448 research outputs found
Parallel algorithms for normalization
Given a reduced affine algebra A over a perfect field K, we present parallel
algorithms to compute the normalization \bar{A} of A. Our starting point is the
algorithm of Greuel, Laplagne, and Seelisch, which is an improvement of de
Jong's algorithm. First, we propose to stratify the singular locus Sing(A) in a
way which is compatible with normalization, apply a local version of the
normalization algorithm at each stratum, and find \bar{A} by putting the local
results together. Second, in the case where K = Q is the field of rationals, we
propose modular versions of the global and local-to-global algorithms. We have
implemented our algorithms in the computer algebra system SINGULAR and compare
their performance with that of the algorithm of Greuel, Laplagne, and Seelisch.
In the case where K = Q, we also discuss the use of modular computations of
Groebner bases, radicals, and primary decompositions. We point out that in most
examples, the new algorithms outperform the algorithm of Greuel, Laplagne, and
Seelisch by far, even if we do not run them in parallel.Comment: 19 page
Synthetic inversions for density using seismic and gravity data
Density variations drive mass transport in the Earth from plate tectonics to convection in the mantle and core. Nevertheless, density remains poorly known because most geophysical measurements used to probe the Earth's interior either have little sensitivity to density, suffer from trade-offs or from non-uniqueness. With the ongoing expansion of computational power, it has become possible to accurately model complete seismic wavefields in a 3-D heterogeneous Earth, and to develop waveform inversion techniques that account for complicated wavefield effects. This may help to improve resolution of density. Here, we present a pilot study where we explore the extent to which waveform inversion may be used to better recover density as a separate, independent parameter. We perform numerical simulations in 2-D to investigate under which conditions, and to what extent density anomalies may be recovered in the Earth's mantle. We conclude that density can indeed be constrained by seismic waveforms, mainly as a result of scattering effects at density contrasts. As a consequence, the low-frequency part of the wavefield is the most important for constraining the actual extent of anomalies. While the impact of density heterogeneities on the wavefield is small compared to the effects of velocity variations, it is likely to be detectable in modern regional- to global-scale measurements. We also conclude that the use of gravity data as additional information does not help to further improve the recovery of density anomalies unless strong a priori constraints on the geometry of density variations are applied. This is a result of the inherent physical non-uniqueness of potential-field inverse problems. Finally, in the limited numerical setup that we employ, we find that the initially supplied anomalies in S- and P-velocity models are of minor importance
Grounded Theory - wie aus Texten Modelle und Theorien gemacht werden
Grounded Theory lƤĆt sich als gegenstandsverankerte Theorienbildung Ć¼bersetzen.
Damit wird bereits angedeutet, daĆ das Ziel der Arbeiten in der Grounded Theory
meist bereichsspezifisch ist, daĆ es nicht darum geht, universell gĆ¼ltige Theorien
und Modelle zu bilden. Die amerikanischen Soziologen Anselm Strauss und
Bamey Glaser schufen mit der Grounded Theory (GT) eine umfassende Konzeption
des sozialwissenschaftlichen Erkenntnis- und Forschungsprozesses. Sie reicht von
ersten Ideen zu einer Forschungsfragestellung Ć¼ber die Konzeption einer Untersuchung,
Auswahl von Datenmaterial, Analyse und Interpretation von Daten bis
zum Erstellen eines Manuskripts. Die GT erlaubt auf der Basis von Forschung in
einem bestimmten Gegenstandsbereich eine Theorie zu formulieren, die aus miteinander
verknĆ¼pften Konzepten besteht (Netzwerk) und geeignet ist, eine Beschreibung
und ErklƤrung der untersuchten sozialen PhƤnomene zu geben
Extractor for ESI quadrupole TOF tandem MS data enabled for high throughput batch processing
BACKGROUND: Mass spectrometry based proteomics result in huge amounts of data that has to be processed in real time in order to efficiently feed identification algorithms and to easily integrate in automated environments. We present wiff2dta, a tool created to convert MS/MS data obtained using Applied Biosystem's QStar and QTrap 2000 and 4000 series. RESULTS: Comparing the performance of wiff2dta with the standard tools, we find wiff2dta being the fastest solution for extracting spectrum data from ABIs raw file format. wiff2dta is at least 10% faster than the standard tools. It is also capable of batch processing and can be easily integrated in high throughput environments. The program is freely available via , and is also available from Applied Biosystems. CONCLUSIONS: wiff2dta offers the possibility to run as stand-alone application or within a batch process as command-line tool integrated in automation and high-throughput environments. It is more efficient than the state-of-the-art tools provided
