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Mechanism and control of Genipa americana seed germination

Ester Queiroz, Sue Ellen; Amaral da Silva, Edvaldo Aparecido; Davide, Antonio Claudio; Jose, Anderson Cleiton; Silva, Anderson Tadeu; Resende Fraiz, Ana Carla; Rocha Faria, Jose Marcio; Hilhorst, Henk W. M.
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica Formato: 263-276
ENG
Relevância na Pesquisa
26.25%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Genipa americana (Rubiaceae) is important for restoration of riparian forest in the Brazilian Cerrado. The objective was to characterize the mechanism and control of germination of G. americana to support uniform seedling production. Morphology and morphometrics of seeds, embryo and endosperm were assessed by light and scanning electron microscopy during germination. Imbibition and germination curves were generated and over the same time interval endosperm digestion and resistance were measured by puncture force analysis and activity assay of endo-beta-mannanase (EBM) in water and in abscisic acid (ABA). The gene encoding for EBM was partially cloned and its expression monitored by quantitative real-time-polymerase chain reaction. Embryos displayed growth prior to radicle protrusion. A two-phase increase in EBM activity coincided with the two stages of weakening of the micropylar endosperm. The second stage also coincided with growth of the embryo prior to radicle protrusion. Enzyme activity was initiated in the micropylar endosperm but spread to the lateral endosperm. ABA completely inhibited germination by inhibiting embryo growth, the second stage of weakening and expression of the EBM gene...

Seed priming improves endosperm weakening, germination, and subsequent seedling development of Solanum lycocarpum St. Hil.

Anese, S.; da Silva, E. A. A.; Davide, A. C.; Rocha Faria, J. M.; Soares, G. C. M.; Matos, A. C. B.; Toorop, P. E.
Fonte: Ista-int Seed Testing Assoc Publicador: Ista-int Seed Testing Assoc
Tipo: Artigo de Revista Científica Formato: 125-139
ENG
Relevância na Pesquisa
26.25%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Seed priming is a treatment to improve seed quality and plant growth upon germination and is applied widely to crop species to improve uniformity and yield. The present study aimed to establish a priming protocol for Solanum lycocarpum St.Hil., to improve germination of the dormant seeds and seedling development for in situ restoration, and to determine the mechanism underlying priming. Priming for 15 d at 15 degrees C in water delivered the optimal priming effect, resulting in the fastest and most uniform germination and a high final germination percentage compared with shorter treatments, higher temperatures and lower water potentials. Seedling development following priming was significantly improved. To determine the role of endosperm weakening during priming, the force required to puncture the endosperm and endo-B-mannanase activity were determined during priming and subsequent germination. Mechanical weakening of the endosperm and development of endo-B-mannanase activity appeared to contribute to the priming effect. Despite the difference in dormancy the mechanism behind priming is similar to that in tomato. Seedling production of S. lycocarpum...

Mechanism of lysis of Escherichia coli by ethanol and other chaotropic agents.

Ingram, L O
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1981 EN
Relevância na Pesquisa
26.13%
Ethanol has been shown to inhibit the assembly of cross-linked peptidoglycan and to induce cell lysis in Escherichia coli. These effects of ethanol appear to result from the weakening of hydrophobic interactions by ethanol rather than from the intercalation of ethanol into membranes. Other chaotropic agents also inhibited cross-linking and induced lysis. The potency of chaotropic anions with regard to this effect followed the expected chaotropic series. Antichaotropic agents, which strengthened hydrophobic interactions, antagonized ethanol-induced lysis. The weakening of hydrophobic interactions by ethanol is proposed as a general mechanism by which ethanol and other chaotropic agents could affect membrane-associated enzyme activities.

Alpha-Lipoic Acid Inhibits Tumor Necrosis Factor-Induced Remodeling and Weakening of Human Fetal Membranes1

