Bridging Angle Research Articles

Dicarboxylic ligands directing two Zn(II)-organic frameworks with distinct structures and significantly enhanced luminescence detection performances

Choosing different dicarboxylic ligands to construct MOFs with different structures and significantly improved luminescence detection properties has been studied. [Zn(L)(BDC)]n (1), [Zn4(L)4(ISO)4]n (2) (L = 1,4-Bis(4-pyridyl)naphthalene, H2BDC = terephthalic acid, H2ISO = isophthalic acid) have been successfully synthesized and characterized. Their structural features vary from a 3D pillar-layered 5-fold interpenetrated dia framework (1) to a 2D double-layered non-interpenetrated sql net (2). The different structures between 1 and 2 can be attributed to distinct bridging angles from dicarboxylic ligands. Furthermore, luminescent sensing experiments exhibit that 1 and 2 are efficient dual-responsive sensors for the detection of acetylacetone (acac) and Cr2O72−. Especially, 2 performs very highly sensitive quenching response towards acac in aqueous medium. More interestingly, 2 exhibits significantly enhanced quenching efficiencies than 1 (Ksv of detecting acac: 7.87 × 103 M−1 for 1 and 4.9 × 104 M−1 for 2; Ksv of detecting Cr2O72−: 3.95 × 103 M−1 for 1 and 1.41 × 104 M−1 for 2). The cause for higher quenching efficiencies of 2 has been preliminary discussed. The efficient luminescence quenching mechanisms of 1/2 towards acac/Cr2O72− have been elucidated.

Synthesis, crystal structure, vibrational spectroscopy and electrochemical investigations of a new acidic metal pyrophosphate NiK1.18N0.82(H2P2O7)2.2H2O

The new complex NiK1.18N0.82(H2P2O7)2.2H2O was synthesized using the co-precipitation method and structurally characterized by X-ray single crystal diffraction, infrared spectroscopy (IR) and SEM-EDS analysis. This salt crystallizes in the triclinic system, space group Pī. The crystal structure has been refined up to a final R value of 0.0353 using independent reflexion 2073. The results showed that nickel (Ni) octahedrally coordinated by two water molecules and four oxygen atoms belonging to two (H2P2O7) diphosphate groups. Potassium (K) and nitrogen (N) cations are involved in a complex coordination within resulting cavities from phosphorus tetrahedra and Nickel octahedra. The infrared spectrum of title compound was recorded and interpreted showing a bent POP bridging angle in this material. In addition, the inhibition effect of this acidic metal pyrophosphate on mild steel corrosion in 1.0 M HCl solution was studied. For this aim, electrochemical techniques such as potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) were used. The polarization curves showed that NiK1.18N0.82(H2P2O7)2.2H2O behaves mainly as an cathodic-type inhibitor.

Crack growth properties in granite specimens consisting non-persistent joint under punch shear through test

Experimental and numerical methods were used to investigate the effect of echelon notchs on the shear behaviour of joint’s bridge area in granite. A punch-through shear test was used to model the granite cracks under shear loading. Granite samples with dimension of 20 mm×150 mm×40 mm were prepared in the laboratory. Within the specimen model and near the edges, four edge notches were provided. Nine different configuration systems were prepared for notches. In these configurations, the length of each notch was taken as 3 cm, 4cm and 5 cm. Assuming a plane strain condition, special rectangular models were prepared with dimensions of 100 mm×100 mm using particle flow code in two dimensions. similar to those for joints configuration systems in the experimental tests i.e. 9 models with different rock bridge lengths and rock bridge joint angle were prepared. The axial load was applied to the punch through the central portion of the model. This testing showed that the failure process was mostly governed by the rock bridge length and rock bridge angle. The shear strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the rock bridge angle. The strength of samples decreases by increasing the joint length. The failure pattern and failure strength are similar in both methods i.e. the experimental testing and the numerical simulation methods.

