Mechanical properties of calcareous sand : the role of initial fabric, particle characteristics and gradation

Natural sandy soils always show highly different properties such as ingredientcomposition, gradation, particle characteristic and internal fabric, causing significant differences in mechanical behavior within small to large strain range. Calcareous sand is a special construction material which is commonly used in the reclamation projects in marine areas. Due to its marine organismorigin, the grain characteristic of calcareous sand is different form from that of silica sand, behaving in the extremely irregular grain shape with the a high particle angularity. It has been proved that natural sediments exhibit fabric anisotropy, especially for sandy soils. During the deposition process of a granular material with non-rounded grain shape under gravity, the long axis of the grain tends to be parallel to the horizontal direction, leading to the formation of a highly anisotropic soil fabric. In this thesis, a calcareous sand from Persian Gulf was tested in a series of static and dynamic triaxial tests. The effects of initial fabric, particle characteristic, gradation and fine content on the mechanical properties of the calcareous sands are investigated. The small strain stiffness ( G_0) is an important elastic soil parameter indicating the deformation or the seismic response of the ground. The anisotropic small strain stiffness of granular materials has been studied extensively in the last decades. Most of the studies were only conducted on the measurement of the anisotropic stiffness and the factors affecting this mechanical behavior were not well investigated. In this thesis, the initial fabric, particle size, gradation and fine content are studied as the variant variables affecting the small strain stiffness of the calcareous sands. Firstly, in order to make laboratory samples having various initial fabric, a literature review on the sample preparation method is given and five methods as air and water pluviation, dry and moist tamping and dry funnel deposition are selected for this study. The new pluviators were specially designed for the air and water pluviation methods respectively. In order to figure out the difference in fabric induced by the sample preparation method, X-ray tomography tests were performed on the samples prepared following the five methods and the differences in the homogeneity and fabric anisotropy were analyzed from the microscopic view. The scan results show that the air pluviation samples exhibit the highest fabric anisotropy. The fabric anisotropy of the five samples can be ordered as: air pluviation > water pluviation > dry tamping > moist tamping > dry funnel deposition. For the uniformity, it is concluded that the zones close to the sample boundary show lower densities for all the preparation methods. The air pluviation and dry tamping samples are respectively the least and the most affected by the boundary. Along the height, the sample prepared by the air pluviation method shows the highest homogeneity. The density decreases and increases from the top to the bottom for the water pluviation and dry funnel deposition samples respectively. The density in the samples prepared in layers shows variation along the sample height and the fluctuation is the most significant in the dry tamping sample. Concerning To investigate the effect of particle characteristic and gradation, several sands with the artificial gradation were prepared with the materials sieved from the original calcareous sands. Similarly, the sand-fine mixtures with the variouvarious amounts ofs fine contents were prepared by mixing the original calcareous sands with the sieved calcareous fines. The small strain shear modulus on both the vertical and horizontal planes were evaluated by the multidirectional bender element tests. Then the stiffness anisotropy was obtained. It is was found that the initial fabric, particle size and fine content have significant impact on the anisotropic stiffness of the calcareous sands. Calcareous samples prepared by the air pluviation method possesses the highest anisotropic ratios. The lowest stiffness anisotropy exists in the samples prepared by moist tamping and dry funnel deposition methods. The difference induced by the initial fabric can be explained by the X-ray tomography results. The less prominent stiffness anisotropy is found in calcareous sands with smaller particle sizes and the effect of the coefficient of uniformity (Cu) on the stiffness anisotropy is negligible. The equation proposed by Hardin and Black (1966) for predicting the small strain stiffness of soils was updated for the calcareous sands in this study. The sample preparation method has a slight impact on the constants in the Hardin equation, concluding that the sample having a stronger fabric has larger A and m but lower n. The modified Hardin equation is applicable for the anisotropic consolidation tests. The fine content has significant influence on the small strain stiffness of the calcareous sands, showing that the shear modulus decreases with the increase of the fine content before the threshold. The stiffness anisotropy decreases with the increase of the fine content and drops faster after the threshold fine content. Finally, the constants in the Hardin equation are updated by taking the fine content into account. The difference induced by the initial fabric can be explained by the X-ray tomography results. In this thesis, the models for predicting G_0 are updated by taking into account the over-consolidation ratio ( OCR ) and the fine content ( FC ). For sand-fine mixtures, three models are introduced and modified and their prediction ability is compared. To further study the initial fabric on the mechanical property of the calcareous sands, the K0 consolidation tests and the undrained monotonic and cyclic loading tests were performed on the samples prepared by different methods. The influences of the initial fabric on the coefficient of earth pressure at rest (K0 ) and the undrained strength under monotonic and cyclic loadings were evaluated. It is shown that the values of K0 and the liquefaction resistance of the calcareous sands are highly affected by the sample preparation method. Test results show that the air pluviation and moist tamping samples own the highest and the lowest K0 respectively. All the samples at medium loose and medium dense states show strain hardening subjected to the undrained monotonic loading. The air pluviation samples are more contractive than the other samples at the phase transformation points and the moist tamping samples exhibit an over-consolidated behavior. In the cyclic loading tests, the air pluviation and the moist tamping samples exhibit the highest and the lowest liquefaction resistance. The cyclic undrained strength of the water pluviation and dry tamping samples is close, which is higher than that of the dry funnel deposition samples. It is also concluded that explaining differences in the mechanical properties from the fabric discrepancy induced by the sample preparation method is not comprehensive. Other factors such as homogeneity and stress history should be considered. In a conclusion, this study mainly investigates the factors affecting the anisotropic small strain stiffness and the role of initial fabric in the mechanical behavior of the calcareous sands. Of particular importance is that the results show a referential value for the evaluation of the soil property in situ based on the laboratory data. Therefore, oneit should bear in mind that underestimation or overestimation of soil state may happen if an improper sample preparation method is selected, especially for the sandy soils

