318 research outputs found
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Field responsive mechanical metamaterials.
Typically, mechanical metamaterial properties are programmed and set when the architecture is designed and constructed, and do not change in response to shifting environmental conditions or application requirements. We present a new class of architected materials called field responsive mechanical metamaterials (FRMMs) that exhibit dynamic control and on-the-fly tunability enabled by careful design and selection of both material composition and architecture. To demonstrate the FRMM concept, we print complex structures composed of polymeric tubes infilled with magnetorheological fluid suspensions. Modulating remotely applied magnetic fields results in rapid, reversible, and sizable changes of the effective stiffness of our metamaterial motifs
Chandra follow up of the Hectospec Cluster Survey: Comparison of Caustic and Hydrostatic Masses and Constraints on the Hydrostatic Bias
Clusters of galaxies are powerful probes with which to study cosmology and
astrophysics. However, for many applications an accurate measurement of a
cluster's mass is essential. A systematic underestimate of hydrostatic masses
from X-ray observations (the so-called hydrostatic bias) may be responsible for
tension between the results of different cosmological measurements. We compare
X-ray hydrostatic masses with masses estimated using the caustic method (based
on galaxy velocities) in order to explore the systematic uncertainties of both
methods and place new constraints on the level of hydrostatic bias. Hydrostatic
and caustic mass profiles were determined independently for a sample of 44
clusters based on Chandra observations of clusters from the Hectospec Cluster
Survey. This is the largest systematic comparison of its kind. Masses were
compared at a standardised radius () using a model that includes
possible bias and scatter in both mass estimates. The systematics affecting
both mass determination methods were explored in detail. The hydrostatic masses
were found to be systematically higher than caustic masses on average, and we
found evidence that the caustic method increasingly underestimates the mass
when fewer galaxies are used to measure the caustics. We limit our analysis to
the 14 clusters with the best-sampled caustics where this bias is minimised
( galaxies), and find that the average ratio of hydrostatic to caustic
mass at is . We interpret this result
as a constraint on the level of hydrostatic bias, favouring small or zero
levels of hydrostatic bias (less than at the level). However,
we find systematic uncertainties associated with both mass estimation methods
remain at the level, which would permit significantly larger levels
of hydrostatic bias.Comment: 15 pages plus appendices. Updated to match version accepted for
publication in A&A. Updates include additional tests of systematics. Main
results are unchange
Structural Basis for α-Conotoxin Potency and Selectivity
Parkinson\u27s disease is a debilitating movement disorder characterized by altered levels of α6β2* nicotinic acetylcholine receptors (nAChRs) localized on presynaptic striatal catecholaminergic neurons. α-Conotoxin MII (α-CTx MII) is a highly useful ligand to probe α6ß2 nAChRs structure and function, but it does not discriminate among closely related α6* nAChR subtypes. Modification of the α-CTx MII primary sequence led to the identification of α-CTx MII[E11A], an analog with 500-5300 fold discrimination between α6* subtypes found in both human and non-human primates. α-CTx MII[E11A] binds most strongly (femtomolar dissociation constant) to the high affinity α6* nAChR, a subtype that is selectively lost in Parkinson\u27s disease. Here we present the three-dimensional solution structure for α-CTx MII[E11A] as determined by two-dimensional 1H NMR spectroscopy to 0.13 +/- 0.09 Ǻ backbone and 0.45 +/- 0.08 Ǻ heavy atom root mean square deviation from mean structure. Structural comparisons suggest that the increased hydrophobic area of α-CTx MII[E11A] relative to other members of the α-CTx family may be responsible for its exceptionally high affinity for α6α4β2* nAChR as well as discrimination between α6ß2 and α3β2 containing nAChRs. This finding may enable the rational design of novel peptide analogs that demonstrate enhanced specificity for α6* nAChR subunit interfaces and provide a means to better understand nAChR structural determinants that modulate brain dopamine levels and the pathophysiology of Parkinson\u27s disease
Commercial weight loss diets meet nutrient requirements in free living adults over 8 weeks: A randomised controlled weight loss trial
Objective: To investigate the effect of commercial weight loss programmes on macronutrient composition and micronutrient adequacy over a 2 month period
Ornithine Decarboxylase G316A Genotype Is Prognostic for Colorectal Adenoma Recurrence and Predicts Efficacy of Aspirin Chemoprevention
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Archaeological Central American maize genomes suggest ancient gene flow from South America
Maize (Zea mays ssp. mays) domestication began in southwestern Mexico ∼9,000 calendar years before present (cal. BP) and humans dispersed this important grain to South America by at least 7,000 cal. BP as a partial domesticate. South America served as a secondary improvement center where the domestication syndrome became fixed and new lineages emerged in parallel with similar processes in Mesoamerica. Later, Indigenous cultivators carried a second major wave of maize southward from Mesoamerica, but it has been unclear until now whether the deeply divergent maize lineages underwent any subsequent gene flow between these regions. Here we report ancient maize genomes (2,300–1,900 cal. BP) from El Gigante rock shelter, Honduras, that are closely related to ancient and modern maize from South America. Our findings suggest that the second wave of maize brought into South America hybridized with long-established landraces from the first wave, and that some of the resulting newly admixed lineages were then reintroduced to Central America. Direct radiocarbon dates and cob morphological data from the rock shelter suggest that more productive maize varieties developed between 4,300 and 2,500 cal. BP. We hypothesize that the influx of maize from South America into Central America may have been an important source of genetic diversity as maize was becoming a staple grain in Central and Mesoamerica
Chronic testicular Chlamydia muridarum infection impairs mouse fertility and offspring development
With approximately 131 million new genital tract infections occurring each year, Chlamydia is the most common sexually transmitted bacterial pathogen worldwide. Male and female infections occur at similar rates and both cause serious pathological sequelae. Despite this, the impact of chlamydial infection on male fertility has long been debated, and the effects of paternal chlamydial infection on offspring development are unknown. Using a male mouse chronic infection model, we show that chlamydial infection persists in the testes, adversely affecting the testicular environment. Infection increased leukocyte infiltration, disrupted the blood:testis barrier and reduced spermiogenic cell numbers and seminiferous tubule volume. Sperm from infected mice had decreased motility, increased abnormal morphology, decreased zona-binding capacity, and increased DNA damage. Serum anti-sperm antibodies were also increased. When both acutely and chronically infected male mice were bred with healthy female mice, 16.7% of pups displayed developmental abnormalities. Female offspring of chronically infected sires had smaller reproductive tracts than offspring of noninfected sires. The male pups of infected sires displayed delayed testicular development, with abnormalities in sperm vitality, motility, and sperm-oocyte binding evident at sexual maturity. These data suggest that chronic testicular Chlamydia infection can contribute to male infertility, which may have an intergenerational impact on sperm quality
Resistance to autosomal dominant Alzheimer's disease in an APOE3 Christchurch homozygote: a case report.
We identified a PSEN1 (presenilin 1) mutation carrier from the world's largest autosomal dominant Alzheimer's disease kindred, who did not develop mild cognitive impairment until her seventies, three decades after the expected age of clinical onset. The individual had two copies of the APOE3 Christchurch (R136S) mutation, unusually high brain amyloid levels and limited tau and neurodegenerative measurements. Our findings have implications for the role of APOE in the pathogenesis, treatment and prevention of Alzheimer's disease
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