Experimental Study of the Damage and Failure Characteristics of the Backfill-Surrounding Rock Contact Zone.

Due to obvious differences in the properties of the filling body and surrounding rock, deformation always develops near the contact zone. Thus, determining the damage and failure characteristics of the contact zone between the backfill and surrounding rock is a precondition for safe production in mines. Taking Jinchuan mine as study area, the backfill-surrounding rock contact zones are divided into three models according to their different geometric shapes, namely, a linear model, embedded model, and multiple broken line model. A combined numerical simulation and physical model test method was adopted in this study. The research results show that the damage in the linear model begins at the seam, the failure is mainly concentrated in the filling body, and shear failure is dominant. The damage in the embedded model initially occurs around the inflection points, while the damage in the multiple broken line model initially occurs at the seams, and cracks always appear on the vertical contact surface first. Among the three contact models, the stability increases as follows: embedded > multiple broken line > linear. Moreover, the filling body enclosed by surrounding rock is the most stable, and the surrounding rock located in the footwall is more stable than the filling body located in the footwall. The conclusions of this study provide a theoretical basis for designing a mining scheme for Jinchuan mine and other mines with similar geological conditions and mining methods, and they provide a reference for studying the mechanical properties and stability of composite materials.

Numerical Simulation of Failure Behavior of Brittle Heterogeneous Rock under Uniaxial Compression Test.

Rocks have formed heterogeneous characteristics after experiencing complex natural geological processes. Studying the heterogeneity of rocks is significant for rock mechanics. In this study, a linear parallel bond model with Weibull distribution in two-dimensional particle flow code (PFC2D) is adopted to study the mechanical characteristics and brittle failure mode of granite rock specimens with different heterogeneity. Firstly, we selected several combinations of key micro-parameters of the parallel bond model. Then, we subjected them to a Weibull distribution to satisfy heterogeneity, respectively. Finally, we chose one optimal combination plan after comparing the stress-strain curves of heterogeneous rock specimens. We analyzed the simulated results of heterogeneous rock specimens. The crack distribution of rock specimens under peak stress shows different characteristics: a diagonal shape in rock specimens with low heterogeneity indexes, or a rotated "y" shape in rock specimens with high heterogeneity indexes. As for failure mode, the numerical simulation results show high consistency with the laboratory experiment results. The rock specimen breaks down almost diagonally, and the whole specimen tends to form an x-shaped conjugate shear failure or the well-known "hour-glass" failure mode. With the increase of the homogeneity index of the rock specimen, the shear rupture angle becomes larger and larger. Generally, the crack number increases with time, and when the rock specimen reaches the peak failure point, the number of cracks increases sharply. The development of cracks in numerical rock specimens under compression test is a result of the coalescence of many microscopic cracks. Furthermore, tensile cracks formed initially, followed by shear behavior along the macroscopic crack plane. We also preliminarily study the mechanical characteristics of heterogeneous rock specimens with discontinuous structural planes. The discontinuous structural planes are simulated by the smooth-joint model. We can conclude that the discontinuous structural planes and the microscopic structural planes which contribute to the heterogeneity have a mutual influence on each other.

Analysis of Acoustic Emission Characteristics and Failure Mode of Deep Surrounding Rock of Sanshandao Gold Mine.

In mining engineering, crack distribution has a considerable influence on the mechanical behavior and stability of the surrounding rock mass. Using the granite of the Sanshandao gold mine as experimental samples, the deformation and failure of fractured rock were analyzed based on a rock uniaxial compression test with acoustic emission monitoring. We analyzed the characteristics of different stages of rock sample deformation, and evaluated the failure mode of seven types of rock samples. The results show that the cracks had a considerable impact on rock sample strength and mechanical behavior, and the strength of intact rock was the highest, while that of the sample with parallel double cracks was the lowest. The acoustic emission parameters, AF, RA, and lg(AF/RA), have different change trends in different stages of rock deformation and failure. Based on these change trends, the failure modes of rock samples with different crack distributions were identified. Additionally, for the rock samples with seven types of crack distribution, a sudden or progressive failure caused by the b-value curves was observed. The research findings provide a database for deep surrounding rock stability in the study area and provide suggestions for failure prediction.