Investigation on the mechanical properties of a calcareous sand : the role of the initial fabric

This study examines the effect of the initial fabric on the coefficient of the lateral earth pressure at rest K-0, the undrained monotonic loading strength and the liquefaction resistance of a calcareous sand from a reclamation land in Persian Gulf. K(0)consolidation, undrained compression and extension and cyclic undrained loading triaxial tests are performed on laboratory samples reconstituted by air and water pluviation, dry and moist tamping and dry funnel deposition methods. Test results show that the air pluviation and moist tamping samples own the highest and the lowest K(0)respectively. All the samples at medium loose and medium dense states show strain hardening when subjected to undrained monotonic loading. The air pluviation samples are more contractive than the other samples at the phase transformation points and the moist tamping samples exhibit an over-consolidated behavior. In the cyclic loading tests, the air pluviation and the moist tamping samples exhibit the lowest and the highest liquefaction resistance. It is shown that the evaluation and comparison of the cyclic undrained strength of various sands should take the sample preparation method into consideration scrupulously. The test results also indicate that although the mechanical property of soil sample is influenced by the fabric differences induced by sample preparation method, other factors such as homogeneity and stress history should not be neglected

Theory and application of mining mechanics and strata control

Studying the dynamic response of rock mass mining and strata control technology is of great significance for promoting safe and efficient coal production and ensuring stable energy supply. It is the theoretical basis for scientific mining of coal resources. Mine rock mass disasters (surrounding rock deformation, rock burst, etc.) occur frequently, and their formation-evolution-occurrence process is closely related to the evolution and distribution of mine-induced stress, strata movement, mine-induced disturbance and energy evolution. Based on the practical theory of ground pressure control, the progress and control criteria of strata control in the stope are presented. The mechanical models and design methods for quantitative analysis are established. Also, the targeted rock disaster control technology and the assorted equipment are innovatively developed. In the theory of mining mechanics and strata control, the strata control is divided into rock control in stope and surrounding rock control in roadway. The control or utilization of strata movement to change the conditions of disaster is proposed, and the criteria of “given deformation” and “limited deformation” are provided. The self-stabilization ability of surrounding rock can be changed by regulating the “3S” factors criteria (stress environment, structural properties, and support structure). With the goal of controlling rock mass disasters, the system of control and energy release with core of stress control in roadway surrounding rock is presented. The principle of rock mass disaster control considering stress and energy and the assessment criteria for weak surface (safety factor K and impact hazard factor U) are established. The ground pressure mechanical simulation test system in stope, the mining-induced stress test system, and the creep and dynamic disturbance impact loading test system are independently developed. The series equipment can realize the laboratory-scale reduction of the deformation-fracture-movement process of rock mass under the action of mine-induced stress, providing experimental equipment for studying the mechanical response of rock mass. Engineering case studies are conducted from four directions: rock control in the mining area, geological soft rock control, engineering soft rock roadway control, and rockburst control. The relevant research results are validated in engineering applications