Correction to: Experimental study on strength properties, fracture patterns, and permeability behaviors of sandstone containing two filled fissures under triaxial compression

Rock masses generally contain many fissures filled with weak materials. At present, the interaction mechanisms of crack coalescence and seepage in rock with filled fissures are still poorly understood. Therefore, this study conducts systematic laboratory tests on sandstone samples with two filled fissures under hydromechanical coupling conditions. The influences of the fissures, filling, ligament length, and bridge angle on the strength, fracture pattern, and permeability are explored. The results show that the strength properties of the sandstone are weakened more significantly by fissures than by water pressure. The increase of strength properties induced by the fillings is more remarkable in the samples with either a longer ligament length or a lower bridge angle. Unlike for mud filling, for sand filling, most of the sand particles in the fissures are crushed after loading, reflecting that the bearing capacity of the sand filling is fully utilized. Thus, sand filling generally has a greater effect on the strength properties than mud filling does. Furthermore, the failure of double-fissure sandstone can be divided into five modes. With the exception of the samples with a high bridge angle, the samples undergo failure modes that change with the existence of fillings, and for samples with a long ligament length or a low bridge angle, the change is more sensitive to the filling type. The weakening effect of fillings on permeability is associated with the failure mode, and it is more remarkable in samples with the “wing cracks + indirect crack coalescence” or “wing cracks + direct crack coalescence” failure modes than in other samples.

Linear Structural Trends and Multi-Phase Intergrowths in Helvine-Group Minerals, (Zn,Fe,Mn)8[Be6Si6O24]S2

Synchrotron high-resolution powder X-ray diffraction (HRPXRD) and Rietveld structure refinements were used to examine the crystal structure of single phases and intergrowths (either two or three phases) in 13 samples of the helvine-group minerals, (Zn,Fe,Mn)8[Be6Si6O24]S2. The helvine structure was refined in the cubic space group P4¯3n. For the intergrowths, simultaneous refinements were carried out for each phase. The structural parameters for each phase in an intergrowth are only slightly different from each other. Each phase in an intergrowth has well-defined unit-cell and structural parameters that are significantly different from the three endmembers and these do not represent exsolution or immiscibility gaps in the ternary solid-solution series. The reason for the intergrowths in the helvine-group minerals is not clear considering the similar radii, identical charge, and diffusion among the interstitial M cations (Zn2+, Fe2+, and Mn2+) that are characteristic of elongated tetrahedral coordination. The difference between the radii of Zn2+ and Mn2+ cations is 10%. Depending on the availability of the M cations, intergrowths may occur as the temperature, pressure, fugacity fS2, and fluid composition change on crystallization. The Be–Si atoms are fully ordered. The Be–O and Si–O distances are nearly constant. Several structural parameters (Be–O–Si bridging angle, M–O, M–S, average <M–O/S>[4] distances, and TO4 rotational angles) vary linearly with the a unit-cell parameter across the series because of the size of the M cation.

Crack coalescence in rock-like specimens with two dissimilar layers and pre-existing double parallel joints under uniaxial compression

Layered rock masses with joints are widely found in nature. Their mechanical behavior plays a key role in rock engineering applications. However, previous studies have concentrated on the single lithologic layer, and few studies have reported the crack coalescence mechanism in layered rock masses with joints. In this study, uniaxial compression tests were performed on jointed rock-like specimens with two dissimilar layers. The acoustic emission (AE) and the digital image correlation (DIC) techniques are employed to investigate the crack coalescence process of specimens with two dissimilar layers. The influence of the joint angle and rock bridge angle on the mechanical behavior and failure processes in layered rock masses is investigated. The results show that the peak strength is associated with the joint angle and the rock bridge angle. Seven types of crack coalescence have been identified in the specimens, which are not only related to the joint angle and the rock bridge angle but also influenced by the rock layers. Cracks easily coalesce when the joint angle and the rock bridge angle are small. However, when the joint angle and the rock bridge angle are larger, it is difficult for cracks to initiate and propagate in the layer with higher strength. The failure mechanism of the specimens is primarily caused by crack propagation in the layer with lower strength.

