Página 1 dos resultados de 4762 itens digitais encontrados em 0.020 segundos

## Correlação entre a densidade óssea mandibular, femural, lombar e cervical; Correlation among mandibular, femoral, lumbar and cervical bone density

SCHEIBEL, Paula Cabrini; MATHEUS, Paula Daniele; ALBINO, Cláudio Cordeiro; RAMOS, Adilson Luiz
Fonte: Dental Press Editora Publicador: Dental Press Editora
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
45.83%

## Soil density evaluated by spectral reflectance as an evidence of compaction effects

DEMATTE, J. A. M.; NANNI, M. R.; SILVA, A. P. da; MELO FILHO, J. F. de; SANTOS, W. C. Dos; CAMPOS, R. C.
Fonte: TAYLOR & FRANCIS LTD Publicador: TAYLOR & FRANCIS LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
45.89%
Soil compaction, reflected by high bulk density, is an environmental degradation process and new technologies are being developed for its detection. Despite the proven efficiency of remote sensing, it has not been widely used for soil density. Our objective was to evaluate the density of two soils: a Typic Quartzpisament (TQ) and a Rhodic Paleudalf (RP), using spectral reflectance obtained by a laboratory spectroradiometer between 450 and 2500 nm. Undisturbed samples were taken at two depths (0-20 and 60-80 cm), and were artificially compacted. Spectral data, obtained before and after compaction, were compared for both wet and dried compacted samples. Results demonstrated that soil density was greater in RP than in TQ at both depths due to its clayey texture. Spectral data detected high density (compacted) from low density (non-compacted) clayey soils under both wet and dry conditions. The detection of density in sandy soils by spectral reflectance was not possible. The intensity of spectral reflectance of high soil bulk density (compacted) samples was higher than for low density (non-compacted) soils due to changes in soil structure and porosity. Dry samples with high bulk density showed differences in the spectral intensity, but not in the absorption features. Wet samples in equal condition had statistically higher reflectance intensity than that of the low soil bulk density (non-compacted)...

## EFEITO DA IDADE E POSIÇÃO DE AMOSTRAGEM NA DENSIDADE E CARACTERÍSTICAS ANATÔMICAS DA MADEIRA DE Eucalyptus grandis; EFFECT OF AGE AND SAMPLING POSITION ON DENSITY AND ANATOMICAL CHARACTERISTICS OF WOOD IN EUCALYPTUS TREES

Sette Jr., Carlos Roberto; Oliveira, Ivanka Rosada de; Tomazello Filho, Mario; Yamaji, Fabio Minoru; Laclau, Jean Paul
Fonte: UNIV FEDERAL VICOSA; VIÇOSA Publicador: UNIV FEDERAL VICOSA; VIÇOSA
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
36.02%
The knowledge of the variations in the wood characteristics produced by eucalyptus trees according to age and sampling positions is essential for its proper use. This study had as objective to evaluate the influence of the age, longitudinal and radial positions on basic density and anatomical characteristics in Eucalyptus grandis wood. The trees were planted in 3x2 m spacing and fertilized with commercial fertilizers in planting, 6th and 12th months. According to basal area distribution, fifteen trees were selected (24, 36 and 72 months of age) - five trees per age. Disks at DBH position (1.3 m) were taken for fiber determination (length, wall thickness, lumen diameter and width) and vessels (tangential diameter, frequency and area occupied) and in other different sampling positions for basic density determination. Wood basic density increased from 0.43 to 0.46 g.cm(-3) as well as the trees age increases with a longitudinal variation model, characterized through a decrease in base-3m (0.42-0.49 -> 0.40-0.46 g.cm(-3)) and an increase to the top of the trunk (0.46 -> 0.54 g.cm(-3)) Fibers and vessels dimensions showed variations related to age and to pit-bark direction. Wood properties behavior and variations indicate that, until this period...

