Search

We analyse 870  |$\mu$| m Atacama Large Millimetre Array (ALMA) dust continuum detections of 41 canonically selected |$z$| ≃ 3 Lyman-break galaxies (LBGs), as well as 209 ALMA-undetected LBGs, in follow-up of SCUBA-2 mapping of the UKIDSS Ultra Deep Survey (UDS) field. We find that our ALMA-bright LBGs lie significantly off the local IRX-beta relation and have relatively bluer rest-frame UV slopes (as parametrized by β), given their high values of the 'infrared excess' (IRX ≡ L IR/ L UV), relative to the average 'local' IRX-β relation. We attribute this finding in part to the young ages of the underlying stellar populations but we find that the main reason behind the unusually blue UV slopes are the relatively shallow slopes of the corresponding dust attenuation curves. We show that, when stellar masses, M *, are being established via SED fitting, it is absolutely crucial to allow the attenuation curves to vary (rather than fixing it on Calzetti-like law), where we find that the inappropriate curves may underestimate the resulting stellar masses by a factor of ≃2–3× on average. In addition, we find these LBGs to have relatively high specific star-formation rates (sSFRs), dominated by the dust component, as quantified via the fraction of obscured star formation |$(f_{\rm obs}\equiv {\rm SFR_{\rm IR}/{\rm SFR}_{\rm UV+IR}})$|⁠. We conclude that the ALMA-bright LBGs are, by selection, massive galaxies undergoing a burst of a star formation (large sSFRs, driven, for example, by secular or merger processes), with a likely geometrical disconnection of the dust and stars, responsible for producing shallow dust attenuation curves. [ABSTRACT FROM AUTHOR]

Accurate synthetic seismic wavefields can now be computed in 3-D earth models using the spectral element method (SEM), which helps improve resolution in full waveform global tomography. However, computational costs are still a challenge. These costs can be reduced by implementing a source stacking method, in which multiple earthquake sources are simultaneously triggered in only one teleseismic SEM simulation. One drawback of this approach is the perceived loss of resolution at depth, in particular because high-amplitude fundamental mode surface waves dominate the summed waveforms, without the possibility of windowing and weighting as in conventional waveform tomography. This can be addressed by redefining the cost-function and computing the cross-correlation wavefield between pairs of stations before each inversion iteration. While the Green's function between the two stations is not reconstructed as well as in the case of ambient noise tomography, where sources are distributed more uniformly around the globe, this is not a drawback, since the same processing is applied to the 3-D synthetics and to the data, and the source parameters are known to a good approximation. By doing so, we can separate time windows with large energy arrivals corresponding to fundamental mode surface waves. This opens the possibility of designing a weighting scheme to bring out the contribution of overtones and body waves. It also makes it possible to balance the contributions of frequently sampled paths versus rarely sampled ones, as in more conventional tomography. Here we present the results of proof of concept testing of such an approach for a synthetic 3-component long period waveform data set (periods longer than 60 s), computed for 273 globally distributed events in a simple toy 3-D radially anisotropic upper mantle model which contains shear wave anomalies at different scales. We compare the results of inversion of 10 000 s long stacked time-series, starting from a 1-D model, using source stacked waveforms and station-pair cross-correlations of these stacked waveforms in the definition of the cost function. We compute the gradient and the Hessian using normal mode perturbation theory, which avoids the problem of cross-talk encountered when forming the gradient using an adjoint approach. We perform inversions with and without realistic noise added and show that the model can be recovered equally well using one or the other cost function. The proposed approach is computationally very efficient. While application to more realistic synthetic data sets is beyond the scope of this paper, as well as to real data, since that requires additional steps to account for such issues as missing data, we illustrate how this methodology can help inform first order questions such as model resolution in the presence of noise, and trade-offs between different physical parameters (anisotropy, attenuation, crustal structure, etc.) that would be computationally very costly to address adequately, when using conventional full waveform tomography based on single-event wavefield computations. [ABSTRACT FROM AUTHOR]

S -wave spectral amplitudes from 312 crustal earthquakes recorded at the Iranian National Broadband Seismic Network in the Alborz region between 2005 and 2017 are analysed in order to evaluate earthquake source parameters, path attenuation and site amplification functions using the non-parametric generalized inversion technique (GIT). We exploit a total number of 1117 seismograms with M L 3–5.6 in the frequency range 0.3–20 Hz. The evaluated non-parametric attenuation functions decay uniformly with distance for the entire frequency range and the estimated S -wave quality factor shows low Q values with relatively strong frequency dependence. We assume the omega-square source model to retrieve earthquake source parameters from the inverted source spectra. The obtained stress drops range from 0.02 to 16 MPa with a mean value of 1.1 MPa. Stress drop and radiated energy show fairly self-similar scaling with seismic moment over the available magnitude range; however, the magnitude range of this study is too narrow to draw a definite conclusion on source scaling characteristics. The obtained moment magnitude M w and the local magnitude M L are linearly correlated and approximately equivalent in the range of M w 3–4. For larger events, M w generally underestimates M L by about 0.1–0.5 magnitude units. The estimated site amplification functions for horizontal component (GIT H) are nearly flat with no obvious pre-dominant frequency peaks for most stations, as expected for the sites of permanent broad-band seismic stations located on rock, though a few stations show amplification peaks from 1 to 8 Hz, with a maximum amplification of about a factor of 7 with respect to the reference site. The evaluated site responses for the vertical components present remarkable amplification or deamplification, leading to differences of the H/V amplitude levels in comparison with the GIT H amplification curves. The results of this study provide a valuable basis for predicting appropriate ground motions in a context of seismic hazard assessment. [ABSTRACT FROM AUTHOR]

In this work, we characterize the contributions from both ongoing star formation and the ambient radiation field in Local Group galaxy M33, as well as estimate the scale of the local dust-energy balance (i.e. the scale at which the dust is re-emitting starlight generated in that same region) in this galaxy through high-resolution radiative transfer (RT) modelling, with defined stellar and dust geometries. We have characterized the spectral energy distribution (SED) of M33 from UV to sub-mm wavelengths, at a spatial scale of 100 pc. We constructed input maps of the various stellar and dust geometries for use in the RT modelling. By modifying our dust mix (fewer very small carbon grains and a lower silicate-to-carbon ratio as compared to the Milky Way), we can much better fit the sub-mm dust continuum. Using this new dust composition, we find that we are able to well reproduce the observed SED of M33 using our adopted model. In terms of stellar attenuation by dust, we find a reasonably strong, broad UV bump, as well as significant systematic differences in the amount of dust attenuation when compared to standard SED modelling. We also find discrepancies in the residuals of the spiral arms versus the diffuse interstellar medium (ISM), indicating a difference in properties between these two regimes. The dust emission is dominated by heating due to the young stellar populations at all wavelengths (∼80 per cent at 10  |$\mu$| m  to ∼50 per cent at 1 mm). We find that the local dust-energy balance is restored at spatial scales greater than around 1.5 kpc. [ABSTRACT FROM AUTHOR]

Understanding how dust attenuation laws vary between and within galaxies is a key question if we want to reliably measure the physical properties of galaxies at both global and local scales. To shed new light on this question, we present a detailed study of the slope and bump strength of the attenuation law in the nearby spiral galaxy NGC 628 at the resolved spatial scale of 325 pc. To do so, we have modelled a broad multiwavelength data set from the ultraviolet (UV) to the infrared (IR) with the state-of-the-art SED fitting code cigale, including SWIFT UVOT data for which we have developed a new optimized reduction pipeline. We find that the median dust attenuation curve of NGC 628 is fairly steep, but not as steep as the SMC curve, and has a sub-MW-type UV bump. We observe intriguing variations within the galaxy, with regions of high A V exhibiting a shallower attenuation curve. We argue that the flattening of the curve is due to a dominance of absorption over scattering events at higher A V. No trend between the bump strength and the IRAC 8.0  |$\mu$| m emission was found. However, this does not necessarily rule out polycyclic aromatic hydrocarbons as the main contributors to the UV bump. [ABSTRACT FROM AUTHOR]

