| 1. |
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| 2. |
- Wang, Q.Z., et al.
(författare)
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The flattened Brazilian disc specimen used for testing elastic modulus, tensile strength and fracture toughness of brittle rocks : analytical and numerical results
- 2004
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 41:2, s. 245-253
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Tidskriftsartikel (refereegranskat)abstract
- The flattened Brazilian disc specimen is proposed for determination of the elastic modulus E, tensile strength sigma (sub t) and opening mode fracture toughness K (sub IC) for brittle rocks in just one test. This paper is concerned with the theoretical analysis as well as analytical and numerical results for the formulas. According to the results of stress analysis and Griffith's strength criteria, in order to guarantee crack initiation at the centre of the specimen, which is considered to be crucial for the test validity, the loading angle corresponding to the flat end width must be greater than a critical value (2alpha > or =20 degrees ). The analysis shows that, based on the recorded complete load-displacement curve of the specimen (the curve should include the "fluctuation" section after the maximum load), E can be determined by the slope of the section before the maximum load, sigma (sub t) by the maximum load, and K (sub IC) by the local minimum load immediately subsequent to the maximum load. The relevant formulas for the calculation of E, sigma (sub t) , K (sub IC) are obtained, and the key coefficients in these formulas are calibrated by finite-element analysis. In addition, some approximate closed-form formulas based on elasticity are provided, and their accuracy is shown to be adequate by comparison with the finite-element results.
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| 3. |
- Chen, C. N., et al.
(författare)
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Aggregate manganese Schiff base moieties by terephthalate or acetate : Dinuclear manganese and trinuclear mixed metal Mn-2/Na complexes
- 2003
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 42:11, s. 3540-3548
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Tidskriftsartikel (refereegranskat)abstract
- A reaction system consisting of terephthalic acid, NaOH, inorganic Mn(II) or Mn(III) salt, and salicylidene alkylimine resulted in dinuclear manganese complexes (salpn)(2)Mn-2(mu-phth)(CH3OH)(2) (1, salpn = N,N'-1,3-propylene-bis(salicylideneiminato); phth = terephthalate dianion), (salen)(2)Mn-2(mu-phth)(CH3OH)(2) (2, salen = N,N'-ethylene-bis(salicylideneiminato)), (salen)(2)Mn-2(mu-phth)(CH3OH)(H2O) (3), and (salen)(2)Mn-2(mu-phth) (4), while the absence of NaOH in the reaction led to a mononuclear Mn complex (salph)Mn(CH3OH)(NO3) (5, salph = N,N'-1,2-phenylene-bis(salicylideneiminato)). In addition, a trinuclear mixed metal complex H{Mn2Na(salpn)(2)(mu-OAc)(2)(H2O)(2)}(OAc)(2) (6) was obtained from the reaction system by using maleic acid instead of terephthalic acid. Five-coordinate Mn ions were found in 4 giving rise to an intermolecular interaction and constructing a one-dimensional linear structure. Antiferromagnetic exchange interactions were observed for 1-3, and a total ferromagnetic exchange of 4 was considered to stem from intermolecular magnetic coupling. H-1 NMR signals of phenolate ring and alkylene (or phenylene) backbone of the diamine are similar to those reported in the literature, and the phth protons are at -2.3 to -10.1 ppm. Studies on structure, bond valence sum analysis, and magnetic properties indicate the oxidation states of the Mn ions in 6 to be +3, which are also indicated by ESR spectra in dual mode. Ferromagnetic exchange interaction between the Mn(III) sites was observed with J = 1.74 cm(-1). A quasireversible redox pair at -0.29V/0.12V has been assigned to the redox of Mn-2(III)/Mn(III)Mn(II), implying the intactness of the complex backbone in solution.
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| 4. |
- Li, H. Y., et al.
(författare)
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Properties of a dinuclear Mn(III,III) complex with a tri-phenolate ligand N4O3 (3-) and a new complex containing a ligand covalently linked to ruthenium tris-bipyridine
- 2004
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Ingår i: Huaxue xuebao. - 0567-7351. ; 62:9, s. 916-922
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Tidskriftsartikel (refereegranskat)abstract
- A new high valent complex [Mn-2(III, III)L(mu-OAc)(2)].PF6 (2a) was prepared, where L was the trianion of 2, 6-bis {[(2-hydroxy-5-tert-butylbenzyl) (pyridyl-2-methyl)-amino]-methyl}-4-methylphenol, which contains two additional phenolate groups and two tert-butyl groups compared to its parent [Mn-2(II, II)(bpmp)(mu-OAc)(2)].ClO4 (1). These improvements narrowed the disparity between the new model and (Mn)(4) cluster (OEC in nature). Moreover, L was modified to be covalently linked with Ru(II) tris-bipyridine through an amide bond to construct a complex 2b for the study of photoinduced electron transfer (PET). UV-vis, IR, emission spectra and electrochemistry were used to investigate their photochemistry properties. The results showed that 2b has good photochemistry properties and the E-1/2 of Ru3+/Ru2+ was higher than those of phenol(+)/phenol and Mn(III, IV)/Mn(III, III). After coordination of manganese ions, the electron transfer process in the model complex conforms to the basic principles of electron donor side of photosystem II (PS II) in nature.
