Understanding the role of calcium on the reaction mechanism of geopolymer cements through addition of nucleation seeds

Geopolymer cement is an innovative binder proposed by Davidovits as an alternative to conventional Portland cements for construction use. It is made from minimally processed industrial byproducts (fly ash, slag) activated by a low concentration alkaline solution (Na, K) and cured at room temperature. The use of low concentration alkaline activators (2 M), unlike the high concentration used for conventional geopolymer binders (8-12 M), makes these cements environmentally friendly (using industrial waste products) and user-friendly. Geopolymer cements gain strength quite rapidly and have been formulated to achieve nearly 100 MPa in 28 days, however, at the cost of low workability. The loss of workability is usually attributed to the presence of free calcium. It is predicted that calcium silicate hydrate/calcium aluminosilicate hydrate gel (C-S-H/C-A-S-H, a main binding phase of fly ash modified Portland cements binder) and aluminosilicate gel ((Na,K)-A-S-H, a main binding phase in geopolymer binders) co-exist in these systems. The precipitation of C-S-H/C-A-S-H is known to initiate the rapid hardening which then is hypothesized to act as a nucleation site for the precipitation of aluminosilicate gel. This study verified the hypothesis through the addition of synthesized C-S-H/C-A-S-H as an external seed during the processing of geopolymer cement. Isothermal conduction calorimetry, scanning electron microscopy, shear wave ultrasonic wave reflection method, and Fourier Transform Infrared spectroscopy are employed to study the effects of seed on reaction kinetics, extent of product formation, nature of reaction products, and dissolution of raw materials. Through the addition of seeds, it has been concluded that the reaction mechanism in fly ash-slag cements depends on the activator solution. In hydroxide activated fly ash-slag geopolymers, the rate controlling step is the nucleation-growth controlled reaction, early age hardening behavior in these systems can be controlled via mechanisms that increases or decreases the rate of nucleation and growth of C-S-H. The reaction can be accelerated by adding synthesized C-S-H seed or a small percentage of nanoparticles which will promote nucleation of the product in the pore space. In silicate activated systems, the rate determining step is gelation which depends exclusively on the extent and the rate of aluminosilicate oligomers formation in the solution. Any factor that will affect the availability of silicate species or the rate of aluminosilicate oligomer formation will effect the reaction mechanism. Retarders that will selectively polymerize with silicate species in the pore solution can be used to develop retardation in these cements. The addition of nucleation seeds to study reaction kinetics is shown to effectively capture the shift in the reaction mechanism from nucleation-growth controlled to the gelation with varying silica concentration in the solution. The protocol developed in the study to separate the responses of two amorphous gels (C-A-S-H and (Na,K)-A-S-H) from the amorphous precursors can be extended to understand the structural evolution of phases in other alkali activated blends of complex chemistry. The fundamental understanding gained through this research can pave a way for large-scale adaptation of alkaline cement technology. The research output will enable engineers to understand the early age reaction mechanism, the knowledge of which will provide greater control over the length of induction period, setting time, and workability of geopolymer cements. Research will provide a unique tool for tailoring the nanostructure of the reaction products through the addition of synthetic seeds for optimizing engineering performance

Deep Multilayer Convolution Frameworks for Data-Driven Learning of Nonlinear Dynamics in Fluid Flows

Abundance of measurement and simulation data has led to the proliferation of machine learning tools for model-based analysis and prediction of fluid flows over the past few years. In this work we explore globally optimal multilayer convolution models such as feed forward neural-networks (FFNN) for learning and predicting dynamics from transient fluid flow data. While machine learning in general depends on data quality relative to the underlying dynamics of the system, it is important for a given data-driven learning architecture to make the most of this available information. To this end, we cast the suite of recently popular data-driven learning approaches that approximate Markovian dynamics through a linear model in a higher-dimensional feature space as a multilayer architecture similar to neural networks, but with layer-wise locally optimal convolution mappings. As a contrast, we also represent the traditional neural networks with some slight modifications as a multilayer architecture, with convolution maps optimized to minimize the global learning cost (i.e., not the cost of learning across two immediate layers). We show through examples of data-driven learning of canonical fluid flows that globally optimal FFNN-like methods owe their success to leveraging the extended learning parameter space available in multilayer models to achieve a common goal of minimizing the training cost function while incorporating nonlinear function maps between layers. On the other hand, locally optimal multilayer models also show improvement from the same factors, but behave like shallow neural networks requiring much larger hidden layers to achieve comparable learning and prediction accuracy. While locally optimal methods allow for forward-backward convolutions, the standard globally optimal FFNNs can only handle forward maps which prevent their use as Koopman approximation tools. To this end we developed novel deep learning neural network architecture, deep Koopman network which overcome this limitation of symmetry by addition of penalty network. Further, we explored the feasibility of deep autoencoder networks (DAENs) as data-driven mappings into the observable space where the dynamics of the system can be approximated as a linear time-invariant (LTI) system. The eigenmodes and the eigenvalues of the Koopman operator provide information about the structures in the data that are associated with their unique growth rate and frequency. Naturally, the relevance of these structures and eigenvalues to the real system represented by the data is tied to how closely the Markov Linear or Koopman operator-based model approximates the real dynamics, which, in turn depends on the choice of observable. Traditional approaches for non-local optimization such as those in neural networks and deep learning are gradient-based and hence, limited to convolution basis functions whose derivatives are either known or computed accurately using numerical means. To realize the full potential of this deep learning framework, these algorithms need to be extended to arbitrary choice of convolution basis. To this end, we explored the use of gradient free optimization techniques for learning using a wider choice of functions. we illustrate these ideas by learning the dynamics from snapshots of training data and predicting the temporal evolution of canonical nonlinear fluid flows including the transient limit-cycle attractor in a cylinder wake and the instability-driven dynamics of buoyant Boussinesq flow.Mechanical and Aerospace Engineerin