## Simulação física de fluxos gravitacionais : efeitos da variação de concentração e vazão do fluxo no depósito gerado; Physical simulation of gravitational flows : the effects of variations in concertration and output of the flow in the deposit generated

Lenita de Souza Fioriti
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
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36.09%

## Plant- and stand-level variation in biophysical and physiological traits along tree density gradients in the Cerrado

Scholz,Fabian G.; Bucci,Sandra J.; Goldstein,Guillermo; Meinzer,Frederick C.; Franco,Augusto C.; Salazar,Ana
Fonte: Brazilian Journal of Plant Physiology Publicador: Brazilian Journal of Plant Physiology
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
36.07%
The objective of this study was to characterize and understand morphological and physiological variation in traits related to water economy, at the plant and stand level, along a gradient of tree density in a Neotropical savanna (Cerrado). Cerrado plots subjected to long-term fertilization and gallery forests were also included in the analysis to expand the axes of ecosystem variation. Consistent changes in stand level biophysical traits observed along the gradient of increasing tree density included a decrease in weighted-average wood density, and increases in leaf surface area per plant, leaf specific hydraulic conductivity, specific leaf area and stomatal conductance. A conceptual model of biophysical, morphological and physiological trait interactions was developed in an attempt to explain determinants of hydraulic architecture and variations in water economy of Cerrado trees. Consistent with the model minimum leaf water potentials were higher, during the dry season, in low wood density trees compared to high wood density trees, and higher leaf water potential was associated with higher stomatal conductance. On the other hand, variations in stand level physiological and morphological traits along the tree density gradient could not be explained by variations in single environmental factors. Some of the potential contributing factors are: higher concentration and availability of soil nutrients in the upper portion of the gradient where tree density is greatest and constrains to tree establishment and growth by waterlogging and presence of concretions in the soil profile where tree density is lowest.

## Influence of the tidal and rainfall cycles on the population structure and density of Mesacanthion hirsutum gerlach (nematoda, thoracostomopsidae) on a tropical sandy beach (Tamandaré Bay, Pernambuco, Brazil)

Venekey,Virag; Fonsêca-Genevois,Verônica Gomes da; Santos,Paulo Jorge Parreira dos
Tipo: Artigo de Revista Científica Formato: text/html
Relevância na Pesquisa
45.89%
The population structure (males, females and juveniles) and density of Mesacanthion hirsutum Gerlach were studied during the tides (low, flood, high and ebb) of two consecutive tidal cycles in four different months of the year (May, July, September and November). Mesacanthion hirsutum density variations showed association with the rainfall cycle, with lower densities during July and September and significantly higher values in May and November. The population structure was constituted mostly by juveniles indicating a continuous reproduction during all the studied period. There were no significant differences between light and dark periods of the day, however, the higher densities detected during the high and ebb tidal stages demonstrate that this species could be dispersing through the water column and/or migrating within the sediment.

## The role of background flow variations in stratified flows over topography

Skopovi, Ivan, 1976-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 91 leaves
ENG
Relevância na Pesquisa
36.02%
As the atmosphere and oceans feature density variations with depth, the flow of a density-stratified fluid over topography is central to various geophysical and meteorological applications and has been studied extensively. For reasons of convenience and mathematical tractability, the majority of theoretical treatments of stratified flow over a finite-amplitude obstacle assume idealized background flow conditions, namely constant free-stream velocity and either a homogeneous or two-layer buoyancy-frequency profile. In this work, a numerical model is developed that accounts for general variations in the buoyancy-frequency profile far upstream and the presence of unsteadiness in the free-stream velocity. The model employs a second-order projection method for solving the Euler equations for stratified flow over locally confined topography in a horizontally and vertically unbounded domain - the flow configuration most pertinent to atmospheric applications - combined with absorbing viscous layers at the upper and lateral boundaries of the computational domain. Using this model, a study is first made of the effect of variations in the buoyancy frequency on the generation of mountain gravity waves.; (cont.) Balloon measurements reveal that...