Roadmap on perovskite light-emitting diodes

In recent years, the field of metal-halide perovskite emitters has rapidly emerged as a new community in solid-state lighting. Their exceptional optoelectronic properties have contributed to the rapid rise in external quantum efficiencies (EQEs) in perovskite light-emitting diodes (PeLEDs) from <1% (in 2014) to over 30% (in 2023) across a wide range of wavelengths. However, several challenges still hinder their commercialization, including the relatively low EQEs of blue/white devices, limited EQEs in large-area devices, poor device stability, as well as the toxicity of the easily accessible lead components and the solvents used in the synthesis and processing of PeLEDs. This roadmap addresses the current and future challenges in PeLEDs across fundamental and applied research areas, by sharing the community’s perspectives. This work will provide the field with practical guidelines to advance PeLED development and facilitate more rapid commercialization

Roadmap on Perovskite Light-Emitting Diodes

In recent years, the field of metal-halide perovskite emitters has rapidly emerged as a new community in solid-state lighting. Their exceptional optoelectronic properties have contributed to the rapid rise in external quantum efficiencies (EQEs) in perovskite light-emitting diodes (PeLEDs) from <1% (in 2014) to approaching 30% (in 2023) across a wide range of wavelengths. However, several challenges still hinder their commercialization, including the relatively low EQEs of blue/white devices, limited EQEs in large-area devices, poor device stability, as well as the toxicity of the easily accessible lead components and the solvents used in the synthesis and processing of PeLEDs. This roadmap addresses the current and future challenges in PeLEDs across fundamental and applied research areas, by sharing the community's perspectives. This work will provide the field with practical guidelines to advance PeLED development and facilitate more rapid commercialization.Comment: 103 pages, 29 figures. This is the version of the article before peer review or editing, as submitted by an author to Journal of Physics: Photonics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Two Antarctic penguin genomes reveal insights into their evolutionary history and molecular changes related to the Antarctic environment. GigaScience

Abstract Background: Penguins are flightless aquatic birds widely distributed in the Southern Hemisphere. The distinctive morphological and physiological features of penguins allow them to live an aquatic life, and some of them have successfully adapted to the hostile environments in Antarctica. To study the phylogenetic and population history of penguins and the molecular basis of their adaptations to Antarctica, we sequenced the genomes of the two Antarctic dwelling penguin species, the Adélie penguin [Pygoscelis adeliae] and emperor penguin [Aptenodytes forsteri]. Results: Phylogenetic dating suggests that early penguins arose~60 million years ago, coinciding with a period of global warming. Analysis of effective population sizes reveals that the two penguin species experienced population expansions from~1 million years ago to~100 thousand years ago, but responded differently to the climatic cooling of the last glacial period. Comparative genomic analyses with other available avian genomes identified molecular changes in genes related to epidermal structure, phototransduction, lipid metabolism, and forelimb morphology. Conclusions: Our sequencing and initial analyses of the first two penguin genomes provide insights into the timing of penguin origin, fluctuations in effective population sizes of the two penguin species over the past 10 million years, and the potential associations between these biological patterns and global climate change. The molecular changes compared with other avian genomes reflect both shared and diverse adaptations of the two penguin species to the Antarctic environment

Molecular and cellular impact of Psoriasin (S100A7) on the healing of human wounds

Psoriasin, which is also known as S100A7, is a member of the S100 protein family, a group of calcium‑responsive signalling proteins. Psoriasin expression remains high in patients with psoriasis, whereas it is downregulated in patients with invasive breast carcinoma. This observation suggests that this protein may be a notable marker of keratinocyte function and differentiation during wound healing. The aim of the present study was to determine the cellular impact of Psoriasin in keratinocytes, which are the primary cell type associated with wound healing. Psoriasin expression in wound tissues was examined using reverse transcription‑quantitative polymerase chain reaction and immunochemical staining. Knockdown of Psoriasin in HaCaT cells was performed using anti‑Psoriasin ribozyme transgenes and the effect on growth, adhesion and migration of keratinocytes was subsequently determined using in vitro cellular functional assays. Psoriasin expression is upregulated in wounds, particularly at the wound edges. The present study demonstrated that Psoriasin is expressed in keratinocytes and is a fundamental regulator of keratinocyte migration. Significant increases in the rate of keratinocyte adhesion, migration and growth were observed in Psoriasin‑deficient cells (P<0.01 vs. control). Application of small inhibitors identified the potential association of neural Wiskott‑Aldrich syndrome protein, focal adhesion primase and rho‑associated protein kinase signalling pathways with Psoriasin‑regulated cell adhesion and motility. In conclusion, Psoriasin serves an important role in the wound healing process, suggesting that it may be utilized as a potential wound healing biomarker