Experimental Study on Mechanical Properties and Failure Laws of Granite with Artificial Flaws under Coupled Static and Dynamic Loads.

Rock is the main construction material of rock engineering, such as the engineering of mines and tunnels; in addition, its mechanical properties and failure laws are of great significance to the stability evaluation of rock engineering, especially under the conditions of coupled static-static stresses. In this study, granite specimens were manufactured with artificial flaws. Coupled static and dynamic loads tests were carried out with a modified split Hopkinson pressure bar (SHPB) apparatus; and six typical levels of axial pre-stresses and three crack inclination angles were designed. Three-dimensional digital image correlation (3D-DIC) was also applied to record and analyze the fracturing process and damage evolution of the specimens. The test results show that there was no compaction stage in the stress-strain curve under combined dynamic and static loading. The dynamic strength of the specimens increased first and then decreased with the increase in the static pressure; moreover, the specimens reached the maximum dynamic strength when the static pressure was 10% UCS. The dynamic strength decreased first and then increased with the increase in the crack inclination angle; and the lowest strength appeared when the inclination angle was 45°. The change in axial compression had a significant influence on the failure mode, and the failure mode gradually transformed from shear-tensile failure to shear failure with the increase in the pre-stress. The tensile strain was usually generated at the end of the fractures or near the rock bridge. When the axial pressure was small, the tensile strain zone parallel to the loading direction was easily generated; and when the axial pressure was large, a shear strain zone developed, extending along the diagonal direction. The research results can provide a theoretical reference for the correct understanding of the failure mechanisms of granite and its engineering stability under actual conditions.

Experimental research on deformation failure process of roadway tunnel in fractured rock mass induced by mining excavation.

Deformation failure of roadways in fractured rock can lead to large-volume collapse and other engineering accidents. Failure mechanisms in fractured rock are complex and poorly understood, so to explore this issue, we simulated fractured rock masses using physical model tests in combination with numerical computations. A set of experimental techniques for roadway excavation under jointed surrounding rock included a mixed pouring-bricking method and a roadway excavation device, which can reproduce the structural characteristics of the prototype and replicate the excavation conditions of the roadway. Stress distribution characteristics of the roadway, from loading to excavation, were obtained based on strain monitoring and image acquisition, and the process of roadway deformation and failure was described in detail. A series of numerical simulations were conducted to investigate the deformation failure mechanisms of roadways under different excavation conditions. Results indicate that the deformation failure modes of roadways including collapse, rock burst, and floor heaving that were similar regardless of depth. Deformation failure modes of the roadway were determined by rock mass structure, and the deformation intensity was determined by geo-stress. Model testing and numerical simulation were consistent; hence, findings provide a theoretical basis and technical guidance for roadway engineering in fractured rock masses.

Investigating the permeability of fractured rock masses and the origin of water in a mine tunnel in Shandong Province, China.

The coastal Sanshandao mine is threatened by the overlying Quaternary water and seawater. Following an introduction to the geology and hydrogeological conditions in the mine area, a detailed hydrogeological survey and sampling were conducted and hydrochemical and stable isotopic (δ2H and δ18O) tests on various waters were carried out to characterize the origin of water in the mine tunnels. Investigation and statistical analysis indicated that the northwest-trending fractures with large dip angles and long trace lengths are well developed in the northeast compared with those in the southwest of the mine. The permeability coefficients of the rock masses are in the range 4.19×10(-8)-2.25×10(-5) m/s, indicating that the fractured rock masses have generally low permeability. The seepage water had higher values of EC, total dissolved solids, and concentrations of most elements than the seawater and saline groundwater. Besides, the isotope composition of the waters indicated that the seepage water was more isotopically enriched than seawater but less than brine. The proportions of the three different sources were calculated based on hydrochemical and isotopic analyses. Overall, the mine water was composed of 72% seawater, 14.8% brine, and 13.2% atmospheric precipitation, respectively. Therefore, some preventive measures are essential to avoid the probability of seawater inrush.

