10,159 research outputs found
Influence of Superabsorbent Polymers on Properties of High-Performance Concrete with Active Supplementary Cementitious Materials of Nigeria
Concrete of strengths classes ≥ C55/67 referred to as high strength or highperformance
concrete (HSC/HPC) are noted to be generally of low water/binder
(W/B), made from binary or ternary cements with silica fume (SF) being a necessary
constituent, and often requiring internal curing. Non-availability and high cost of SF in
most sub-Saharan Africa like Nigeria however makes HSC/HPC production in this
region very difficult and hence the continued search for alternative supplementary
cementitious materials (SCM) with good performance properties as constituents of
ternary/binary cements in HPC. This study thereby examines the strength properties of
metastable calcined clay (MCC) based HPC cured internally with superabsorbent
polymer (SAP) 0.2–0.3% (by weight of binder (bwob)). HPC mixtures of varied MCC and
Rice husk ash (RHA) contents containing two SAP grain sizes labelled (SP1 ˂ 300 μm
and SP2 ˂ 600 μm) were cast in 100 mm cubes and cured for varying ages (7, 14, 28 and
56 days) before testing. The hardened specimens were subjected to compressive
strength and water absorption tests at the varied curing ages for the performance
assessment of the binder types and SAP grain sizes in HPC with age. This study
revealed the possibility of achieving Class 1 HPC (50–75 N/mm2) utilizing industry
manufactured calcined clay and locally produced RHA in Nigeria. The compressive
strength of HPCs increased as the curing age increases for both SCM type, SAP contents
and grain sizes. RHA based HPCs however showed better strength performance at the early ages than the MCC based. SAP addition in MCC based HPCs led to slight decrease
in compressive strength as the SAP contents increased while the RHA based HPCs on
the other hand, revealed slight increase in compressive strength with increase in SAP
contents
Approach of describing dynamic production of volatile fatty acids from sludge alkaline fermentation
© 2017 Elsevier Ltd In this work, a mathematical model was developed to describe the dynamics of fermentation products in sludge alkaline fermentation systems for the first time. In this model, the impacts of alkaline fermentation on sludge disintegration, hydrolysis, acidogenesis, acetogenesis, and methanogenesis processes are specifically considered for describing the high-level formation of fermentation products. The model proposed successfully reproduced the experimental data obtained from five independent sludge alkaline fermentation studies. The modeling results showed that alkaline fermentation largely facilitated the disintegration, acidogenesis, and acetogenesis processes and severely inhibited methanogenesis process. With the pH increase from 7.0 to 10.0, the disintegration, acidogenesis, and acetogenesis processes respectively increased by 53%, 1030%, and 30% while methane production decreased by 3800%. However, no substantial effect on hydrolysis process was found. The model also indicated that the pathway of acetoclastic methanogenesis was more severely inhibited by alkaline condition than that of hydrogentrophic methanogenesis
Mitochondrial targeting adaptation of the hominoid-specific glutamate dehydrogenase driven by positive Darwinian selection
Many new gene copies emerged by gene duplication in hominoids, but little is known with respect to their functional evolution. Glutamate dehydrogenase (GLUD) is an enzyme central to the glutamate and energy metabolism of the cell. In addition to the single, GLUD-encoding gene present in all mammals (GLUD1), humans and apes acquired a second GLUD gene (GLUD2) through retroduplication of GLUD1, which codes for an enzyme with unique, potentially brain-adapted properties. Here we show that whereas the GLUD1 parental protein localizes to mitochondria and the cytoplasm, GLUD2 is specifically targeted to mitochondria. Using evolutionary analysis and resurrected ancestral protein variants, we demonstrate that the enhanced mitochondrial targeting specificity of GLUD2 is due to a single positively selected glutamic acid-to-lysine substitution, which was fixed in the N-terminal mitochondrial targeting sequence (MTS) of GLUD2 soon after the duplication event in the hominoid ancestor ~18–25 million years ago. This MTS substitution arose in parallel with two crucial adaptive amino acid changes in the enzyme and likely contributed to the functional adaptation of GLUD2 to the glutamate metabolism of the hominoid brain and other tissues. We suggest that rapid, selectively driven subcellular adaptation, as exemplified by GLUD2, represents a common route underlying the emergence of new gene functions
Improved annotation of 3' untranslated regions and complex loci by combination of strand-specific direct RNA sequencing, RNA-seq and ESTs
The reference annotations made for a genome sequence provide the framework
for all subsequent analyses of the genome. Correct annotation is particularly
important when interpreting the results of RNA-seq experiments where short
sequence reads are mapped against the genome and assigned to genes according to
the annotation. Inconsistencies in annotations between the reference and the
experimental system can lead to incorrect interpretation of the effect on RNA
expression of an experimental treatment or mutation in the system under study.
Until recently, the genome-wide annotation of 3-prime untranslated regions
received less attention than coding regions and the delineation of intron/exon
boundaries. In this paper, data produced for samples in Human, Chicken and A.
thaliana by the novel single-molecule, strand-specific, Direct RNA Sequencing
technology from Helicos Biosciences which locates 3-prime polyadenylation sites
to within +/- 2 nt, were combined with archival EST and RNA-Seq data. Nine
examples are illustrated where this combination of data allowed: (1) gene and
3-prime UTR re-annotation (including extension of one 3-prime UTR by 5.9 kb);
(2) disentangling of gene expression in complex regions; (3) clearer
interpretation of small RNA expression and (4) identification of novel genes.