The Effect of Education on the Assessment of Optic Nerve Head Photographs for the Glaucoma Diagnosis
Background: To evaluate the effect of one lesson of continuing medical education (CME) of subjective assessment of optic nerve head appearance on sensitivity and specificity for the diagnosis of glaucoma. Methods: Ophthalmologists and residents in ophthalmology attending an international glaucoma meeting arranged at Malmo University Hospital, Malmo, Sweden, were asked to grade optic nerve head (ONH) photographs of healthy and glaucomatous subjects at two sessions separated by a lecture on glaucoma diagnosis by ONH assessment. Each grader had access to an individual portfolio of 50 ONH photographs randomly selected from a web-based data bank including ONH photographs of 73 glaucoma patients and 123 healthy subjects. The individual portfolio of photographs was graded before and after the lecture, but in different randomized order. Results: Ninety-six doctors, 91% of all attending the meeting, completed both assessment sessions. The number of correct classifications increased from 69 to 72% on the average. Diagnostic sensitivity increased significantly (p < 0.0001) from 70% to 80%, and the number of photographs classified as uncertain decreased significantly (p < 0.0001) from 22% to 13%. Specificity remained at 68%, and intra-grader agreement decreased. Conclusion: CME had only a small effect on the assessment of ONH for the glaucoma diagnosis. Sensitivity increased and the amount of uncertain classifications decreased, while specificity was unchanged
Efficient generation of neural stem cell-like cells from adult human bone marrow stromal cells
Clonogenic neural stem cells (NSCs) are self-renewing cells that maintain the capacity to differentiate into brain-specific cell types, and may also replace or repair diseased brain tissue. NSCs can be directly isolated from fetal or adult nervous tissue, or derived from embryonic stem cells. Here, we describe the efficient conversion of human adult bone marrow stromal cells (hMSC) into a neural stem cell-like population (hmNSC, for human marrow-derived NSC-like cells). These cells grow in neurosphere-like structures, express high levels of early neuroectodermal markers, such as the proneural genes NeuroD1, Neurog2, MSl1 as well as otx1 and nestin, but lose the characteristics of mesodermal stromal cells. In the presence of selected growth factors, hmNSCs can be differentiated into the three main neural phenotypes: astroglia, oligodendroglia and neurons. Clonal analysis demonstrates that individual hmNSCs are multipotent and retain the capacity to generate both glia and neurons. Our cell culture system provides a powerful tool for investigating the molecular mechanisms of neural differentiation in adult human NSCs. hmNSCs may therefore ultimately help to treat acute and chronic neurodegenerative diseases
Particle Physics Implications for CoGeNT, DAMA, and Fermi
Recent results from the CoGeNT collaboration (as well as the annual
modulation reported by DAMA/LIBRA) point toward dark matter with a light (5-10
GeV) mass and a relatively large elastic scattering cross section with nucleons
(\sigma ~ 10^{-40} cm^2). In order to possess this cross section, the dark
matter must communicate with the Standard Model through mediating particles
with small masses and/or large couplings. In this Letter, we explore with a
model independent approach the particle physics scenarios that could
potentially accommodate these signals. We also discuss how such models could
produce the gamma rays from the Galactic Center observed in the data of the
Fermi Gamma Ray Space Telescope. We find multiple particle physics scenarios in
which each of these signals can be accounted for, and in which the dark matter
can be produced thermally in the early Universe with an abundance equal to the
measured cosmological density.Comment: 4 pages, 2 figure
Noise Regularization for Conditional Density Estimation
Modelling statistical relationships beyond the conditional mean is crucial in
many settings. Conditional density estimation (CDE) aims to learn the full
conditional probability density from data. Though highly expressive, neural
network based CDE models can suffer from severe over-fitting when trained with
the maximum likelihood objective. Due to the inherent structure of such models,
classical regularization approaches in the parameter space are rendered
ineffective. To address this issue, we develop a model-agnostic noise
regularization method for CDE that adds random perturbations to the data during
training. We demonstrate that the proposed approach corresponds to a smoothness
regularization and prove its asymptotic consistency. In our experiments, noise
regularization significantly and consistently outperforms other regularization
methods across seven data sets and three CDE models. The effectiveness of noise
regularization makes neural network based CDE the preferable method over
previous non- and semi-parametric approaches, even when training data is
scarce
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