Protective effects of flavonoid extract from Apocynum venetum leaves against corticosterone-induced neurotoxicity in PC12 cells.

Depression is a major psychiatric disorder affecting nearly 21% of the world population and imposes a substantial health burden on society. Although significant progress has been made in depression research, the common molecular mechanism of antidepressants is still far from clearly understood. The neuroprotective effect of antidepressants has been proposed as a possible mechanism. Although Apocynum venetum (AV) L. (Apocynaceae) was previously shown to produce an antidepressant-like effect in the tail suspension test, the mechanisms underlying such antidepressant-like effect are yet to be understood. In this work, we studied the neuroprotective effect of AV leaf flavonoid extract in corticosterone-induced neurotoxicity, using PC12 cells as a suitable in vitro model of depression. Cell viability was quantitated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The release amount of lactic dehydrogenase (LDH) and intracellular Ca(2+) concentration were measured using kit, cell period change was tested by flow cytometry, and transcript abundances of brain-derived neurotrophic factor (BDNF) and microtubule-associated protein 4 (MAP4) were determined by real-time RT-PCR. The results showed that AV extract (25, 50, and 100 µg/ml) increased the A490 nm values, but decreased LDH release and Ca(2+) concentration, suppressed the apoptosis of PC12 cells and up-regulated BDNF and MAP4 transcript abundances compared with the corresponding corticosterone-treated group. These results suggest that the AV extract could generate a neuroprotective effect on corticosterone-induced neurotoxicity in PC12 cells, pointing to a possible action pathway by decreasing the Ca(2+) concentration and up-regulating BDNF and MAP4 genes.

Quality evaluation of snow lotus (Saussurea): quantitative chemical analysis and antioxidant activity assessment.

Snow lotus is commonly used as a medicinal plant and has great pharmacological value. To protect these endangered plants, in vitro propagation and cell cultures have been established in order to meet the growing market demand. The phenolic composition, antioxidant activities, total phenolic content (TPC) and total flavonoid content (TFC) from three most commonly used species, in vitro propagated lines and the cell cultures were investigated to qualify their pharmacological value. Quantitative analysis showed that the phenolics varied greatly among different species and the same species at different habitats. From this it can be inferred that the phenolics were influenced by genetic background and the environmental conditions. Significant correlations were observed between the antioxidant activity and several phenolics/TPC/TFC, suggesting that the phenolics are a major contributor of the antioxidant activity and are important for quality evaluation of snow lotus. Based on the abundance of phenolics, TPC, TFC and antioxidant activity, the order of the quality for wild species would be Saussurea involucrata > Saussurea medusa > Saussurea gossypiphora. For S. medusa, its quality judged by origin would be Shigatse > Lhasa > Nagqu. For in vitro propagated plants, the matured plants could be a reliable substitute for wild plants, and the dynamics of phenolics is critical for quality control of this monocarpic species. We provide the first report of quality comparison between the wild plants and the cell cultures. The advantages of developing cell cultures as alternatives for plants collected from the wild are discussed.

Arabidopsis eIF5A3 influences growth and the response to osmotic and nutrient stress.