Partial feedback linearization for a path control in a gantry crane used in lifting machinery in civil engineering

This paper presents an alternate form for the dynamic modelling of a mechanical system that simulates in real life a gantry crane type, using Euler Lagrange classical mechanics, which allows find the equations of motion that our model describes. In order to verify the theoretical results obtained, a comparison was made between solutions obtained by simulation in SimMechanics-Matlab and Euler Lagrange equations system, has been solved through Matlab libraries for solving equations systems of the type and order obtained. Based on the partial feedback linearization, an improved nonlinear controller is analyzed and designed for the movement of an overhead crane or industrial shed. Three control inputs composed of bridge movement forces, carriage displacement, and pendulum or load angle are used to handle the state variables consisting of bridge movement, carriage movement, load displacement, and angle of turn of the same. The objective is to bring the mass of the pendulum from one point to another with a specified distance without the oscillation from it, so that, the answer was overdamped. The asymptotic stability of Lyapunov is also studied and the control scheme is of position of the load, constituted by the non-linear feedback of the actuated and non-actuated states. To verify the quality of the control process, verify numerical simulations. The proposed controller asymptotically stabilizes all states in the system.

Effects of the Rock Bridge Ligament on Fracture and Energy Evolution of Preflawed Granite Exposed to Dynamic Loads

This paper aims to reveal the mechanical properties, energy evolution characteristics, and dynamic rupture process of preflawed granite under impact loading with different rock bridge angles and strain rates. A series of dynamic impact experiments were conducted along with the separate Hopkinson press bar (SHPB) testing system to analyze and study the overall rock fracture process. Under the impact load, the peak stress of granite increases with the increase of rock bridge angle and strain rate, but the increase gradually decreases. The peak strain also increases gradually with the increase of rock bridge angle, but there is an upper limit value; the total input strain energy increases with the increase of strain rate and rock bridge angle. It is shown that the higher the strain rate, the higher the unit dissipation energy, and the greater the degree of rock fragmentation. For rock under impact loads, the crack first initiates from the wing end of the prefabricated flaw, the preflaw closes gradually, and finally the crack propagates at the locking section leading to the coalescence of rock bridge. With the increase of strain rate, the fragmentation degree of the specimen increases asymptotically, and the average fragmentation size of the specimen decreases with the increase of strain rate. It is suggested that the stability of large rocked slopes is controlled by the locked section, and understanding the fracture evolution of the rock bridge is the key to slope instability prediction.

Experimental investigation of crack propagation behavior and failure characteristics of cement infilled rock

A detailed understanding of the failure characteristics of infilled jointed rock is a key concern in underground engineering and is critical to the design, construction and maintenance of relevant projects. In this paper, uniaxial compression tests were performed to investigate the effect of the joint arrangement (different rock bridge angles) on the strength and crack propagation of red sandstone containing a set of preexisting infilled flaws of the same sizes and angles, while the crack fracturing process was observed by AE and strain monitoring. When the angle between the rock bridge and loading stress was less than 24°, the rock mass failure form was tensile failure with some localized shear failure occurring in the rock bridge damaged by crack penetration, leading to an overall decrease in the carrying capacity. The turning points of the strain and AE signal were clearly observed to be caused by the initiation and propagation of cracks, and the energy consumed by the initiation of shear cracks was greater than that of tensile cracks. The study was further conducted using the fracture mechanics numerical code FRACOD to investigate the crack propagation law and failure mechanism under different loading stress conditions. Simulation results from three 2D similar models showed that the percentage of open fractures decreased, but slipping increased; in addition, the total length of the fractures was greatly reduced with increasing confining stress. These results are important and valuable for understanding the crack mechanism of rock engineering in deep underground mining excavations.

