2,699 research outputs found
Constitutive modeling of the anisotropic behavior of Mullins softened filled rubbers
Original constitutive modeling is proposed for filled rubber materials in order to capture the anisotropic softened behavior induced by general non-proportional pre-loading histo-ries. The hyperelastic framework is grounded on a thorough analysis of cyclic experimental data. The strain energy density is based on a directional approach. The model leans on the strain amplification factor concept applied over material directions according to the Mul-lins softening evolution. In order to provide a model versatile that applies for a wide range of materials, the proposed framework does not require to postulate the mathematical forms of the elementary directional strain energy density and of the Mullins softening evo-lution rule. A computational procedure is defined to build both functions incrementally from experimental data obtained during cyclic uniaxial tensile tests. Successful compari-sons between the model and the experiments demonstrate the model abilities. Moreover, the model is shown to accurately predict the non-proportional uniaxial stress-stretch responses for uniaxially and biaxially pre-stretched samples. Finally, the model is effi-ciently tested on several materials and proves to provide a quantitative estimate of the anisotropy induced by the Mullins softening for a wide range of filled rubbers
Low temperature superlattice in monoclinic PZT
TEM has shown that the strongly piezoelectric material Pb(Zr0.52Ti0.48)O3
separates into two phases at low temperatures. The majority phase is the
monoclinic phase previously found by x-ray diffraction. The minority phase,
with a nanoscale coherence length, is a slightly distorted variant of the first
resulting from the anti-phase rotation of the oxygen octahedra about [111].
This work clears up a recent controversy about the origin of superlattice peaks
in these materials, and supports recent theoretical results predicting the
coexistence of ferroelectric and rotational instabilities.Comment: REVTeX4, 4 eps figures embedded. JPG version of figs. 2&4 is also
include
Stylish Risk-Limiting Audits in Practice
Risk-limiting audits (RLAs) can use information about which ballot cards
contain which contests (card-style data, CSD) to ensure that each contest
receives adequate scrutiny, without examining more cards than necessary. RLAs
using CSD in this way can be substantially more efficient than RLAs that sample
indiscriminately from all cast cards. We describe an open-source Python
implementation of RLAs using CSD for the Hart InterCivic Verity voting system
and the Dominion Democracy Suite(R) voting system. The software is demonstrated
using all 181 contests in the 2020 general election and all 214 contests in the
2022 general election in Orange County, CA, USA, the fifth-largest election
jurisdiction in the U.S., with over 1.8 million active voters. (Orange County
uses the Hart Verity system.) To audit the 181 contests in 2020 to a risk limit
of 5% without using CSD would have required a complete hand tally of all
3,094,308 cast ballot cards. With CSD, the estimated sample size is about
20,100 cards, 0.65% of the cards cast--including one tied contest that required
a complete hand count. To audit the 214 contests in 2022 to a risk limit of 5%
without using CSD would have required a complete hand tally of all 1,989,416
cast cards. With CSD, the estimated sample size is about 62,250 ballots, 3.1%
of cards cast--including three contests with margins below 0.1% and 9 with
margins below 0.5%
The FEATURE framework for protein function annotation: modeling new functions, improving performance, and extending to novel applications
Structural genomics efforts contribute new protein structures that often lack significant sequence and fold similarity to known proteins. Traditional sequence and structure-based methods may not be sufficient to annotate the molecular functions of these structures. Techniques that combine structural and functional modeling can be valuable for functional annotation. FEATURE is a flexible framework for modeling and recognition of functional sites in macromolecular structures. Here, we present an overview of the main components of the FEATURE framework, and describe the recent developments in its use. These include automating training sets selection to increase functional coverage, coupling FEATURE to structural diversity generating methods such as molecular dynamics simulations and loop modeling methods to improve performance, and using FEATURE in large-scale modeling and structure determination efforts