We investigate the spatial variations of coda attenuation (Q c) structure in the tectonically complex Andaman–Nicobar subduction zone (ANSZ). This is probably the first attempt to map the Q c variations across the whole ANSZ. A total of 289 high-quality events recorded at a network of broad-band stations operational since 2009 have been used for the analysis. The variations in attenuation characteristics at different frequencies reveal a marked contrast from the northern to the southern Andaman region, consistent with the geotectonic diversity of the region. At low frequencies, low Q c values are observed in the northern part of ANSZ in the vicinity of the Narcondum volcanic island, which does not appear in the high-frequency image. The low values are in agreement with the 3 - D tomogram, which suggests a distinct low-velocity structure below this volcanic island. The Andaman trench also exhibits a relatively low Q c, which is well correlated with the low- Vp zone. The spatial distributions of Q 0 (Q c at 1 Hz) structure of the region are further projected onto three east–west profiles to capture the detailed attenuation characteristics from north to south. Results show that the northernmost part of ANSZ is more attenuative than the southern part, which may be indicative of the changes in physical properties of the crust. The frequency relation parameter (n) shows an inverse correlation with the observed Q 0 values. Furthermore, we have observed a good correlation between the Q 0 variation and the seismicity pattern of the area that enables us to enhance our understanding about the role of crustal heterogeneity in the earthquake occurrence in this area. [ABSTRACT FROM AUTHOR]

We combine data from the Sloan Digital Sky Survey (SDSS) and the Galaxy Evolution Explorer (GALEX) to simultaneously analyse optical spectra and ultraviolet photometry of 231 643 galaxies with the starlight spectral synthesis code using state-of-the-art stellar population models. We present a new method to estimate GALEX photometry in the SDSS spectroscopic aperture, which proves quite reliable if applied to large samples. In agreement with previous experiments with CALIFA, we find that adding UV constraints leads to a moderate increase on the fraction of ∼107–108 yr populations and a concomitant decrease of younger and older components, yielding slightly older luminosity-weighted mean stellar ages. These changes are most relevant in the low-mass end of the blue cloud. An increase in dust attenuation is observed for galaxies dominated by young stars. We investigate the contribution of different stellar populations to the fraction of light in GALEX and SDSS bands across the UV optical colour–magnitude diagram. As an example application, we use this λ dependence to highlight differences between retired galaxies with and without emission lines. In agreement with an independent study by Herpich et al. we find that the former shows an excess of intermediate-age populations when compared to the later. Finally, we test the suitability of two different prescription for dust, finding that our data set is best-fitting using the attenuation law of starburst galaxies. However, results for the Milky Way extinction curve improve with decreasing τV, especially for edge-on galaxies. [ABSTRACT FROM AUTHOR]

A new method is proposed to estimate separately 3-D heterogeneities of intrinsic and scattering attenuation parameters of seismic shear waves. The method, which assumes isotropic scattering, consists of two steps. First, the source, site and mean path (both intrinsic and scattering attenuations) terms are estimated by an envelope-fitting method for each earthquake event; second, these attenuation parameters are mapped to 3-D space in a tomographic manner by using sensitivity kernels of the attenuation parameters. Monte Carlo simulation is adopted to take account of the effect of the depth-dependent velocity structure in the envelope calculation. The proposed method was then applied in southwestern Japan. The result showed that both intrinsic and scattering attenuations were stronger in the Kyushu region, where tectonic activity was higher than in other studied regions. This association of attenuation parameters with tectonic activity is consistent with previous findings. The proposed method thus provides an alternative to multiple lapse time window analysis, a widely used method for separately estimating intrinsic and scattering attenuation factors. [ABSTRACT FROM AUTHOR]

In this paper, we derive a time-domain complex-valued wave equation for modelling visco-acoustic wave propagation in frequency-independent Q media. Starting from the frequency-domain visco-acoustic wave equation, we use a second-order polynomial to approximate the dispersion term and a pseudo-differential operator to approximate the dissipation term. These two approximations enable us to transform the frequency-domain visco-acoustic wave equation to the time domain. Due to the introduction of an imaginary unit in the dispersion approximation, the new wave equation is complex valued, which is similar to the time-dependent Schrödinger equation. The advantages of the proposed visco-acoustic wave equation include: (1) the dispersion and dissipation effects are naturally separated, which can be used to compensate amplitude loss in reverse-time migration by simply flipping the sign of the dissipation term; (2) the quality factor Q is explicitly incorporated in the wave equation, making it easier to derive the misfit gradient with respect to Q in full-waveform inversion in comparison with the traditional standard linear solid method; and (3) the new visco-acoustic wave equation can be numerically solved using finite-difference time marching and Fourier transform, which requires lower memory costs than frequency-domain visco-acoustic modelling solvers. The accuracy of the proposed equation is first verified by comparing with the analytical Green's function in a homogeneous medium. Then, two numerical examples are used to demonstrate that the new wave equation is capable of describing attenuation effects in heterogeneous frequency-independent Q media. [ABSTRACT FROM AUTHOR]

We present a new 3-D anelastic attenuation model for the upper mantle of the southern Aegean Sea subduction area, by inverting whole-path attenuation operators (t*) data, for both P - and S - waves. For the attenuation tomography, we have employed 383 intermediate-depth earthquakes, recorded by two temporary networks between 2002 and 2007, namely the EGELADOS seismic monitoring project installed in the broader southern Aegean Sea area, and the smaller local CYCNET network which operated in the central part of southern Aegean Sea. Frequency-independent t * values were computed for both P and S waves from acceleration amplitude spectra using two approaches. Initially, we estimated t * values from the slope of the acceleration spectra above the corner frequency, using an automated procedure based on the signal-to-noise ratio. A more standard approach was also followed, where t* values were estimated from the manual (visual) selection of the linearly decaying segment of the acceleration spectrum by an analyst. The t* value data set was inverted to determine the 3-D Q -structure of Southern Aegean Sea, similar to traveltime tomography. The inversion results show high P - and S -wave attenuation in the upper mantle of the back-arc area, with significant low QP and QS anomalies in the mantle wedge of the subducting eastern Mediterranean slab under the Aegean, and higher QP and QS values in the outer Hellenic arc. The strongest anomalies are observed beneath and to the north of the volcanic arc, mainly at depths between 60 and 80 km. At larger depths, the lowest QP and QS anomalies are observed in the area of highest deep (100–170 km) microseismicity, in the easternmost part of the Hellenic volcanic arc. P -wave attenuation models from both the automated and manual t* determination approach are in good agreement. On the contrary, the automated S -wave attenuation models show significant but random spatial variability, while the manual S -wave attenuation models show a similar spatial pattern with the P -wave results, with stronger attenuation in the mantle wedge area. The final anelastic attenuation models are in good agreement with previous results for the study area (e.g. 3-D velocity models, Ground Motion Prediction Equations proposed for intermediate-depth events), as well as with attenuation models proposed for similar subduction zones. [ABSTRACT FROM AUTHOR]

Most sonic logging data acquired in hydrate-bearing zones have shown increasing velocity of P and S waves accompanied by high attenuation of P and S waves. In the eastern Nankai Trough, the attenuation values of P and S wave estimated in the sonic logging frequency range (10–20 kHz for P waves and 0.5–1 kHz for S waves) also show a significant increase in hydrate-bearing sediments. However, P -wave attenuation values from zero-offset vertical seismic profiling (VSP) data (30–110 Hz) indicate a lower attenuation compared to the values in the sonic logging frequency range at the same well locations, which implies frequency-dependent P -wave attenuation in hydrate-bearing sediments. In order to elucidate the attenuation mechanisms responsible for this frequency-dependent P -wave attenuation in hydrate-bearing sediments, we apply two different rock physics models that have recently been developed to consider the squirt flow in porous/microporous hydrate and the interaction between sand and hydrate grains. The predicted attenuation values are compared with those derived from field sonic logging and VSP data. Finally, we infer that this frequency-dependent P -wave attenuation may be due to the squirt flow caused by the combined effect of the degree of hydrate saturation and two permeable systems (one is between sand grains and the other is between hydrate grains), and/or due to the squirt flow caused by fluid inclusions with different aspect ratios in a microporous hydrate. [ABSTRACT FROM AUTHOR]

We estimated the radiated seismic energy (E S) of 65 earthquakes located in the south–central region of the Gulf of California. Most of these events occurred along active transform faults that define the Pacific–North America plate boundary and have magnitudes between M 3.3 and M 5.9. We corrected the spectral records for attenuation using non-parametric S -wave attenuation functions determined with the whole data set. The path effects were isolated from the seismic source using a spectral inversion. We computed radiated seismic energy of the earthquakes by integrating the square velocity source spectrum and estimated their apparent stresses. We found that most events have apparent stress between 3 × 10−4 and 3 MPa. Model independent estimates of the ratio between seismic energy and moment (E S/ M 0) indicate that this ratio is independent of earthquake size. We conclude that in general the apparent stress is low (σa  < 3 MPa) in the south–central and southern Gulf of California. [ABSTRACT FROM AUTHOR]

