1,256 research outputs found
Use of coconut fibre as an enhancement of concrete
This research describes experimental studies on the use of coconut fibre as enhancement of concrete.
The addition of coconut-fibres significantly improved many of the engineering properties of the
concrete, notably torsion, toughness and tensile strength. The ability to resist cracking and spalling
were also enhanced. However, the addition of fibres adversely affected the compressive strength. When
coconut fibre was added to plain concrete, the torsional strength increased (by up to about 25%) as
well as the energy-absorbing capacity, but there is an optimum weight fraction (0.5% by weight of
cement) beyond which the torsional strength started to decrease again. Similar results were also
obtained for different fibre aspect ratios, where again results showed there was an optimum aspect ratio
(125). An increase in fibre weight fraction provided a consistent increase in ductility up to the optimum
content (0.5%) with corresponding fibre aspect ratio of 125. Overall the study has demonstrated that
addition of coconut fibre to concrete leads to improvement of concrete the toughness torsion and the
tensile stress, Further work is however ,required to assess the long term durability of concrete
enhanced with coconut fibres.
Scaling of information costs in firms
What a firm does is more revealing than how much it makes, but firms are
often described with economic metrics. Here, we characterize what firms read,
their information footprint, using a data set of hundreds of millions of
records of news articles accessed by employees in millions of firms. We relate
a firm's information footprint with economic variables, showing that the former
grows superlinearly with the latter. This exaggerates the classic Zipf's law
inequality in the economic size of firms and reveals an economy of scale with
respect to information. Second, we discover that the reading habits of firms
are of limited diversity. Firms above a certain size reduce the relative
diversity of information they consume, indicating the sudden onset of a
coordination cost. Third, we reconstruct the topic graph firms inhabit and
propose a simple model of firm growth in this space. Firms adhere to a mixed
strategy of local exploration and recurrent exploitation on the topic graph.
This strategy is costly, and we predict that firms consume a prodigious amount
of information over their lifetime because they cumulatively add to their
information portfolio instead of diversifying. This shows that the costs of
information and the structure of the space of ideas provide a useful but little
explored perspective on firm growth
High-Throughput Precision Phenotyping of Left Ventricular Hypertrophy with Cardiovascular Deep Learning
Left ventricular hypertrophy (LVH) results from chronic remodeling caused by
a broad range of systemic and cardiovascular disease including hypertension,
aortic stenosis, hypertrophic cardiomyopathy, and cardiac amyloidosis. Early
detection and characterization of LVH can significantly impact patient care but
is limited by under-recognition of hypertrophy, measurement error and
variability, and difficulty differentiating etiologies of LVH. To overcome this
challenge, we present EchoNet-LVH - a deep learning workflow that automatically
quantifies ventricular hypertrophy with precision equal to human experts and
predicts etiology of LVH. Trained on 28,201 echocardiogram videos, our model
accurately measures intraventricular wall thickness (mean absolute error [MAE]
1.4mm, 95% CI 1.2-1.5mm), left ventricular diameter (MAE 2.4mm, 95% CI
2.2-2.6mm), and posterior wall thickness (MAE 1.2mm, 95% CI 1.1-1.3mm) and
classifies cardiac amyloidosis (area under the curve of 0.83) and hypertrophic
cardiomyopathy (AUC 0.98) from other etiologies of LVH. In external datasets
from independent domestic and international healthcare systems, EchoNet-LVH
accurately quantified ventricular parameters (R2 of 0.96 and 0.90 respectively)
and detected cardiac amyloidosis (AUC 0.79) and hypertrophic cardiomyopathy
(AUC 0.89) on the domestic external validation site. Leveraging measurements
across multiple heart beats, our model can more accurately identify subtle
changes in LV geometry and its causal etiologies. Compared to human experts,
EchoNet-LVH is fully automated, allowing for reproducible, precise
measurements, and lays the foundation for precision diagnosis of cardiac
hypertrophy. As a resource to promote further innovation, we also make publicly
available a large dataset of 23,212 annotated echocardiogram videos
Cortical oxygen extraction fraction using quantitative BOLD MRI and cerebral blood flow during vasodilation
Introduction: We aimed to demonstrate non-invasive measurements of regional oxygen extraction fraction (OEF) from quantitative BOLD MRI modeling at baseline and after pharmacological vasodilation. We hypothesized that OEF decreases in response to vasodilation with acetazolamide (ACZ) in healthy conditions, reflecting compensation in regions with increased cerebral blood flow (CBF), while cerebral metabolic rate of oxygen (CMRO2) remained unchanged. We also aimed to assess the relationship between OEF and perfusion in the default mode network (DMN) regions that have shown associations with vascular risk factors and cerebrovascular reactivity in different neurological conditions. Material and methods: Eight healthy subjects (47 ± 13 years, 6 female) were scanned on a 3 T scanner with a 32-channel head coil before and after administration of 15 mg/kg ACZ as a pharmacological vasodilator. The MR imaging acquisition protocols included: 1) A Gradient Echo Slice Excitation Profile Imaging Asymmetric Spin Echo scan to quantify OEF, deoxygenated blood volume, and reversible transverse relaxation rate (R2 ’) and 2) a multi-post labeling delay arterial spin labeling scan to measure CBF. To assess changes in each parameter due to vasodilation, two-way t-tests were performed for all pairs (baseline versus vasodilation) in the DMN brain regions with Bonferroni correction for multiple comparisons. The relationships between CBF versus OEF and CBF versus R2’ were analyzed and compared across DMN regions using linear, mixed-effect models. Results: During vasodilation, CBF significantly increased in the medial frontal cortex ( P = 0.004 ), posterior cingulate gyrus (pCG) ( P = 0.004 ), precuneus cortex (PCun) ( P = 0.004 ), and occipital pole ( P = 0.001 ). Concurrently, a significant decrease in OEF was observed only in the pCG (8.8%, P = 0.003 ) and PCun ( 8.7 % , P = 0.001 ). CMRO2 showed a trend of increased values after vasodilation, but these differences were not significant after correction for multiple comparisons . Although R2’ showed a slightly decreasing trend, no statistically significant changes were found in any regions in response to ACZ. The CBF response to ACZ exhibited a stronger negative correlation with OEF ( β = − 0.104 ± 0.027 ; t = − 3.852 , P < 0.001 ), than with R2’ ( β = − 0.016 ± 0.006 ; t = − 2.692 , P = 0.008 ). Conclusion: Quantitative BOLD modeling can reliably measure OEF across multiple physiological conditions and captures vascular changes with higher sensitivity than R2’ values. The inverse correlation between OEF and CBF across regions in DMN, suggests that these two measurements, in response to ACZ vasodilation, are reliable indicators of tissue health in this healthy cohort
