2,712 research outputs found
On Extracting Mechanical Properties from Nanoindentation at Temperatures up to 1000C
Alloyed MCrAlY bond coats, where M is usually cobalt and/or nickel, are
essential parts of modern turbine blades, imparting environmental resistance
while mediating thermal expansivity differences. Nanoindentation allows the
determination of their properties without the complexities of traditional
mechanical tests, but was not previously possible near turbine operating
temperatures.
Here, we determine the hardness and modulus of CMSX-4 and an Amdry-386 bond
coat by nanoindentation up to 1000C. Both materials exhibit a
constant hardness until 400C followed by considerable softening,
which in CMSX-4 is attributed to the multiple slip systems operating underneath
a Berkovich indenter.
The creep behaviour has been investigated via the nanoindentation hold
segments. Above 700C, the observed creep exponents match the
temperature-dependence of literature values in CMSX-4. In Amdry-386,
nanoindentation produces creep exponents very close to literature data,
implying high-temperature nanoindentation may be powerful in characterising
these coatings and providing inputs for material, model and process
optimisations
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Rare variants contribute disproportionately to quantitative trait variation in yeast.
How variants with different frequencies contribute to trait variation is a central question in genetics. We use a unique model system to disentangle the contributions of common and rare variants to quantitative traits. We generated ~14,000 progeny from crosses among 16 diverse yeast strains and identified thousands of quantitative trait loci (QTLs) for 38 traits. We combined our results with sequencing data for 1011 yeast isolates to show that rare variants make a disproportionate contribution to trait variation. Evolutionary analyses revealed that this contribution is driven by rare variants that arose recently, and that negative selection has shaped the relationship between variant frequency and effect size. We leveraged the structure of the crosses to resolve hundreds of QTLs to single genes. These results refine our understanding of trait variation at the population level and suggest that studies of rare variants are a fertile ground for discovery of genetic effects
Severe Lumbar Disability Is Associated With Decreased Psoas Cross-Sectional Area in Degenerative Spondylolisthesis
Study Design: Retrospective cohort. Objectives: Alterations in lumbar paraspinal muscle cross-sectional area (CSA) may correlate with lumbar pathology. The purpose of this study was to compare paraspinal CSA in patients with degenerative spondylolisthesis and severe lumbar disability to those with mild or moderate lumbar disability, as determined by the Oswestry Disability Index (ODI). Methods: We retrospectively reviewed the medical records of 101 patients undergoing lumbar fusion for degenerative spondylolisthesis. Patients were divided into ODI score ≤40 (mild/moderate disability, MMD) and ODI score \u3e40 (severe disability, SD) groups. The total CSA of the psoas and paraspinal muscles were measured on preoperative magnetic resonance imaging (MRI). Results: There were 37 patients in the SD group and 64 in the MMD group. Average age and body mass index were similar between groups. For the paraspinal muscles, we were unable to demonstrate any significant differences in total CSA between the groups. Psoas muscle CSA was significantly decreased in the SD group compared with the MMD group (1010.08 vs 1178.6 mm2, P =.041). Multivariate analysis found that psoas CSA in the upper quartile was significantly protective against severe disability (P =.013). Conclusions: We found that patients with severe lumbar disability had no significant differences in posterior lumbar paraspinal CSA when compared with those with mild/moderate disability. However, severely disabled patients had significantly decreased psoas CSA, and larger psoas CSA was strongly protective against severe disability, suggestive of a potential association with psoas atrophy and worsening severity of lumbar pathology. © The Author(s) 2018
Novel Small Leucine-Rich Protein Chondroadherin-like (CHADL) is Expressed in Cartilage and Modulates Chondrocyte Differentiation.