Comprised of S waves trapped in the Earth's crust, the high-frequency (2–10 Hz) Lg wave is important to discriminating earthquakes from explosions by comparing its amplitude and waveform to those of Pg and Pn waves. Lateral variations in crustal structure, including variations in crustal thickness, intrinsic attenuation and scattering, affect the efficiency of Lg propagation and its consistency as a source discriminant at regional (200–1500 km) distances. To investigate the effects of laterally varying Earth structure on the efficiency of propagation of Lg and Pg, we apply a radiative transport algorithm to model complete, high-frequency (2–4 Hz), regional coda envelopes. The algorithm propagates packets of energy with ray theory through large-scale 3-D structure and includes stochastic effects of multiple scattering by small-scale heterogeneities within the large-scale structure. Source-radiation patterns are described by moment tensors. Seismograms of explosion and earthquake sources are synthesized in canonical models to predict effects on waveforms of paths crossing regions of crustal thinning (pull-apart basins and ocean/continent transitions) and thickening (collisional mountain belts). For paths crossing crustal thinning regions, Lg is amplified at receivers within the thinned region but strongly disrupted and attenuated at receivers beyond the thinned region. For paths crossing regions of crustal thickening, Lg amplitude is attenuated at receivers within the thickened region, but experiences little or no reduction in amplitude at receivers beyond the thickened region. The length of the Lg propagation within a thickened region and the complexity of over- and underthrust crustal layers can produce localized zones of Lg amplification or attenuation. Regions of intense scattering within laterally homogeneous models of the crust increase Lg attenuation but do not disrupt its coda shape. [ABSTRACT FROM AUTHOR]

The Pacific–Australian plate boundary in the South Island of New Zealand is a transpressive boundary through continental lithosphere consisting of multiple terranes that were amalgamated during previous periods of subduction and plate reorganization. The style and locus of deformation within the present-day plate boundary is controlled by the mechanical behaviour and distribution of these different lithospheric blocks. Geological studies are limited when it comes to illuminating lithospheric structure and rheology at depth. Imaging the 3-D seismic velocity and attenuation (1/ Q), with distributed local earthquakes, helps unravel regional structure and variations in strength, fractures and fluids. We determine the 3-D distribution of Qp and Qs, which show much more variation than seismic velocity (Vp), underlining the utility of Q (1/attenuation). The Haast schist belt, previously shown as ca. 25-km thick dry unit with moderate Vp and low Vp / Vs, is imaged with high Qs, and the highest Qs areas correlate with zones of higher grade schist. Below 25-km depth, the distribution of high Qp and Qs is markedly different from that of the overlying geological terranes. Both the strike and depth of the high Q regions indicate that they represent the subducted Hikurangi Plateau and its adjacent Cretaceous oceanic crust. The thickest part of the plateau, previously identified by Vp  > 8.5 km s−1 from seismic tomography and P -wave precursors and associated with an eclogite layer at the base of the plateau, also has the highest Q. This confirms that the strong plateau extends southwestwards as a narrow salient to the northern Fiordland subduction zone, where moderate- Q Eocene oceanic crust on the Australian plate is being subducted and bent to vertical. In the ductile crust, Q results suggest fluid saturation and elevated temperature conditions in the crustal root of the Southern Alps, and confirm that the shape of this crustal root is influenced by both the orientation and depth of the underlying plateau. Q also provides insight into the failed rifting that occurred in oceanic crust at the edges of the Hikurangi Plateau, with a region of relatively low Q at the on-land extension of the Bounty Trough and Canterbury Basin, at the narrowest part of the South Island. In the brittle crust above 10-km depth, low Q is related to regions of active recent seismicity that have high fracture density, with low Qs where fluids are present. In contrast, the locked Alpine Fault does not exhibit low Q in the brittle crust. [ABSTRACT FROM AUTHOR]

We present the analysis of rotational and translational ground motions from earthquakes recorded during October-November 2016, in association with the Central Italy seismic sequence. We use co-located measurements of the vertical ground rotation rate from a large ring laser gyroscope and the three components of ground velocity from a broad-band seismometer. Both instruments are positioned in a deep underground environment, within the Gran Sasso National Laboratories of the Istituto Nazionale di Fisica Nucleare. We collected dozens of events spanning the 3.5-5.9 magnitude range and epicentral distances between 30 and 70 km. This data set constitutes an unprecedented observation of the vertical rotational motions associated with an intense seismic sequence at local distance. Under the plane-wave approximation we process the data set in order to get an experimental estimation of the events backazimuth. Peak values of rotation rate (PRR) and horizontal acceleration (PGA) are markedly correlated, according to a scaling constant which is consistent with previous measurements from different earthquake sequences. We used a prediction model in use for Italy to calculate the expected PGA at the recording site, obtaining consequently predictions for PRR. Within the modelling uncertainties, predicted rotations are consistent with the observed ones, suggesting the possibility of establishing specific attenuation models for ground rotations, like the scaling of peak velocity and peak acceleration in empirical ground-motion prediction relationships. In a second step, after identifying the direction of the incoming wavefield, we extract phase-velocity data using the spectral ratio of the translational and rotational components. This analysis is performed over time windows associated with the P-coda, S-coda and Lg phase. Results are consistent with independent estimates of shear wave velocities in the shallow crust of the Central Apennines. [ABSTRACT FROM AUTHOR]

In this paper we characterize the high-frequency (1.0-10 Hz) seismic wave crustal attenuation and the source excitation in the Sicily Channel and surrounding regions using background seismicity from weak-motion database. The data set includes 15 995 waveforms related to earthquakes having local magnitude ranging from 2.0 to 4.5 recorded between 2006 and 2012. The observed and predicted ground motions form the weak-motion data are evaluated in several narrow frequency bands from 0.25 to 20.0 Hz. The filtered observed peaks are regressed to specify a proper functional form for the regional attenuation, excitation and site specific term separately. The results are then used to calibrate effective theoretical attenuation and source excitation models using the random vibration theory. In the log-log domain, the regional seismic wave attenuation and the geometrical spreading coefficient are modelled together. The geometrical spreading coefficient, g(r), modelled with a bilinear piecewise functional form and given as g(r) ∝ r-1.0 for the short distances (r < 50 km) and as g(r) ∝ r-0.8 for the larger distances (r<50 km). A frequency-dependent quality factor, inverse of the seismic attenuation parameter, Q(f) = 160f/fref 0. 35 (where fref = 1.0 Hz), is combined to the geometrical spreading. The source excitation terms are defined at a selected reference distance with a magnitude independent roll-off spectral parameter, κ 0.04 s and with a Brune stress drop parameter increasing with moment magnitude, from Δσ = 2 MPa for Mw = 2.0 to Δσ = 13 MPa for Mw = 4.5. For events M ≤ 4.5 (being Mwmax = 4.5 available in the data set) the stress parameters are obtained by correlating the empirical/excitation source spectra with the Brune spectral model as function of magnitude. For the larger magnitudes (Mw>4.5) outside the range available in the calibration data set where we do not have recorded data, we extrapolate our results through the calibration of the stress parameters of the Brune source spectrum over the Bindi et al. ground-motion prediction equation selected as a reference model (hereafter also ITA10). Finally, the weak-motion-based model parameters are used through a stochastic approach in order to predict a set of region specific spectral ground-motion parameters (peak ground acceleration, peak ground velocity, and 0.3 and 1.0 Hz spectral acceleration) relative to the generic rock site as a function of distance between 10 and 250 km and magnitude between M 2.0 and M 7.0. [ABSTRACT FROM AUTHOR]

We analyse a sample of eight highly magnified galaxies at redshift 0.6 < z < 1.5 observed with MUSE, exploring the resolved properties of these galaxies at sub-kiloparsec scales. Combining multiband HST photometry and MUSE spectra, we derive the stellar mass, global star formation rates (SFRs), extinction and metallicity from multiple nebular lines, concluding that our sample is representative of z ~ 1 star-forming galaxies. We derive the 2D kinematics of these galaxies from the [OII ] emission and model it with a new method that accounts for lensing effects and fits multiple images simultaneously. We use these models to calculate the 2D beam-smearing correction and derive intrinsic velocity dispersion maps. We find them to be fairly homogeneous, with relatively constant velocity dispersions between 15 and 80 km s-1 and Gini coefficient of ≲0.3. We do not find any evidence for higher (or lower) velocity dispersions at the positions of bright star-forming clumps. We derive resolved maps of dust attenuation and attenuation-corrected SFRs from emission lines for two objects in the sample. We use this information to study the relation between resolved SFR and velocity dispersion. We find that these quantities are not correlated, and the high-velocity dispersions found for relatively low star-forming densities seems to indicate that, at sub-kiloparsec scales, turbulence in high-z discs is mainly dominated by gravitational instability rather than stellar feedback. [ABSTRACT FROM AUTHOR]