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| 5. |
- Liu, X. H., et al.
(författare)
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High-temperature X-ray diffraction studies on polyamide6/clay nanocomposites upon annealing
- 2002
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Ingår i: Polymer Bulletin. - : Springer Science and Business Media LLC. - 0170-0839 .- 1436-2449. ; 48:05-apr, s. 381-387
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Tidskriftsartikel (refereegranskat)abstract
- The influence of nanodispersed clay on the alpha crystalline structure of polyamide 6 (PA6) was examined in-situ with X-ray diffraction (XRD) between room temperature and melting. In pure PA6 upon annealing the alpha crystalline phase was substituted by an unstable pseudohexagonal phase at 150degreesC, then it transformed into a new stable crystalline structure - high temperature alpha' phase above the transition temperature. However, in PA6/clay nanocomposite (PA6CN), the alpha phase did not present crystalline phase transition on heating. The increase in the annealing temperature only led to continuous intensity variation. The different behaviors were caused by the confined spaces formed by silicate layers, which constrained the mobility of the polymer chains in-between.
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| 6. |
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| 7. |
- Huang, D. G., et al.
(författare)
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Synthesis, structural characterizations and magnetic properties of a series of mono-, di- and polynuclear manganese pyridinecarboxylate compounds
- 2004
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; :7, s. 1454-1464
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Tidskriftsartikel (refereegranskat)abstract
- Seven new manganese(II, III, IV) pyridinecarboxylate compounds (Et4N)[MnCl2(pic)(2)] (1, Hpic = picolinic acid) [MnCl(Pic)(2)(H2O)].H2O (2), [MnCl(pic)(H2O)2](n) (3), [Mn(Pic)(2)](n) (4), [MnCl(pic)](n) (5), [MnCl2(4-C5H4NHCOO)](n) (6) and [Mn2O2(pic)(4)] (7) were synthesized and structurally characterized. The picolinate ligand coordinates to the Mn ion forming a chelating five-membered ring which constructs diverse architectures by various bridging modes, such as mu-Cl, mu(1,1)(-) and mu(1,3)-carboxylate bridges (syn-syn and syn-anti modes). The interaction between the pyridyl rings is discussed, displaying a face-to-face pi-pi stacking for complex 6 and a T-shaped C-H...pi attraction for complex 4. Complex 3 has an infinite zigzag chain structure in which two neighboring Mn ions are linked by a carboxylate bridge in a syn-anti mode. In complex 4, the Mn(pic)(2) fragments are joined to each other by double mu(1,1)-carboxylate bridges, forming a 2D layer structure. Complex 5 contains Mn4O4 square subunits which are connected by double mu-Cl bridges to form a grid-like 2D structure. The isonicotinate complex 6 has a zigzag chain structure containing mixed double mu-Cl and mu(1,3)-carboxylate bridges in a syn-syn mode. Protonation at the pyridyl-N position was found and identified by the IR and magnetic properties of 6. The participation of an oxidizing agent like MnO4- leads to complexes containing higher valent manganese (1, 2 and 7). The IR spectra of these complexes are discussed and found to be consistent with the structural features. The magnetic properties of complexes 4, 5 and 6 have been investigated. Antiferromagnetic coupling interactions were observed and satisfactory fitting results were obtained with J values ranging from -0.63 cm(-1) to -2.35 cm(-1). The magnetic parameters of these complexes, together with the parameters of other Mn complexes with comparable structures, are compared and discussed based on the bridging modes. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).
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| 8. |
- Huang, D. U., et al.
