show that the result for inertial mass can be extended to passive gravitational mass. As a consequence the weak equivalence principle, which equates inertial to passive gravitational mass, appears to be explainable. This in turn leads to a straightforward derivation of the classical Newtonian gravitational force. We call the inertia and gravitation connection with the vacuum fields the quantum vacuum inertia hypothesis. To date only the electromagnetic field has been considered. It remains to extend the hypothesis to the effects of the vacuum fields of the other interactions. We propose an idealized experiment involving a cavity resonator which, in principle, would test the hypothesis for the simple case in which only electromagnetic interactions are involved. This test also suggests a basis for the free parameter ,(,) which we have previously defined to parametrize the interaction between charge and the electromagnetic zero-point field contributing to the inertial mass of a particle or object. [source] In search of the Royal Ptolemaic Cemetery in central Alexandria, Egypt,the first contactARCHAEOLOGICAL PROSPECTION, Issue 3 2003St. P. Papamarinopoulos Abstract At Chatby in central Alexandria, Egypt, a team from the University of Patras conducted a detailed geophysical study as part of an investigation for locating the Royal Ptolemaic Cemetery. The exploration site is located in the Latin and Greek cemeteries in the southeast corner of the modern cemeteries of Alexandria. An area of 10,000,m2 was investigated down to a depth of 10,m. Gravity, electromagnetic prospecting, electrical, ground-penetrating radar and seismic methods were applied. The use of various methods allowed as much information from the subsurface as possible to be obtained and comparison of the data in order to enhance interpretation. Despite the increased geophysical noise present in such a highly urbanized environment, intelligent selection of field parameters, use of advanced processing techniques and specialized software made it possible to reveal important information from the subsurface data. Interpreted geophysical features may be related to buried archaeological structures at some locations of the area explored. Copyright © 2003 John Wiley & Sons, Ltd. [source] Dissecting galaxies with quantitative spectroscopy of the brightest stars in the UniverseASTRONOMISCHE NACHRICHTEN, Issue 5 2010R.-P. KudritzkiArticle first published online: 20 MAY 2010 Abstract Measuring distances to galaxies, determining their chemical composition, investigating the nature of their stellar populations and the absorbing properties of their interstellar medium are fundamental activities in modern extragalactic astronomy helping to understand the evolution of galaxies and the expanding universe. The optically brightest stars in the universe, blue supergiants of spectral A and B, are unique tools for these purposes. With absolute visual magnitudes up to MV , -9.5 they are ideal to obtain accurate quantitative information about galaxies through the powerful modern methods of quantitative stellar spectroscopy. The spectral analysis of individual blue supergiant targets provides invaluable information about chemical abundances and abundance gradients, which is more comprehensive than the one obtained from HII regions, as it includes additional atomic species, and which is also more accurate, since it avoids the systematic uncertainties inherent in the strong line studies usually applied to the HII regions of spiral galaxies beyond the Local Group. Simultaneously, the spectral analysis yields stellar parameters and interstellar extinction for each individual supergiant target, which provides an alternative very accurate way to determine extragalactic distances through a newly developed method, called the Flux-weighted Gravity,Luminosity Relationship (FGLR). With the present generation of 10 m-class telescopes these spectroscopic studies can reach out to distances of 10 Mpc. The new generation of 30 m-class telescopes will allow to extend this work out to 30 Mpc, a substantial volume of the local universe (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Galactic Sun's motion in the cold dark matter, MOdified Newtonian Dynamics and modified gravity scenariosASTRONOMISCHE NACHRICHTEN, Issue 8 2009L. Iorio Abstract We numerically integrate the equations of motion of the Sun in Galactocentric Cartesian rectangular coordinates for ,4.5 Gyr , t , 0 in Newtonian mechanics with two different models for the Cold Dark Matter (CDM) halo, in MOdified Newtonian Dynamics (MOND) and in MOdified Gravity (MOG) without resorting to CDM. The initial conditions used come from the latest kinematical determination of the 3D Sun's motion in the Milky Way (MW) by assuming for the rotation speed of the Local Standard of Rest (LSR) the recent value ,0 = 268 km s,1 and the IAU recommended value ,0 = 220 km s,1; the Sun is assumed located at 8.5 kpc from the Galactic Center (GC). For ,0 = 268 km s,1 the birth of the Sun, 4.5 Gyr ago, would have occurred at large Galactocentric distances (12,27 kpc depending on the model used), while for ,0 = 220 km s,1 it would have occurred at about 8.8,9.3 kpc for almost all the models used. The integrated trajectories are far from being circular, especially for ,0 = 268 km s,1, and differ each other with the CDM models yielding the widest spatial extensions for the Sun's orbital path (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Age-Dependent Radial Increases in Wood Specific Gravity of Tropical Pioneers in Costa RicaBIOTROPICA, Issue 5 2010G. Bruce Williamson ABSTRACT Wood specific gravity is the single best descriptor of wood functional properties and tree life-history traits, and it is the most important variable in estimating carbon stocks in forests. Tropical pioneer trees produce wood of increasing specific gravity across the trunk radius as they grow in stature. Here, we tested whether radial increases in wood specific gravity were dependent on a tree's diameter or its age by comparing trees of different diameters within cohorts. We cored trunks of four pioneer species in naturally regenerating, even-aged stands in the lowland, wet forests of Costa Rica. For each core, specific gravity was determined for 1-cm radial wood segments, pith to bark. Increases across the radius were evident in all four species studied, and in four different stands for one species. For any given species in a given stand, the rate of radial increase in specific gravity as a function of radial distance from the pith was greater in smaller diameter trees. As the trees in a stand represent a colonizing cohort, these results strongly suggest that the radial increases in specific gravity in lowland pioneers are associated with tree age, not with tree diameter. Furthermore, the specific gravity of the outermost wood was not associated with tree radius, further negating size dependence. One consequence of these results is that species-specific biomass estimates for trees in secondary forests are likely to be confounded by age, as diameter alone may be a poor indicator of specific gravity in individual trees for pioneers of tropical wet forests. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source] Interspecific and Inter-site Variation in Wood Specific Gravity of Tropical TreesBIOTROPICA, Issue 1 2004Article first published online: 15 MAR 200, Helene C. Muller-Landau ABSTRACT Variation in climate and soils results in inter-site differences in the assemblages of tree life history strategies within a community, which has important implications for ecosystem structure and dynamics. I investigated interspecific and inter-site variation in wood specific gravity,an easily measured indicator of tree life history strategy,in four Neotropical forests and analyzed its correlates. Mean wood specific gravity (oven-dry weight divided by fresh volume, sometimes also referred to as wood density in the literature) differed significantly among sites, varying inversely with soil fertility and independently of rainfall, seasonality, and temperature. Mean wood specific gravity values were much higher at Kilometer 41, Manaus, Brazil, where soils are extremely poor, than at Cocha Cashu, Peru, Barro Colorado Island, Panama, or La Selva, Costa Rica, where soils are better and mortality rates of trees are higher. Within sites, wood specific gravity varied widely among species. On Barro Colorado Island, among-species variation was significantly, albeit weakly, negatively correlated with sapling and tree mortality and relative growth rates. Altogether, the results suggest that the distribution of tree life history strategies in a community varies substantially among sites, with important consequences for community and ecosystem properties such as aboveground carbon stores. RESUMEN La variación climática y edáfica da lugar a diferencias entre sitios con respecto a los ensambles de las estrategias de historia de vida de los árboles de una comunidad, lo cual tiene consecuencias importantes para la estructura y la dinámica del ecosistema. Investigué la variación interespecífica y espacial en la gravedad específica de la Madera,un indicador de fácil medición de la estrategia de historia de vida de los árboles,en cuatro bosques neotropicales y analizé sus factores asociados. La gravedad especifica media de la madera (el peso seco dividido por el volumen fresco, frecuentemente llamado "densidad de la madera" en la literatura ecológica) fue significativamente diferente entre sitios, variando inversamente con la fertilidad del suelo, e independientemence de la precipitación, la estacionalidad, y la temperatura. La gravedad especifica media de la madera fue mucho más alta en Kilómetro 41, Manaus, Brasil, donde los suelos son extremadamente pobres, en comparación con Cocha Cashu, Perú, Barro Colorado, Panamá, o La Selva, Costa Rica, donde los suelos son mejores y las tasas de mortalidad de los árboles son más altas. Dentro de los sitios, la gravedad especifica de la madera varió extensamente entre especies. En Barro Colorado, la variación entre especies estuvo correlacionada negativamente, aunque sólo débilmente, con las tasas de mortalidad y de crecimiento relativo de los árboles juveniles y adultos. En conjunto, los resultados sugieren que la distribución de las estrategias de historia de vida de los árboles en una comunidad varía sustancialmente entre sitios, con consecuencias importantes para características comunitarias y del ecosistema tales como las reservas de carbono. [source] Gelifluction: viscous flow or plastic creep?EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2003Charles Harris Abstract This paper reports results from two scaled centrifuge modelling experiments, designed to simulate thaw-related geli,uction. A planar 12° prototype slope was modelled in each experiment, using the same natural ,ne sandy silt