(Keynote) Gaining Control over the Morphology of Metal–Organic Frameworks

Owing to their vast ratio of surface area to mass and volume, metal-organic frameworks (MOFs) revolutionized many applications that rely on chemical and physical interactions at surfaces. However, a great challenge today is to build MOF materials that translate the functionality at the molecular level effectively to the macroscopic world. To do this, effective transport of reagents to, from, and within MOF materials is critical. To overcome this barrier, porous materials will need to be structured with feature sizes from below one micrometre to the millimetre or centimetre scale. In fact, the challenge of morphology control over multiple length scales of MOF materials is overlooked by researchers so far but is the key to enable groundbreaking real-world applications.The synthesis of a MOF material always starts with the strategic selection of precursor materials. Besides an organic building block, an inorganic compound providing metal ions is necessary, which most commonly is a metal salt, as it easily dissolves. A relatively new and different approach is the use of metal oxides (MOs). Even though their use is challenging due to low solubility issues and slow and non-homogenous conversion, by carefully optimizing the experimental conditions the MO–to–MOF conversion can be carried out with preserving the morphology of the MO (Figure 1). Thus, the use of MO precursors, which offers a huge number of different morphologies that can be synthesized with high precision, potentially provides an easy and smart way for the precise synthesis of different MOF morphologies. This strategy opens the door to morphologies that cannot be achieved using reactions based on metal salt precursors or other approaches.This contribution focuses on (1) the study of different MOs as precursors for MOF formation, (2) giving a deep insight in the underlying chemistry, and (3) application of this knowledge to convert different complex 3D morphologies of MOs into MOFs. Our findings demonstrate that all MOs tested so far can be used as precursors for the synthesis of MOFs, although they not always preserve the parent shape. To illustrate the capacity of the SP approach and to uncover the full mechanistic details of the early stages of this process we explored the conversion of ZnO into the zeolitic imidazolate framework (ZIF) ZIF-8 in detail. ZIFs are a group of MOFs that are structurally very similar to the well-known zeolites. Zeolites are composed of [TO4] (T = Si, Al) tetrahedrons covalently joined by bridging oxygen atoms and ZIFs of [MN4] (M = transition metal ion) tetrahedrons with bridging five-membered imidazolate units with very similar bridging angles and framework topologies. Finally, we used the gained knowledge to convert different three dimensional 3D ZnO morphologies into ZIFs.Figure: Conversion of metal oxides (MOs) into metal—organic frameworks (MOFs) with the competing rates k1 (MO dissolution), k2 (diffusion), k3 (MOF nucleation), and k4 (MOF growth). Certain conditions of the reaction medium lead to MO dissolution, followed by diffusion of metal ions and organic linkers. Depending on the ratios of the different rates either homogeneous nucleation within the solution or heterogeneous nucleation on the MO-medium interface occurs (or a mixture of both). The former can be understood as a dissolution-crystallization (DC) mechanism, analogous to reactions using metal salt precursors, the latter as a shape-preservation (SP) mechanism. Figure 1

Two Zn(II)-organic frameworks based on “V”-shaped terpyridine ligand and dicarboxylic ligands: Fascinating architectures and efficient luminescent aqueous-phase dual-responsive detection

A “V”-shaped terpyridine ligand 3,3’:5′,3″-terpyridine (L) was firstly applied to construct metal-organic frameworks. Two Zn-MOFs, [Zn2(L) (BDC)2(H2O)]n (1) and {[Zn(L) (ISO)]·H2O}n (2) (H2BDC ​= ​terephthalic acid, H2ISO ​= ​isophthalic acid) had been successfully synthesized by L and auxiliary dicarboxylic ligands. Structurally, 1 features an unprecedented (3,3,8)-connected framework constructed from tridentate L units, mononuclear Zn units, binuclear [Zn2(CO)2] units and BDC2− bridges. While 2 shows a rare (3,5)-connected architecture assembled from tridentate L units, mononuclear Zn units and ISO2− bridges. The different structures and topological diversities between 1 and 2 can be attributed to different twist angles between pyridine rings in L and distinct bridging angles from auxiliary ligands. Moreover, luminescent sensing experiments exhibit that 1 can act as a promising dual-responsive sensor for detecting TNP and Fe3+ in aqueous phase with high efficiency. The luminescence test paper was successfully developed to detect TNP for the practical applications. In addition, the emission quenching mechanisms of 1 towards TNP and Fe3+ were elucidated.

