5,614 research outputs found
Projected Constraints on Modified Gravity Cosmologies from 21 cm Intensity Mapping
We present projected constraints on modified gravity models from the
observational technique known as 21 cm intensity mapping, where cosmic
structure is detected without resolving individual galaxies. The resulting map
is sensitive to both BAO and weak lensing, two of the most powerful
cosmological probes. It is found that a 200 m x 200 m cylindrical telescope,
sensitive out to z=2.5, would be able to distinguish DGP from most dark energy
models, and constrain the Hu & Sawicki f(R) model to |f_{R0}| < 9*10^(-6) at
95% confidence. The latter constraint makes extensive use of the lensing
spectrum in the nonlinear regime. These results show that 21 cm intensity
mapping is not only sensitive to modifications of the standard model's
expansion history, but also to structure growth. This makes intensity mapping a
powerful and economical technique, achievable on much shorter time scales than
optical experiments that would probe the same era.Comment: 10 pages, 5 figures, 1 table. Added references and expanded
discussion. As resubmitted to Phys. Rev. D, in response to reviewer comment
Stimulation of Transforming Growth Factor-β1-Induced Endothelial-To-Mesenchymal Transition and Tissue Fibrosis by Endothelin-1 (ET-1): A Novel Profibrotic Effect of ET-1.
TGF-β-induced endothelial-to-mesenchymal transition (EndoMT) is a newly recognized source of profibrotic activated myofibroblasts and has been suggested to play a role in the pathogenesis of various fibrotic processes. Endothelin-1 (ET-1) has been implicated in the development of tissue fibrosis but its participation in TGF-β-induced EndoMT has not been studied. Here we evaluated the role of ET-1 on TGF-β1-induced EndoMT in immunopurified CD31+/CD102+ murine lung microvascular endothelial cells. The expression levels of ι-smooth muscle actin (ι-SMA), of relevant profibrotic genes, and of various transcription factors involved in the EndoMT process were assessed employing quantitative RT-PCR, immunofluorescence histology and Western blot analysis. TGF-β1 caused potent induction of EndoMT whereas ET-1 alone had a minimal effect. However, ET-1 potentiated TGF-β1-induced EndoMT and TGF-β1-stimulated expression of mesenchymal cell specific and profibrotic genes and proteins. ET-1 also induced expression of the TGF-β receptor 1 and 2 genes, suggesting a plausible autocrine mechanism to potentiate TGF-β-mediated EndoMT and fibrosis. Stimulation of TGF-β1-induced skin and lung fibrosis by ET-1 was confirmed in vivo in an animal model of TGF-β1-induced tissue fibrosis. These results suggest a novel role for ET-1 in the establishment and progression of tissue fibrosis
Metrics and Isometries for Convex Functions
We introduce a class of functional analogs of the symmetric difference metric
on the space of coercive convex functions on with
full-dimensional domain. We show that convergence with respect to these metrics
is equivalent to epi-convergence. Furthermore, we give a full classification of
all isometries with respect to some of the new metrics. Moreover, we introduce
two new functional analogs of the Hausdorff metric on the spaces of coercive
convex functions and super-coercive convex functions, respectively, and prove
equivalence to epi-convergence
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Flow measurement inside a zinc-nickel flow cell battery using FBG based sensor system
Downloading of the abstract is permitted for personal use only. A detailed knowledge of the internal flow distribution inside a zinc-nickel flow battery is of critical importance to ensure smooth flow of the electrolyte through the battery cell and better operation of the device. Information of this type can be used as a useful means of early detection of zinc deposition and dendrite formation inside the cell, negative factors which affect the flow and thus which can lead to internal short circuiting, this being a primary failure mode of these types of batteries. This deposition occurs at low pH levels when zinc reacts with the electrolyte to form solid zinc oxide hydroxides. Traditionally, manual inspection is conducted, but this is time consuming and costly, only providing what are often inaccurate results-overall it is an impractical solution especially with the wider use of batteries in the very near future. Fibre Bragg grating (FBG) sensors integrated inside the flow cell offer the advantage of measuring flow changes at multiple locations using a single fibre and that then can be used as an indicator of the correlation between the internal flow distribution and the deposition characteristics. This work presents an initial study, where two networks of FBGs have been installed and used for flow change detection in an active zinc-nickel flow battery. Data have been obtained from the sensor networks and information of battery performance completed and summarized in this paper. The approach shows promising results and thus scope for the future research into the development of this type of sensor system
Using a landscape ecological perspective to analyze regime shifts in socialâecological systems: a case study on grassland degradation of the Tibetan Plateau
Context
Landscape ecology thinking and socialâecological system (SES) thinking investigate humanâenvironment relationships from the perspective of âspaceâ and âsystemâ, respectively. To date, empirical landscape ecology studies attempting to understand SES complexities are rare.
Objectives
Using the Tibetan pastoral landscape as an empirical example, we conceptualize the black-soil formation as SES regime shifts. We seek to illustrate the spatial patterns of black-soil formation in the Tibetan SES, and to reveal their underlying ecological processes.
Methods
We conducted interdisciplinary research in a Tibetan pastoral village. We obtained quantitative data on historical land-use intensity (LUI) and the associated management narratives. Landsat-based NDVI time series were used to derive a grassland productivity proxy and to reconstruct the process leading to the up-scaling of the regime shift of degradation.
Results
Important SES features, such as LUI, productivity and degradation risk are heterogeneously distributed in space. Land-use intensification at farm-scales in the 1990s increased landscape-scale degradation risks. Eventually the regime shift of degradation scaled up from the plot level to the landscape level in the 2010s. The time lag was related to the gradual invasion of a native burrowing animal, the plateau pika, which inhabits low-vegetation height pastures.
Conclusions
Our study shows that landscape ecology thinking provides an important spatial perspective to understanding SES complexities. The finding that unfavorable SES regime shifts are strongly linked across spatial scales implies that an âentry pointâ into an adaptive management circle should be initiated when local-scale regime shifts are perceived and interpreted as early warning signals
Effect of local chemistry and structure on thermal transport in doped GaAs
Using a first-principles approach, we analyze the impact of \textit{DX}
centers formed by S, Se, and Te dopant atoms on the thermal conductivity of
GaAs. Our results are in good agreement with experiments and unveil the physics
behind the drastically different effect of each kind of defect. We establish a
causal chain linking the electronic structure of the dopants to the thermal
conductivity of the bulk solid, a macroscopic transport coefficient.
Specifically, the presence of lone pairs leads to the formation of structurally
asymmetric \textit{DX} centers that cause resonant scattering of incident
phonons. The effect of such resonances is magnified when they affect the part
of the spectrum most relevant for thermal transport. We show that these
resonances are associated with localized vibrational modes in the perturbed
phonon spectrum. Finally, we illustrate the connection between flat adjacent
minima in the energy landscape and resonant phonon scattering through detailed
analyses of the energy landscape of the defective structures.Comment: 7 pages, 7 figure
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