We present a global upper-mantle shear wave attenuation model that is built through a hybrid full-waveform inversion algorithm applied to long-period waveforms, using the spectral element method for wavefield computations. Our inversion strategy is based on an iterative approach that involves the inversion for successive updates in the attenuation parameter (δQμ-1) and elastic parameters (isotropic velocity VS, and radial anisotropy parameter ξ) through a Gauss--Newton-type optimization scheme that employs envelope- and waveform-type misfit functionals for the two steps, respectively. We also include source and receiver terms in the inversion steps for attenuation structure. We conducted a total of eight iterations (six for at- tenuation and two for elastic structure), and one inversion for updates to source parameters. The starting model included the elastic part of the relatively high-resolution 3-D whole mantle seismic velocity model, SEMUCB-WM1, which served to account for elastic focusing effects. The data set is a subset of the three-component surface waveform data set, filtered between 400 and 60 s, that contributed to the construction of the whole-mantle tomographic model SEMUCB-WM1. We applied strict selection criteria to this data set for the attenuation iteration steps, and investigated the effect of attenuation crustal structure on the retrieved mantle attenuation structure. While a constant 1-D Qμ model with a constant value of 165 throughout the upper mantle was used as starting model for attenuation inversion, we were able to recover, in depth extent and strength, the high-attenuation zone present in the depth range 80-200 km. The final 3-D model, SEMUCB-UMQ, shows strong correlation with tectonic features down to 200-250 km depth, with low attenuation beneath the cratons, stable parts of continents and regions of old oceanic crust, and high attenuation along mid-ocean ridges and backarcs. Below 250 km, we observe strong attenuation in the southwestern Pacific and eastern Africa, while low attenuation zones fade beneath most of the cratons. The strong negative correlation of Qμ-1 and VS anomalies at shallow upper-mantle depths points to a common dominant origin for the two, likely due to variations in thermal structure. A comparison with two other global upper-mantle attenuation models shows promising consistency. As we updated the elastic 3-D model in alternate iterations, we found that the VS part of the model was stable, while the ξ structure evolution was more pronounced, indicating that it may be important to include 3-D attenuation effects when inverting for ξ, possibly due to the influence of dispersion corrections on this less well-constrained parameter. [ABSTRACT FROM AUTHOR]

We make use of the Survey of High-z Absorption Red and Dead Sources, an ultradeep (<26.5AB) galaxy survey that provides optical photospectra at resolution R~50, viamediumband filters (FWHM ~ 150 Å). This data set is combined with ancillary optical and NIR fluxes to constrain the dust attenuation law in the rest-frame NUV region of star-forming galaxies within the redshift window 1.5 < z < 3. We focus on the NUV bump strength (B) and the total-to-selective extinction ratio (RV), targeting a sample of 1753 galaxies. By comparing the data with a set of population synthesis models coupled to a parametric dust attenuation law, we constrain RV and B, as well as the colour excess, E(B - V). We find a correlation between RV and B, which can be interpreted either as a result of the grain size distribution, or a variation of the dust geometry among galaxies. According to the former, small dust grains are associated with a stronger NUV bump. The latter would lead to a range of clumpiness in the distribution of dust within the interstellar medium of star-forming galaxies. The observed wide range of NUV bump strengths can lead to a systematic in the interpretation of the UV slope β typically used to characterize the dust content. In this study, we quantify these variations, concluding that the effects are Δβ ~ 0.4. [ABSTRACT FROM AUTHOR]

With the prevalence of traumatic brain injury (TBI) in the military and athletics, several commercial and military environmental sensors (ES) have been developed to quantify head impact exposures. The performance of five ES in controlled laboratory exposures from direct and indirect loadings, and the effect on impact protection and dynamic retention of the worn Advanced Combat Helmet (ACH) was evaluated. Direct impacts were conducted on a drop tower and indirect impacts used a mini-sled. The ES data were compared with laboratory sensors through cross-correlation and comparison of peak values. The effects of ES on dynamic retention were assessed using a one-way ANOVA with Tukey's post hoc analysis against baseline ACH performance. Two ES provided data during the blunt impact tests: one, attached to the side of the headform, correlated well (φ > 0.92) with the laboratory data; the other, mounted in the helmet crown, calculated peak headform velocity, which predicted laboratory velocity well. During indirect impact tests, one environmental sensor (attached to the side of the headform) provided usable data, which correlated well (φ > 0.92) with laboratory data. The inclusion of the environmental sensors did not introduce any safety hazards during the blunt impact attenuation tests or the dynamic retention tests. [ABSTRACT FROM AUTHOR]

We present the result of the in-flight calibration of the effective area of the Soft X-ray Spectrometer (SXS) on board the Hitomi X-ray satellite using an observation of the Crab nebula. We corrected for artifacts when observing high count rate sources with the Xray microcalorimeter. We then constructed a spectrum in the 0.5-20 keV band, which we modeled with a single power-law continuum attenuated by interstellar extinction. We evaluated the systematic uncertainty of the spectral parameters by various calibration items. In the 2-12 keV band, the SXS result is consistent with the literature values in flux (2.20±0.08×10-8 erg s-1 cm-2 with a 1 s statistical uncertainty) but is softer in the powerlaw index (2.19±0.11). The discrepancy is attributable to the systematic uncertainty of about +6%/-7% and +2%/-5% respectively for the flux and the power-law index. The softer spectrum is affected primarily by the systematic uncertainty of the Dewar gate valve transmission and the event screening. [ABSTRACT FROM AUTHOR]

We present the results of synthetic tests that aim at evaluating the relative performance of three different definitions of misfit functionals in the context of 3-D imaging of shear wave attenuation in the earth's upper mantle at the global scale, using long-period full-waveform data. The synthetic tests are conducted with simple hypothetical upper-mantle models that contain Qμ anomalies centred at different depths and locations, with or without additional seismic velocity anomalies. To build synthetic waveform data sets, we performed simulations of 50 events in the hypothetical (target) models, using the spectral element method, filtered in the period range 60-400 s. The selected events are chosen among 273 events used in the development of radially anisotropic model SEMUCB-WM1 and recorded at 495 stations worldwide. The synthetic Z-component waveforms correspond to paths and time intervals (fundamental mode and overtone Rayleigh waves) that exist in the real waveform data set. The inversions for shear attenuation structure are carried out using a Gauss-Newton optimization scheme in which the gradient and Hessian are computed using normal mode perturbation theory. The three different misfit functionals considered are based on time domain waveform (WF) and waveform envelope (E-WF) differences, as well as spectral amplitude ratios (SA), between observed and predicted waveforms. We evaluate the performance of the three misfit functional definitions in the presence of seismic noise and unresolved S-wave velocity heterogeneity and discuss the relative importance of physical dispersion effects due to 3-D Qμ structure. We observed that the performance of WF is poorer than the other two misfit functionals in recovering attenuation structure, unless anelastic dispersion effects are taken into account in the calculation of partial derivatives. WF also turns out to be more sensitive to seismic noise than E-WF and SA. Overall, SA performs best for attenuation imaging. Our tests show that it is important to account for 3-D elastic effects (focusing) before inverting for Qμ. Additionally, we show that including high signal-to-noise ratio overtone wave packets is necessary to resolve Qμ structure at depths greater than 250 km. [ABSTRACT FROM AUTHOR]

In this study, we derived the first 3-D P-wave seismic attenuation images (QP) as well as new 3-D VP and VP/VS models for the crust in southeastern Sicily. We used a large data set of local seismic events occurring in the time span 1994-2013. The results of this tomographic study have important implications on the seismic behaviour of the region. Based on velocity and attenuation images, we identified distinct volumes characterized by different fluid content, which correlate well with seismicity distribution. Moreover, the obtained velocity and attenuation tomographies help us to provide a more complete picture of the crustal structure of the area. High VP, high QP and high VP/VS values have been obtained in the crustal basement, below a depth of 8 km, and may be interpreted as due to the presence of serpentinized peridotites. Accordingly, the new model for the degree of serpentinization, retrieved from VP values, shows that the basement has an average serpentinization value of 96 ± 3 vol.% at 8 km, decreasing to 44 ± 5 vol.% at about 18-20 km. Our joint interpretation of geophysical and petrophysical evidence suggests that the nature and composition of the Hyblean upper lithosphere may differ from accepted and longestablished geological models, which consider this lithospheric block a continuation of the Africa continental plate. [ABSTRACT FROM AUTHOR]