Pleistocene Calcareous Nannofossil Biostratigraphy and Gephyrocapsid Occurrence in Site U1431D, IODP 349, South China Sea

We reinvestigated the Pleistocene calcareous nannofossil biostratigraphy of Site U1431D (International Ocean Discovery Program (IODP) Expedition 349) in the South China Sea (SCS). Twelve calcareous nannofossil Pleistocene datums are identified in the site. The analysis confirms that the last occurrence (LO) of Calcidiscus macintyrei is below the first occurrence (FO) of large Gephyrocapsa spp. (>5.5 μm). The FO of medium Gephyrocapsa spp. (4–5.5 μm) is also identified in the samples through morphometric measurements, which was unreported in shipboard results. Magnetobiochronologic calibrations of the numerical ages of LO of Pseudoemiliania lacunosa and FO of Emiliania huxleyi are underestimated and need reassessment. Other potential markers such as a morphological turnover of circular to elliptical variants of Pseudoemiliania lacunosa and a small Gephyrocapsa acme almost synchronous with the FO of Emiliania huxleyi may offer biostratigraphic significance in the SCS. The morphologic changes in Gephyrocapsa coccoliths are also examined for the first time in Site U1431D. Placolith length and bridge angle changes are comparable with other ocean basins, suggesting that morphologic changes are most likely evolutionary novelties rather than being caused by local climate anomalies.

Evaluation of Fixed Denture Prosthetic Restorations with Pier Abutment

The aim of this study is to evaluate the prosthetic, periodontal, radiographic and clinical findings of the fixed on-tooth restorations with middle base and observe the changes of these values over time. 24 patients were included in our study, and these patients were measured twice, one year between measurements. Statistical analyzes were performed in IBM SPSS Statistical Software program (version 21; IBM, Armonk, NY). In these analyzes, parameters such as age, gender, distance between the abutments, bridge angle, occlusion type, opposite arc type, vitality of the teeth, amount of attached gingiva, root length, restoration length, gingival pocket amount of the abutment teeth, gingival index, gingival bleeding index, plaque index, their relationship with clinical attachment loss changes, ceramic fracture and complications were evaluated. According to the data of our study, findings that are compatible with the literature and provide new information to the literature in terms of clinical loss of attachment, occurrence of periodontal diseases or complications related to restoration in patients who underwent rigid fixed prosthetic restoration, and the changes recorded in the controls performed. For this reason, we believe that rigid fixed prosthetic restorations will be more advantageous in laboratory practice, since non-rigid restorations require more complicated laboratory work, and we believe that clinical and radiological complications do not have a definite relationship with the type of restoration. Keywords : Pier abutment, fixed prosthesis, periodontal tissue, prosthetic complication, tooth supported prosthesis. DOI : 10.7176/JSTR/6 10 11

The caesium phosphates Cs3(H1.5PO4)2(H2O)2, Cs3(H1.5PO4)2, Cs4P2O7(H2O)4, and CsPO3

The caesium phosphates Cs3(H1.5PO4)2(H2O)2 and Cs3(H1.5PO4)2 were obtained from aqueous solutions, and Cs4P2O7(H2O)4 and CsPO3 from solid state reactions, respectively. Cs3(H1.5PO4)2, Cs4P2O7(H2O)4, and CsPO3 were fully structurally characterized for the first time on basis of single-crystal X-ray diffraction data recorded at − 173 °C. Monoclinic Cs3(H1.5PO4)2 (Z = 2, C2/m) represents a new structure type and comprises hydrogen phosphate groups involved in the formation of a strong non-symmetrical hydrogen bond (accompanied by a disordered H atom over a twofold rotation axis) and a very strong symmetric hydrogen bond (with the H atom situated on an inversion centre) with symmetry-related neighbouring anions. Triclinic Cs4P2O7(H2O)4 (Z = 2, Pbar{1}) crystallizes also in a new structure type and is represented by a diphosphate group with a P–O–P bridging angle of 128.5°. Although H atoms of the water molecules were not modelled, O···O distances point to hydrogen bonds of medium strengths in the crystal structure. CsPO3 is monoclinic (Z = 4, P21/n) and belongs to the family of catena-polyphosphates (MPO3)n with a repetition period of 2. It is isotypic with the room-temperature modification of RbPO3. The crystal structure of Cs3(H1.5PO4)2(H2O)2 was re-evaluated on the basis of single-crystal X-ray diffraction data at − 173 °C, revealing that two adjacent hydrogen phosphate anions are connected by a very strong and non-symmetrical hydrogen bond, in contrast to the previously described symmetrical bonding situation derived from room temperature X-ray diffraction data. In the four title crystal structures, coordination numbers of the caesium cations range from 7 to 12.Graphic abstract