(författare)
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Synthesis, structural characterization and magnetic properties of 2-pyrazinecarboxylate manganese compounds Mn(pyz)(2)(H2O)(4) and MnCl(pyz)(H2O) (n) (pyz=2-pyrazinecarboxylate)
- 2003
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Ingår i: Inorganica Chimica Acta. - 0020-1693 .- 1873-3255. ; 353, s. 284-291
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Tidskriftsartikel (refereegranskat)abstract
- Two pyz complexes [Mn(pyz)(2)(H2O)(4)] (1) and [MnCl(pyz)(H2O)] (2) have been synthesized and structurally characterized. Complex 1 contains an eight-coordinate Mn(II) ion with square anti-prismatic geometry. The extensive intermolecular hydrogen-bonding interactions of O-carboxyl...H-O-aqua correlate the complex molecules, forming 2D polymeric layer structure. The structure of complex 2 contains 1D Mn/pyz chains, which link to each other by double mu(2)-Cl bridges to form 2D layer with Mn...Mn distance of 3.664 Angstrom. Hydrogen-bonding interactions of O-carboxyl...H-O-aqua are found between the layers to correlate the 2D layers to form a 3D framework. In addition, the variable temperature magnetic susceptibilities of complex 2 were measured and weak ferromagnetic exchange interactions between the neighboring magnetic species were found with J = 0.42 cm(-1).
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| 9. |
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| 10. |
- Zhang, H Q, et al.
(författare)
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P21-activated kinase 4 interacts with integrin alpha v beta 5 and regulates alpha v beta 5-mediated cell migration
- 2002
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Ingår i: Journal of Cell Biology. - : Rockefeller University Press. - 0021-9525 .- 1540-8140. ; 158:7, s. 1287-1297
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Tidskriftsartikel (refereegranskat)abstract
- P21-activated kinase 1 (PAK1) can affect cell migration (Price et al., 1998; del Pozo et al., 2000) and modulate myosin light chain kinase and LIM kinase, which are components of the cellular motility machinery (Edwards, D.C., L.C. Sanders, G.M. Bokoch, and G.N. Gill. 1999. Nature Cell Biol. 1:253-259; Sanders, L.C., F. Matsumura, G.M. Bokoch, and P. de Lanerolle. 1999. Science. 283: 2083-2085). We here present a novel cell motility pathway by demonstrating that PAK4 directly interacts with an integrin intracellular domain and regulates carcinoma cell motility in an integrin-specific manner. Yeast two-hybrid screening identified PAK4 binding to the cytoplasmic domain of the integrin beta5 subunit, an association that was also found in mammalian cells between endogenous PAK4 and integrin alphavbeta5. Furthermore, we mapped the PAK4 binding to the membrane-proximal region of integrin beta5, and identified an integrin-binding domain at aa 505-530 in the COOH terminus of PAK4. Importantly, engagement of integrin alphavbeta5 by cell attachment to vitronectin led to a redistribution of PAK4 from the cytosol to dynamic lamellipodial structures where PAK4 colocalized with integrin alphavbeta5. Functionally, PAK4 induced integrin alphavbeta5-mediated, but not beta1-mediated, human breast carcinoma cell migration, while no changes in integrin cell surface expression levels were observed. In conclusion, our results demonstrate that PAK4 interacts with integrin alphavbeta5 and selectively promotes integrin alphavbeta5-mediated cell migration.
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| 11. |
- Zhang, Z. R., et al.
(författare)
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Fractal geometry of element distribution on mineral surfaces
- 2001
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Ingår i: Mathematical Geology. - 0882-8121 .- 1573-8868. ; 33:2, s. 217-228
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Tidskriftsartikel (refereegranskat)abstract
- Fractal models hate been established for the distributions of Au, As. S. Fe. and Si on mineral surface based on perimeter-area power-law association observed in mineral samples from fine-disseminated gold deposits at Jinya (JY), Larima (LRM), and Dongbeizhai (DBZ). The fractal index DAL, involved in the fractal perimeter-area relationship is a function of the formation conditions of the mineral. Minerals formed at higher temperatures have a larger value of DAL. For the same mineral, the values of DAL obtained for different elements care approximately the same. DAL may serve as a quantitative index characterizing the distribution configuration of elements on mineral surface.
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| 12. |
- Zhang, Z. X., et al.
(författare)
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Effects of high temperatures on dynamic rock fracture
- 2001
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 38:2, s. 211-225
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Tidskriftsartikel (refereegranskat)abstract
- The dynamic fracture toughness of Fangshan Gabbro and Fangshan Marble subjected to high temperature was measured by means of the split Hopkinson pressure bar (SHPB) system. The specimens for measuring the fracture toughness were manufactured according to the requirements for the Short Rod (SR) specimen suggested by ISRM. Two cases were investigated: (1) the SR specimens of the gabbro and marble were fractured at high temperature (100-330 degrees C), and (2) the specimens of the rocks were first pre-heat-treated at 200 degrees C for the marble and 600 degrees C for the gabbro, and then fractured at room temperature. The experimental results showed that under dynamic loading the fracture toughness of both the gabbro and the marble tested in the above-mentioned cases increased with increasing loading rates. The relationship between the fracture toughness and the loading rates in the two cases is similar to that obtained in the room temperature environment, i.e., without high temperature. (This is defined as the third case.) It can be concluded that temperature variation affects the dynamic fracture toughness of the two rocks to a limited extent within the temperature ranges tested. This is different from the results obtained under the static loading condition. Furthermore, by means of the scanning electronic microscope (SEM), the vertical sections of the fracture surfaces for some gabbro specimens were examined. In addition, the fractal dimensions of the fracture surfaces of some specimens were measured by means of fractal geometry. The results showed that under dynamic loading: (1) macro-crack branching near the fracture surfaces was universal; (2) the fractal dimensions increased with increasing loading rates; (3) in the sections of the specimens tested at high temperature there were many micro-cracks that were probably induced by thermal cracking. On the basis of the above macro- and micro-experimental investigation, an energy analysis of the process of dynamic rock fracture was performed. The results showed that the energy utilisation in dynamic fracture was much lower than that in static fracture.