We present very-high-energy γ-ray observations of the BL Lac object 1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array System between 2007 and 2015. 1ES 2344+514 is detected with a statistical significance above the background of 20.8σ in 47.2 h (livetime) of observations, making this the most comprehensive very-high-energy study of 1ES 2344+514 to date. Using these observations, the temporal properties of 1ES 2344+514 are studied on short and long times-scales. We fit a constant-flux model to nightly and seasonally binned light curves and apply a fractional variability test to determine the stability of the source on different time-scales.We reject the constant-flux model for the 2007-2008 and 2014-2015 nightly binned light curves and for the long-term seasonally binned light curve at the >3σ level. The spectra of the time-averaged emission before and after correction for attenuation by the extragalactic background light are obtained. The observed time-averaged spectrum above 200 GeV is satisfactorily fitted (χ2/NDF = 7.89/6) by a power-law function with an index Γ = 2.46 ± 0.06stat ± 0.20sys and extends to at least 8 TeV. The extragalactic-background-light-deabsorbed spectrum is adequately fit (χ2/NDF = 6.73/6) by a power-law function with an index Γ = 2.15 ± 0.06stat ± 0.20sys while an F-test indicates that the power law with an exponential cut-off function provides a marginally better fit (χ2/NDF = 2.56/5) at the 2.1σ level. The source location is found to be consistent with the published radio location and its spatial extent is consistent with a point source. [ABSTRACT FROM AUTHOR]

Dust attenuation in galaxies has been extensively studied nearby, however, there are still many unknowns regarding attenuation in distant galaxies. We contribute to this effort using observations of star-forming galaxies in the redshift range z = 0.05-0.15 from the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. Highly star-forming DYNAMO galaxies share many similar attributes to clumpy, star-forming galaxies at high redshift. Considering integrated Sloan Digital Sky Survey observations, trends between attenuation and other galaxy properties for DYNAMO galaxies are well matched to star-forming galaxies at high redshift. Integrated gas attenuations of DYNAMO galaxies are 0.2-2.0 mag in the V band and the ratio of E(B - V)stars and E(B - V)gas is 0.78-0.08 (compared to 0.44 at low redshift). Four highly star-forming DYNAMO galaxies were observed at Hα using the Hubble Space Telescope (HST) and at Paa using integral field spectroscopy at Keck. The latter achieve similar resolution (~0.8-1 kpc) to our HST imaging using adaptive optics, providing resolved observations of gas attenuations of these galaxies on sub-kiloparsec scales. We find <1.0 mag of variation in attenuation (at Ha) from clump to clump, with no evidence of highly attenuated star formation. Attenuations are in the range 0.3-2.2 mag in the V band, consistent with the attenuations of low-redshift star-forming galaxies. The small spatial variation on attenuation suggests that a majority of the star formation activity in these four galaxies occurs in relatively unobscured regions and thus star formation is well characterized by our Hα observations. [ABSTRACT FROM AUTHOR]

The K-SVD algorithm has been successfully utilized for adaptively learning the sparse dictionary in 2-D seismic denoising. Because of the high computational cost of many singular value decompositions (SVDs) in the K-SVD algorithm, it is not applicable in practical situations, especially in 3-D or 5-D problems. In this paper, I extend the dictionary learning based denoising approach from 2-D to 3-D. To address the computational efficiency problem in K-SVD, I propose a fast dictionary learning approach based on the sequential generalized K-means (SGK) algorithm for denoising multidimensional seismic data. The SGK algorithm updates each dictionary atom by taking an arithmetic average of several training signals instead of calculating an SVD as used in K-SVD algorithm. I summarize the sparse dictionary learning algorithm using K-SVD, and introduce SGK algorithm together with its detailed mathematical implications. 3-D synthetic, 2-D and 3-D field data examples are used to demonstrate the performance of both K-SVD and SGK algorithms. It has been shown that SGK algorithm can significantly increase the computational efficiency while only slightly degrading the denoising performance. [ABSTRACT FROM AUTHOR]

Objectives: (1) To investigate whether the occlusion effect and hearing attenuation produced by 3M Combat Arms Ear Plugs (CAEP) affects balance when compared to no hearing protection and (2) to investigate whether the occlusion effect and noise-canceling capabilities of the Nacre QuietPro system affects balance when compared to no hearing protection.Methods: This prospective study collected pilot data for investigation of mechanisms of balance. 20 subjects with normal hearing and no vestibular dysfunction were tested with blackened goggles in three conditions-no hearing protection, CAEP, and with the Nacre QuietPro.Results: A static posturogrpahy forceplate was used to measure center of gravity angular acceleration for a period of 20 seconds. The order of the conditions tested was randomized for each individual. Mean angular acceleration and standard deviation (degrees/second) of the three conditions were: (1) no hearing protection (control), 0.65 + 0.19, (2) CAEP, 0.69 + 0.23, and (3) QuietPro, 0.70 + 0.20 (one-way analysis of variance [ANOVA], df = 2, F = 0.38, p = 0.706).Conclusions: The components of an intact balance system include a variety of neural inputs, to include vesitbuloocular, vestibulospinal, and labyrinthine afferents. Both the CAEP and Nacre QuietPro are hearing preservation devices utilized during Operation Iraqi Freedom and Operation Enduring Freedom in Afghanistan. Our pilot data show no decrement in balance with utilization of these combat hearing preservation devices. [ABSTRACT FROM AUTHOR]

We analyse how intrinsic attenuation and bedrock elasticity affect the amplitude and frequency of the resonance peaks of the S-wave amplification function. The Zener model (with a single relaxation peak) and the constant-Q model are used to describe attenuation. We consider two different cases, namely, the soil is softer than the bedrock (the usual situation, that is, a sediment overlying a stiff formation) and the upper layer is stiffer than the lower half-space (e.g. basalt over sediment). The presence of Zener loss in the upper layer causes a shift of the fundamental peak towards the low frequencies, while no shift is observed due to the non-rigid (viscoelastic) character of the half-space. In the constant-Q case, the shift to the low frequencies is not significant implying that it is difficult to estimate the attenuation parameters on the basis of the location of the resonance peaks. However, attenuation affects the amplitude of the higher modes, while these modes have the same amplitude of the fundamental mode no matter the degree of elasticity of the half-space. Attenuation of the layer and non-rigidity of the half-space affect the peaks, with the latter having a stronger effect. Examples are given, considering two real cases representing a glacier in Northern Italy and an ice stream in the Antarctic continent. [ABSTRACT FROM AUTHOR]

A method using modified attenuation factor function is suggested to determine the parameters of the generalized Zener model approximating the attenuation factor function. This method is applied to constitute the poroviscoelastic model based on the effective Biot theory which considers the attenuative solid frame of reservoir. In the poroviscoelastic model, frequencydependent bulk modulus and shear modulus of solid frame are represented by generalized Zener models. As an application, the borehole logging dispersion equations from Biot theory are extended to include effects from the intrinsic body attenuation in formation media in full-frequency range. The velocity dispersions of borehole guided waves are calculated to investigate the influence from attenuative bore fluid, attenuative solid frame of the formation and impermeable bore wall. [ABSTRACT FROM AUTHOR]

In radio interferometry, observed visibilities are intrinsically sampled at some interval in time and frequency. Modern interferometers are capable of producing data at very high time and frequency resolution; practical limits on storage and computation costs require that some form of data compression be imposed. The traditional form of compression is a simple averaging of the visibilities over coarser time and frequency bins. This has an undesired side effect: the resulting averaged visibilities 'decorrelate', and do so differently depending on the baseline length and averaging interval. This translates into a non-trivial signature in the image domain known as 'smearing', which manifests itself as an attenuation in amplitude towards off-centre sources. With the increasing fields of view and/or longer baselines employed in modern and future instruments, the trade-off between data rate and smearing becomes increasingly unfavourable. In this work, we investigate alternative approaches to low-loss data compression. We show that averaging of the visibility data can be treated as a form of convolution by a boxcar-like window function, and that by employing alternative baseline-dependent window functions a more optimal interferometer smearing response may be induced. In particular, we show improved amplitude response over a chosen field of interest, and better attenuation of sources outside the field of interest. The main cost of this technique is a reduction in nominal sensitivity; we investigate the smearing versus sensitivity trade-off, and show that in certain regimes a favourable compromise can be achieved. We show the application of this technique to simulated data from the Karl G. Jansky Very Large Array (VLA) and the European Very-long-baseline interferometry Network (EVN). [ABSTRACT FROM AUTHOR]