Role of bone morphogenetic proteins on cochlear hair cell formation: Analyses of Noggin and Bmp2 mutant mice

The mammalian organ of Corti of the inner ear is a highly sophisticated sensory end organ responsible for detecting sound. Noggin is a secreted glycoprotein, which antagonizes bone morphogenetic proteins 2 and 4 (Bmp2 and Bmp4). The lack of this antagonist causes increased rows of inner and outer hair cells in the organ of Corti. In mice, Bmp2 is expressed transiently in nascent cochlear hair cells. To investigate whether Noggin normally modulates the levels of Bmp2 for hair cell formation, we deleted Bmp2 in the cochlear hair cells using two cre strains, Foxg1 cre /+ and Gfi1 cre /+ . Bmp2 conditional knockout cochleae generated using these two cre strains show normal hair cells. Furthermore, Gfi1 cre /+ ; Bmp2 lox /− mice are viable and have largely normal hearing. The combined results of Noggin and Bmp2 mutants suggest that Noggin is likely to regulate other Bmps in the cochlea such as Bmp4. Developmental Dynamics 239:505–513, 2010. Published 2010 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64918/1/22200_ftp.pd

Fgfr3 Is a Transcriptional Target of Ap2δ and Ash2l-Containing Histone Methyltransferase Complexes

Polycomb (PcG) and trithorax (trxG) proteins play important roles in establishing lineage-specific genetic programs through induction of chromatin modifications that lead to gene silencing or activation. Previously, we described an association between the MLL/SET1 complexes and a highly restricted, gene-specific DNA-binding protein Ap2δ that is required for recruitment of the MLL/SET1 complex to target Hoxc8 specifically. Here, we reduced levels of Ap2δ and Ash2l in the neuroblastoma cell line, Neuro2A, and analyzed their gene expression profiles using whole-genome mouse cDNA microarrays. This analysis yielded 42 genes that are potentially co-regulated by Ap2δ and Ash2l, and we have identified evolutionarily conserved Ap2-binding sites in 20 of them. To determine whether some of these were direct targets of the Ap2δ-Ash2l complex, we analyzed several promoters for the presence of Ap2δ and Ash2l by chromatin immunoprecipitation (ChIP). Among the targets we screened, we identified Fgfr3 as a direct transcriptional target of the Ap2δ-Ash2l complex. Additionally, we found that Ap2δ is necessary for the recruitment of Ash2l-containing complexes to this promoter and that this recruitment leads to trimethylation of lysine 4 of histone H3 (H3K4me3). Thus, we have identified several candidate targets of complexes containing Ap2δ and Ash2l that can be used to further elucidate their roles during development and showed that Fgfr3 is a novel direct target of these complexes

Hearing loss in a mouse model of Muenke syndrome

The heterozygous Pro250Arg substitution mutation in fibroblast growth factor receptor 3 (FGFR3), which increases ligand-dependent signalling, is the most common genetic cause of craniosynostosis in humans and defines Muenke syndrome. Since FGF signalling plays dosage-sensitive roles in the differentiation of the auditory sensory epithelium, we evaluated hearing in a large group of Muenke syndrome subjects, as well as in the corresponding mouse model (Fgfr3P244R). The Muenke syndrome cohort showed significant, but incompletely penetrant, predominantly low-frequency sensorineural hearing loss, and the Fgfr3P244R mice showed dominant, fully penetrant hearing loss that was more severe than that in Muenke syndrome individuals, but had the same pattern of relative high-frequency sparing. The mouse hearing loss correlated with an alteration in the fate of supporting cells (Deiters'-to-pillar cells) along the entire length of the cochlear duct, with the most extreme abnormalities found at the apical or low-frequency end. In addition, there was excess outer hair cell development in the apical region. We conclude that low-frequency sensorineural hearing loss is a characteristic feature of Muenke syndrome and that the genetically equivalent mouse provides an excellent model that could be useful in testing hearing loss therapies aimed at manipulating the levels of FGF signalling in the inner ear