While the specific examples displayed here may become obsolete as genome
sequences and their annotations are refined, the principles laid out in this
paper will be of general use both to those annotating genomes and those seeking
to interpret existing publically available annotations in the context of their
own experimental dataComment: 44 pages, 9 figure
An integrated approach to determine left atrial volume, mass and function in hypertrophic cardiomyopathy by two-dimensional echocardiography
Methods: The study included 25 hypertrophic cardiomyopathy (HCM) patients (15 non-obstructive and 10 obstructive) and 25 controls for assessment of left atrial (LA) volume, mass and function by two-dimensional echocardiography. Measurement included mean LA diameter (LAD), LA mass = {(mean LAD + anterior LA wall + posterior LA wall)3- mean LAD3} × 0.8 + 0.6, LA volume = [(8/3 φ L ̇ A1 ̇ A2), where L is LA length, A1 and A2 are LA area in 4-chambers and 2-chambers, respectively] including maximum (Vmax), minimum (Vmin), and pre-atrial contraction (Vpre-A), total atrial stroke volume (TA-SV), TA emptying fraction (TA-EF), active atrial SV (AA-SV), AA-EF, passive atrial SV (PA-SV), PA-EF, atrial expansion index (AEI), and LA kinetic energy (LA-KE) = 1/2 × AA-SV × P × V2. Results: LAD, LA mass, Vmax, Vmin, and Vpre-Awere significantly higher in HCM than controls. TA-SV and TA-EF were comparable in both HCM subgroups and controls. AA-SV and LA-KE were significantly higher in both HCM subgroups than controls. LA-KE was significantly higher in obstructive HCM than non-obstructive (P < 0.001). PA-EF and AEI were significantly lower in obstructive HCM than controls (P < 0.05). Conclusion: HCM is associated with increased LA size and augmented LA pump function especially obstructive type. LA conduit and reservoir functions are impaired in obstructive HCM
Janus monolayers of transition metal dichalcogenides.
Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS2 monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements
On Bayesian Search for the Feasible Space Under Computationally Expensive Constraints
We are often interested in identifying the feasible subset of a decision space under multiple constraints to permit effective design exploration. If determining feasibility required computationally expensive simulations, the cost of exploration would be prohibitive. Bayesian search is data-efficient for such problems: starting from a small dataset, the central concept is to use Bayesian models of constraints with an acquisition function to locate promising solutions that may improve predictions of feasibility when the dataset is augmented. At the end of this sequential active learning approach with a limited number of expensive evaluations, the models can accurately predict the feasibility of any solution obviating the need for full simulations. In this paper, we propose a novel acquisition function that combines the probability that a solution lies at the boundary between feasible and infeasible spaces (representing exploitation) and the entropy in predictions (representing exploration). Experiments confirmed the efficacy of the proposed function
Social Algorithms
This article concerns the review of a special class of swarm intelligence
based algorithms for solving optimization problems and these algorithms can be
referred to as social algorithms. Social algorithms use multiple agents and the
social interactions to design rules for algorithms so as to mimic certain
successful characteristics of the social/biological systems such as ants, bees,
bats, birds and animals.Comment: Encyclopedia of Complexity and Systems Science, 201
Increased insolation threshold for runaway greenhouse processes on Earth like planets
Because the solar luminosity increases over geological timescales, Earth
climate is expected to warm, increasing water evaporation which, in turn,
enhances the atmospheric greenhouse effect. Above a certain critical
insolation, this destabilizing greenhouse feedback can "runaway" until all the
oceans are evaporated. Through increases in stratospheric humidity, warming may
also cause oceans to escape to space before the runaway greenhouse occurs. The
critical insolation thresholds for these processes, however, remain uncertain
because they have so far been evaluated with unidimensional models that cannot
account for the dynamical and cloud feedback effects that are key stabilizing
features of Earth's climate. Here we use a 3D global climate model to show that
the threshold for the runaway greenhouse is about 375 W/m, significantly
higher than previously thought. Our model is specifically developed to quantify
the climate response of Earth-like planets to increased insolation in hot and
extremely moist atmospheres. In contrast with previous studies, we find that
clouds have a destabilizing feedback on the long term warming. However,
subsident, unsaturated regions created by the Hadley circulation have a
stabilizing effect that is strong enough to defer the runaway greenhouse limit
to higher insolation than inferred from 1D models. Furthermore, because of
wavelength-dependent radiative effects, the stratosphere remains cold and dry
enough to hamper atmospheric water escape, even at large fluxes. This has
strong implications for Venus early water history and extends the size of the
habitable zone around other stars.Comment: Published in Nature. Online publication date: December 12, 2013.
Accepted version before journal editing and with Supplementary Informatio
A Convolutional Approach to Vertebrae Detection and Labelling in Whole Spine MRI
We propose a novel convolutional method for the detection and identification
of vertebrae in whole spine MRIs. This involves using a learnt vector field to
group detected vertebrae corners together into individual vertebral bodies and
convolutional image-to-image translation followed by beam search to label
vertebral levels in a self-consistent manner. The method can be applied without
modification to lumbar, cervical and thoracic-only scans across a range of
different MR sequences. The resulting system achieves 98.1% detection rate and
96.5% identification rate on a challenging clinical dataset of whole spine
scans and matches or exceeds the performance of previous systems on lumbar-only
scans. Finally, we demonstrate the clinical applicability of this method, using
it for automated scoliosis detection in both lumbar and whole spine MR scans.Comment: Accepted full paper to Medical Image Computing and Computer Assisted
Intervention 2020. 11 pages plus appendi
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