3D facial morphometry in Italian patients affected by Aicardi syndrome

Aicardi syndrome (AIC) is a rare congenital neurodevelopmental disorder of unknown etiology, that affects almost exclusively females, originally characterized by corpus callosum agenesis, chorioretinal lacunae, and infantile spasms. The current diagnostic criteria also include qualitative facial features (prominent premaxilla, upturned nasal tip, decreased nasal bridge angle, sparse lateral eyebrows, and microphthalmia) that still need quantification. A three-dimensional (3D) photogrammetric assessment of 11 Italian females, age 7-32 years, who satisfied AIC criteria, was performed. Linear distances and angles were computed from soft-tissue facial landmarks coordinates. The z-score values were calculated using data of 850 healthy reference females matched for age and compared by Mann-Whitney test (p < .01). Patients showed a shorter philtrum and right side orbital height (mean z-scores: -1.7, -0.9), shorter superior, middle, and inferior facial depths (mean z-scores: -1.3, -2.2, -2.3), and a smaller length of mandibular ramus (mean z-score: -2.1); conversely, they showed larger nasal and lower facial widths, and lower facial convexity (mean z-scores: 1.7, 1.4, 2.4). The inclinations of the orbit versus the true horizontal were increased bilaterally (mean z-scores: 1.8, 1.1). Some common facial abnormalities were quantified in AIC patients using a noninvasive instrument. They may help clinicians in performing a definite AIC diagnosis in atypical or doubt cases.

The crystal structure of KScP2O7.

Single crystals of KScP2O7, potassium scandium diphosphate, were grown in a borate flux. The title compound crystallizes isotypically with KAlP2O7 in space-group type P21/c, Z = 4. The main building block is an {ScP2O11}9- unit, forming layers parallel to (001). These layers are stacked along [001] via common corners of octa-hedral and tetra-hedral units to span up large hepta-gonal cavities that host the potassium cations with a coordination number of 10. The P-O-P bridging angle increases with increasing size of the octa-hedrally coordinated M III cation, as do the K-O distances within a series of KM IIIP2O7 compounds (M III = Al to Y with ionic radii r = 0.538 to 0.90 Å).

Azido and thiocyanato bridged dinuclear Ni(II) complexes involving 8-aminoquinoline based Schiff base as blocking ligands: Crystal structures, ferromagnetic properties and magneto-structural correlations

The use of two 8-aminoquinoline-based tridentate N3-donor rigid Schiff base ligands (L1 and L2) with Ni(II) in the presence of the pseudohalides, NaN3 and NaSCN results in the crystallization of the two novel Ni(II) dimers: [Ni2(L1)2(µ1,1′-N3)2(N3)2] (1) and [Ni2(L2)2(µ1,3-NCS)2(NCS)2] (2). Both complexes are centrosymmetric Ni(II) dimers where the Schiff base ligands coordinate the octahedral Ni(II) centres in a mer configuration with one terminal and two bridging pseudohalide ligands in the remaining positions. Complex 1 shows Ni(II) ions connected by a double µ1,1′-N3− bridge whereas in complex 2 the Ni(II) ions are connected by a double µ1,3-NCS− bridge. The magnetic properties show the presence of a weak ferromagnetic coupling in both compounds that can be fit with g = 2.290(6), J = 6.1(2) cm−1, zJ′ = −0.32(1) cm−1 and |D| = 4.34(5) cm−1 for 1 and g = 2.096(2), J = 4.71(5) cm−1, zJ′ = −0.054(2) cm−1 and |D| = 1.52(2) cm−1 for 2 (the Hamiltonian is written as −2JS1S2). Both J values have been rationalized in terms of previous magneto structural correlations based on the Ni-N-Ni bridging angle in 1 and on the asymmetry of the Ni-S-C-N-Ni bridges in 2.