AteIF5A3, one of three genes encoding eukaryotic translation initiation factor 5A (eIF5A) in Arabidopsis thaliana, and corresponding genes PdeIF5A3 from Populus deltoides (eastern cottonwood) and SleIF5A4 from Solanum lycopersicum (tomato) were constitutively over-expressed in A. thaliana. The resultant transgenic plants exhibited enhanced vegetative and reproductive growth. Indeed, the increase in seed yield relative to empty vector controls for the PdeIF5A3 over-expressing plants ranged from 50% to 300% depending on the line. The PdeIF5A3 over-expressing plants also exhibited enhanced fitness when exposed to osmotic and nutrient (N, P and K) stress. The spatial localization of AteIF5A3 was visualized by confocal microscopy using transgenic plants expressing P(AteIF5A3) :GFP-AteIF5A3. GFP fluorescence reflecting expression of AteIF5A3 was detectable in the phloem, particularly companion cells, of roots, stems and leaves, in the epidermal cells of the root tip, in the columella cells of the root cap and in the chalazal tissue of fertilized ovules, which all play a pivotal role in nutrient or hormone translocation. Thus, AteIF5A3 appears to be involved in supporting growth and to play a regulatory role in the response of plants to sub-lethal osmotic and nutrient stress.

Modulation of eIF5A1 expression alters xylem abundance in Arabidopsis thaliana.

Eukaryotic translation initiation factor 5A (eIF5A) is thought to facilitate protein synthesis by participating in the nuclear export of specific mRNAs. In Arabidopsis, there are three isoforms of eIF5A. One of them, AteIF5A1, has been shown to be expressed in vascular tissue, specifically developing vessel members, using GUS as a reporter. In order to determine whether AteIF5A1 plays a role in xylem formation, its full-length cDNA was constitutively over-expressed in transgenic Arabidopsis plants. Microscopic analysis revealed that the cross-sectional area of the xylem in the main inflorescence stems of transgenic plants was 1.9-fold higher than those of corresponding inflorescence stems of wild-type plants. In wild-type stems, the primary xylem typically comprised six cell layers and was approximately 105 mum thick, but increased to 9-11 cell layers, 140-155 mum thick, in transgenic stems. Similarly, the secondary xylem increased from six cell layers, approximately 70 mum thick, in control stems to approximately 9 cell layers, 95-105 mum thick, in transgenic stems. Moreover, constitutive down-regulation of AteIF5A1 using antisense technology resulted in the major suppression of xylem formation compared with control plants, and the antisense transgenic plants were also stunted. These data collectively indicate that eIF5A1 plays a role in xylogenesis.

Regulation and execution of molecular disassembly and catabolism during senescence.

Senescence is a highly orchestrated developmental stage in the life cycle of plants. The onset of senescence is tightly controlled by signaling cascades that initiate changes in gene expression and the synthesis of new proteins. This complement of new proteins includes hydrolytic enzymes capable of executing catabolism of macromolecules, which in turn sets in motion disassembly of membrane molecular matrices, leading to loss of cell function and, ultimately, complete breakdown of cellular ultrastructure. A distinguishing feature of senescence that sets it apart from other types of programmed cell death is the recovery of carbon and nitrogen from the dying tissue and their translocation to growing parts of the plant such as developing seeds. For this to be accomplished, the initiation of senescence and its execution have to be meticulously regulated. For example, the initiation of membrane disassembly has to be intricately linked with the recruitment of nutrients because their ensuing translocation out of the senescing tissue requires functional membranes. Molecular mechanisms underlying this linkage and its integration with the catabolism of macromolecules in senescing tissues are addressed.

The outermost cuticle of soybean seeds: chemical composition and function during imbibition.

Seeds of different cultivars of Glycine max (L.) Merr. (soybean) have strikingly different rates of water imbibition. Seeds that readily imbibe water are termed 'soft', while those that remain non-permeable, even after several days in water, are referred to as 'hard', 'stone', or 'impermeable' seeds. What prevents soybean hard seeds from taking up water? Previous work established that the initial imbibition of soft soybean seeds correlates with the presence of small cracks in the outermost cuticle that covers the seed coat, prompting a detailed analysis of soybean seed coat cutin. In this paper, it is shown that the outermost cuticle of the seed coat has an unusual chemical composition, lacking typical mid-chain-hydroxylated fatty acids but being relatively rich in other types of hydroxylated fatty acids. The cuticle of the impermeable cultivar studied contained a disproportionately high amount of hydroxylated fatty acids relative to that of the permeable ones. Moreover, a brief treatment with hot alkali released the omega-hydroxy fatty acid component of the outermost cuticle and created holes in it that caused the seeds to become permeable. This demonstrates that the outermost cuticle of the seed is the critical structure that prevents water uptake by hard seeds.

