Structural evolution of a 2M 1 phengite mica up to 11 GPa: an in situ single-crystal X-ray diffraction study     

G. Diego Gatta  Nicola Rotiroti  Paolo Lotti  Alessandro Pavese  Nadia Curetti 《Physics and Chemistry of Minerals》2010,37(8):581-591

The structural evolution at high pressure of a natural 2M ₁-phengite [(K_0.98Na_0.02)_Σ=1.00(Al_1.55Mg_0.24Fe_0.21Ti_0.02)_Σ=2.01(Si_3.38Al_0.62)O₁₀(OH)₂; a = 5.228(2), b = 9.057(3), c = 19.971(6)Å, β = 95.76(2)°; space group: C2/c] from the metamorphic complex of Cima Pal (Sesia Zone, Western Alps, Italy) was studied by single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions up to ~11 GPa. A series of 12 structure refinements were performed at selected pressures within the P range investigated. The compressional behaviour of the same phengite sample was previously studied up to ~25 GPa by synchrotron X-ray powder diffraction, showing an irreversible transformation with a drastic decrease of the crystallinity at P > 15–17 GPa. The elastic behaviour between 0.0001 and 17 GPa was modelled by a third-order Birch–Murnaghan Equation of State (BM-EoS), yielding to K _T0 = 57.3(10) GPa and K′ = ?K _T0/?P = 6.97(24). The single-crystal structure refinements showed that the significant elastic anisotropy of the 2M ₁-phengite (with β(a):β(b):β(c) = 1:1.17:4.60) is mainly controlled by the anisotropic compression of the K-polyhedra. The evolution of the volume of the inter-layer K-polyhedron as a function of P shows a negative slope, Fitting the P–V(K-polyhedron) data with a truncated second-order BM-EoS we obtain a bulk modulus value of K _T0(K-polyhedron) = 26(1) GPa. Tetrahedra and octahedra are significantly stiffer than the K-polyhedron. Tetrahedra behave as quasi-rigid units within the P range investigated. In contrast, a monotonic decrease is observed for the octahedron volume, with K _T0 = 120(10) GPa derived by a BM-EoS. The anisotropic response to pressure of the K-polyhedron affects the P-induced deformation mechanism on the tetrahedral sheet, consisting in a cooperative rotation of the tetrahedra and producing a significant ditrigonalization of the six-membered rings. The volume of the K-polyhedron and the value of the ditrigonal rotation parameter (α) show a high negative correlation (about 93%), though a slight discontinuity is observed at P >8 GPa. α increases linearly with P up to 7–8 GPa (with ?α/?P ≈ 0.7°/GPa), whereas at higher Ps a “saturation plateau” is visible. A comparison between the main deformation mechanisms as a function of pressure observed in 2M ₁- and 3T-phengite is discussed.  相似文献   

Effects of temperature on the crystal structure of epidote: a neutron single-crystal diffraction study at 293 and 1,070 K     

G. Diego Gatta  Martin Meven  Geoffrey Bromiley 《Physics and Chemistry of Minerals》2010,37(7):475-485

The effects of temperature on the crystal structure of a natural epidote [Ca_1.925 Fe_0.745Al_2.265Ti_0.004Si_3.037O₁₂(OH), a = 8.890(6), b = 5.630(4), c = 10.150(6) Å and β = 115.36(5)°, Sp. Gr. P2₁ /m] have been investigated by means of neutron single-crystal diffraction at 293 and 1,070 K. At room conditions, the structural refinement confirms the presence of Fe³⁺ at the M₃ site [%Fe(M3) = 73.1(8)%] and all attempts to refine the amount of Fe at the M(1) site were unsuccessful. Only one independent proton site was located. Two possible hydrogen bonds, with O(2) and O(4) as acceptors [i.e. O(10)–H(1)···O(2) and O(10)–H(1)···O(4)], occur. However, the topological configuration of the bonds suggests that the O(10)–H(1)···O(4) is energetically more favourable, as H(1)···O(4) = 1.9731(28) Å, O(10)···O(4) = 2.9318(22) Å and O(10)–H(1)···O4 = 166.7(2)°, whereas H(1)···O(2) = 2.5921(23) Å, O(10)···O(2) = 2.8221(17) Å and O(10)–H(1)···O2 = 93.3(1)°. The O(10)–H(1) bond distance corrected for “riding motion” is 0.9943 Å. The diffraction data at 1,070 K show that epidote is stable within the T-range investigated, and that its crystallinity is maintained. A positive thermal expansion is observed along all the three crystallographic axes. At 1,070 K the structural refinement again shows that Fe³⁺ share the M(3) site along with Al³⁺ [%Fe(M3)_1,070K = 74(2)%]. The refined amount of Fe³⁺ at the M(1) is not significant [%Fe(M1)_1,070K = 1(2)%]. The tetrahedral and octahedral bond distances and angles show a slight distortion of the polyhedra at high-T, but a significant increase of the bond distances compared to those at room temperature is observed, especially for bond distances corrected for “rigid body motions”. The high-T conditions also affect the inter-polyhedral configurations: the bridging angle Si(2)–O(9)–Si(1) of the Si₂O₇ group increases significantly with T. The high-T structure refinement shows that no dehydration effect occurs at least within the T-range investigated. The configuration of the H-bonding is basically maintained with temperature. However, the hydrogen bond strength changes at 1,070 K, as the O(10)···O(4) and H(1)···O(4) distances are slightly longer than those at 293 K. The anisotropic displacement parameters of the proton site are significantly larger than those at room condition. Reasons for the thermal stability of epidote up to 1,070 K observed in this study, the absence of dehydration and/or non-convergent ordering of Al and Fe³⁺ between different octahedral sites and/or convergent ordering on M(3) are discussed.  相似文献   

