282 research outputs found
A proposal for Marchenko-based target-oriented full waveform inversion
The Hessian matrix plays an important role in correct interpretation of the
multiple scattered wave fields inside the FWI frame work. Due to the high
computational costs, the computation of the Hessian matrix is not feasible.
Consequently, FWI produces overburden related artifacts inside the target zone
model, due to the lack of the exact Hessian matrix. We have shown here that
Marchenko-based target-oriented Full Waveform Inversion can compensate the need
of Hessian matrix inversion by reducing the non-linearity due to overburden
effects. This is achieved by exploiting Marchenko-based target replacement to
remove the overburden response and its interactions with the target zone from
residuals and inserting the response of the updated target zone into the
response of the entire medium. We have also shown that this method is more
robust with respect to prior information than the standard gradient FWI.
Similarly to standard Marchenko imaging, the proposed method only requires
knowledge of the direct arrival time from a focusing point to the surface and
the reflection response of the medium.Comment: 5 pages, 4 figures, 82th EAGE Conference & Exhibitio
Patient-Reported and Patient-Recorded Outcomes in Interstitial Lung Diseases and Pulmonary Hypertension
The research described in this thesis is focused on translating and validating patient-reported outcome measures for Dutch patients with interstitial lung diseases and pulmonary hypertension (part 1), develop patient-recorded outcome measures (part 2), and interventions aimed at improving quality of life for patients (part 3)
A home monitoring program including real-time wireless home spirometry in idiopathic pulmonary fibrosis
In idiopathic pulmonary fibrosis (IPF), home monitoring experiences are limited, not yet real-time available nor implemented in daily care. We evaluated feasibility and potential barriers of a new home monitoring program with real-time wireless home spirometry in IPF. Ten patients with IPF were asked to test this home monitoring program, including daily home spirometry, for four weeks. Measurements of home and hospital spirometry showed good agreement. All patients considered real-time wireless spirometry useful and highly feasible. Both patients and researchers suggested relatively easy solutions for the identified potential barriers regarding real-time home monitoring in IPF
Filtering Deterministic Layer Effects in Imaging
Sensor array imaging arises in applications such as nondestructive evaluation of materials
with ultrasonic waves, seismic exploration, and radar. The sensors probe a medium with
signals and record the resulting echoes, which are then processed to determine the location
and reflectivity of remote reflectors. These could be defects in materials such as voids,
fault lines or salt bodies in the earth, and cars, buildings, or aircraft in radar applications.
Imaging is relatively well understood when the medium through which the signals
propagate is smooth, and therefore nonscattering. But in many problems the medium is
heterogeneous, with numerous small inhomogeneities that scatter the waves. We refer to
the collection of inhomogeneities as clutter, which introduces an uncertainty in imaging
because it is unknown and impossible to estimate in detail. We model the clutter as a
random process. The array data is measured in one realization of the random medium,
and the challenge is to mitigate cumulative clutter scattering so as to obtain robust images
that are statistically stable with respect to different realizations of the inhomogeneities.
Scatterers that are not buried too deep in clutter can be imaged reliably with the coherent
interferometric (CINT) approach. But in heavy clutter the signal-to-noise ratio (SNR)
is low and CINT alone does not work. The “signal,” the echoes from the scatterers to be
imaged, is overwhelmed by the “noise,” the strong clutter reverberations. There are two
existing approaches for imaging at low SNR: The first operates under the premise that data
are incoherent so that only the intensity of the scattered field can be used. The unknown
coherent scatterers that we want to image are modeled as changes in the coefficients of
diffusion or radiative transport equations satisfied by the intensities, and the problem becomes
one of parameter estimation. Because the estimation is severely ill-posed, the results
have poor resolution, unless very good prior information is available and large arrays are
used. The second approach recognizes that if there is some residual coherence in the data,
that is, some reliable phase information is available, it is worth trying to extract it and
use it with well-posed coherent imaging methods to obtain images with better resolution.