## Density Variations in the NW Star Stream of M31

Carlberg, R. G.; Richer, Harvey B.; McConnachie, Alan W.; Irwin, Mike; Ibata, Rodrigo A.; Dotter, Aaron L.; Chapman, Scott; Fardal, Mark; Ferguson, A. M. N.; Lewis, G. F.; Navarro, Julio F.; Puzia, Thomas H.; Valls-Gabaud, David
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.09%
The Pan Andromeda Archeological Survey (PAndAS) CFHT Megaprime survey of the M31-M33 system has found a star stream which extends about 120 kpc NW from the center of M31. The great length of the stream, and the likelihood that it does not significantly intersect the disk of M31, means that it is unusually well suited for a measurement of stream gaps and clumps along its length as a test for the predicted thousands of dark matter sub-halos. The main result of this paper is that the density of the stream varies between zero and about three times the mean along its length on scales of 2 to 20 kpc. The probability that the variations are random fluctuations in the star density is less than 10^-5. As a control sample we search for density variations at precisely the same location in stars with metallicity higher than the stream, [Fe/H]=[0, -0.5] and find no variations above the expected shot noise. The lumpiness of the stream is not compatible with a low mass star stream in a smooth galactic potential, nor is it readily compatible with the disturbance caused by the visible M31 satellite galaxies. The stream's density variations appear to be consistent with the effects of a large population of steep mass function dark matter sub-halos, such as found in LCDM simulations...

## On a molecular based Q-tensor model for liquid crystals with density variations

Mei, Song; Zhang, Pingwen
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.93%
In this article, we study the new Q-tensor model previously derived from Onsager's molecular theory by Han \textit{et al.} [Arch. Rational Mech. Anal., 215.3 (2014), pp. 741-809] for static liquid crystal modeling. Taking density and Q-tensor as order parameters, the new Q-tensor model not only characterizes important phases while capturing density variation effects, but also remains computationally tractable and efficient. We report the results of two numerical applications of the model, namely the isotropic--nematic--smectic-A--smectic-C phase transitions and the isotropic--nematic interface problem, in which density variations are indispensable. Meanwhile, we show the connections of the new Q-tensor model with classical models including generalized Landau-de Gennes models, generalized McMillan models, and the Chen-Lubensky model. The new Q-tensor model is the pivot and an appropriate trade-off between the classical models in three scales.

## Evidence of Short Timescale Flux Density Variations of UC HII regions in Sgr B2 Main and North

De Pree, C. G.; Peters, T.; Mac Low, M. -M.; Wilner, D. J.; Goss, W. M.; Galván-Madrid, R.; Keto, E. R.; Klessen, R. S.; Monsrud, A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.03%
We have recently published observations of significant flux density variations at 1.3 cm in HII regions in the star forming regions Sgr B2 Main and North (De Pree et al. 2014). To further study these variations, we have made new 7 mm continuum and recombination line observations of Sgr B2 at the highest possible angular resolution of the Karl G. Jansky Very Large Array (VLA). We have observed Sgr B2 Main and North at 42.9 GHz and at 45.4 GHz in the BnA configuration (Main) and the A configuration (North). We compare these new data to archival VLA 7 mm continuum data of Sgr B2 Main observed in 2003 and Sgr B2 North observed in 2001. We find that one of the 41 known ultracompact and hypercompact HII regions in Sgr B2 (K2-North) has decreased $\sim$27% in flux density from 142$\pm$14 mJy to 103$\pm$10 mJy (2.3$\sigma$) between 2001 and 2012. A second source, F3c-Main has increased $\sim$30% in flux density from 82$\pm$8 mJy to 107 $\pm$11 mJy (1.8$\sigma$) between 2003 and 2012. F3c-Main was previously observed to increase in flux density at 1.3 cm over a longer time period between 1989 and 2012 (De Pree et al. 2014). An observation of decreasing flux density, such as that observed in K2-North, is particularly significant since such a change is not predicted by the classical hypothesis of steady expansion of HII regions during massive star accretion. Our new observations at 7 mm...

