4,061 research outputs found
A geometrically controlled rigidity transition in a model for confluent 3D tissues
The origin of rigidity in disordered materials is an outstanding open problem
in statistical physics. Previously, a class of 2D cellular models has been
shown to undergo a rigidity transition controlled by a mechanical parameter
that specifies cell shapes. Here, we generalize this model to 3D and find a
rigidity transition that is similarly controlled by the preferred surface area:
the model is solid-like below a dimensionless surface area of
, and fluid-like above this value. We demonstrate that,
unlike jamming in soft spheres, residual stresses are necessary to create
rigidity. These stresses occur precisely when cells are unable to obtain their
desired geometry, and we conjecture that there is a well-defined minimal
surface area possible for disordered cellular structures. We show that the
behavior of this minimal surface induces a linear scaling of the shear modulus
with the control parameter at the transition point, which is different from the
scaling observed in particulate matter. The existence of such a minimal surface
may be relevant for biological tissues and foams, and helps explain why cell
shapes are a good structural order parameter for rigidity transitions in
biological tissues.Comment: 6 pages main text + 13 pages appendix, 3 main text figures + 6
appendix figure
How Partisan News’ Coverage of Polarizing Supreme Court Decisions Differs in Framing the Nation’s Highest Court
The U.S. Supreme Court is isolated from the public, yet dependent on high
levels of public support to maintain its legitimacy. Due to its distance, the
media has great control over how the nation’s highest court is presented to
the public. Partisan news outlets cater their stories to audiences with
distinct ideological beliefs, reinforcing them while opposing opposite
beliefs. This can lead to partisan polarization, which has previously been
exclusive to the political realm. However, recent polls have revealed an
existing party gap in the Supreme Court’s level of public support, which
implies a politicization of the judiciary branch. When the Supreme Court
appears to be just another political institution or simply an extension of the
other two governmental branches, its integrity is greatly impaired, and, as a
consequence, the public’s confidence in the Justices is likely to deteriorate.
This study analyzes Fox News’ and MSNBC’s news coverage of two polarizing
Supreme Court cases to find out if partisan outlets politicize the Court. The
findings show if the channel’s ideological stance aligns with the Court’s
decision, the Supreme Court is presented as an apolitical institution, whereas
it is politicized when the decision is contrary the channel’s partisan stance.
This implies that the partisan divide, once only common to the political realm
has now reached the judiciary
A Comparative Analysis of Television News Coverage of the U.S. Supreme Court (1990 - 2018)
The U.S. Supreme Court holds profound influence over American law and society, yet public understanding depends heavily on the news media. This dissertation presents a comprehensive empirical analysis of television news coverage of the Court’s 1990-2018 terms, comparing how the volume, format, and presentation of Supreme Court case mentions in evening news transcripts varied across time periods, channel types, and cable programs. My research involves quantitative content analysis, qualitative assessments, and statistical comparisons of 595 transcripts containing 717 case mentions of 154 cases. The findings compel us to consider how institutional constraints and practices shape coverage decisions in ways that may restrict substantive reporting on governance institutions like the Court, potentially impacting public awareness and understanding of the judicial branch. This rigorous study provides needed investigation into overlooked facets of Court news coverage and by making the comprehensive dataset publicly available, it establishes a foundation to motivate future studies at the nexus of journalism, the Supreme Court, and the public
Non-overlapping block smoothers for the Stokes equations
Overlapping block smoothers efficiently damp the error contributions from
highly oscillatory components within multigrid methods for the Stokes equations
but they are computationally expensive. This paper is concentrated on the
development and analysis of new block smoothers for the Stokes equations that
are discretized on staggered grids. These smoothers are non-overlapping and
therefore desirable due to reduced computational costs. Traditional geometric
multigrid methods are based on simple pointwise smoothers. However, the
efficiency of multigrid methods for solving more difficult problems such as the
Stokes equations lead to computationally more expensive smoothers, e.g.,
overlapping block smoothers. Non-overlapping smoothers are less expensive, but
have been considered less efficient in the literature. In this paper, we
develop new non-overlapping smoothers, the so-called triad-wise smoothers, and
show their efficiency within multigrid methods to solve the Stokes equations.