This paper takes the latter approach and presents a first attempt at enhancing the SNR
of the array data by suppressing medium reverberations. It introduces filters, or annihilators of layer backscatter, that are designed to remove primary echoes from strong, isolated
layers in a medium with additional random layering at small, subwavelength scales. These
strong layers are called deterministic because they can be imaged from the data. However,
our goal is not to image the layers, but to suppress them and thus enhance the echoes
from compact scatterers buried deep in the medium. Surprisingly, the layer annihilators
work better than intended, in the sense that they suppress not only the echoes from the
deterministic layers, but also multiply scattered ones in the randomly layered structure.
Following the layer annihilators presented here, other filters of general, nonlayered
heavy clutter have been developed. We review these more recent developments and the
challenges of imaging in heavy clutter in the introduction in order to place the research
presented here in context. We then present in detail the layer annihilators and show with
analysis and numerical simulations how they work
Endomicroscopic and transcriptomic analysis of impaired barrier function and malabsorption in environmental enteropathy
Introduction: Environmental enteropathy (EE) is associated with growth failure, micronutrient malabsorption and impaired responses to oral vaccines. We set out to define cellular mechanisms of impaired barrier function in EE and explore protective mechanisms. Methods: We studied 49 adults with environmental enteropathy in Lusaka, Zambia using confocal laser endomicroscopy (CLE); histology, immunohistochemistry and mRNA sequencing of small intestinal biopsies; and correlated these with plasma lipopolysaccharide (LPS) and a zinc uptake test. Results: CLE images (median 134 for each study) showed virtually ubiquitous small intestinal damage. Epithelial defects, imaged by histology and claudin 4 immunostaining, were predominantly seen at the tips of villi and corresponded with leakage imaged in vivo by CLE. In multivariate analysis, circulating log-transformed LPS was correlated with cell shedding events (β = 0.83; P = 0.035) and with serum glucagon-like peptide-2 (β = -0.13; P = 0.007). Zinc uptake from a test dose of 25mg was attenuated in 30/47 (64%) individuals and in multivariate analysis was reduced by HIV, but positively correlated with GLP-2 (β = 2.72; P = 0.03). There was a U-shaped relationship between circulating LPS and villus surface area. Transcriptomic analysis identified 23 differentially expressed genes in severe enteropathy, including protective peptides and proteins. Conclusions: Confocal endomicroscopy, claudin 4 immunostaining and histology identify epithelial defects which are probably sites of bacterial translocation, in the presence of which increased epithelial surface area increases the burden of translocation. GLP 2 and other protective peptides may play an important role in mucosal protection in EE
Single station Monitoring of Volcanoes Using Seismic ambient noise
Seismic ambient noise cross correlation is increasingly used to monitor volcanic activity. However, this method is usually limited to volcanoes equipped with large and dense networks of broadband stations. The single station approach may provide a powerful and reliable alternative to the classical “cross-stations” approach when measuring variation of seismic velocities. We implemented it on the Piton de la Fournaise in Reunion Island, a very active volcano with a remarkable multi-disciplinary continuous monitoring. Over the past decade, this volcano was increasingly studied using the traditional cross-correlation technique and therefore represents a unique laboratory to validate our approach. Our results, tested on stations located up to 3.5 km from the eruptive site, performed as well as the classical approach to detect the volcanic eruption in the 1-2 Hz frequency band. This opens new perspectives to successfully forecast volcanic activity at volcanoes equipped with a single 3-component seismometer
The Spatial Cross-Correlation Method for Dispersive Surface Waves
Dispersive surface waves are routinely used to estimate the subsurface shear-wave velocity distribution, at all length scales. In the well-known Spatial Autocorrelation method, dispersion information is gained from the correlation of seismic noise signals recorded on the vertical (or radial) components. We demonstrate practical advantages of including the cross-correlation between radial and vertical components of the wavefield in a spatial cross-correlation method. The addition of cross-correlation information increases the resolution and robustness of the phase velocity dispersion information, as demonstrated in numerical simulations and a near-surface field study with active seismic sources, where our method confirms the presence of a fault-zone conduit in a geothermal field
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