Moore, Robert M.; Novak, Jillian B.; Kumar, Deepak; Mansour, Joseph M.; Mercer, Brian M.; Moore, John J.
Fonte: Society for the Study of Reproduction, Inc. Publicador: Society for the Study of Reproduction, Inc.
Tipo: Artigo de Revista Científica
Publicado em /04/2009 EN
Relevância na Pesquisa
26.22%
Untimely rupture of the fetal membranes (FMs) is a major precipitant of preterm birth. Although the mechanism of FM weakening leading to rupture is not completely understood, proinflammatory cytokines, including tumor necrosis factor (TNF) and interleukin 1 beta (IL1B), have been shown to weaken FMs concomitant with the induction of reactive oxygen species, collagen remodeling, and prostaglandin release. We hypothesized that alpha-lipoic acid, a dietary antioxidant, may block the effect of inflammatory mediators and thereby inhibit FM weakening. Full-thickness FM fragments were incubated with control media or TNF, with or without alpha-lipoic acid pretreatment. Fetal membrane rupture strength and the release of matrix metalloproteinase 9 (MMP9) and prostaglandin E2 (PGE2) from the full-thickness FM fragments were determined. The two constituent cell populations in amnion, the mechanically strongest FM component, were similarly examined. Amnion epithelial and mesenchymal cells were treated with TNF or IL1B, with or without alpha-lipoic acid pretreatment. MMP9 and PGE2 were analyzed by ELISA, Western blot, and zymography. TNF decreased FM rupture strength 50% while increasing MMP9 and PGE2 release. Lipoic acid inhibited these TNF-induced effects. Lipoic acid pretreatment also inhibited TNF- and IL1B-induced increases in MMP9 protein activity and release in amnion epithelial cells...

HEME DISPLACEMENT MECHANISM OF CooA ACTIVATION: MUTATIONAL AND RAMAN SPECTROSCOPIC EVIDENCE*

Ibrahim, Mohammed; Kerby, Robert L.; Puranik, Mrinalini; Wasbotten, Ingar H.; Youn, Hwan; Roberts, Gary P.; Spiro, Thomas G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.25%
The heme-containing protein CooA of Rhodospirillum rubrum regulates the expression of genes involved in CO oxidation. CooA binds its target DNA sequence in response to CO binding to its heme. Activity measurements and resonance Raman (RR) spectra are reported for CooA variants that bind DNA even in the absence of CO, those in which the wild-type residues at the 121-126 positions, TSCMRT, are replaced by the residues AYLLRL or RYLLRL, and also for variants that bind DNA poorly in the presence of CO, such as L120S and L120F. The Fe-C and C-O stretching RR frequencies of all CooAs examined deviate from the expected backbonding correlation in a manner indicating weakening of the Fe-His77 proximal ligand bond, and the extent of weakening correlates positively with DNA-binding activity. The A(R)YLLRL variants have detectable populations of 5-coordinate heme resulting from partial dissociation of the endogenous distal ligand, Pro2. Selective excitation of this population reveals downshifted Fe-His77 stretching RR bands, confirming the proximal bond weakening. These results support our previous hypothesis that the conformational change required for DNA binding is initiated by displacement of the heme into an adjacent hydrophobic cavity, once CO displaces the Pro2 ligand. Examination of the crystal structure reveals a physical basis for these results...

Olanzapine and risperidone disrupt conditioned avoidance responding by selectively weakening motivational salience of conditioned stimulus: further evidence

Zhang, Chen; Fang, Yiru; Li, Ming
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.13%
Suppression of conditioned avoidance response is a preclinical behavioral index of antipsychotic activity. Previous work shows that olanzapine and risperidone disrupt avoidance response elicited by a less salient conditioned stimulus (CS2) to a greater extent than avoidance elicited by a more salient stimulus (CS1), suggesting that antipsychotic drugs may have a weakening action on motivational salience of stimuli. In the present study, we further examined this mechanism of antipsychotic action, focusing on the possible impact of baseline difference of CS1 and CS2 response rates on the avoidance-disruptive effect of olanzapine and risperidone. Rats were first trained to acquire avoidance responding in a procedure in which the number of CS2 trials (i.e. 20) was twice the number of CS1 trials (i.e. 10), but the percentage of CS2-shock pairing was set at 25 % lower (15 trials out of 20) than the percentage of CS1-shockpairing ( 20 trials out of 20). They were then tested daily under olanzapine (0.5 and 1.0 mg/kg, sc) or risperidone (0.33 and 1.0 mg/kg, sc) for 5 consecutive days. Repeated olanzapine and risperidone treatment dose-dependently disrupted avoidance responding to both CS1 and CS2.B oth drugs at the high dose disrupted the CS2 avoidance to a greater extent than the CS1 avoidance. In the final challenge test...

