150 research outputs found
Model based MIN/MAX override control of centrifugal compressor systems
We consider an application-oriented nonlinear control of centrifugal
compressors. Industrial applications require the compressor system to adjust to
variable process demands and to be restricted to the valid operation range
(e.g. surge limit). We modify a compressor model of Gravdahl and Egeland to
account for characteristic features of industrial compressors and combine the
framework of nonlinear output regulation via the internal model principle with
MIN/MAX-override control in order to implement trajectory tracking between
given state constraints. Furthermore the switching scheme as well as the
practical stability of the closed-loop MIMO system is analysed by the
corresponding switched and impulsive error system. The override control is
demonstrated by applying discharge pressure control, anti-surge control and
maximum discharge pressure limitation
Large-Scale Evaluation of Topic Models and Dimensionality Reduction Methods for 2D Text Spatialization
Topic models are a class of unsupervised learning algorithms for detecting
the semantic structure within a text corpus. Together with a subsequent
dimensionality reduction algorithm, topic models can be used for deriving
spatializations for text corpora as two-dimensional scatter plots, reflecting
semantic similarity between the documents and supporting corpus analysis.
Although the choice of the topic model, the dimensionality reduction, and their
underlying hyperparameters significantly impact the resulting layout, it is
unknown which particular combinations result in high-quality layouts with
respect to accuracy and perception metrics. To investigate the effectiveness of
topic models and dimensionality reduction methods for the spatialization of
corpora as two-dimensional scatter plots (or basis for landscape-type
visualizations), we present a large-scale, benchmark-based computational
evaluation. Our evaluation consists of (1) a set of corpora, (2) a set of
layout algorithms that are combinations of topic models and dimensionality
reductions, and (3) quality metrics for quantifying the resulting layout. The
corpora are given as document-term matrices, and each document is assigned to a
thematic class. The chosen metrics quantify the preservation of local and
global properties and the perceptual effectiveness of the two-dimensional
scatter plots. By evaluating the benchmark on a computing cluster, we derived a
multivariate dataset with over 45 000 individual layouts and corresponding
quality metrics. Based on the results, we propose guidelines for the effective
design of text spatializations that are based on topic models and
dimensionality reductions. As a main result, we show that interpretable topic
models are beneficial for capturing the structure of text corpora. We
furthermore recommend the use of t-SNE as a subsequent dimensionality
reduction.Comment: To be published at IEEE VIS 2023 conferenc
[S IV] in the NGC 5253 Supernebula: Ionized Gas Kinematics at High Resolution
The nearby dwarf starburst galaxy NGC 5253 hosts a deeply embedded
radio-infrared supernebula excited by thousands of O stars. We have observed
this source in the 10.5{\mu}m line of S+3 at 3.8 kms-1 spectral and 1.4"
spatial resolution, using the high resolution spectrometer TEXES on the IRTF.
The line profile cannot be fit well by a single Gaussian. The best simple fit
describes the gas with two Gaussians, one near the galactic velocity with FWHM
33.6 km s-1 and another of similiar strength and FWHM 94 km s-1 centered \sim20
km s-1 to the blue. This suggests a model for the supernebula in which gas
flows towards us out of the molecular cloud, as in a "blister" or "champagne
flow" or in the HII regions modelled by Zhu (2006).Comment: Accepted for publication in the Astrophysical Journal 4 June 201
Micromechanical Analysis of the Hyaluronan-Rich Matrix Surrounding the Oocyte Reveals a Uniquely Soft and Elastic Composition
The cumulus cell-oocyte complex (COC) matrix is an extended coat that forms around the oocyte a few hours before ovulation and plays vital roles in oocyte biology. Here, we analyzed the micromechanical response of mouse COC matrix by colloidal-probe atomic force microscopy. We found that the COC matrix is elastic insofar as it does not flow and its original shape is restored after force release. At the same time, the COC matrix is extremely soft. Specifically, the most compliant parts of in vivo and in vitro expanded COC matrices yielded Young's modulus values of 0.5 ± 0.1 Pa and 1.6 ± 0.3 Pa, respectively, suggesting both high porosity and a large mesh size (≥100 nm). In addition, the elastic modulus increased progressively with indentation. Furthermore, using optical microscopy to correlate these mechanical properties with ultrastructure, we discovered that the COC is surrounded by a thick matrix shell that is essentially devoid of cumulus cells and is enhanced upon COC expansion in vivo. We propose that the pronounced nonlinear elastic behavior of the COC matrix is a consequence of structural heterogeneity and serves important functions in biological processes such as oocyte transport in the oviduct and sperm penetration
Non-communicable disease governance in the era of the sustainable development goals:A qualitative analysis of food industry framing in WHO consultations
Ions modulate stress-induced nano-texture in supported fluid lipid bilayers.