## Monitoring RXTE Observations of Markarian 348: the origin of the column density variations

Akylas, A.; Georgantopoulos, I.; Griffiths, R. G.; Papadakis, I. E.; Mastichiadis, A.; Warwick, R. S.; Nandra, K.; Smith, D. A.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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We analyze 37 RXTE observations of the type 2 Seyfert galaxy Mrk348 obtained during a period of 14 months. We confirm the spectral variability previous reported by Smith et al., in the sense that thecolumn density decreases by a factor of ~3 as the count rate increases. Column density variations could possibly originate either due to the random drift of clouds within the absorption screen, or due to photoionization processes. Our modeling of the observed variations implies that the first scenario is more likely. These clouds should lie in a distance of >2 light years from the source, having a diameter of a few light days and a density of >10^7 cm^(-3), hence probably residing outside the Broad Line Region.; Comment: 6 pages, 3 figures, to appear in MNRAS

## Azimuthal Density Variations Around the Rim of Tycho's Supernova Remnant

Williams, Brian J.; Borkowski, Kazimierz J.; Ghavamian, Parviz; Hewitt, John W.; Mao, S. Alwin; Petre, Robert; Reynolds, Stephen P.; Blondin, John M.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.1%
{\it Spitzer} images of Tycho's supernova remnant in the mid-infrared reveal limb-brightened emission from the entire periphery of the shell and faint filamentary structures in the interior. As with other young remnants, this emission is produced by dust grains, warmed to $\sim 100$ K in the post-shock environment by collisions with energetic electrons and ions. The ratio of the 70 to 24 $\mu$m fluxes is a diagnostic of the dust temperature, which in turn is a sensitive function of the plasma density. We find significant variations in the 70/24 flux ratio around the periphery of Tycho's forward shock, implying order-of-magnitude variations in density. While some of these are likely localized interactions with dense clumps of the interstellar medium, we find an overall gradient in the ambient density surrounding Tycho, with densities 3-10 times higher in the NE than in the SW. This large density gradient is qualitatively consistent with the variations in the proper motion of the shock observed in radio and X-ray studies. Overall, the mean ISM density around Tycho is quite low ($\sim 0.1-0.2$ cm$^{-3}$), consistent with the lack of thermal X-ray emission observed at the forward shock. We perform two-dimensional hydrodynamic simulations of a Type Ia SN expanding into a density gradient in the ISM...

## Interstellar absorptions towards the LMC: Small-scale density variations in Milky Way disc gas

Nasoudi-Shoar, Soroush; Richter, Philipp; de Boer, Klaas S.; Wakker, Bart P.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.06%
Observations show that the ISM contains sub-structure on scales less than 1 pc, detected in the form of spatial and temporal variations in column densities or optical depth. Despite the number of detections, the nature and ubiquity of the small-scale structure in the ISM is not yet fully understood. We use UV absorption data mainly from FUSE and partly from STIS of six LMC stars (Sk-67{\deg}111, LH54-425, Sk-67{\deg}107, Sk-67{\deg}106, Sk-67{\deg}104, and Sk-67{\deg}101), all located within 5 arcmin of each other, and analyse the physical properties of the Galactic disc gas in front of the LMC on sub-pc scales. We analyse absorption lines of a number of ions within the UV spectral range. Most importantly, interstellar molecular hydrogen, neutral oxygen, and fine-structure levels of neutral carbon have been used in order to study changes in the density and the physical properties of the Galactic disc gas over small angular scales. While most species do not show any significant variation in their column densities, we find an enhancement of almost 2 dex for H_2 from Sk-67{\deg}111 to Sk-67{\deg}101, accompanied by only a small variation in the OI column density. Based on the formation-dissociation equilibrium, we trace these variations to the actual density variations in the molecular gas. On the smallest spatial scale of < 0.08 pc...