Small area contextual effects on self-reported health: Evidence from Riverside, Calgary
<p>Abstract</p> <p>Background</p> <p>We study geographic variation within one community in the City of Calgary using a more fine-grained geographic unit than the Census tract, the Census Dissemination Area (DA). While most Riverside residents consider their neighbourhood to be a fairly cohesive community, we explore the effect of socio-economic variation between these small geographic areas on individuals' self-reported health, net of individual level determinants.</p> <p>Methods</p> <p>We merge data from the 2001 Census for Riverside, Calgary with a 2004 random telephone survey of Riverside residents. Our data are unique in that we have information on individuals from every DA wholly contained in the Riverside community. These data enable us to conduct multinomial logistic regression analyses of self-reported health using both individual-level and DA-level variables as predictors.</p> <p>Results</p> <p>We find significant variation in measures of DA socio-economic status within the Riverside community. We find that individual self-reported health is affected by variation in an index of DA-level socio-economic disadvantage, controlling for individual variation in gender, age, and socio-economic status. We investigate each aspect of the DA index of disadvantage separately, and find that average education and the percent of households that are headed by a lone parent are most important.</p> <p>Conclusions</p> <p>These findings demonstrate that, even within a cohesive community, contextual effects on health can be located at a smaller geographic level than the Census tract. Research on the effects of local area socio-economic disadvantage on health that combines administrative and survey data enables researchers to develop more comprehensive measures of social and material deprivation. Our findings suggest that both social and material deprivation affect health at the local level.</p
Emodin Suppresses Migration and Invasion through the Modulation of CXCR4 Expression in an Orthotopic Model of Human Hepatocellular Carcinoma
10.1371/journal.pone.0057015PLoS ONE83
First M87 Event Horizon Telescope Results and the Role of ALMA
In April 2019, the Event Horizon Telescope (EHT) collaboration revealed the
first image of the candidate super-massive black hole (SMBH) at the centre of
the giant elliptical galaxy Messier 87 (M87). This event-horizon-scale image
shows a ring of glowing plasma with a dark patch at the centre, which is
interpreted as the shadow of the black hole. This breakthrough result, which
represents a powerful confirmation of Einstein's theory of gravity, or general
relativity, was made possible by assembling a global network of radio
telescopes operating at millimetre wavelengths that for the first time included
the Atacama Large Millimeter/ submillimeter Array (ALMA). The addition of ALMA
as an anchor station has enabled a giant leap forward by increasing the
sensitivity limits of the EHT by an order of magnitude, effectively turning it
into an imaging array. The published image demonstrates that it is now possible
to directly study the event horizon shadows of SMBHs via electromagnetic
radiation, thereby transforming this elusive frontier from a mathematical
concept into an astrophysical reality. The expansion of the array over the next
few years will include new stations on different continents - and eventually
satellites in space. This will provide progressively sharper and
higher-fidelity images of SMBH candidates, and potentially even movies of the
hot plasma orbiting around SMBHs. These improvements will shed light on the
processes of black hole accretion and jet formation on event-horizon scales,
thereby enabling more precise tests of general relativity in the truly strong
field regime.Comment: 11 pages + cover page, 6 figure
First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole
We present measurements of the properties of the central radio source in M87 using Event Horizon Telescope data obtained during the 2017 campaign. We develop and fit geometric crescent models (asymmetric rings with interior brightness depressions) using two independent sampling algorithms that consider distinct representations of the visibility data. We show that the crescent family of models is statistically preferred over other comparably complex geometric models that we explore. We calibrate the geometric model parameters using general relativistic magnetohydrodynamic (GRMHD) models of the emission region and estimate physical properties of the source. We further fit images generated from GRMHD models directly to the data. We compare the derived emission region and black hole parameters from these analyses with those recovered from reconstructed images. There is a remarkable consistency among all methods and data sets. We find that >50% of the total flux at arcsecond scales comes from near the horizon, and that the emission is dramatically suppressed interior to this region by a factor >10, providing direct evidence of the predicted shadow of a black hole. Across all methods, we measure a crescent diameter of 42 +/- 3 mu as and constrain its fractional width to be <0.5. Associating the crescent feature with the emission surrounding the black hole shadow, we infer an angular gravitational radius of GM/Dc(2) = 3.8 +/- 0.4 mu as. Folding in a distance measurement of 16.8(-0.7)(+0.8) gives a black hole mass of M = 6.5. 0.2 vertical bar(stat) +/- 0.7 vertical bar(sys) x 10(9) M-circle dot. This measurement from lensed emission near the event horizon is consistent with the presence of a central Kerr black hole, as predicted by the general theory of relativity
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