Most plasma membranes comprise a large number of different molecules including lipids and proteins. In the standard fluid mosaic model, the membrane function is effected by proteins whereas lipids are largely passive and serve solely in the membrane cohesion. Here we show, using supported 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid bilayers in different saline solutions, that ions can locally induce ordering of the lipid molecules within the otherwise fluid bilayer when the latter is supported. This nanoordering exhibits a characteristic length scale of ∼20 nm, and manifests itself clearly when mechanical stress is applied to the membrane. Atomic force microscopy (AFM) measurements in aqueous solutions containing NaCl, KCl, CaCl2, and Tris buffer show that the magnitude of the effect is strongly ion-specific, with Ca2+ and Tris, respectively, promoting and reducing stress-induced nanotexturing of the membrane. The AFM results are complemented by fluorescence recovery after photobleaching experiments, which reveal an inverse correlation between the tendency for molecular nanoordering and the diffusion coefficient within the bilayer. Control AFM experiments on other lipids and at different temperatures support the hypothesis that the nanotexturing is induced by reversible, localized gel-like solidification of the membrane. These results suggest that supported fluid phospholipid bilayers are not homogenous at the nanoscale, but specific ions are able to locally alter molecular organization and mobility, and spatially modulate the membrane’s properties on a length scale of ∼20 nm. To illustrate this point, AFM was used to follow the adsorption of the membrane-penetrating antimicrobial peptide Temporin L in different solutions. The results confirm that the peptides do not absorb randomly, but follow the ion-induced spatial modulation of the membrane. Our results suggest that ionic effects have a significant impact for passively modulating the local properties of biological membranes, when in contact with a support such as the cytoskeleton
Mutational mechanisms shaping the coding and noncoding genome of germinal center derived B-cell lymphomas
B cells have the unique property to somatically alter their immunoglobulin (IG) genes by V(D)J recombination, somatic hypermutation (SHM) and class-switch recombination (CSR). Aberrant targeting of these mechanisms is implicated in lymphomagenesis, but the mutational processes are poorly understood. By performing whole genome and transcriptome sequencing of 181 germinal center derived B-cell lymphomas (gcBCL) we identified distinct mutational signatures linked to SHM and CSR. We show that not only SHM, but presumably also CSR causes off-target mutations in non-IG genes. Kataegis clusters with high mutational density mainly affected early replicating regions and were enriched for SHM- and CSR-mediated off-target mutations. Moreover, they often co-occurred in loci physically interacting in the nucleus, suggesting that mutation hotspots promote increased mutation targeting of spatially co-localized loci (termed hypermutation by proxy). Only around 1% of somatic small variants were in protein coding sequences, but in about half of the driver genes, a contribution of B-cell specific mutational processes to their mutations was found. The B-cell-specific mutational processes contribute to both lymphoma initiation and intratumoral heterogeneity. Overall, we demonstrate that mutational processes involved in the development of gcBCL are more complex than previously appreciated, and that B cell-specific mutational processes contribute via diverse mechanisms to lymphomagenesis
DNA methylome analysis in Burkitt and follicular lymphomas identifies differentially methylated regions linked to somatic mutation and transcriptional control
Although Burkitt lymphomas and follicular lymphomas both have features of germinal center B cells, they are biologically and clinically quite distinct. Here we performed whole-genome bisulfite, genome and transcriptome sequencing in 13 IG-MYC translocation-positive Burkitt lymphoma, nine BCL2 translocation-positive follicular lymphoma and four normal germinal center B cell samples. Comparison of Burkitt and follicular lymphoma samples showed differential methylation of intragenic regions that strongly correlated with expression of associated genes, for example, genes active in germinal center dark-zone and light-zone B cells. Integrative pathway analyses of regions differentially methylated in Burkitt and follicular lymphomas implicated DNA methylation as cooperating with somatic mutation of sphingosine phosphate signaling, as well as the TCF3-ID3 and SWI/SNF complexes, in a large fraction of Burkitt lymphomas. Taken together, our results demonstrate a tight connection between somatic mutation, DNA methylation and transcriptional control in key B cell pathways deregulated differentially in Burkitt lymphoma and other germinal center B cell lymphomas
Harnessing demographic differences in organizations:what moderates the effects of workplace diversity?
To account for the double-edged nature of demographic workplace diversity (i.e,. relational demography, work group diversity, and organizational diversity) effects on social integration, performance, and well-being related variables, research has moved away from simple main effect approaches and started examining variables that moderate these effects. While there is no shortage of primary studies of the conditions under which diversity leads to positive or negative outcomes, it remains unclear which contingency factors make it work. Using the Categorization-Elaboration Model as our theoretical lens, we review variables moderating the effects of workplace diversity on social integration, performance, and well-being outcomes, focusing on factors that organizations and managers have control over (i.e., strategy, unit design, human resource, leadership, climate/culture, and individual differences). We point out avenues for future research and conclude with practical implications
Monitoring of the radio galaxy M87 during a low emission state from 2012 to 2015 with MAGIC
M87 is one of the closest (z=0.00436) extragalactic sources emitting at very-high-energies (VHE, E > 100 GeV). The aim of this work is to locate the region of the VHE gamma-ray emission and to describe the observed broadband spectral energy distribution (SED) during the low VHE gamma-ray state. The data from M87 collected between 2012 and 2015 as part of a MAGIC monitoring programme are analysed and combined with multi-wavelength data from Fermi-LAT, Chandra, HST, EVN, VLBA and the Liverpool Telescope. The averaged VHE gamma-ray spectrum can be fitted from 100GeV to 10TeV with a simple power law with a photon index of (-2.41 0.07), while the integral flux above 300GeV is . During the campaign between 2012 and 2015, M87 is generally found in a low emission state at all observed wavelengths. The VHE gamma-ray flux from the present 2012-2015 M87 campaign is consistent with a constant flux with some hint of variability () on a daily timescale in 2013. The low-state gamma-ray emission likely originates from the same region as the flare-state emission. Given the broadband SED, both a leptonic synchrotron self Compton and a hybrid photo-hadronic model reproduce the available data well, even if the latter is preferred. We note, however, that the energy stored in the magnetic field in the leptonic scenario is very low suggesting a matter dominated emission region
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