The constitution and biophysical properties of extracellular matrices can dramatically influence cellular phenotype during development, homeostasis, or pathogenesis. These effects can be signaled through a differentially regulated assembly of collagen fibrils, orchestrated by a family of collagen-associated Small Leucine-Rich Proteins, SLRPs. In this report, we describe the tissue-specific expression and function of a previously uncharacterized SLRP Chondroadherin-like (CHADL). We have developed antibodies against CHADL and, by immunohistochemistry, detected CHADL expression mainly in skeletal tissues, particularly in fetal cartilage and in pericellular space of adult chondrocytes. In situ hybridizations and immunoblots on tissue lysates confirmed this tissue-specific expression pattern. Recombinant CHADL bound collagen in cell culture, and inhibited in vitro collagen fibrillogenesis. After Chadl shRNA knockdown chondrogenic ATDC5 cells increased their proliferation and differentiation, indicated by increased transcript levels of Sox9, Ihh, Col2a1, and Col10a1. The knockdown increased collagen II and aggrecan deposition in the cell layers. Microarray analysis of the knockdown samples suggested collagen receptor-related changes, although other upstream effects could not be excluded. Together, our data indicate that the novel SLRP CHADL is expressed in cartilaginous tissues, influences collagen fibrillogenesis, and modulates chondrocyte proliferation and differentiation. CHADL appears to have a negative regulatory role, possibly ensuring the formation of a stable extracellular matrix
Integrating Brain and Biomechanical Models—A New Paradigm for Understanding Neuro-muscular Control
To date, realistic models of how the central nervous system governs behavior have been restricted in scope to the brain, brainstem or spinal column, as if these existed as disembodied organs. Further, the model is often exercised in relation to an in vivo physiological experiment with input comprising an impulse, a periodic signal or constant activation, and output as a pattern of neural activity in one or more neural populations. Any link to behavior is inferred only indirectly via these activity patterns. We argue that to discover the principles of operation of neural systems, it is necessary to express their behavior in terms of physical movements of a realistic motor system, and to supply inputs that mimic sensory experience. To do this with confidence, we must connect our brain models to neuro-muscular models and provide relevant visual and proprioceptive feedback signals, thereby closing the loop of the simulation. This paper describes an effort to develop just such an integrated brain and biomechanical system using a number of pre-existing models. It describes a model of the saccadic oculomotor system incorporating a neuromuscular model of the eye and its six extraocular muscles. The position of the eye determines how illumination of a retinotopic input population projects information about the location of a saccade target into the system. A pre-existing saccadic burst generator model was incorporated into the system, which generated motoneuron activity patterns suitable for driving the biomechanical eye. The model was demonstrated to make accurate saccades to a target luminance under a set of environmental constraints. Challenges encountered in the development of this model showed the importance of this integrated modeling approach. Thus, we exposed shortcomings in individual model components which were only apparent when these were supplied with the more plausible inputs available in a closed loop design. Consequently we were able to suggest missing functionality which the system would require to reproduce more realistic behavior. The construction of such closed-loop animal models constitutes a new paradigm of computational neurobehavior and promises a more thoroughgoing approach to our understanding of the brain’s function as a controller for movement and behavior
Complex Radio Spectral Energy Distributions in Luminous and Ultraluminous Infrared Galaxies
We use the Expanded Very Large Array to image radio continuum emission from
local luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) in 1 GHz
windows centered at 4.7, 7.2, 29, and 36 GHz. This allows us to probe the
integrated radio spectral energy distribution (SED) of the most energetic
galaxies in the local universe. The 4-8 GHz flux densities agree well with
previous measurements. They yield spectral indices \alpha \approx -0.67 (where
F_\nu \propto \nu^\alpha) with \pm 0.15 (1\sigma) scatter, typical of
nonthermal (synchrotron) emission from star-forming galaxies. The contrast of
our 4-8 GHz data with literature 1.5 and 8.4 GHz flux densities gives further
evidence for curvature of the radio SED of U/LIRGs. The SED appears flatter
near \sim 1 GHz than near \sim 6 GHz, suggesting significant optical depth
effects at the lower frequencies. The high frequency (28-37 GHz) flux densities
are low compared to extrapolations from the 4-8 GHz data. We confirm and extend
to higher frequency a previously observed deficit of high frequency radio
emission for luminous starburst galaxies.Comment: 7 pages, 3 figures, 1 table, accepted for publication in the EVLA
Special Issue of ApJ Letter
Angle-dependence of quantum oscillations in YBa2Cu3O6.59 shows free spin behaviour of quasiparticles
Measurements of quantum oscillations in the cuprate superconductors afford a
new opportunity to assess the extent to which the electronic properties of
these materials yield to a description rooted in Fermi liquid theory. However,
such an analysis is hampered by the small number of oscillatory periods
observed. Here we employ a genetic algorithm to globally model the field,
angular, and temperature dependence of the quantum oscillations observed in the
resistivity of YBa2Cu3O6.59. This approach successfully fits an entire data set
to a Fermi surface comprised of two small, quasi-2-dimensional cylinders. A key
feature of the data is the first identification of the effect of Zeeman
splitting, which separates spin-up and spin-down contributions, indicating that
the quasiparticles in the cuprates behave as nearly free spins, constraining
the source of the Fermi surface reconstruction to something other than a
conventional spin density wave with moments parallel to the CuO2 planes.Comment: 8 pages, 4 figure
Hard and soft news: A review of concepts, operationalizations and key findings
Over 30 years, a large body of research on what is often called ‘hard’ and ‘soft news’ has accumulated in communication studies. However, there is no consensus about what hard and soft news exactly is, or how it should be defined or measured. Moreover, the concept has not been clearly differentiated from or systematically related to concepts addressing very similar phenomena – tabloidization and ‘infotainment’. Consequently, the results of various studies are hard to compare and different scientific discourses on related issues remain unconnected. Against this backdrop, this article offers a conceptual analysis of the concept based on studies in English and other languages. We identify key dimensions of the concept and make suggestions for a standardized definition and multi-dimensional measurement of harder and softer news. In doing so, we propose to distinguish thematic, focus and style features as basic dimensions that – in their combination – make up harder and softer types of news
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