Rapid freezing of saturated clays under large thermal gradients

This study investigates the rapid freezing behavior of saturated clays under large thermal gradients. Although the freezing characteristics of soils under natural/low thermal gradients such as ice lens formation and water migration have been extensively studied, the freezing of a saturated soil under a large thermal gradient is not understood. This study presents rapid freezing tests to examine the freezing behavior of saturated fine-grained soils in a closed system under large thermal gradients using liquid nitrogen (LN). Temperatures are measured inside specimens during freezing and micro-CT visualized internally after freezing. Results show that large thermal gradients develop near the surfaces of specimens upon their submersion in LN. The specimens freeze homogeneously, and no visible ice lenses form, owing to the insufficient time for water migration and ice segregation under rapid freezing. The specimens fracture and split into major pieces, under no confining stresses in this study; freezing first occurs near the boundaries, and the freezing front propagates inward, creating temporal, differential volume changes between the outer and inner parts of the specimens, which leads to fractures in the unconfined state. The fractures affect subsequent temperature propagation and thermal gradients.

MAB21L1 modulates gene expression and DNA metabolic processes in the lens placode

Mutations in human MAB21L1 cause aberrations in lens ectoderm morphogenesis and lead to congenital cerebellar, ocular, craniofacial, and genital (COFG) syndrome. Murine Mab21l1-null mutations cause severe cell-autonomous defects in lens formation leading to microphthalmia, and therefore is used as a mouse model for COFG syndrome. In this study, we investigated the early-onset, single-cell-level phenotypes of murine Mab21l1-null lens ectoderms using electron microscopy (EM) and single-cell RNA sequencing (scRNA-seq). EM and immunohistochemical analyses indicated endoplasmic reticulum stress in the 24- to 26-somite stage in Mab21l1-null lens placodes. scRNA-seq analysis revealed that 131 genes were downregulated and 148 were upregulated in Mab21l1-null lens ectoderms relative to the wild type. We successfully identified 21 lens-specific genes that were downregulated in Mab21l1-null cells including three key genes involved in lens formation: Pitx3, Maf, and Sfrp2. Moreover, gene ontology analysis of the 279 differentially expressed genes indicated enrichment in housekeeping genes associated with DNA/nucleotide metabolism prior to cell death. These findings suggest that MAB21L1 acts as a nuclear factor that modulates not only lens-specific gene expression but also DNA/nucleotide metabolic processes during lens placode formation.

Experimental study and numerical modeling of the thermo-hydro-mechanical processes in soil freezing with different frost penetration directions

This research work presents an experimental and numerical study of the coupled thermo-hydro-mechanical (THM) processes that occur during soil freezing. With focusing on the artificial ground freezing (AGF) technology, a new testing device is built, which considers a variety of AGF-related boundary conditions and different freezing directions. In the conducted experiments, a distinction is made between two thermal states: (1) The thermal transient state, which is associated with ice penetration, small deformations, and insignificant water suction. (2) The thermal (quasi-) steady state, which has a much longer duration and is associated with significant ice lens formation due to water suction. In the numerical modeling, a special focus is laid on the processes that occur during the thermal transient state. Besides, a demonstration of the micro-cryo-suction mechanism and its realization in the continuum model through a phenomenological retention-curve-like formulation is presented. This allows modeling the ice lens formation and the stiffness degradation observed in the experiments. Assuming a fully saturated soil as a biphasic porous material, a phase-change THM approach is applied in the numerical modeling. The governing equations are based on the continuum mechanical theory of porous media (TPM) extended by the phase-field modeling (PFM) approach. The model proceeds from a small-strain assumption, whereas the pore fluid can be found in liquid water or solid ice state with a unified kinematics treatment of both states. Comparisons with the experimental data demonstrate the ability and usefulness of the considered model in describing the freezing of saturated soils.