Weakening density dependence from climate change and agricultural intensification triggers pest outbreaks: a 37-year observation of cotton bollworms

Ouyang, Fang; Hui, Cang; Ge, Saiying; Men, Xin-Yuan; Zhao, Zi-Hua; Shi, Pei-Jian; Zhang, Yong-Sheng; Li, Bai-Lian
Fonte: Blackwell Publishing Ltd Publicador: Blackwell Publishing Ltd
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.15%
Understanding drivers of population fluctuation, especially for agricultural pests, is central to the provision of agro-ecosystem services. Here, we examine the role of endogenous density dependence and exogenous factors of climate and human activity in regulating the 37-year population dynamics of an important agricultural insect pest, the cotton bollworm (Helicoverpa armigera), in North China from 1975 to 2011. Quantitative time-series analysis provided strong evidence explaining long-term population dynamics of the cotton bollworm and its driving factors. Rising temperature and declining rainfall exacerbated the effect of agricultural intensification on continuously weakening the negative density dependence in regulating the population dynamics of cotton bollworms. Consequently, ongoing climate change and agricultural intensification unleashed the tightly regulated pest population and triggered the regional outbreak of H. armigera in 1992. Although the negative density dependence can effectively regulate the population change rate to fluctuate around zero at stable equilibrium levels before and after outbreak in the 1992, the population equilibrium jumped to a higher density level with apparently larger amplitudes after the outbreak. The results highlight the possibility for exogenous factors to induce pest outbreaks and alter the population regulating mechanism of negative density dependence and...

Stability and Localization of Rapid Shear in Fluid-Saturated Fault Gouge: 2. Localized Zone Width and Strength Evolution

Platt, John Daniel; Rudnicki, John W.; Rice, James Robert
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
26.04%
Field and laboratory observations indicate that at seismic slip rates most shearing is confined to a very narrow zone, just a few tens to hundreds of microns wide, and sometimes as small as a few microns. Rice et al. (2014) analyzed the stability of uniform shear in a fluid-saturated gouge material. They considered two distinct mechanisms to limit localization to a finite thickness zone, rate-strengthening friction, and dilatancy. In this paper we use numerical simulations to extend beyond the linearized perturbation context in Rice et al. (2014), and study the behavior after the loss of stability. Neglecting dilatancy we find that straining localizes to a width that is almost independent of the gouge layer width, suggesting that the localized zone width is set by the physical properties of the gouge material. Choosing parameters thought to be representative of a crustal depth of 7 km, this predicts that deformation should be confined to a zone between 4 and 44 μm wide. Next, considering dilatancy alone we again find a localized zone thickness that is independent of gouge layer thickness. For dilatancy alone we predict localized zone thicknesses between 1 and 2 μm wide for a depth of 7 km. Finally, we study the impact of localization on the shear strength and temperature evolution of the gouge material. Strain rate localization focuses frictional heating into a narrower zone...

Seismic response control of structures using novel adaptive passive and semi-active variable stiffness and negative stiffness devices

Pasala, Dharma Theja
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
26.3%
Current seismic design practice promotes inelastic response in order to reduce the design forces. By allowing the structure to yield while increasing the ductility of the structure, the global forces can be kept within the limited bounds dictated by the yield strength. However, during severe earthquakes, the structures undergo significant inelastic deformations leading to stiffness and strength degradation, increased interstory drifts, and damage with residual drift. The research presented in this thesis has three components that seek to address these challenges. To prevent the inelastic effects observed in yielding systems, a new concept “apparent weakening” is proposed and verified through shake table studies in this thesis. “Apparent weakening” is introduced in the structural system using a complementary “adaptive negative stiffness device” (NSD) that mimics "yielding” of the global system thus attracting it away from the main structural system. Unlike the concept of weakening and damping, where the main structural system strength is reduced, the new system does not alter the original structural system, but produces effects compatible with an early yielding. Response reduction using NSD is achieved in a two step sequence. First the NSD...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): implications for deformation mechanisms and central uplift formation

Yokoyama, Elder; Trindade, Ricardo Ivan Ferreira da; Lana, Cristiano de Carvalho; Souza Filho, Carlos Roberto de; Baratoux, D.; Marangoni, Y?ra Regina; Tohver, Eric
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
EN_US
Relevância na Pesquisa
36.04%
The weakening mechanisms involved in the collapse of compleximpact craters are controversial. The Araguainhaimpact crater, in Brazil, exposes a complexstructure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (< 10 ?m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magneticfabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of compleximpactstructures. The widespread occurrence of cataclasis in the central peak...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.04%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: Elsevier; Amsterdam Publicador: Elsevier; Amsterdam
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.04%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Bond-Weakening Catalysis: Conjugate Aminations Enabled by the Soft Homolysis of Strong N–H Bonds