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| 13. |
- Zhang, Z. X., et al.
(författare)
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Effects of loading rate on rock fracture: fracture characteristics and energy partitioning
- 2000
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - 1365-1609 .- 1873-4545. ; 37:5, s. 745-762
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Tidskriftsartikel (refereegranskat)abstract
- By means of the Scanning Electron Microscope (SEM), an examination was performed of the fracture surfaces (including their vertical sections) of both Fangshan gabbro and Fangshan marble specimens fractured at the loading rates k = 10-2 ≈ 106 MPa m1/2 s-1. The results showed that one or more branching cracks near the fracture surfaces of dynamic rock specimens were clear and the cracks increased with increasing loading rates. However, such branching cracks were rarely seen near the static fracture surfaces. In addition, with the aid of the Split Hopkinson Pressure Bar (SHPB) testing system and a high-speed framing camera, the energy partitioning in the dynamic fracture process of a short rod (SR) rock specimen was analysed quantitatively. The total energy WL absorbed by an SR specimen in the dynamic fracture process mainly consisted of the fracture and damage energy WFD and the kinetic energy WK of flying fragments. The energies WL and WK could be quantitatively calculated through stress wave measurement and high-speed photography in the SHPB testing system. Thus, the fracture and damage energy WFD could be obtained. The results showed that: (1) the energy WK increased with an increase in the impact speed of the striker bar or the loading rate; (2) the energy WFD for dynamic rock fracture was markedly greater than that for static rock fracture, and the WFD increased with an increase in the impact speed of the striker bar or the loading rate; and (3) the value WL/WB (WB is the energy input into the loading system) in the case of dynamic fracture is much lower than that in the case of static fracture. In addition, the ratio decreases with an increase in the loading rate or the impact speed of the striker bar. This means that the energy utilisation decreases when the loading rate or the impact speed of the striker bar rises. Finally, some application problems are discussed in the paper.
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| 14. |
- Zhang, Z X, et al.
(författare)
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Measurements of cutter forces and cutter temperature of boring machine in Äspö Hard Rock Laboratory
- 2001
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report presents both the testing methods used and the testing results obtained for cutter forces and cutter temperature during field boring in Äspö Hard Rock Laboratory. In order to estimate the strains induced by cutter forces in the cutter shaft and choose proper transducers, first a numerical simulation was performed. The simulation results indicated that the cutter forces should be measurable by ordinary strain gauges. Furthermore, an independent three-direction loading system for laboratory calibration was set up to solve force-coupling problems appearing in field measurements. By means of the established measuring system, which was proved successful in the laboratory, the normal forces, tangential forces, and side forces of two button cutters in the boring machine were measured in the field. In addition, the temperature in the shaft of the front cutter was measured. After the measurements of the cutter forces and cutter temperature, rock core samples were taken from the bottom and the wall of the testing borehole. Then the samples were cut, polished, and examined by means of the Scanning Electron Microscope (SEM). After that, the lengths of major cracks induced by the cutters in the rock samples were measured, and an approximate relationship between the length of the medium cracks and the relevant cutter forces was obtained. This relationship was compared with the theoretical relationship established before. Finally, according to the measured results, the cracked zones around the borehole were described. The results show that: (1) there are two kinds of cracked zones: one in the borehole wall and the other in the bottom of the borehole. The depth of the cracked zone in the borehole bottom is much larger than that in the borehole wall because the maximum normal force of the front cutter is always much larger than that of the gauge cutter. (2) Each cracked zone includes a densely cracked zone and all the longest medium cracks caused by mechanical boring. (3) According to the measurements for four rock core samples, the maximum depth of the cracked zone in the borehole bottom is 27.1 mm, and the maximum depth of the densely cracked zone is 2.5-3 mm.
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| 15. |
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