Methyl jasmonate stimulates jaceosidin and hispidulin production in cell cultures of Saussurea medusa.

Cell cultures of Saussurea medusa produce valuable secondary metabolites, and jaceosidin and hispidulin are the major bioactive compounds. In the present study, the cultures were challenged by methyl jasmonate (MJ). The highest jaceosidin and hispidulin concentrations (65.2 +/- 3.67 mg/L and 12.3 +/- 0.47 mg/L) were achieved with 5 microM MJ added to 9-d-old subcultures, being 2.2-fold and 4.2-fold, respectively, higher than those from controls. The elicitor had little influence on cell growth, indicating that the changed biological processes did not include alterations in cell division. Furthermore, we observed that the activities of phenylalanine ammonia lyase were transiently increased after treatment with MJ, which suggests that this elicitor modifies jaceosidin and hispidulin production by regulating the phenylpropanoid pathway.

Overexpression of the Saussurea medusa chalcone isomerase gene in S. involucrata hairy root cultures enhances their biosynthesis of apigenin.

Saussurea involucrata is a medicinal plant well known for its flavonoids, including apigenin, which has been shown to significantly inhibit tumorigenesis. Since naturally occurring apigenin is in very low abundance, we took a transgenic approach to increase apigenin production by engineering the flavonoid pathway. A construct was made to contain the complete cDNA sequence of the Saussurea medusa chalcone isomerase (CHI) gene under the control of the cauliflower mosaic virus (CaMV) 35S promoter. Using an Agrobacterium rhizogenes-mediated transformation system, the chi overexpression cassette was incorporated into the genome of S. involucrata, and transgenic hairy root lines were established. CHI converts naringenin chalcone into naringenin that is the precursor of apigenin. We observed that transgenic hairy root lines grew faster and produced higher levels of apigenin and total flavonoids than wild-type hairy roots did. Over a culture period of 5 weeks, the best-performing line (C46) accumulated 32.1 mgL(-1) apigenin and 647.8 mgL(-1) total flavonoids, or 12 and 4 times, respectively, higher than wild-type hairy roots did. The enhanced productivity corresponded to elevated CHI activity, confirming the key role that CHI played for total flavonoids and apigenin synthesis and the efficiency of the current metabolic engineering strategy.

Cellular aggregate size as the critical factor for flavonoid production by suspension cultures of Saussurea medusa.

Three previously established cell lines (yellow, red and white) of Saussurea medusa were investigated for jaceosidin and hispidulin production. Maximum yields of the jaceosidin and hispidulin were obtained in the red cell line at 75+/-0.41 and 6.4+/-0.31 mg l-1. Production of jaceosidin and hispidulin correlated with the sizes of compact callus aggregates (CCA) and cellular viability. In the red cell line, the sizes of CCA were predominantly of 2-4 mm diameter and accounted for 64% biomass. This line had a sustained cell viability over 10 successive sub-cultures.

Transformation of Saussurea medusa for hairy roots and jaceosidin production.

Axenically grown Saussurea medusa plantlets were inoculated with four Agrobacterium rhizogenes strains, and hairy root lines were established with A. rhizogenes strain R1601 in N6 medium. PCR and Southern hybridization confirmed integration of the T-DNA fragment of the Ri plasmid from A. rhizogenes into the genome of S. medusa hairy roots. In N6 medium, maximum biomass of the hairy root cultures was achieved [8 g (dry weight) per liter; growth ratio 35-fold] after 21 days of culture. The amount of jaceosidin extracted from the hairy root cultures was 46 mg/l (production ratio of 37-fold) after 27 days of culture. The maximum jaceosidin content obtained using N6 medium was higher than that obtained with Modified White, MS or B5 medium. In N6 medium, the tip segments were more efficient for hairy root growth and jaceosidin production than the middle and basal regions of the root.