Tarantino, Kyle T.; Miller, David C.; Callon, Ted A.; Knowles, Robert R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
26.13%
The ability of redox-active metal centers to weaken the bonds in associated ligands is well precedented, but has rarely been utilized as a mechanism of substrate activation in catalysis. Here we describe a catalytic bond-weakening protocol for conjugate amination wherein the strong N–H bonds in N-aryl amides (N–H bond dissociation free energies ~100 kcal/mol) are destabilized by ~33 kcal/mol upon by coordination to a reducing titanocene complex, enabling their abstraction by the weak H-atom acceptor TEMPO through a proton-coupled electron transfer process. Significantly, this soft homolysis mechanism provides a method to generate closed-shell, metalated nucleophiles under neutral conditions in the absence of a Brønsted base.

Shear strain localization in elastodynamic rupture simulations

Daub, Eric G.; Manning, M. Lisa; Carlson, Jean M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/03/2008
Relevância na Pesquisa
26.04%
We study strain localization as an enhanced velocity weakening mechanism on earthquake faults. Fault friction is modeled using Shear Transformation Zone (STZ) Theory, a microscopic physical model for non-affine rearrangements in granular fault gouge. STZ Theory is implemented in spring slider and dynamic rupture models of faults. We compare dynamic shear localization to deformation that is uniform throughout the gouge layer, and find that localized slip enhances the velocity weakening of the gouge. Localized elastodynamic ruptures have larger stress drops and higher peak slip rates than ruptures with homogeneous strain.; Comment: 6 pages, 3 figures

A Model for Compression-Weakening Materials and the Elastic Fields due to Contractile Cells

Rosakis, Phoebus; Notbohm, Jacob; Ravichandran, Guruswami
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
26.04%
We construct a homogeneous, nonlinear elastic constitutive law, that models aspects of the mechanical behavior of inhomogeneous fibrin networks. Fibers in such networks buckle when in compression. We model this as a loss of stiffness in compression in the stress-strain relations of the homogeneous constitutive model. Problems that model a contracting biological cell in a finite matrix are solved. It is found that matrix displacements and stresses induced by cell contraction decay slower (with distance from the cell) in a compression weakening material, than linear elasticity would predict. This points toward a mechanism for long-range cell mechanosensing. In contrast, an expanding cell would induce displacements that decay faster than in a linear elastic matrix.; Comment: 18 pages, 2 figures

Faulting of rocks at three-dimensional stress field by micro-anticracks

Ghaffari, H. O.; Nasseri, M. H. B.; Young, R. Paul
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/01/2014
Relevância na Pesquisa
26.04%
Using 9-sets of different laboratory earthquake tests, we examined the nature of cracking under true triaxial stress conditions in the lithosphere . We found that 3D stress state can induce oblique nucleation of many fractures, forming final plane of complex polymodal faults. Our fully 3D experiments indicate unconventional fault nucleation with 2-3 times faster slip phase, implying a new slip-weakening mechanism for earthquakes in upper crust. In addition, We compared our observations of irregular cracks with typical anti-cracks signals in multi-anvil High Pressure and Temperature test. For the first time, we showed oblique faulting can change slip-weakening rate and accelerate the rate of energy release. This implicates a sharper source time function for further modeling of our experiments. Indeed, our results can be assumed as an ex tension to detachment fronts in micro-faults to a general concept of quasi-anti rupture fronts. We showed events from deep-focus earthquakes can share some similarity to shallow earthquakes, promoting recent approach on similarity of deep earthquakes to their shallow counterparts .

Thermal imaging on simulated faults during frictional sliding

Mair, Karen; Renard, François; Gundersen, Olav
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/01/2008
Relevância na Pesquisa
26.04%
Heating during frictional sliding is a major component of the energy budget of earthquakes and represents a potential weakening mechanism. It is therefore important to investigate how heat dissipates during sliding on simulated faults. We present results from laboratory friction experiments where a halite (NaCl) slider held under constant load is dragged across a coarse substrate. Surface evolution and frictional resistance are recorded. Heat emission at the sliding surface is monitored using an infra-red camera. We demonstrate a link between plastic deformations of halite and enhanced heating characterized by transient localized heat spots. When sand 'gouge' is added to the interface, heating is more diffuse. Importantly, when strong asperities concentrate deformation, significantly more heat is produced locally. In natural faults such regions could be nucleation patches for melt production and hence potentially initiate weakening during earthquakes at much smaller sliding velocities or shear stress than previously thought.

