Predicting Mechanical Properties of High-Performance Fiber-Reinforced Cementitious Composites by Integrating Micromechanics and Machine Learning.

Current development of high-performance fiber-reinforced cementitious composites (HPFRCC) mainly relies on intensive experiments. The main purpose of this study is to develop a machine learning method for effective and efficient discovery and development of HPFRCC. Specifically, this research develops machine learning models to predict the mechanical properties of HPFRCC through innovative incorporation of micromechanics, aiming to increase the prediction accuracy and generalization performance by enriching and improving the datasets through data cleaning, principal component analysis (PCA), and K-fold cross-validation. This study considers a total of 14 different mix design variables and predicts the ductility of HPFRCC for the first time, in addition to the compressive and tensile strengths. Different types of machine learning methods are investigated and compared, including artificial neural network (ANN), support vector regression (SVR), classification and regression tree (CART), and extreme gradient boosting tree (XGBoost). The results show that the developed machine learning models can reasonably predict the concerned mechanical properties and can be applied to perform parametric studies for the effects of different mix design variables on the mechanical properties. This study is expected to greatly promote efficient discovery and development of HPFRCC.

Hydraulic conductivity and self-healing performance of Engineered Cementitious Composites exposed to Acid Mine Drainage.

Engineered Cementitious Composite (ECC) is proposed as a promising vertical cutoff wall material to contain acid mine drainage (AMD). The study presents comprehensive investigations of hydraulic conductivity of ECC permeated with AMD and self-healing of ECC subjected to wet-dry cycles. The effectiveness of incorporating reactive magnesia (MgO) into ECC for self-healing enhancement is also investigated. The chemical species formed in ECC and MgO-ECC specimens after exposure to AMD are investigated via SEM, FTIR, XRD and TGA analyses. The results show hydraulic conductivity of un-cracked and cracked ECC and MgO-ECC specimens pre-strained up to 1.32% is below commonly accepted limits of 10-8 m/s when permeated with AMD. The self-healing capacity of ECC specimens subjected to wet-dry cycles using both tap water and AMD as immersing liquids is improved by MgO addition. MgO addition is also beneficial for reducing hydraulic conductivity of un-cracked and cracked ECC specimens permeated with AMD. MgO addition results formation of new self-healing products including hydromagnesite and brucite when exposed to tap water, and hydrotalcite-like phase (Ht) when exposed to AMD.

Mouse embryonic stem cells can differentiate via multiple paths to the same state.

In embryonic development, cells differentiate through stereotypical sequences of intermediate states to generate particular mature fates. By contrast, driving differentiation by ectopically expressing terminal transcription factors (direct programming) can generate similar fates by alternative routes. How differentiation in direct programming relates to embryonic differentiation is unclear. We applied single-cell RNA sequencing to compare two motor neuron differentiation protocols: a standard protocol approximating the embryonic lineage, and a direct programming method. Both initially undergo similar early neural commitment. Later, the direct programming path diverges into a novel transitional state rather than following the expected embryonic spinal intermediates. The novel state in direct programming has specific and uncharacteristic gene expression. It forms a loop in gene expression space that converges separately onto the same final motor neuron state as the standard path. Despite their different developmental histories, motor neurons from both protocols structurally, functionally, and transcriptionally resemble motor neurons isolated from embryos.

Molecular ties between the cell cycle and differentiation in embryonic stem cells.

Attainment of the differentiated state during the final stages of somatic cell differentiation is closely tied to cell cycle progression. Much less is known about the role of the cell cycle at very early stages of embryonic development. Here, we show that molecular pathways involving the cell cycle can be engineered to strongly affect embryonic stem cell differentiation at early stages in vitro. Strategies based on perturbing these pathways can shorten the rate and simplify the lineage path of ES differentiation. These results make it likely that pathways involving cell proliferation intersect at various points with pathways that regulate cell lineages in embryos and demonstrate that this knowledge can be used profitably to guide the path and effectiveness of cell differentiation of pluripotent cells.

Self-Healing of Microcracks in Engineered Cementitious Composites (ECC) Under a Natural Environment.

This paper builds on previous self-healing engineered cementitious composites (ECC) research by allowing ECC to heal outdoors, in the natural environment, under random and sometimes extreme environmental conditions. Development of an ECC material that can heal itself in the natural environment could lower infrastructure maintenance costs and allow for more sustainable development in the future by increasing service life and decreasing the amount of resources and energy needed for repairs. Determining to what extent current ECC materials self-heal in the natural environment is the first step in the development of an ECC that can completely heal itself when exposed to everyday environmental conditions. This study monitored outdoor ECC specimens for one year using resonant frequency (RF) and mechanical reloading to determine the rate and extent of self-healing in the natural environment. It was found that the level of RF, stiffness, and first cracking strength recovery increased as the duration of natural environment exposure increased. For specimens that underwent multiple damage cycles, it was found that the level of recovery was highly dependent on the average temperature and amount of precipitation between each damage event. However, RF, stiffness, and first cracking strength recovery data for specimens that underwent multiple loading cycles suggest that self-healing functionality can be maintained under multiple damage events.

Gap 1 phase length and mouse embryonic stem cell self-renewal.

In somatic cells, the length of the G1 phase of the cell cycle is tightly linked to differentiation, and its elongation can drive differentiation in many cases. Although it has been suggested that the situation is very similar in embryonic stem cells (ESCs), where a rapid cell cycle and a short G1 phase maintain the pluripotent state, evidence has been contradictory. Here we show that, in murine ESCs, elongation of the cell cycle and elongation of G1 are compatible with their pluripotent state. Multiple methods that lengthen the cell cycle and that target cyclin-dependent kinase, retinoblastoma protein, and E2F activity all fail to induce differentiation on their own or even to facilitate differentiation. The resistance of murine ESCs to differentiation induced by lengthening G1 and/or the cell cycle could allow for separate control of these events and provide new opportunities for investigation and application.

Molecular evolution of the testis TAFs of Drosophila.

The basal transcription machinery is responsible for initiating transcription at core promoters. During metazoan evolution, its components have expanded in number and diversified to increase the complexity of transcriptional regulation in tissues and developmental stages. To explore the evolutionary events and forces underlying this diversification, we analyzed the evolution of the Drosophila testis TAFs (TBP-associated factors), paralogs of TAFs from the basal transcription factor TFIID that are essential for normal transcription during spermatogenesis of a large set of specific genes involved in terminal differentiation of male gametes. There are five testis-specific TAFs in Drosophila, each expressed only in primary spermatocytes and each a paralog of a different generally expressed TFIID subunit. An examination of the presence of paralogs across taxa as well as molecular clock dating indicates that all five testis TAFs likely arose within a span of approximately 38 My 63-250 Ma by independent duplication events from their generally expressed paralogs. Furthermore, the evolution of the testis TAFs has been rapid, with apparent further accelerations in multiple Drosophila lineages. Analysis of between-species divergence and intraspecies polymorphism indicates that the major forces of evolution on these genes have been reduced purifying selection, pervasive positive selection, and coevolution. Other genes that exhibit similar patterns of evolution in the Drosophila lineages are also characterized by enriched expression in the testis, suggesting that the pervasive positive selection acting on the tTAFs is likely to be related to their expression in the testis.