Cracks in the palisade cuticle of soybean seed coats correlate with their permeability to water.

BACKGROUND AND AIMS: Soybean (Glycine max) is among the many legumes that are well known for 'hardseededness'. This feature can be beneficial for long-term seed survival, but is undesirable for the food processing industry. There is substantial disagreement concerning the mechanisms and related structures that control the permeability properties of soybean seed coats. In this work, the structural component that controls water entry into the seed is identified. METHODS: Six soybean cultivars were tested for their seed coat permeabilities to water. To identify the structural feature(s) that may contribute to the determination of these permeabilities, fluorescent tracer dyes, and light and electron microscopic techniques were used. KEY RESULTS: The cultivar 'Tachanagaha' has the most permeable seed coat, 'OX 951' the least permeable seed coat, and the permeabilities of the rest ('Harovinton', 'Williams', 'Clark L 67-3469', and 'Harosoy 63') are intermediate. All seeds have surface deposits, depressions, a light line, and a cuticle about 0.2 microm thick overlaying the palisade layer. In permeable cultivars the cuticle tends to break, whereas in impermeable seeds of 'OX 951' it remains intact. In the case of permeable seed coats, the majority of the cracks are from 1 to 5 micro m wide and from 20 to 200 micro m long, and occur more frequently on the dorsal side than in other regions of the seed coat, a position that correlates with the site of initial water uptake. CONCLUSIONS: The cuticle of the palisade layer is the key factor that determines the permeability property of a soybean seed coat. The cuticle of a permeable seed coat is mechanically weak and develops small cracks through which water can pass. The cuticle of an impermeable seed coat is mechanically strong and does not crack under normal circumstances.

The Commelina yellow mottle virus promoter drives companion-cell-specific gene expression in multiple organs of transgenic tobacco.

Previous work has demonstrated that some endogenous plant gene promoters are active in selective companion cells of the phloem, depending on organ types and developmental stages. Here we report that the Commelina yellow mottle virus (CoYMV) promoter is active in the companion cells of leaves, stems and roots of transgenic Nicotiana tabacum cv. Xanthi NN, using beta-glucuronidase (GUS) as a reporter. Thus, the CoYMV promoter has a broad organ specificity. This promoter can be useful in molecular studies on the functions of companion cells in many aspects of phloem biology, such as regulation of long-distance transport, macromolecular traffic, plant development and interaction with pathogens. It may also be useful in engineering crops that produce specific gene products in the companion cells to block long-distance movement of pathogens.

Plasmodesma-mediated selective protein traffic between "symplasmically isolated" cells probed by a viral movement protein.

Intercellular communication is essential for differentiation and development. In plants, plasmodesmata (PD) form cytoplasmic channels for direct communication. During plant development, programmed reduction in PD number and transport capacity creates the so-called symplasmic domains. Small fluorescent dyes and ions can diffuse among cells within a domain but not across domain boundaries. Such symplasmic isolation is thought to allow groups of cells to differentiate and develop into tissues with distinct structures and functions. Whether or how "symplasmically isolated" cells communicate with one another is poorly understood. One well-documented symplasmic domain is the sieve element-companion cell (SE-CC) complex in the phloem tissue. We report here that, when produced in the CC of transgenic tobacco, the 3a movement protein (3a MP) of Cucumber mosaic virus fused to green fluorescent protein (GFP) can traffic out of the SE-CC complex via PD. The extent of 3a MP:GFP traffic across the boundary between vascular and nonvascular tissues depends on organ type and developmental stage. Our findings provide experimental evidence that endogenous machinery exists for protein traffic between the symplasmically isolated SE-CC complex and neighboring cells. We suggest that PD-mediated traffic of selected macromolecules can be a mechanism for symplasmically isolated cells to communicate with one another.