Grain fragmentation in sheared granular flow: weakening effects, energy dissipation, and strain localization

Lieou, Charles K. C.; Elbanna, Ahmed E.; Carlson, Jean M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.04%
We describe the shear flow of a disordered granular material in the presence of grain fracture using the shear-transformation-zone (STZ) theory of amorphous plasticity adapted to systems with a hard-core inter-particle interaction. To this end, we develop the equations of motion for this system within a statistical-thermodynamic framework analogous to that used in the analysis of molecular glasses. For hard-core systems, the amount of internal, configurational disorder is characterized by the compactivity $X = \partial V / \partial S_C$, where $V$ and $S_C$ are respectively the volume and configurational entropy. Grain breakage is described by a constitutive equation for the temporal evolution of a characteristic grain size $a$, based on fracture mechanics. We show that grain breakage is a weakening mechanism, significantly lowering the flow stress at large strain rates, if the material is rate-strengthening in character. We show in addition that if the granular material is sufficiently aged, spatial inhomogeneity in configurational disorder results in strain localization. We also show that grain splitting contributes significantly to comminution at small shear strains, while grain abrasion becomes dominant at large shear displacements.; Comment: 16 pages...

Solubility and diffusional uptake of hydrogen in quartz at high water pressures: Implications for hydrolytic weakening

Kronenberg, A. K.; Kirby, S. H.; Aines, R. D.; Rossman, G. R.
Fonte: American Geophysical Union Publicador: American Geophysical Union
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 10/11/1986
Relevância na Pesquisa
26.3%
Attempts to introduce molecular water into dry, natural quartz crystals by diffusive transport and thus weaken them hydrolytically at T = 700°–900°C and PH_2O = 400–1550 MPa have failed. Infrared spectroscopy of hydrothermally annealed single crystals of natural quartz reveals the diffusive uptake of interstitial hydrogen (resulting in hydroxyl groups) at rates similar to those previously proposed for intracrystalline water at high water pressures. The solubility of interstitial hydrogen at these conditions is independent of temperature and pressure; instead, it depends upon the initial aluminum concentration by the local charge neutrality condition [H_i·] = [Al_(Si)′]. The rate of interstitial hydrogen diffusion parallel to c is given by an Arrhenius relation with D_0 = 1.4 × 10^(−1) m^2/s and Q = 200 ± 20 kJ/mol, in close agreement with H diffusivities reported for much lower pressures (PH_2O = 2.5 MPa). Deformation experiments following hydrothermal annealing show no mechanical weakening, and the lack of any detectable broadband absorption associated with molecular water shows that the diffusion rates of structural water are much lower than those of hydrogen. These results are consistent with the available oxygen diffusion data for quartz and with the failure to observe weakening in previous studies of quartz deformation at pressures of 300–500 MPa; they call into question the rapid rates of diffusion originally suggested for the hydrolytic weakening defect. It is suggested that the observed weakening in many previous experiments was complicated by microcracking processes in response to nonhydrostatic stresses and low effective confining pressures. Extensive microcracking may provide a mechanism for molecular water to enter quartz and allow local plastic deformation to occur. It does not appear that molecular water can diffuse far enough into uncracked quartz to allow hydrolytic weakening over annealing times that are feasible in the laboratory.

Cracks, pulses and macroscopic asymmetry of dynamic rupture on a bimaterial interface with velocity-weakening friction

Ampuero, J.-P.; Ben-Zion, Y.
Fonte: Royal Astronomical Society Publicador: Royal Astronomical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /05/2008
Relevância na Pesquisa
26.27%
We study in-plane ruptures on a bimaterial fault governed by a velocity-weakening friction with a regularized normal stress response. Numerical simulations and analytical estimates provide characterization of the ranges of velocity-weakening scales, nucleation lengths and background stresses for which ruptures behave as cracks or pulses, decaying or sustained, bilateral or unilateral. With strongly velocity-weakening friction, ruptures occur under a wide range of conditions as large-scale pulses with a preferred propagation direction, that of slip of the more compliant material. Such ruptures have macroscopic asymmetry manifested by significantly larger seismic potency and propagation distance in the preferred direction, and clearly quantified by the directivity ratio derived from the second order moments of the spatio-temporal distribution of slip rate. The macroscopic rupture asymmetry of the large-scale pulses stems from the difference in the criticality conditions for self-sustained propagation in each rupture direction, induced by the asymmetric normal stress changes operating in bimaterial interfaces. In contrast, crack-like ruptures show macroscopic asymmetry under restrictive conditions. The discussed mechanism is robust with respect to regularization parameters...