Neurod1 Suppresses Hair Cell Differentiation in Ear Ganglia and Regulates Hair Cell Subtype Development in the Cochlea

Background: At least five bHLH genes regulate cell fate determination and differentiation of sensory neurons, hair cells and supporting cells in the mammalian inner ear. Cross-regulation of Atoh1 and Neurog1 results in hair cell changes in Neurog1 null mice although the nature and mechanism of the cross-regulation has not yet been determined. Neurod1, regulated by both Neurog1 and Atoh1, could be the mediator of this cross-regulation. Methodology/Principal Findings: We used Tg(Pax2-Cre) to conditionally delete Neurod1 in the inner ear. Our data demonstrate for the first time that the absence of Neurod1 results in formation of hair cells within the inner ear sensory ganglia. Three cell types, neural crest derived Schwann cells and mesenchyme derived fibroblasts (neither expresses Neurod1) and inner ear derived neurons (which express Neurod1) constitute inner ear ganglia. The most parsimonious explanation is that Neurod1 suppresses the alternative fate of sensory neurons to develop as hair cells. In the absence of Neurod1, Atoh1 is expressed and differentiates cells within the ganglion into hair cells. We followed up on this effect in ganglia by demonstrating that Neurod1 also regulates differentiation of subtypes of hair cells in the organ of Corti. We show that in Neurod1 conditional null mice there is a premature expression of several genes in the apex of the developing cochlea and outer hair cells are transformed into inner hair cells. Conclusions/Significance: Our data suggest that the long noted cross-regulation of Atoh1 expression by Neurog1 migh

The histone demethylase LSD1 regulates inner ear progenitor differentiation through interactions with Pax2 and the NuRD repressor complex

The histone demethylase LSD1 plays a pivotal role in cellular differentiation, particularly in silencing lineage-specific genes. However, little is known about how LSD1 regulates neurosensory differentiation in the inner ear. Here we show that LSD1 interacts directly with the transcription factor Pax2 to form the NuRD co-repressor complex at the Pax2 target gene loci in a mouse otic neuronal progenitor cell line (VOT-N33). VOT-N33 cells expressing a Pax2-response element reporter were GFP-negative when untreated, but became GFP positive after forced differentiation or treatment with a potent LSD inhibitor. Pharmacological inhibition of LSD1 activity resulted in the enrichment of mono- and di-methylation of H3K4, upregulation of sensory neuronal genes and an increase in the number of sensory neurons in mouse inner ear organoids. Together, these results identify the LSD1/NuRD complex as a previously unrecognized modulator for Pax2-mediated neuronal differentiation in the inner ear

The Prosensory Function of Sox2 in the Chicken Inner Ear Relies on the Direct Regulation of Atoh1

The proneural gene Atoh1 is crucial for the development of inner ear hair cells and it requires the function of the transcription factor Sox2 through yet unknown mechanisms. In the present work, we used the chicken embryo and HEK293T cells to explore the regulation of Atoh1 by Sox2. The results show that hair cells derive from Sox2-positive otic progenitors and that Sox2 directly activates Atoh1 through a transcriptional activator function that requires the integrity of Sox2 DNA binding domain. Atoh1 activation depends on Sox transcription factor binding sites (SoxTFBS) present in the Atoh1 3′ enhancer where Sox2 directly binds, as shown by site directed mutagenesis and chromatin immunoprecipitation (ChIP). In the inner ear, Atoh1 enhancer activity is detected in the neurosensory domain and it depends on Sox2. Dominant negative competition (Sox2HMG-Engrailed) and mutation of the SoxTFBS abolish the reporter activity in vivo. Moreover, ChIP assay in isolated otic vesicles shows that Sox2 is bound to the Atoh1 enhancer in vivo. However, besides activating Atoh1, Sox2 also promotes the expression of Atoh1 negative regulators and the temporal profile of Atoh1 activation by Sox2 is transient suggesting that Sox2 triggers an incoherent feed-forward loop. These results provide a mechanism for the prosensory function of Sox2 in the inner ear. We suggest that sensory competence is established early in otic development through the activation of Atoh1 by Sox2, however, hair cell differentiation is prevented until later stages by the parallel activation of negative regulators of Atoh1 function