soil. However two different scales were used. In Experiment 1, the model scale was 1/10, tested in the centrifuge at 10 gravities (g) and in Experiment 2, the scale was 1/30, tested at 30 g. Centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is N2, where N is the number of gravities under which the model was tested. However, the equivalent time scaling for viscous ,ow is 1/1. If geli,uction is a viscosity-controlled ,ow process, scaling con,icts will therefore arise during centrifuge modelling of thawing slopes, and rates of displacement will not scale accurately to the prototype. If, however, no such scaling con,icts are observed, we may conclude that geli,uction is not controlled by viscosity, but rather by elasto-plastic soil deformation in which frictional shear strength depends on effective stress, itself a function of the thaw consolidation process. Models were saturated, consolidated and frozen from the surface downwards on the laboratory ,oor. The frozen models were then placed in the geotechnical centrifuge and thawed from the surface down. Each model was subjected to four freeze,thaw cycles. Soil temperatures and pore water pressures were monitored, and frost heave, thaw settlement and downslope displacements measured. Pore water pressures, displacement rates and displacement pro,les re,ecting accumulated shear strain, were all similar at the two model scales and volumetric soil transport per freeze,thaw cycle, when scaled to prototype, were virtually identical. Displacement rates and pro,les were also similar to those observed in earlier full-scale laboratory ,oor experiments. It is concluded therefore that the modelled geli,uction was not a time-dependent viscosity-controlled ,ow phenomenon, but rather elasto-plastic in nature. A ,rst approximation ,,ow' law is proposed, based on the ,Cam Clay' constitutive model for soils. Copyright © 2003 John Wiley & Sons, Ltd. [source] Post-common-envelope binaries from SDSS , I. 101 white dwarf main-sequence binaries with multiple Sloan Digital Sky Survey spectroscopyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007A. Rebassa-Mansergas ABSTRACT We present a detailed analysis of 101 white dwarf main-sequence binaries (WDMS) from the Sloan Digital Sky Survey (SDSS) for which multiple SDSS spectra are available. We detect significant radial velocity variations in 18 WDMS, identifying them as post-common-envelope binaries (PCEBs) or strong PCEB candidates. Strict upper limits to the orbital periods are calculated, ranging from 0.43 to 7880 d. Given the sparse temporal sampling and relatively low spectral resolution of the SDSS spectra, our results imply a PCEB fraction of ,15 per cent among the WDMS in the SDSS data base. Using a spectral decomposition/fitting technique we determined the white dwarf effective temperatures and surface gravities, masses and secondary star spectral types for all WDMS in our sample. Two independent distance estimates are obtained from the flux-scaling factors between the WDMS spectra, and the white dwarf models and main-sequence star templates, respectively. Approximately one-third of the systems in our sample show a significant discrepancy between the two distance estimates. In the majority of discrepant cases, the distance estimate based on the secondary star is too large. A possible explanation for this behaviour is that the secondary star spectral types that we determined from the SDSS spectra are systematically too early by one to two spectral classes. This behaviour could be explained by stellar activity, if covering a significant fraction of the star by cool dark spots will raise the temperature of the interspot regions. Finally, we discuss the selection effects of the WDMS sample provided by the SDSS project. [source] Testing the accuracy of synthetic stellar librariesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007Lucimara P. Martins ABSTRACT One of the main ingredients of stellar population synthesis models is a library of stellar spectra. Both empirical and theoretical libraries are used for this purpose, and the question about which one is preferable is still debated in the literature. Empirical and theoretical libraries are being improved significantly over the years, and many libraries have become available lately. However, it is not clear in the literature what are the advantages of using each of these new libraries, and how far behind models are compared to observations. Here we compare in detail some of the major theoretical libraries available in the literature with observations, aiming at detecting weaknesses and strengths from the stellar population modelling point of view. Our test is twofold: we compared model predictions and observations for broad-band colours and for high-resolution spectral features. Concerning the broad-band colours, we measured the stellar colour given by three recent sets of model atmospheres and flux distributions, and compared them with a recent UBVRIJHK calibration which is mostly based on empirical data. We found that the models can reproduce with reasonable accuracy the stellar colours for a fair interval in effective temperatures and gravities. The exceptions are (1) the U,B colour, where the models are typically redder than the observations, and (2) the very cool stars in general (V,K, 3). Castelli & Kurucz is the set of models that best reproduce the bluest colours (U,B, B,V) while Gustafsson et al. and Brott & Hauschildt