## X-Ray Evidence for Flare Density Variations and Continual Chromospheric Evaporation in Proxima Centauri

Guedel, Manuel; Audard, Marc; Skinner, Stephen L.; Horvath, Matthias I.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.84%
Using the XMM-Newton X-ray observatory to monitor the nearest star to the Sun, Proxima Centauri, we recorded the weakest X-ray flares on a magnetically active star ever observed. Correlated X-ray and optical variability provide strong support for coronal energy and mass supply by a nearly continuous sequence of rapid explosive energy releases. Variable emission line fluxes were observed in the He-like triplets of OVII and NeIX during a giant flare. They give direct X-ray evidence for density variations, implying densities between 2x10^{10} - 4x10^{11} cm^{-3} and providing estimates of the mass and the volume of the line-emitting plasma. We discuss the data in the context of the chromospheric evaporation scenario.; Comment: 10 pages, 2 figures, accepted by The Astrophysical Journal, Letters; improved calculations of radiative loss of cool plasma (toward end of paper)

## Flux density variations of radio sources in M82 over the last 3 decades

Gendre, M. A.; Fenech, D. M.; Beswick, R. J.; Muxlow, T. W. B.; Argo, M. K.
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.01%
This paper presents the results of the 2009-2010 monitoring sessions of the starburst galaxy M82, obtained with the Multi-Element Radio-Linked Interferometer Network (MERLIN) at 5GHz and e-MERLIN at 6GHz. Combining several 5GHz MERLIN epochs to form a map with 33.0 uJy/bm noise level, 52 discrete sources, mostly supernova remnants and HII regions, are identified. These include three objects which were not detected in the 2002 5GHz MERLIN monitoring session: supernova SN2008iz, the transient source 43.78+59.3, and a new supernova remnant shell. Flux density variations, in the long (1981 to 2010), medium (2002 to 2010) and short (2009 to 2010) term, are investigated. We find that flux densities of SNRs in M82 stay constant in most of the sample (~95%). In addition, aside from SN2008iz and the well-known variable source 41.95+57.5, two sources display short and medium term variations over the period 2009-2010. These sources being among the most compact SNR in M82, these flux density variations could be due to changes in the circumstellar and interstellar medium in which the shocks travel.; Comment: 15 pages, 10 figures

## The Radio and X-Ray Luminous SN 2003bg and the Circumstellar Density Variations around Radio Supernovae

Soderberg, A. M.; Chevalier, R. A.; Kulkarni, S. R.; Frail, D. A.
Fonte: American Astronomical Society Publicador: American Astronomical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Relevância na Pesquisa
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We report extensive radio and X-ray observations of SN 2003bg, whose spectroscopic evolution shows a transition from a broad-lined Type Ic to a hydrogen-rich Type II, and later to a typical hydrogen-poor Type Ibc. We show that the extraordinarily luminous radio emission is well described by a self-absorption-dominated synchrotron spectrum, while the observed X-ray emission at t ≈ 30 days is adequately fit by inverse Compton scattering of the optical photons off of the synchrotron-emitting electrons. Our radio model implies a subrelativistic ejecta velocity, ν(overbar) ≈ 0.24c, at t_0 ≈ 10 days after the explosion, which emphasizes that broad optical absorption lines do not imply relativistic ejecta. We find that the total energy of the radio-emitting region evolves as E ≈ 7.3 × 10^(48)(t/t_0)^(0.4) ergs, assuming equipartition of energy between relativistic electrons and magnetic fields (ε_e = ε_B = 0.1). The circumstellar density is well described by a stellar wind profile, with modest (factor of ~2) episodic density enhancements that produce abrupt achromatic flux variations. We estimate an average mass-loss rate of M ≈ 3 × 10^(-4) M_☉ yr^(-1) (assuming a wind velocity of ν_w = 10^3 km s^(-1)) for the progenitor...

## Comparison between crustal density and velocity variations in southern California

Langenheim, V. E.; Hauksson, Egill
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Relevância na Pesquisa
36.09%
We predict gravity from a three-dimensional V_p model of the upper crust and compare it to the observed isostatic residual gravity field. In general this comparison shows that the isostatic residual gravity field reflects the density variations in the upper to middle crust. Both data sets show similar density variations for the upper crust in areas such as the Peninsular Ranges and the Los Angeles basin. Both show similar variations across major faults, such as the San Andreas and Garlock faults in the Mojave Desert. The difference between the two data sets in regions such as the Salton Trough, the Eastern California Shear Zone, and the eastern Ventura basin (where depth to Moho is <30 km), however, suggests high-density middle to lower crust beneath these regions. Hence the joint interpretation of these data sets improves the depth constraints of crustal density variations.