A Functional Map of Genomic HIF1α-DNA Complexes in The Eye Lens Revealed Through Multiomics Analysis

Background: During eye lens development the fetal vasculature regresses leaving the lens without a direct oxygen source. Both embryonically and throughout adult life, the lens contains a decreasing oxygen gradient from the surface to the core that parallels the natural differentiation of immature surface epithelial cells into mature core transparent fiber cells. These properties of the lens suggest a potential role for hypoxia in the regulation of genes required for mature lens structure and function. Since HIF1α is a master regulator of the hypoxic response, these lens properties also implicate HIF1α as a potential requirement for lens formation and homeostasis. Here, we employed a multiomics approach combining CUT&RUN, RNAseq and ATACseq analysis to establish the genomic complement of lens HIF1α binding sites, genes activated or repressed by HIF1α and the chromatin states of HIF1α-regulated genes.Results: CUT&RUN analysis revealed 8,375 HIF1α-DNA binding complexes in the chick lens genome. 1,190 HIF1α-DNA binding complexes were significantly clustered within chromatin accessible regions (χ2 test p < 1x10-55) identified by ATACseq. Formation of the identified HIF1α-DNA complexes paralleled the activation or repression of 526 genes, 116 of which contained HIF1α binding sites within 10kB of the transcription start sites. Some of the identified HIF1α genes have previously established lens functions while others have novel functions never before examined in the lens. GO and pathway analysis of these genes implicate HIF1α in the control of a wide-variety of cellular pathways potentially critical for lens formation, structure and function including glycolysis, cell cycle regulation, chromatin remodeling, Notch and Wnt signaling, differentiation, development, and transparency. Conclusions: These data establish the first functional map of genomic HIF1α-DNA complexes in the eye lens. They identify HIF1α as an important regulator of a wide-variety of genes previously shown to be critical for lens formation and function and they reveal a requirement for HIF1α in the regulation of a wide-variety of genes not yet examined for lens function. They support a requirement for HIF1α in lens development, structure and function and they provide a basis for understanding the potential roles and requirements for HIF1α in the development, structure and function of more complex tissues.

Study on the Mechanical Criterion of Ice Lens Formation Based on Pore Size Distribution

Ice lens is the key factor which determines the frost heave in engineering construction in cold regions. At present, several theories have been proposed to describe the formation of ice lens. However, most of these theories analyzed the ice lens formation from a macroscopic view and ignored the influence of microscopic pore sizes and structures. Meanwhile, these theories lacked the support of measured data. To solve this problem, the microscopic crystallization stress was converted into the macro mean stress through the principle of statistics with the consideration of pore size distribution. The mean stress was treated as the driving force of the formation of ice lens and induced into the criterion of ice lens formation. The influence of pore structure and unfrozen water content on the mean stress was analyzed. The results indicate that the microcosmic crystallization pressure can be converted into the macro mean stress through the principle of statistics. Larger mean stress means the ice lens will be formed easier in the soil. The mean stress is positively correlated with initial water content. At the same temperature, an increase to both the initial water content and the number of pores can result in a larger mean stress. Under the same initial water content, mean stress increases with decreasing temperature. The result provides a theoretical basis for studying ice lens formation from the crystallization theory.

The growth of faults and fracture networks in a mechanically evolving, mechanically stratified rock mass: a case study from Spireslack Surface Coal Mine, Scotland

Fault architecture and fracture network evolution (and resulting bulk hydraulic properties) are highly dependent on the mechanical properties of the rocks at the time the structures developed. This paper investigates the role of mechanical layering and pre-existing structures on the evolution of strike–slip faults and fracture networks. Detailed mapping of exceptionally well exposed fluvial–deltaic lithologies at Spireslack Surface Coal Mine, Scotland, reveals two phases of faulting with an initial sinistral and later dextral sense of shear with ongoing pre-faulting, syn-faulting, and post-faulting joint sets. We find fault zone internal structure depends on whether the fault is self-juxtaposing or cuts multiple lithologies, the presence of shale layers that promote bed-rotation and fault-core lens formation, and the orientation of joints and coal cleats at the time of faulting. During ongoing deformation, cementation of fractures is concentrated where the fracture network is most connected. This leads to the counter-intuitive result that the highest-fracture-density part of the network often has the lowest open fracture connectivity. To evaluate the final bulk hydraulic properties of a deformed rock mass, it is crucial to appreciate the relative timing of deformation events, concurrent or subsequent cementation, and the interlinked effects on overall network connectivity.