Incorporation of attenuation into the normal mode sum representations of seismic signals is commonly effected by applying perturbation theory. This is fine for weak attenuation, but problematic for stronger attenuation. In this work, modes of the anelastic medium are represented as complex superpositions of elastic eigenfunctions. For the P-SV system, a generalized eigenvalue equation for the complex eigenwavenumbers and complex coefficients used to construct the anelastic eigenfunctions is derived. The generalized eigenvalue problem for the P-SV problem is exactly linear in the eigenwavenumber at the expense of doubling the dimension. The SH problem is exactly linear in the square of the eigenwavenumber. This is in contrast to a similar standing wave problem for the earth free oscillations. Attenuation is commonly incorporated into synthetic seismogram calculations by introduction of complex frequency-dependent elastic moduli. The moduli depend nonlinearly on the frequency. The independent variable in the standing wave free oscillation problem is the frequency, which makes the eigenvalue problem nonlinear. The choice of the wavenumber as the independent variable for the travelling wave problem leads to a linear problem. The Earth model may be transversely isotropic. Compressional waves and both polarizations of shear waves (SV, SH) are treated. [ABSTRACT FROM AUTHOR]

SN 2011ja was a bright (I=-18.3) Type II supernova occurring in the nearby edge on spiral galaxy NGC 4945. Flat-topped and multipeaked Hα and Hβ spectral emission lines appear between 64 and 84 d post-explosion, indicating interaction with a disc-like circumstellar medium inclined ~45° from edge-on. After day 84, an increase in the H- and K-band flux along with heavy attenuation of the red wing of the emission lines are strong indications of early dust formation, likely located in the cool dense shell created between the forward shock of the SN ejecta and the reverse shock created as the ejecta plows into the existing circumstellar material. Radiative transfer modelling reveals both≈1×10-5M☉ of pre-existing dust located ~1016.7 cm away and up to ≈6 × 10-4M☉ of newly formed dust. Spectral observations after 1.5 yr reveal the possibility that the fading SN is located within a young (3-6 Myr) massive stellar cluster, which when combined with tentative 56Ni mass estimates of 0.2 M☉ may indicate a massive (≥25 M☉) progenitor for SN 2011ja. [ABSTRACT FROM AUTHOR]

Deep geological repositories, isolated from the geosphere by an engineered bentonite barrier, are currently considered the safest solution for high-level radioactive waste (HLRW) disposal. As the physical conditions and properties of the bentonite barrier are anticipated to change with time, seismic tomography was suggested as a viable technique to monitor the physical state and integrity of the barrier and to timely detect any unforeseen failure. To do so, the seismic monitoring system needs to be optimized, and this can be achieved by conducting numerical simulations of wave propagation in the repository geometry. Previous studies treated bentonite as an elastic medium, whereas recent experimental investigations indicate its pronounced viscoelastic behaviour. The aims of this contribution are (i) to numerically estimate the effective attenuation of bentonite as a function of temperature T and water content Wc, so that synthetic data can accurately reproduce experimental traces and (ii) assess the feasibility and limitation of the HLRW repository monitoring by simulating the propagation of sonic waves in a realistic repository geometry. A finite difference method was utilized to simulate the wave propagation in experimental and repository setups. First, the input of the viscoelastic model was varied to achieve a match between experimental and numerical traces. The routine was repeated for several values of Wc and T, so that quality factors Qp(Wc, T) and Qs(Wc, T) were obtained. Then, the full-scale monitoring procedure was simulated for six scenarios, representing the evolution of bentonite's physical state. The estimated Qp and Qs exhibited a minimum at Wc = 20 per cent and higher sensitivity to Wc, rather than T, suggesting that pronounced inelasticity of the clay has to be taken into account in geophysical modelling and analysis. The repository-model traces confirm that active seismic monitoring is, in principle, capable of depicting physical changes in the bentonite barrier. However, the locations of sources and receivers relative to the tunnel need to be optimized to achieve best sensitivity to the changes. It was also observed that first arrivals do not necessarily represent the most informative part of the signal; thus the time windows of the analysis need to be selected, accounting for the geometry of the acquisition system. This contribution should be considered as a next step towards the development of a numerical approach to aid in the design and optimization of a non-intrusive monitoring system in HLRW repositories. [ABSTRACT FROM AUTHOR]

On 2013 April 13, an inland earthquake of Mw 5.8 occurred in Awaji Island, which forms the western boundary of the Osaka sedimentary basin in western Japan. The strong ground motion data were collected from more than 100 stations within the basin and it was found that in the Osaka Plain, the pseudo velocity response spectra at a period of around 6.5 s were significantly larger than at other stations of similar epicentral distance outside the basin. The ground motion lasted longer than 3 min in the Osaka Plain where its bedrock depth spatially varies from approximately 1 to 2 km. We modelled long-period (higher than 2 s) ground motions excited by this earthquake, using the finite difference method assuming a point source, to validate the present velocity structure model and to obtain better constraint of the attenuation factor of the sedimentary part of the basin. The effect of attenuation in the simulation was included in the form of Q(f) = Q0(f/f0), where Q0 at a reference frequency f0 was given by a function of the S-wave velocity, Q0 = αVS. We searched for appropriate Q0 values by changing α for a fixed value of f0 = 0.2 Hz. It was found that values of α from 0.2 to 0.5 fitted the observations reasonably well, but that the value of α = 0.3 performed best. Good agreement between the observed and simulated velocity waveforms was obtained for most stations within the Osaka Basin in terms of both amplitude and ground motion duration. However, underestimation of the pseudo velocity response spectra in the period range of 5-7 s was recognized in the central part of the Osaka Plain, which was caused by the inadequate modelling of later phases or wave packets in this period range observed approximately 2 min after the direct S-wave arrival.We analysed this observed later phase and concluded that it was a Love wave originating from the direction of the east coast of Awaji Island. [ABSTRACT FROM AUTHOR]

Attenuating random noise is of great significance in seismic data processing. In recent years, Time-frequency peak filtering (TFPF) has been successfully applied to seismic random noise attenuation field. However, a fixed window length (WL) is used in the conventional TFPF. Since a short WL in the TFPF is used to preserve signals while a long WL can eliminate random noise effectively, signal preserving and noise attenuation cannot be balanced by a fixed WL especially when the signal-to-noise ratio of the noisy seismic record is low. Thus, we need to divide a noisy signal into signal and noise segments before the filtering. Then a short WL is used to the signal segments to preserve signals and a long WL is chosen for noise segments to eliminate random noise. In this paper, we test the smoothness of signals and random noise in time using the Hurst exponent which is a statistic for representing smoothness characteristics of signals. The time-series of signals with higher smoothness which lead to larger Hurst exponent values, however random noise is a random series in time without fixed waveforms and thus its smoothness is low, so the signal and noise segments can be divided by the Hurst exponent values. After the segmentation, we can adopt different filtering WLs in the TFPF for different segments to make a trade-off between signal preserving and random noise attenuation. Synthetic and real data experiments demonstrate that the proposed method can remove random noise from seismic record and preserve reflection events effectively. [ABSTRACT FROM AUTHOR]

The determination of near-surface attenuation for hard rock sites is an important issue in a wide range of seismological applications, particularly seismic hazard analysis. In this article we choose six hard to very-hard rock sites (Vs30 1030-3000ms-1) and apply a range of analysis methods to measure the observed attenuation at distance based on a simple exponential decay model with whole-path attenuation operator κr. The κr values are subsequently decoupled from path attenuation (Q) so as to obtain estimates of near-surface attenuation (κ0). Five methods are employed to measure κr which can be split into two groups: broad-band methods and high-frequency methods. Each of the applied methods has advantages and disadvantages, which are explored and discussed through the comparison of results from common data sets. In our first step we examine the variability of the individual measured κr values. Some variation between methods is expected due to simplifications of source, path, and site effects. However, we find that significant differences arise between attenuation measured on individual recordings, depending on the method employed or the modelling decisions made during a particular approach. Some of the differences can be explained through site amplification effects: although usually weak at rock sites, amplification may still lead to bias of themeasured κr due to the chosen fitting frequency bandwidth, which often varies between methods. At some sites the observed high-frequency spectral shape was clearly different to the typical κr attenuation model, with curved or bi-linear rather than linear decay at high frequencies. In addition to amplification effects this could be related to frequency-dependent attenuation effects [e.g. Q( f )]: since the κr model is implicitly frequency independent, κr will in this case be dependent on the selected analysis bandwidth. In our second step, using thewhole-path κr data sets from the five approaches, we investigate the robustness of the near-surface attenuation parameter 0 and the influence of constraints, such as assuming a value for the regional crustal attenuation (Q).We do this by using a variety of fitting methods: least squares, absolute amplitude and regressions with and without fixing Q to an a priori value. We find that the value to which we fix Q strongly influences the near-surface attenuation term 0. Differences in Q derived from the data at the six sites under investigation could not be reconciled with the average values found previously over the wider Swiss region. This led to starkly different 0 values, depending on whether we allowed for a data-driven Q, or whether we forced Q to be consistent with existing simulation models or ground motion prediction equations valid for the wider region. Considering all the possible approaches we found that the contribution to epistemic uncertainty for 0 determination at the six hard-rock sites in Switzerland could be represented by a normal distribution with standard deviation σk0 = 0.0083 ± 0.0014 s. [ABSTRACT FROM AUTHOR]

