187 research outputs found
Quivers, Geometric Invariant Theory, and Moduli of Linear Dynamical Systems
We use geometric invariant theory and the language of quivers to study
compactifications of moduli spaces of linear dynamical systems. A general
approach to this problem is presented and applied to two well known cases: We
show how both Lomadze's and Helmke's compactification arises naturally as a
geometric invariant theory quotient. Both moduli spaces are proven to be smooth
projective manifolds. Furthermore, a description of Lomadze's compactification
as a Quot scheme is given, whereas Helmke's compactification is shown to be an
algebraic Grassmann bundle over a Quot scheme. This gives an algebro-geometric
description of both compactifications. As an application, we determine the
cohomology ring of Helmke's compactification and prove that the two
compactifications are not isomorphic when the number of outputs is positive.Comment: 24 pages, based on my Diplomarbeit completed in February 2005, to
appear in Linear Algebra and its Applications (LAA
Coverings of Laura Algebras: the Standard Case
In this paper, we study the covering theory of laura algebras. We prove that
if a connected laura algebra is standard (that is, it is not quasi-tilted of
canonical type and its connecting components are standard), then this algebra
has nice Galois coverings associated to the coverings of the connecting
component. As a consequence, we show that the first Hochschild cohomology group
of a standard laura algebra vanishes if and only if it has no proper Galois
coverings.Comment: The main result on the non-standard case was reformulated due to an
inaccuracy in the previous version. Lemma 6.1 was removed due to a
simplification. The last section on the special biserial case was removed.
Typos corrected and bibliography updated. Final version to appear in Journal
of Algebr
Universal Resistances of the Quantum RC circuit
We examine the concept of universal quantized resistance in the AC regime
through the fully coherent quantum RC circuit comprising a cavity (dot)
capacitively coupled to a gate and connected via a single spin-polarized
channel to a reservoir lead. As a result of quantum effects such as the Coulomb
interaction in the cavity and global phase coherence, we show that the charge
relaxation resistance is identical for weak and large transmissions and
it changes from to when the frequency (times ) exceeds
the level spacing of the cavity; is the Planck constant and the
electron charge. For large cavities, we formulate a correspondence between the
charge relaxation resistance and the Korringa-Shiba relation of the
Kondo model. Furthermore, we introduce a general class of models, for which the
charge relaxation resistance is universal. Our results emphasize that the
charge relaxation resistance is a key observable to understand the dynamics of
strongly correlated systems.Comment: 12 pages, 3 figure
Emerging roles of hnRNPA1 inmodulating malignanttransformation
Heterogeneous nuclear ribonucleoproteins (hnRNPs) are RNA-binding proteins associated with complex and diverse biological processes such as processing of heterogeneous nuclear RNAs (hnRNAs) into mature mRNAs, RNA splicing, transactivation of gene expression, and modulation of protein translation. hnRNPA1 is the most abundant and ubiquitously expressed member of this protein family and has been shown to be involved in multiple molecular events driving malignant transformation. In addition to selective mRNA splicing events promoting expression of specific protein variants, hnRNPA1 regulates the gene expression and translation of several key players associated with tumorigenesis and cancer progression. Here, we will summarize our current knowledge of the involvement of hnRNPA1 in cancer, including its roles in regulating cell proliferation, invasiveness, metabolism, adaptation to stress and immortalization
A Multilaboratory Comparison of Calibration Accuracy and the Performance of External References in Analytical Ultracentrifugation
Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies
A multilaboratory comparison of calibration accuracy and the performance of external references in analytical ultracentrifugation.
Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies
Pan-cancer analysis of whole genomes
Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale(1-3). Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4-5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter(4); identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation(5,6); analyses timings and patterns of tumour evolution(7); describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity(8,9); and evaluates a range of more-specialized features of cancer genomes(8,10-18).Peer reviewe
Impact of cell types and culture methods on the functionality of in vitro liver systems - A review of cell systems for hepatotoxicity assessment.
Xenobiotic safety assessment is an area that impacts a multitude of different industry sectors such as medicinal drugs, agrochemicals, industrial chemicals, cosmetics and environmental contaminants. As such there are a number of well-developed in vitro, in vivo and in silico approaches to evaluate their properties and potential impact on the environment and to humans. Additionally, there is the continual investment in multidisciplinary scientists to explore non-animal surrogate technologies to predict specific toxicological outcomes and to improve our understanding of the biological processes regarding the toxic potential of xenobiotics. Here we provide a concise, critical evaluation of a number of in vitro systems utilised to assess the hepatotoxic potential of xenobiotics
- …