Three-dimensional data capture and analysis of intact eye lenses evidences emmetropia-associated changes in epithelial cell organization

Organ and tissue development are highly coordinated processes; lens growth and functional integration into the eye (emmetropia) is a robust example. An epithelial monolayer covers the anterior hemisphere of the lens, and its organization is the key to lens formation and its optical properties throughout all life stages. To better understand how the epithelium supports lens function, we have developed a novel whole tissue imaging system using conventional confocal light microscopy and a specialized analysis software to produce three-dimensional maps for the epithelium of intact mouse lenses. The open source software package geometrically determines the anterior pole position, the equatorial diameter, and three-dimensional coordinates for each detected cell in the epithelium. The user-friendly cell maps, which retain global lens geometry, allow us to document age-dependent changes in the C57/BL6J mouse lens cell distribution characteristics. We evidence changes in epithelial cell density and distribution in C57/BL6J mice during the establishment of emmetropia between postnatal weeks 4–6. These epithelial changes accompany a previously unknown spheroid to lentoid shape transition of the lens as detected by our analyses. When combined with key findings from previous mouse genetic and cell biological studies, we suggest a cytoskeleton-based mechanism likely underpins these observations.

Moisture Transfer and Formation of Separate Ice in the Freezing Process of Saturated Soils

The formation and layer of ice lenses during the freezing of soil in cold regions is closely related to frozen heave and moisture immigration. The purpose of the paper is to explain the physical mechanisms pertaining to ice lens formation, which were analyzed and verified using numerical simulation results. Based on a few assumptions, the formation and layers of ice lenses are illuminated in the following steps: the initial stage of freezing, formation of the first layer of ice lens, formation of the second layer of ice lens, and formation of the final layer of ice lens. Compared with the numerical results of coupled thermo–hydro–mechanical simulations of one-side freezing of soil columns in an open system, the proposed analysis method of the formation and layers of ice lenses is verified to be reasonable, and it is demonstrated that the classical criterion for the formation of ice lens in freezing saturated soil is only suitable for the final layer of ice lens. Finally, a new criterion, in terms of flux rate, for the formation of ice lens is proposed.

Propagation of Freshwater Lenses as Buoyant Gravity Currents

&lt;p&gt;Freshwater lenses (FWL) deposited by rain create surface salinity and temperature anomalies that can persist for extended periods of time (&gt; 1 day). The resulting patchiness in near-surface density and sea surface temperature influence upper ocean dynamics and air-sea fluxes of heat. For these reasons, understanding lens formation and evolution has been a focus of recent observational and modeling efforts. The work presented here integrates near-surface ocean and atmosphere time series with remote sensing of sea surface roughness (X-band radar) and precipitation (C-band radar) to describe the formation and temporal evolution of lenses within the equatorial Indian Ocean. Twenty-six FWLs are observed at different stages of their evolution from freshly deposited and actively spreading to older, passively advected features. Salinity anomalies reached -1.2 psu near the surface, while temperature anomalies were observed to be both cool (down to -0.8&amp;#176;C) and warm (up to +0.4&amp;#176;C). The largest density anomaly reached -0.5 kg/m&lt;sup&gt;3&lt;/sup&gt;. Remotely-sensed, ship-based radar imagery allows for quantification of the observed propagation speeds of ten lenses, which follow internal gravity wave theory. These results offer a novel perspective on the evolution of FWLs whose dynamics need to be properly accounted for to assess lens longevity, including persistence of salinity and temperature anomalies, as well as influences to air-sea interactions.&lt;/p&gt;