more accurately predict the visual colours. The three sets of models perform in a similar way for the infrared colours. Concerning the high-resolution spectral features, we measured 35 spectral indices defined in the literature on three high-resolution synthetic libraries, and compared them with the observed measurements given by three empirical libraries. The measured indices cover the wavelength range from ,3500 to ,8700 Å. We found that the direct comparison between models and observations is not a simple task, given the uncertainties in parameter determinations of empirical libraries. Taking that aside, we found that in general the three libraries present similar behaviours and systematic deviations. For stars with Teff, 7000 K, the library by Coelho et al.is the one with best average performance. We detect that lists of atomic and molecular line opacities still need improvement, specially in the blue region of the spectrum, and for the cool stars (Teff, 4500 K). [source] A comparison of DA white dwarf temperatures and gravities from Lyman and Balmer line studiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2001M.A. Barstow We present measurements of the effective temperatures and surface gravities for a sample of hot DA white dwarfs, using the Lyman line data available from the HUT, ORFEUS and FUSE FUV space missions. Comparing the results with those from the standard Balmer line technique, we find that there is a general good overall agreement between the two methods. However, significant differences are found for a number of stars, but not always of a consistent nature in that sometimes the Balmer temperature exceeds that derived from the Lyman lines and in other instances it is lower. We conclude that, with the latest model atmosphere calculations, these discrepancies probably do not arise from an inadequate theoretical treatment of the Lyman lines but rather from systematic effects in the observation and data reduction processes, which dominate the statistical errors in these spectra. If these systematic data reduction effects can be adequately controlled, the Lyman line temperature and gravity measurements are consistent with those obtained from the Balmer lines when allowance is made for reasonable observational uncertainties. [source] A method for the direct determination of the surface gravities of transiting extrasolar planetsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2007John Southworth ABSTRACT We show that the surface gravity of a transiting extrasolar planet can be calculated from only the spectroscopic orbit of its parent star and the analysis of its transit light curve. This does not require additional constraints, such as are often inferred from theoretical stellar models or model atmospheres. The surface gravity of the planet can therefore be measured precisely and from only directly observable quantities. We outline the method and apply it to the case of the first known transiting extrasolar planet, HD 209458b. We find a surface gravity of gp= 9.28 ± 0.15 m s,2, which is an order of magnitude more precise than the best available measurements of its mass, radius and density. This confirms that the planet has a much lower surface gravity than that predicted by published theoretical models of gas giant planets. We apply our method to all 14 known transiting extrasolar planets and find a significant correlation between surface gravity and orbital period, which is related to the known correlation between mass and period. This correlation may be the underlying effect as surface gravity is a fundamental parameter in the evaporation of planetary atmospheres. [source] New constraints from the H, line for the temperature of the transiting planet host star OGLE-TR-10,ASTRONOMISCHE NACHRICHTEN, Issue 6 2008M. Ammler-von Eiff Abstract The spectroscopic analysis of systems with transiting planets gives strong constraints on planetary masses and radii as well as the chemical composition of the systems. The properties of the system OGLE-TR-10 are not well-constrained, partly due to the discrepancy of previous measurements of the effective temperature of the host star. This work, which is fully independent from previous works in terms of data reduction and analysis, uses the H, profile in order to get an additional constraint on the effective temperature. We take previously published UVES observations which have the highest available signal-to-noise ratio for OGLE-TR-10. A proper normalization to the relative continuum is done using intermediate data products of the reduction pipeline of the UVES spectrograph. The effective temperature then is determined by fitting synthetic H, profiles to the observed spectrum. With a result of Teff = 6020 ± 140 K, the H, profile clearly favours one of the previous measurements. The H, line is further consistent with dwarf-like surface gravities as well as solar and super-solar metallicities previously derived for OGLE-TR-10. The H, line could not be used to its full potential, partly because of the varying shape of the UVES échelle orders after flat field correction. We suggest to improve this feature when constructing future spectrographs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exclusively breastfed, low birthweight term infants do not need supplemental waterACTA PAEDIATRICA, Issue 5 2000RJ Cohen Breast milk intake, urine volume and urine-specific gravity (USG) of exclusively breastfed, low birthweight (LBW) term male infants in Honduras were measured during 8-h periods at 2 (n= 59) and 8 (n = 68) wk of age. Ambient temperature was 22,36°C and relative humidity was 37,86%. Maximum USG ranged from 1.001 to 1.012, all within normal limits. Conclusions: We conclude that supplemental water is not required for exclusively breastfed, LBW term infants, even in hot conditions. [source] Growth and properties of an organometallic nonlinear optical crystal: bis(isothiocyanato)-bis(4-methylpyridine)zinc(II) (Zn(SCN)2(C6H7N)2)CRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2006L. Y. Zhu Abstract Bis(isothiocyanato)-bis(4-methylpyridine)zinc(II)(Zn(SCN)2(C6H7N)2), (abbreviated as ZBNC) single crystals of optical quality have been grown from acetone solution by the slow temperature-lowering method. Its solubilities at different temperatures in acetone were measured. The X-ray powder diffraction (XRPD) spectroscopy of ZBNC crystal was performed at room temperature. The second harmonic generation (SHG) efficiency was determined by powder technique of Kurtz and Perry using Nd:YAG laser, which is equivalent to KDP crystal. The thermal decomposition process was characterized by thermal gravity and differential thermal analysis (TG\DTA). The specific heat of the crystal is 1440.67 J/mol·K at 325 K. The IR spectrum was recorded in the 500,3500 cm,1 region, using KBr pellets on a Nicolet 170sx FT-IR spectrometer. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Sedimentation as a tool for crystallization from protein mixturesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 11 2006I. Dimitrov Abstract Crystals from apoferritin which is an iron-free form of protein ferritin were obtained from protein mixtures lysozyme/apoferritin using sedimentation under high gravity. Solution containing apoferritin at concentration as high as 5mg/ml in the presence of 25mg/ml lysozyme and overlaid on 5%(w/v) CdSO4 in 0,2M/L NaAC, pH=5 still favors apoferritin crystal formation under normal gravity conditions, but at apoferritin concentrations <0,5mg/ml (,1,14µM/L) in 25mg/ml (,1,71mM/L) lysozyme only the sedimentation in a centrifuge appears to be useful for separating the apoferritin molecules from the mixture followed by apoferritin crystallization in the same system. The very high molecule number ratio (,1:103) of two proteins is used to stress on the observed effect. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Gravity bias in young and adult chimpanzees (Pan troglodytes): tests with a modified opaque-tubes taskDEVELOPMENTAL SCIENCE, Issue 3 2007Masaki Tomonaga Young human children at around 2 years of age fail to predict the correct location of an object when it is dropped from the top of an S-shape opaque tube. They search in the location just below the releasing point (Hood, 1995). This type of error, called a ,gravity bias', has recently been reported in dogs and monkeys. In the present study, we investigated whether young and adult chimpanzees also show such a gravity bias in a modified version of the original opaque-tube task. The original task by Hood and colleagues required the subject to search in a location after the object had fallen, while in the task reported here, subjects were required to predict the location before the object was dropped. Thus the present procedure does not involve explicit invisible displacement operations, one of the important components of the original procedure. In Experiment 1 both young (1.5,2.5-year-old) and adult chimpanzees predicted the location of falling food items below the releasing point even when crossed tubes were used. These gravity errors remained after the extensive experience of using the tubes themselves. Experiment 2 further tested adult and 4-year-old chimpanzees under the set-up in which the straight and crossed tubes were simultaneously presented. The results were the same as those in the previous test, suggesting that developmental changes and learning effect do not affect the gravity bias in chimpanzees. [source] The effect of divided attention on inhibiting the gravity errorDEVELOPMENTAL SCIENCE, Issue 3 2006Bruce M. Hood Children who could overcome the gravity error on Hood's (1995) tubes task were tested in a condition where they had to monitor two falling balls. This condition significantly impaired search performance with the majority of mistakes being gravity errors. In a second experiment, the effect of monitoring two balls was compared in the tubes task and a spatial transposition task not involving gravity. Again, monitoring two objects produced impaired search performance in the gravity task but not in the spatial transposition task. These findings support the view that divided attention disrupts the ability to exercise inhibitory control over the gravity error and that the performance drop on this task is not due to the additional task demands incurred by divided attention. [source] Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands , towards a sediment budgetEARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2008Jan Nyssen Abstract This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100,2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area-weighted average rate of soil erosion by water in the catchment, measured over four years (1998,2001), is 14·8 t ha,1 y,1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha,1 y,1. Calculated sediment yield (5·6 t ha,1 y,1) is similar to sediment yield