In addition, we compare overlapping and non-overlapping smoothers by measuring
their computational costs and analyzing their behavior by the use of local
Fourier analysis.Comment: 17 pages, 34 figure
Correlating Cell Shape and Cellular Stress in Motile Confluent Tissues
Collective cell migration is a highly regulated process involved in wound
healing, cancer metastasis and morphogenesis. Mechanical interactions among
cells provide an important regulatory mechanism to coordinate such collective
motion. Using a Self-Propelled Voronoi (SPV) model that links cell mechanics to
cell shape and cell motility, we formulate a generalized mechanical inference
method to obtain the spatio-temporal distribution of cellular stresses from
measured traction forces in motile tissues and show that such traction-based
stresses match those calculated from instantaneous cell shapes. We additionally
use stress information to characterize the rheological properties of the
tissue. We identify a motility-induced swim stress that adds to the interaction
stress to determine the global contractility or extensibility of epithelia. We
further show that the temporal correlation of the interaction shear stress
determines an effective viscosity of the tissue that diverges at the
liquid-solid transition, suggesting the possibility of extracting rheological
information directly from traction data.Comment: 12 pages, 9 figure
Toward transparency of hybrid open access through publisher-provided metadata: An article-level study of Elsevier
With the growth of open access (OA), the financial flows in scholarly journal publishing have become increasingly complex, but comprehensive data on and transparency of these flows are still lacking. The opacity is especially concerning for hybrid OA, where subscription-based journals publish individual articles as OA if an optional fee is paid. This study addresses the lack of transparency by leveraging Elsevier article metadata and provides the first publisher-level study of hybrid OA uptake and invoicing. Our results show that Elsevier's hybrid OA uptake has grown steadily but slowly from 2015 to 2019, doubling the number of hybrid OA articles published per year and increasing the share of OA articles in Elsevier's hybrid journals from 2.6 to 3.7% of all articles. Further, we find that most hybrid OA articles were invoiced directly to authors, followed by articles invoiced through agreements with research funders, institutions, or consortia, with only a few funding bodies driving hybrid OA uptake. As such, our findings point to the role of publishing agreements and OA policies in hybrid OA publishing. Our results further demonstrate the value of publisher-provided metadata to improve the transparency in scholarly publishing
Microplastic transport in soil by earthworms
Despite great general benefits derived from plastic use, accumulation of
plastic material in ecosystems, and especially microplastic, is becoming an
increasing environmental concern. Microplastic has been extensively studied in
aquatic environments, with very few studies focusing on soils. We here tested
the idea that microplastic particles (polyethylene beads) could be transported
from the soil surface down the soil profile via earthworms. We used Lumbricus
terrestris L., an anecic earthworm species, in a factorial greenhouse
experiment with four different microplastic sizes. Presence of earthworms
greatly increased the presence of microplastic particles at depth (we examined
3 soil layers, each 3.5 cm deep), with smaller PE microbeads having been
transported downward to a greater extent. Our study clearly shows that
earthworms can be significant transport agents of microplastics in soils,
incorporating this material into soil, likely via casts, burrows (affecting
soil hydraulics), egestion and adherence to the earthworm exterior. This
movement has potential consequences for exposure of other soil biota to
microplastics, for the residence times of microplastic at greater depth, and
for the possible eventual arrival of microplastics in the groundwater
Assessments at multiple levels of biological organization allow for an integrative determination of physiological tolerances to turbidity in an endangered fish species.