## Influence of the tidal and rainfall cycles on the population structure and density of Mesacanthion hirsutum gerlach (nematoda, thoracostomopsidae) on a tropical sandy beach (Tamandaré Bay, Pernambuco, Brazil)

Venekey, Virag; Fonsêca-Genevois, Verônica Gomes da; Santos, Paulo Jorge Parreira dos
Tipo: info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion; Formato: application/pdf
Relevância na Pesquisa
45.89%
The population structure (males, females and juveniles) and density of Mesacanthion hirsutum Gerlach were studied during the tides (low, flood, high and ebb) of two consecutive tidal cycles in four different months of the year (May, July, September and November). Mesacanthion hirsutum density variations showed association with the rainfall cycle, with lower densities during July and September and significantly higher values in May and November. The population structure was constituted mostly by juveniles indicating a continuous reproduction during all the studied period. There were no significant differences between light and dark periods of the day, however, the higher densities detected during the high and ebb tidal stages demonstrate that this species could be dispersing through the water column and/or migrating within the sediment.; A estrutura populacional (machos, fêmeas e juvenis) e densidade de Mesacanthion hirsutum Gerlach foram estudadas durante as marés (baixa, enchente, alta e vazante) de dois ciclos de maré consecutivos, em quatro meses diferentes do ano (Maio, Julho, Setembro e Novembro). As variações de densidade de Mesacanthion hirsutum mostraram associação com o ciclo de chuvas, com densidades mais baixas durante Julho e Setembro e significativamente maiores em Maio e Novembro. A estrutura populacional constituiu-se em sua maior parte por juvenis indicando uma reprodução continua durante todo o período de estudo. Não foram encontradas diferenças significativas entre os períodos claros e escuros do dia...

## Density variations in the NW star stream of M31

Carlberg, R G; Richer, Harvey B; McConnachie, Alan W; Irwin, M. J.; Ibata, Rodrigo A; Dotter, Aaron; Chapman, S. C.; Fardal, Mark; Ferguson, A. M. N.; Lewis, Geraint Francis; Navarro, J F; Puzia, Thomas H; Valls-Gabuad, David
Fonte: IOP Publishing Publicador: IOP Publishing
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.09%
The Pan Andromeda Archeological Survey (PAndAS) CFHT Megaprime survey of the M31-M33 system has found a star stream which extends about 120 kpc NW from the center of M31. The great length of the stream, and the likelihood that it does not significantly intersect the disk of M31, means that it is unusually well suited for a measurement of stream gaps and clumps along its length as a test for the predicted thousands of dark matter sub-halos. The main result of this paper is that the density of the stream varies between zero and about three times the mean along its length on scales of 2-20 kpc. The probability that the variations are random fluctuations in the star density is less than 10-5. As a control sample, we search for density variations at precisely the same location in stars with metallicity higher than the stream [Fe/H] = [0, -0.5] and find no variations above the expected shot noise. The lumpiness of the stream is not compatible with a low mass star stream in a smooth galactic potential, nor is it readily compatible with the disturbance caused by the visible M31 satellite galaxies. The stream's density variations appear to be consistent with the effects of a large population of steep mass function dark matter sub-halos, such as found in LCDM simulations...

## Effects of the density perturbation in scattering

Hong, Tae-Kyung; Kennett, Brian; Wu, Ru-Shan
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.04%
The influence of density variation on scattering is investigated in terms of attenuation, coda level, and apparent frequency shift. The influence of density variations is to produce more scattered energy than for velocity perturbations alone with a consequently higher coda level. The temporal decay of the coda is reduced, so that high perturbations in density are associated with a long duration of coda. These effects are particularly important for media with small-scale heterogeneity. Thus inversions for heterogeneity parameters, based on the character of precursors and coda of seismic phases penetrating deep into the Earth, need to take into account the nature of the density variations as well as wave speed variations.