Hepatic metabolite profiling of polychlorinated biphenyl (PCB)-resistant and sensitive populations of Atlantic killifish (Fundulus heteroclitus)
Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Aquatic Toxicology (2018), doi:10.1016/j.aquatox.2018.10.007.Atlantic killifish inhabiting polluted sites along the east coast of the U.S. have evolved
resistance to toxic effects of contaminants. One such contaminated site is the Acushnet River
estuary, near New Bedford Harbor (NBH), Massachusetts, which is characterized by very high
PCB concentrations in the sediments and in the tissues of resident killifish. Though killifish at
this site appear to be thriving, the metabolic costs of survival in a highly contaminated
environment are not well understood. In this study we compared the hepatic metabolite profiles
of resistant (NBH) and sensitive populations (Scorton Creek (SC), Sandwich, MA) using a
targeted metabolomics approach in which polar metabolites were extracted from adult fish livers
and quantified. Our results revealed differences in the levels of several metabolites between fish
from the two sites. The majority of these metabolites are associated with one-carbon
metabolism, an important pathway that supports multiple physiological processes including DNA
and protein methylation, nucleic acid biosynthesis and amino acid metabolism. We measured
the gene expression of DNA methylation (DNA methyltransferase 1, dnmt1) and demethylation
genes (Ten-Eleven Translocation (TET) genes) in the two populations, and observed lower
levels of dnmt1 and higher levels of TET gene expression in the NBH livers, suggesting possible
differences in DNA methylation profiles. Consistent with this, the two populations differed
significantly in the levels of 5-methylcytosine and 5-hydroxymethylcytosine nucleotides. Overall,
our results suggest that the unique hepatic metabolite signatures observed in NBH and SC
reflect the adaptive mechanisms for survival in their respective habitats.This work was supported by the Joint Initiative Awards Fund from the Andrew W. Mellon
Foundation (NA and EBK) and National Institute of Environmental Health Sciences (NIEHS)
Superfund Research Program (P42ES007381) at Boston University. LG was supported by the
Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution (with funding
provided by the Townsend Postdoctoral Scholarship Fund, and the John H. Steele Endowment
in support of Postdoctoral Research)
Inhibition of hypoxia-induced miR-155 radiosensitizes hypoxic lung cancer cells
miR-155 is a prominent microRNA (miRNA) that regulates genes involved in immunity and cancer-related pathways. miR-155 is overexpressed in lung cancer, which correlates with poor patient prognosis. It is unclear how miR-155 becomes increased in lung cancers and how this increase contributes to reduced patient survival. Here, we show that hypoxic conditions induce miR-155 expression in lung cancer cells and trigger a corresponding decrease in a validated target, FOXO3A. Furthermore, we find that increased levels of miR-155 radioprotects lung cancer cells, while inhibition of miR-155 radiosensitizes these cells. Moreover, we reveal a therapeutically important link between miR-155 expression, hypoxia, and irradiation by demonstrating that anti-miR-155 molecules also sensitize hypoxic lung cancer cells to irradiation. Our study helps explain how miR-155 becomes elevated in lung cancers, which contain extensive hypoxic microenvironments, and demonstrates that inhibition of miR-155 may have important therapeutic potential as a means to radiosensitize hypoxic lung cancer cells
Octahedral Tilt Instability of ReO_3-type Crystals
The octahedron tilt transitions of ABX_3 perovskite-structure materials lead
to an anti-polar (or antiferroelectric) arrangement of dipoles, with the low
temperature structure having six sublattices polarized along various
crystallographic directions. It is shown that an important mechanism driving
the transition is long range dipole-dipole forces acting on both displacive and
induced parts of the anion dipole. This acts in concert with short range
repulsion, allowing a gain of electrostatic (Madelung) energy, both
dipole-dipole and charge-charge, because the unit cell shrinks when the hard
ionic spheres of the rigid octahedron tilt out of linear alignment.Comment: 4 page with 3 figures included; new version updates references and
clarifies the argument
- …