Turbidity can influence trophic levels by altering species composition and can potentially affect fish feeding strategies and predator-prey interactions. The estuarine turbidity maximum, described as an area of increased suspended particles, phytoplankton and zooplankton, generally represents a zone with higher turbidity and enhanced food sources important for successful feeding and growth in many fish species. The delta smelt (Hypomesus transpacificus) is an endangered, pelagic fish species endemic to the San Francisco Estuary and Sacramento-San Joaquin River Delta, USA, where it is associated with turbid waters. Turbidity is known to play an important role for the completion of the species' life cycle; however, turbidity ranges in the Delta are broad, and specific requirements for this fish species are still unknown. To evaluate turbidity requirements for early life stages, late-larval delta smelt were maintained at environmentally relevant turbidity levels ranging from 5 to 250 nephelometric turbidity units (NTU) for 24 h, after which a combination of physiological endpoints (molecular biomarkers and cortisol), behavioural indices (feeding) and whole-organism measures (survival) were determined. All endpoints delivered consistent results and identified turbidities between 25 and 80 NTU as preferential. Delta smelt survival rates were highest between 12 and 80 NTU and feeding rates were highest between 25 and 80 NTU. Cortisol levels indicated minimal stress between 35 and 80 NTU and were elevated at low turbidities (5, 12 and 25 NTU). Expression of stress-related genes indicated significant responses for gst, hsp70 and glut2 in high turbidities (250 NTU), and principal component analysis on all measured genes revealed a clustering of 25, 35, 50 and 80 NTU separating the medium-turbidity treatments from low- and high-turbidity treatments. Taken together, these data demonstrate that turbidity levels that are either too low or too high affect delta smelt physiological performance, causing significant effects on overall stress, food intake and mortality. They also highlight the need for turbidity to be considered in habitat and water management decisions
Sublethal salinity stress contributes to habitat limitation in an endangered estuarine fish.
As global change alters multiple environmental conditions, predicting species' responses can be challenging without understanding how each environmental factor influences organismal performance. Approaches quantifying mechanistic relationships can greatly complement correlative field data, strengthening our abilities to forecast global change impacts. Substantial salinity increases are projected in the San Francisco Estuary, California, due to anthropogenic water diversion and climatic changes, where the critically endangered delta smelt (Hypomesus transpacificus) largely occurs in a low-salinity zone (LSZ), despite their ability to tolerate a much broader salinity range. In this study, we combined molecular and organismal measures to quantify the physiological mechanisms and sublethal responses involved in coping with salinity changes. Delta smelt utilize a suite of conserved molecular mechanisms to rapidly adjust their osmoregulatory physiology in response to salinity changes in estuarine environments. However, these responses can be energetically expensive, and delta smelt body condition was reduced at high salinities. Thus, acclimating to salinities outside the LSZ could impose energetic costs that constrain delta smelt's ability to exploit these habitats. By integrating data across biological levels, we provide key insight into the mechanistic relationships contributing to phenotypic plasticity and distribution limitations and advance the understanding of the molecular osmoregulatory responses in nonmodel estuarine fishes
In vivo elimination of MHC-I-deficient lymphocytes by activated natural killer cells is independent of granzymes A and B
NK cells kill target cells mainly via exocytosis of granules containing perforin (perf) and granzymes (gzm). In vitro, gzm delivery into the target cell cytosol results in apoptosis, and induction of apoptosis is severely impaired in the absence of gzm A and B. However, their importance for in vivo cytotoxicity by cytotoxic T cells has been questioned. We used an in vivo NK cytotoxicity assay, in which splenocytes from wild-type and β(2)microglobulin-deficient (MHC-I(neg)) mice are co-injected into recipients whose NK cells were activated by virus infection or synthetic Toll-like receptor ligands. Elimination of adoptively transferred MHC-I(neg) splenocytes was unimpaired in the absence of gzmA and gzmB, but dependent on perforin. This target cell rejection was NK cell dependent, since NK cell depletion abrogated it. Furthermore, target cell elimination in vivo was equally rapid in both wild-type and gzmAxB-deficient recipients, with the majority of specific target cells lost from lymphoid tissue within less than one to two hours after transfer. Thus, similar to T cell cytotoxicity, the contribution of gzmA and B to in vivo target cell elimination remains unresolved.This work was supported by the Australian National Health and Medical Research Council and by a government block grant to the John Curtin School
of Medical Research
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