Motivation: Large genomic datasets combining genotype and sequence data, such as for expression quantitative trait loci (eQTL) detection, require perfect matching between both data types. Results: We described here MBV (Match BAM to VCF); a method to quickly solve sample mislabeling and detect cross-sample contamination and PCR amplification bias. [ABSTRACT FROM AUTHOR]

We present a new method for the modelling of frequency-dependent and frequency-independent Q in time-domain seismic wave propagation. Unlike previous approaches, attenuation models are constructed such that Q as a function of position in the Earth appears explicitly as a parameter in the equations of motion. This feature facilitates the derivation of Fréchet kernels for Q using adjoint techniques. Being simple products of the forward strain field and the adjoint memory variables, these kernels can be computed with no additional cost, compared to Fréchet kernels for elastic properties. The same holds for Fréchet kernels for the power-law exponent of frequency-dependent Q, that we derive as well. To illustrate our developments, we present examples from regional- and global-scale time-domain wave propagation. [ABSTRACT FROM AUTHOR]

Time-reverse modelling (TRM) of acoustic wave propagation has been widely implemented in seismic migration and time-reversal source imaging. The basic assumption of this modelling is that the wave equation is time-invariant in non-attenuating media. In the Earth, attenuation often invalidates this assumption of time-invariance. To overcome this problem, I propose a TRM approach that compensates for attenuation and dispersion effects during the wave propagation in attenuating media. This approach is based on a viscoacoustic wave equation which explicitly separates attenuation and dispersion following a constant-Q model. Compensating for attenuation and dispersion during TRM is achieved by reversing the sign of the attenuation operator coefficient while leaving the counterpart dispersion parameter unchanged in this viscoacoustic wave equation. A low-pass filter is included to avoid amplifying high-frequency noise during TRM. I demonstrate the effects of the filter on the attenuation and the phase velocity by comparing with theoretical solutions in a 1-D Pierre shale homogeneous medium. Three synthetic examples are used to demonstrate the feasibility of attenuation compensation during TRM. The first example uses a 1-D homogeneous model to demonstrate the accuracy of the numerical implementation of the methodology. The second example shows the applicability of source location using a 2-D layering model. The last example uses a 2-D cross-well synthetic experiment to show that the methodology can also be implemented in conjunction with reverse-time migration to image subsurface reflectors. When attenuation compensation is included, I find improved estimation of the source location, the excitation timing of the point source, the magnitude of the focused source wavelet and the reflectivity image of reflectors, particularly for deep structures underneath strongly attenuating zones. [ABSTRACT FROM AUTHOR]

We have used the iterative spectral fitting method to measure both the elastic and anelastic splitting functions of 20 inner core sensitive normal modes. These modes show significant improvement in spectral fit when anelastic splitting function coefficients dst are introduced in addition to the elastic splitting function coefficients cst. We employ two separate anelastic treatments: (i) fully anelastic measurement, in which a complete set of anelastic splitting function coefficients is measured in addition to the elastic coefficients, and (ii) zonal anelastic measurement, in which anelasticity is only allowed in zonal splitting function coefficients. Together, these two approaches confirm that normal modes sensitive to the Earth’s inner core resolve zonally dominant elastic and anelastic structures. The zonal dominance of anelasticity suggests that the inner core exhibit cylindrical attenuation anisotropy in addition to cylindrical velocity anisotropy. In particular, the zonally dominant anelasticity correlates with zonal elastic structure, that is, directions of higher velocity in the inner core also appear more attenuating. [ABSTRACT FROM AUTHOR]

To understand their influence on elastic wave propagation, anisotropic cracked media have been widely investigated in many theoretical and experimental studies. In this work, we report on laboratory ultrasound measurements carried out to investigate the effect of source frequency on the elastic parameters (wave velocities and the Thomsen parameter γ) and shear wave attenuation) of fractured anisotropic media. Under controlled conditions, we prepared anisotropic model samples containing penny-shaped rubber inclusions in a solid epoxy resin matrix with crack densities ranging from 0 to 6.2 per cent. Two of the three cracked samples have 10 layers and one has 17 layers. The number of uniform rubber inclusions per layer ranges from 0 to 100. S-wave splitting measurements have shown that scattering effects are more prominent in samples where the seismic wavelength to crack aperture ratio ranges from 1.6 to 1.64 than in others where the ratio varied from 2.72 to 2.85. The sample with the largest cracks showed a magnitude of scattering attenuation three times higher compared with another sample that had small inclusions. Our S-wave ultrasound results demonstrate that elastic scattering, scattering and anelastic attenuation, velocity dispersion and crack size interfere directly in shear wave splitting in a source-frequency dependent manner, resulting in an increase of scattering attenuation and a reduction of shear wave anisotropy with increasing frequency. [ABSTRACT FROM AUTHOR]

Using galform, a semi-analytical model of galaxy formation in the Λ cold dark matter cosmology, we study the rest-frame ultraviolet (UV) colours of Lyman-break galaxies (LBGs) in the redshift range 2.5 ≤ z ≤ 10. As the impact of dust on UV luminosity can be dramatic, our model includes a self-consistent computation of dust attenuation based on a radiative transfer model. We find that intrinsically brighter galaxies suffer stronger dust attenuation than fainter ones, though the relation has a large scatter. The model predicts galaxies with UV colours consistent with the colour selection regions designed to select LBGs in observational surveys. We find that the drop-out technique that selects LBGs based on two rest-frame UV colours is robust and effective, selecting more than 70 per cent of UV bright galaxies at a given redshift. We investigate the impact on the predicted UV colours of varying selected model parameters. We find that the UV colours are most sensitive to the modelling of dust attenuation and, in particular, to the extinction curve used in the radiative transfer calculation. If we assume a Milky Way dust extinction curve, the predicted UV continuum slopes are, in general, bluer than observed. However, we find that the opposite is true when using the Small Magellanic Cloud dust extinction curve. This demonstrates the strong dependence of UV colours on dust properties and highlights the inadequacy of using the UV continuum slope as a tracer of dust attenuation without any further knowledge of the galaxy inclination or dust characteristics in high-redshift galaxies. [ABSTRACT FROM AUTHOR]

SUMMARY We investigated the temporal changes in the seismic attenuation of a fault zone using near-source recordings of S waves from repeating microearthquakes that occurred both before and after M ∼ 2 earthquakes in the Bambanani gold mine, South Africa. Because the source locations and the mechanisms of repeating earthquakes can be regarded as identical, the attenuation change can be estimated using the spectral ratios for repeating earthquake pairs. We found an increase in the S-wave attenuation parameter on the vertical component which is positively correlated with frequency, corresponding to times before and after the M ∼ 2 earthquakes. This increase can be explained by scattering attenuation, with a typical scale of damage in the fault zone of ∼3 m. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the properties (e.g. star formation rate, dust attenuation, stellar mass and metallicity) of a sample of infrared (IR) luminous galaxies at z ∼ 1 via near-IR spectroscopy with Subaru-FMOS. Our sample consists of Herschel SPIRE and Spitzer MIPS selected sources in the COSMOS field with photometric redshifts in the range of 0.7 < zphot < 1.8, which have been targeted in two pointings (0.5 deg2) with FMOS. We find a modest success rate for emission-line detections, with candidate Hα emission lines detected for 57 of 168 SPIRE sources (34 per cent). By stacking the near-IR spectra we directly measure the mean Balmer decrement for the Hα and Hβ lines, finding a value of 〈 E( B − V)〉 = 0.51 ± 0.27 for 〈 LIR〉 = 1012 L⊙ sources at 〈 z〉 = 1.36. By comparing star formation rates estimated from the IR and from the dust-uncorrected Hα line we find a strong relationship between dust attenuation and star formation rate. This relation is broadly consistent with that previously seen in star-forming galaxies at z ∼ 0.1. Finally, we investigate the metallicity via the N2 ratio, finding that z ∼ 1 IR-selected sources are indistinguishable from the local mass-metallicity relation. We also find a strong correlation between dust attenuation and metallicity, with the most metal-rich IR sources experiencing the largest levels of dust attenuation. [ABSTRACT FROM AUTHOR]

