8 research outputs found
Optimal resolution tomography with error tracking and the structure of the crust and upper mantle beneath Ireland and Britain
The classical Backus–Gilbert method seeks localized Earth-structure averages at the shortest
length scales possible, given a data set, data errors, and a threshold for acceptable model
errors. The resolving length at a point is the width of the local averaging kernel, and the
optimal averaging kernel is the narrowest one such that the model error is below a specified
level. This approach is well suited for seismic tomography, which maps 3-D Earth structure
using large sets of seismic measurements. The continual measurement-error decreases and
data-redundancy increases have reduced the impact of random errors on tomographic models.
Systematic errors, however, are resistant to data redundancy and their effect on the model is
difficult to predict. Here, we develop a method for finding the optimal resolving length at every
point, implementing it for surface-wave tomography. As in the Backus–Gilbert method, every
solution at a point results from an entire-system inversion, and the model error is reduced by
increasing the model-parameter averaging. The key advantage of our method stems from its
direct, empirical evaluation of the posterior model error at a point. We first measure inter-
station phase velocities at simultaneously recording station pairs and compute phase-velocity
maps at densely, logarithmically spaced periods. Numerous versions of the maps with varying
smoothness are then computed, ranging from very rough to very smooth. Phase-velocity curves
extracted from the maps at every point can be inverted for shear-velocity (V S ) profiles. As
we show, errors in these phase-velocity curves increase nearly monotonically with the map
roughness. We evaluate the error by isolating the roughness of the phase-velocity curve that
cannot be explained by any Earth structure and determine the optimal resolving length at a point
such that the error of the local phase-velocity curve is below a threshold. A 3-D V S model is then
computed by the inversion of the composite phase-velocity maps with an optimal resolution
at every point. The estimated optimal resolution shows smooth lateral variations, confirming
the robustness of the procedure. Importantly, the optimal resolving length does not scale with
the density of the data coverage: some of the best-sampled locations display relatively low
lateral resolution, probably due to systematic errors in the data. We apply the method to image
the lithosphere and underlying mantle beneath Ireland and Britain. Our very large data set
was created using new data from Ireland Array, the Irish National Seismic Network, the UK
Seismograph Network and other deployments. A total of 11 238 inter-station dispersion curves,
spanning a very broad total period range (4–500 s), yield unprecedented data coverage of the
area and provide fine regional resolution from the crust to the deep asthenosphere. The lateral
resolution of the 3-D model is computed explicitly and varies from 39 km in central Ireland to
over 800 km at the edges of the area, where the data coverage declines. Our tomography reveals
pronounced, previously unknown variations in the lithospheric thickness beneath Ireland and Britain, with implications for their Caledonian assembly and for the mechanisms of the British
Tertiary Igneous Province magmatism
Pair distribution function analysis of pressure treated zeolite Na-A
Pair distribution function studies using X-ray scattering data from zeolite Na-A samples treated at pressure up to 8 GPa indicate a pressure-induced amorphisation mechanism involving loss of crystallographic order of the aluminosilicate framework but retention of the local sodium to oxygen bonding
Subgroup-specific structural variation across 1,000 medulloblastoma genomes.
Medulloblastoma, the most common malignant paediatric brain tumour, is currently treated with nonspecific cytotoxic therapies including surgery, whole-brain radiation, and aggressive chemotherapy. As medulloblastoma exhibits marked intertumoural heterogeneity, with at least four distinct molecular variants, previous attempts to identify targets for therapy have been underpowered because of small samples sizes. Here we report somatic copy number aberrations (SCNAs) in 1,087 unique medulloblastomas. SCNAs are common in medulloblastoma, and are predominantly subgroup-enriched. The most common region of focal copy number gain is a tandem duplication of SNCAIP, a gene associated with Parkinson's disease, which is exquisitely restricted to Group 4α. Recurrent translocations of PVT1, including PVT1-MYC and PVT1-NDRG1, that arise through chromothripsis are restricted to Group 3. Numerous targetable SCNAs, including recurrent events targeting TGF-β signalling in Group 3, and NF-κB signalling in Group 4, suggest future avenues for rational, targeted therapy
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Subgroup-specific structural variation across 1,000 medulloblastoma genomes.
Medulloblastoma, the most common malignant paediatric brain tumour, is currently treated with nonspecific cytotoxic therapies including surgery, whole-brain radiation, and aggressive chemotherapy. As medulloblastoma exhibits marked intertumoural heterogeneity, with at least four distinct molecular variants, previous attempts to identify targets for therapy have been underpowered because of small samples sizes. Here we report somatic copy number aberrations (SCNAs) in 1,087 unique medulloblastomas. SCNAs are common in medulloblastoma, and are predominantly subgroup-enriched. The most common region of focal copy number gain is a tandem duplication of SNCAIP, a gene associated with Parkinson's disease, which is exquisitely restricted to Group 4α. Recurrent translocations of PVT1, including PVT1-MYC and PVT1-NDRG1, that arise through chromothripsis are restricted to Group 3. Numerous targetable SCNAs, including recurrent events targeting TGF-β signalling in Group 3, and NF-κB signalling in Group 4, suggest future avenues for rational, targeted therapy
Genomic and epigenomic landscapes of adult de novo acute myeloid leukemia
BACKGROUND: Many mutations that contribute to the pathogenesis of acute myeloid leukemia (AML) are undefined. The relationships between patterns of mutations and epigenetic phenotypes are not yet clear. METHODS: We analyzed the genomes of 200 clinically annotated adult cases of de novo AML, using either whole-genome sequencing (50 cases) or whole-exome sequencing (150 cases), along with RNA and microRNA sequencing and DNA-methylation analysis. RESULTS: AML genomes have fewer mutations than most other adult cancers, with an average of only 13 mutations found in genes. Of these, an average of 5 are in genes that are recurrently mutated in AML. A total of 23 genes were significantly mutated, and another 237 were mutated in two or more samples. Nearly all samples had at least 1 nonsynonymous mutation in one of nine categories of genes that are almost certainly relevant for pathogenesis, including transcription-factor fusions (18% of cases), the gene encoding nucleophosmin (NPM1) (27%), tumor-suppressor genes (16%), DNA-methylation-related genes (44%), signaling genes (59%), chromatin-modifying genes (30%), myeloid transcription-factor genes (22%), cohesin-complex genes (13%), and spliceosome-complex genes (14%). Patterns of cooperation and mutual exclusivity suggested strong biologic relationships among several of the genes and categories. CONCLUSIONS: We identified at least one potential driver mutation in nearly all AML samples and found that a complex interplay of genetic events contributes to AML pathogenesis in individual patients. The databases from this study are widely available to serve as a foundation for further investigations of AML pathogenesis, classification, and risk stratification. (Funded by the National Institutes of Health.) Copyright © 2013 Massachusetts Medical Society