Stability analysis of flawed rock slope by using virtual-bond-based general particles dynamics

General particle dynamics code (GPD) with a virtual bond model is adopted to investigate the stability of rock slopes subjected to gravity. The natural discontinuities are represented by straight flaws in the numerical model. The failure process of rock samples containing three pre-existing and four pre-existing flaws subjected to uniaxial compression is simulated. The numerical failure processes of rock samples are in good agreement with the experimental observations as well as the complete stress–strain curves. Moreover, six en-echelon flaw arrays including collinear flaw array, en-echelon flaw array with bridge angle of 90°, en-echelon flaw array with bridge angle more than 90°, en-echelon flaw array with bridge angle less than 90°, multiple rows of en-echelon flaws with doubly periodic rectangular array, multiple rows of en-echelon flaws with diamond-shaped array in rock slope are studied. The crack initiation, propagation and coalescence process in rock slopes with six en-echelon flaw arrays subjected to gravity are analyzed. Two crack initiation modes including primary crack and secondary crack are found as well as nine crack coalescence modes. The stress distributions as well as displacement fields are investigated during the crack evolution. The gravity increase method is implemented into the VB-GPD to obtain the safety factor of rock slopes. The proposed method was then verified by the case study of the Xingluokeng mine in China. The results indicate a good accordance between simulation and field monitoring. This study reveals that the proposed method can tackle flawed rock slope failure problems.

Experimental Study of Mechanical and Permeability Behaviors During the Failure of Sandstone Containing Two Preexisting Fissures Under Triaxial Compression

Rock masses are typical inhomogeneous geological materials that contain many fissures and cracks. The coupling effect of the crack propagation and seepage evolution in rocks is very important to the safety of rock engineering. However, hydromechanical coupling behavior during the failure of fissured rocks has rarely been investigated. In this research, hydromechanical coupling tests are performed to fully explore the behaviors in strength, deformation, permeability and failure mode of sandstone samples with two preexisting fissures. The experimental results show that the ratio of crack initiation threshold/peak strength, the ratio of crack damage threshold/peak strength and the value of the elastic modulus decrease by at most 31.8%, 12.2% and 18.4% due to the existence of the two fissures, while the Poisson’s ratio increases by at most 45.6%. Furthermore, the values of permeability before the sudden increase stage range from 2.1% to 17.6% of the maximum permeability value. The influence of bridge length and angle on permeability is more significant under lower confining pressure or higher water pressure. Five failure modes are observed in the double-fissure samples under hydromechanical coupling conditions. Additionally, the “wing cracks + indirect coalescence” failure mode is generated only when the ligament length is shorter than the fissure length. The corresponding strength is lower than that for other failure modes. CT images show that the expansion of cracks inside the samples is more restricted than that at the surface of the samples, especially near the rock bridge region. The effects of failure modes on the mechanical and permeability properties, from greatest to least, are as follows: crack initiation threshold, peak strength, crack damage threshold, elastic modulus, Poisson’s ratio and permeability. This research is contributed to analyze the stability of water-bearing rocks in underground caverns with many preexisting fissures.

Study on the Magneto-Structural Correlation of a New Dinuclear Cobalt(II) Complex with Double μ-Phenoxo Bridges.

A new μ-phenoxo-bridged dinuclear cobalt(II) complex, [Co2(L)2(acac)2(H2O)] (1), has been synthesized by employing a new ligand, (4-methyl-2-formyl-6-(((2-trifluoromethyl)phenyl)methyliminomethyl) phenol) (HL). Structural analysis of complex 1 reveals that the geometry around cobalt centers is best described as a distorted octahedron and the distance of cobalt neighbors is 3.128(0) Å. The magnetic property studies indicate that complex 1 exhibits strong spin–orbit coupling effects and weak ferromagnetic coupling between two high-spin Co(II) centers linked by double μ-Ophenoxo bridges, with J = 1.87(2) cm–1. The studies show that not only the Co–O–Co angle affects the alignment of the cobalt spins but also the dihedral angle between the CoOCo plane and the phenyl plane plays an important role in the magnetic coupling in this [Co2O2] system. Thus, the small bridging angles (96.96(11) and 96.91(11)°) and the large dihedral angles between the CoOCo plane and the phenyl plane (63.0(1) and 30.6(1)°) induce intramolecular ferromagnetic exchange interaction in complex 1.