ABSTRACT The extragalactic background light (EBL), i.e. the diffuse metagalactic photon field in the ultraviolet to infrared, is dominated by the emission from stars in galaxies. It is, therefore, intimately connected with the integrated star formation rate density (SFRD). In this paper, the SFRD is constrained using recent limits on the EBL density derived from observations of distant sources of high and very high energy gamma-rays. The stellar EBL contribution is modelled utilizing simple stellar population spectra including dust attenuation and emission. For modelling the SFRD up to z = 4, a broken power-law function in z + 1 is assumed. A wide range of values for the different model parameters [SFRD( z), metallicity, dust absorption] is investigated, and their impact on the resulting EBL is studied. The calculated EBL densities are compared with the specific EBL density limits, and constraints on the SFRD are derived. For the fiducial model, by adopting a Chabrier initial mass function (IMF) and a second power-law index for the SFRD of β = 0.3, the SFRD is constrained to ≲0.1 and < 0.2 M⊙ yr−1 Mpc−3 for a redshift of z ∼ 1 and z ∼ 2, respectively. The limits for a redshift of z ∼ 1 are in tension with SFRD measurements derived from instantaneous star formation tracers. While the tension for the conservative fiducial model in this study is not yet overly strong, the tension increases when applying plausible changes to the model parameters, e.g., using a Salpeter IMF instead of a Chabrier one or adopting a sub-solar metallicity. [ABSTRACT FROM AUTHOR]

Objectives: This study evaluated the usefulness of measurements of X-ray attenuation (in Hounsfield units) obtained from unenhanced CT images for attenuation correction of the positron emission tomography (PET) data from PET/CT in the assessment of regional lymph node metastasis in oesophageal squamous cell carcinoma. Methods: 17 patients with oesophageal squamous cell carcinoma underwent surgery after evaluation with PET/CT. After the excised lymph nodes were reviewed, we compared the histopathology and PET/CT findings, and analysed the lymph node metastasis. When 18-F fludeoxyglucose (FDG) uptake in the lymph nodes was focally prominent in comparison with background mediastinal activity (regardless of lymph node size), the lymph nodes were considered to be positive for malignancy by PET/CT. The mean Hounsfield units of mediastinal lymph nodes showing abnormally increased FDG uptake in PET/CT was retrospectively evaluated using images from the unenhanced CT component of PET/CT. Receiver operating characteristic (ROC) curve analysis was applied to determine the optimal cut-off value of mean Hounsfield units for detecting individual lymph node metastases. Results: For depiction of malignant nodal groups in each lymph node group, the sensitivity, specificity and accuracy of PET/CT based on increased FDG uptake were 58.8%, 74.5% and 70.8%, respectively. For patients with nodal groups that were positive for uptake by PET/CT, the mean attenuation in lymph nodes as measured by CT was 48±13 HU for malignant nodes and 75±18 HU for benign nodes. This difference was statistically significant (p<0.001). Using ROC curve analysis, we determined the cut-off as 71 HU. When we excluded lymph nodes with attenuation higher than 71HU from the nodes determined as malignant by PET/CT, the specificity and accuracy for detecting metastatic lymph nodes improved to 90.9% and 83.3%, respectively. Conclusions: When interpreting lymph node metastasis in oesophageal squamous cell carcinoma using PET/CT, the assumption that any lymph node with mean HU>71 is benign can improve diagnostic accuracy. [ABSTRACT FROM AUTHOR]

ABSTRACT High-resolution spectra are necessary to distinguish and correctly measure the Balmer emission lines due to the presence of strong metal and Balmer absorption features in the stellar continuum. This accurate measurement is necessary for use in emission-line diagnostics, such as the Balmer decrement (i.e. Hα/Hβ), used to determine the attenuation of galaxies. Yet at high redshifts, obtaining such spectra becomes costly. Balmer emission-line equivalent widths are much easier to measure, requiring only low-resolution spectra or even simple narrow-band filters and therefore shorter observation times. However, a correction for the stellar continuum is still needed for this equivalent width Balmer decrement. We present here a statistical analysis of the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) emission-line galaxy sample, using the spectrally determined Balmer emission-line fluxes and equivalent widths. Using the large numbers of galaxies available in the SDSS catalogue, we determined an equivalent width Balmer decrement including a statistically based correction for the stellar continuum. Based on this formula, the attenuation of galaxies can now be obtained from low spectral resolution observations. In addition, this investigation also revealed an error in the Hβ line fluxes, within the SDSS DR7 MPA/JHU catalogue, with the equivalent widths underestimated by average ∼0.35 Å in the emission-line galaxy sample. This error means that Balmer decrement determined attenuations are overestimated by a systematic 0.1 mag in A V, and future analyses of this sample need to include this correction. [ABSTRACT FROM AUTHOR]

SUMMARY We propose a wavelet-based method to characterize acoustic impedance discontinuities from a multiscale analysis of seismic reflected waves. Our approach relies on the analysis of ridge functions which contain most of the information of the wavelet transform in a sparse support. This method falls in the framework of the wavelet response (WR) introduced by Le Gonidec et al. which analyses the impedance multiscale behaviour by propagating dilated wavelets into the medium. We further extend the WR by considering its application to broad-band seismic data. We take into account the bandpass filter effect related to the limited frequency range of the seismic source. We apply the method to a deep-water seismic experiment performed in 2008 during the ERIG3D cruise to demonstrate the potential of ridge functions as multiscale seismic attributes. In conjunction to the analysis of seismic data acquired by the deep-towed SYSIF system (200-2200 Hz), we use ground truth data to characterize the fine scale structure of superficial sediments by using the continuous wavelet transform (CWT). The availability of in situ measurements allows to validate the relationship between CWT and WR and to estimate the attenuation of seismic waves into the sediments. Once validated, the method is applied on a whole seismic profile and WR ridge functions are computed for two particular reflectors. The reflector thicknesses fall below the resolution limit of the seismic experiment making the WR seismic attributes a super-resolution method. [ABSTRACT FROM AUTHOR]

SUMMARY We analyse dispersion and attenuation of surface waves at free surfaces of possible vacuum/poroelastic media: permeable-'open pore', impermeable-'closed pore' and partially permeable boundaries, which have not been previously reported in detail by researchers, under different surface-permeable, viscous-damping, elastic and fluid-flowing conditions. Our discussion is focused on their characteristics in the exploration-seismic frequency band (a few through 200 Hz) for near-surface applications. We find two surface-wave modes exist, R1 waves for all conditions, and R2 waves for closed-pore and partially permeable conditions. For R1 waves, velocities disperse most under partially permeable conditions and least under the open-pore condition. High-coupling damping coefficients move the main dispersion frequency range to high frequencies. There is an f1 frequency dependence as a constant- Q model for attenuation at high frequencies. R1 waves for the open pore are most sensitive to elastic modulus variation, but least sensitive to tortuosities variation. R1 waves for partially permeable surface radiate as non-physical waves (Im( k) < 0) at low frequencies. For R2 waves, velocities are slightly lower than the bulk slow P2 waves. At low frequencies, both velocity and attenuation are diffusive of f1/2 frequency dependence, as P2 waves. It is found that for partially permeable surfaces, the attenuation displays − f1 frequency dependence as frequency increasing. High surface permeability, low-coupling damping coefficients, low Poisson's ratios, and low tortuosities increase the slope of the − f1 dependence. When the attenuation coefficients reach 0, R2 waves for partially permeable surface begin to radiate as non-physical waves. [ABSTRACT FROM AUTHOR]

SUMMARY High-resolution 3-D QP and QS models at depths of 0∼14 km in the Longtan reservoir area, which were used to further infer the water infiltration around the reservoir, were constructed by the local earthquake tomography technique. The inversion used t* values measured from velocity spectral amplitudes of 16 134 P-wave and 17 027 S-wave observations of 2828 events recorded by 23 digital seismic stations in the Longtan reservoir area. 3-D QP and QS tomographic images suggest a close relation between the attenuation models and water infiltration. Low QP and QS exist down to 4∼7 km depths beneath the main rivers in the reservoir area, whereas high QP and QS are found both at deep layers and at shallow layers in regions other than the main river area. We inferred that the rocks beneath the main rivers are infiltrated by substantial water and water infiltration reaches 4∼7 km deep, and the ranges of water infiltration vary by region. Specifically, the zone of high water content is estimated to extend up to 10 km away from the Buliu river in the reservoir dam area where water depth in the reservoir reaches maximum, and the extent of water infiltration in rocks can only be about 5 km around from the Hongshui river and the Youla river. Low QP and high QS indicate that the carbonate rocks in the east of the Bala fault area may be saturated with water. Earthquake clusters are mainly concentrated on the low- QP and low- QS zones, indicating that water infiltration beneath the main rivers possibly plays an important role in inducing earthquakes in the Longtan reservoir area. [ABSTRACT FROM AUTHOR]