measured in nearby catchments. Seventy-four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present-day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd. [source] Textural and compositional controls on modern beach and dune sands, New ZealandEARTH SURFACE PROCESSES AND LANDFORMS, Issue 3 2007J. J. Kasper-Zubillaga Abstract Textural, compositional, physical and geophysical determinations were carried out on 111 beach and dune sand samples from two areas in New Zealand: the Kapiti,Foxton coast sourced by terranes of andesite and greywackes and the Farewell Spit,Wharariki coast sourced by a wide variety of Paleozoic terranes. Our aim is to understand how long-shore drift, beach width and source rock control the sedimentological and petrographic characteristics of beach and dune sands. Furthermore, this study shows the usefulness of specific minerals (quartz, plagioclase with magnetite inclusions, monomineralic opaque grains) to interpret the physical processes (fluvial discharges, long-shore currents, winds) that distribute beach and dune sands in narrow and wide coastal plains. This was done by means of direct (grain size and modal analyses) and indirect (specific gravity, magnetic/non-magnetic separations M/NM, magnetic susceptibility measurements, hysteresis loops) methods. Results are compared with beach sands from Hawaii, Oregon, the Spanish Mediterranean, Elba Island and Southern California. Compositionally, the Kapiti,Foxton sands are similar to first-order immature sands, which retain their fluvial signature. This results from the high discharge of rivers and the narrow beaches that control the composition of the Kapiti,Foxton sands. The abundance of feldspar with magnetite inclusions controls the specific gravity of the Kapiti,Foxton sands due to their low content of opaque minerals and coarse grain size. Magnetic susceptibility of the sands is related mainly to the abundance of feldspars with Fe oxides, volcanic lithics and free-opaque minerals. The Farewell Spit,Wharariki sands are slightly more mature than the Kapiti,Foxton sands. The composition of the Farewell Spit,Wharariki sands does not reflect accurately their provenance due to the prevalence of long-shore drift, waves, little river input and a wide beach. Low abundance of feldspar with magnetite inclusions and free opaque grains produces poor correlations between specific gravity (Sg) and Fe oxide bearing minerals. The small correlation between opaque grains and M/NM may be related to grain size. The magnetic susceptibility of Farewell Spit,Wharariki sands is low due to the low content of grains with magnetite inclusions. Hysteresis and isothermal remnant magnetization (IRM) agree with the magnetic susceptibility values. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effects of column axial force , bending moment interaction on inelastic seismic response of steel framesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 12 2003Marina Como Abstract It is well known that axial force , bending moment interaction (N,M interaction) affects to a large extent the cyclic inelastic behaviour of structural elements, especially columns in framed structures, with reduction in bending capacity and loss of available ductility. A few studies have also shown that significant inelastic axial shortening affects the response of column elements subjected to medium,high levels of axial loads and cyclic bending. This paper is primarily aimed at evaluating the effects of column N,M interaction on the inelastic seismic response of steel frames. By considering the contemporaneous action of vertical loads, due to gravity, and of horizontal seismic excitation, it is shown that the progressive axial shortening of adjacent columns may differ substantially, thus inducing significant relative settlements at the ends of the connecting beams and, then, remarkable amplifications in beam plastic rotations. An evaluation of additional beam plastic rotations induced by column N,M interaction is carried out for real structures by investigating the inelastic response of steel frames designed according to European standards under horizontal and vertical earthquake excitations. Copyright © 2003 John Wiley & Sons, Ltd. [source] An experimental evaluation of ice cover effects on the dynamic behaviour of a concrete gravity damEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 12 2002Patrick Paultre Abstract An extensive forced-vibration testing programme has been carried out on an 84-m concrete gravity dam located in northeastern Québec, Canada. The dam was subjected to a harmonic load on the crest in summer and severe winter conditions with temperatures ranging from ,10°C to ,15°C and a 1.0,1.5m ice cover. Acceleration and hydrodynamic frequency responses were obtained in different locations on the dam and in the reservoir. The main objective of the repeated tests was to investigate the effects of the ice cover on the dynamic behaviour of the dam,reservoir,foundation system, by comparing summer and winter results. Modifications in damping and resonance frequencies were observed, as well as an additional resonance that was attributed to an interaction of the dam with the ice cover. These findings provided a reliable and unique database for the investigations of dam,reservoir,foundation interaction and, in particular, the ice-cover effects for dams located in northern regions. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||