Mineralogical and geochemical spatial analyses of a waste-rock dump at the Libiola Fe–Cu sulphide mine (Eastern Liguria,Italy)     

Pietro Marescotti  Eva Azzali  Diego Servida  Cristina Carbone  Giovanni Grieco  Luisa De Capitani  Gabriella Lucchetti 《Environmental Earth Sciences》2010,61(1):187-199

In this work, we investigated a 3 ha sulphide-bearing waste-rock dump (Libiola Mine, Italy) using mineralogical, geochemical, and geostatistical analyses. The dumped materials were highly heterogeneous in grain size and lithology and varied both laterally and vertically. Other than the host rock of the ore, basalts and serpentinites, the dumped materials contained high amounts of low-grade chalcopyrite- and pyrite-rich mineralisations. Due to these characteristics and to the absence of minerals able to neutralise acidity, this waste-rock dump can be classified as an acid mine drainage (AMD) producer. The study confirms that AMD is still active and, in the best scenario, can persist for up to 6.17 × 10³ years. The consequences of this process are of serious environmental concern as it involves strong acidification of the circulating waters, the release of potentially toxic metals into the soil, streams and rivers and the precipitation of huge quantities of secondary Fe-oxides and Fe-oxyhydroxides.  相似文献   

Response of evapotranspiration and water availability to the changing climate in Northern Eurasia     

Yaling Liu  Qianlai Zhuang  Zhihua Pan  Diego Miralles  Nadja Tchebakova  David Kicklighter  Jiquan Chen  Andrey Sirin  Yujie He  Guangsheng Zhou  Jerry Melillo 《Climatic change》2014,125(3-4):413-427

We introduce a probabilistic framework for vulnerability analysis and use it to quantify current and future vulnerability of the US water supply system. We also determine the contributions of hydro-climatic and socio-economic drivers to the changes in projected vulnerability. For all scenarios and global climate models examined, the US Southwest including California and the southern Great Plains was consistently found to be the most vulnerable. For most of the US, the largest contributions to changes in vulnerability come from changes in supply. However, for some areas of the West changes in vulnerability are caused mainly by changes in demand. These changes in supply and demand result mainly from changes in evapotranspiration rather than from changes in precipitation. Importantly, changes in vulnerability from projected changes in the standard deviations of precipitation and evapotranspiration are of about the same magnitude or larger than those from changes in the corresponding means over most of the US, except in large areas of the Great Plains, in central California and southern and central Texas.  相似文献   

The evolution of the bimodal colour distribution of galaxies in Sloan Digital Sky Survey groups     

Héctor J. Martínez  Ana L. O'Mill  Diego G. Lambas 《Monthly notices of the Royal Astronomical Society》2006,372(1):253-258

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Laboratory tests with interferometric optical fibre sensors to monitor shallow landslides triggered by rainfalls     

Longoni  Laura  Ivanov  Vladislav  Ferrario  Maddalena  Brunero  Marco  Papini  Monica  Arosio  Diego 《Landslides》2022,19(3):761-772

Optical fibre–based sensors have now established their place in the field of geohazard monitoring due to their sensitivity to strain and temperature changes. Progressive development in the technology leads to the availability of novel, accurate and durable sensors at a relatively limited cost. This creates room for original monitoring applications that have been, so far, impeded by the shortcomings of conventional monitoring tools. In this work, we explore the applicability of an interferometric optical fibre sensor as a vibration sensing tool at laboratory scale. We tested the ability of the sensor to identify precursors of instability in a downscaled model of a rainfall-induced landslide composed of granular material. We carried out four experimental tests which involved different sensor deployments and soil mixtures. The recorded signals were processed by means of a time–frequency analysis and we identified two frequency-domain parameters—the spectral centroid and band power—that could provide information on the development of instability. Their ratio yielded a unique parameter through which a precursory stage could be outlined by defining a threshold value based on the data collected at the beginning of the experiment. In our lab tests, precursors of instability were detected 2–3 min before a crack was observed at the surface. This may upscale to a lead time of about 20–30 min or more in the field, classifying our monitoring approach in between an alarm and a warning system. The work presented here can be considered a first promising step towards an innovative monitoring system and shows the potential of optical fibre sensing as a shallow landslide monitoring technique, encouraging further testing, especially in real-case studies.

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Characterization of the Frictional Behavior of Steel-Polymer Interfaces with Pronounced Stick-Slip Effect for Use in Seismic Isolation     

Messina  Armando  Miranda  Eduardo 《Bulletin of Earthquake Engineering》2022,20(11):6307-6326

Bulletin of Earthquake Engineering - The frictional behavior of steel-PTFE interfaces for use in seismic isolation has been studied extensively in the past. However, alternative polymers, such as...  相似文献   

Anisotropy in the distribution of satellites around primary galaxies in the 2dF Galaxy Redshift Survey: the Holmberg effect   总被引：1，自引：0，他引：1  

Laura Sales  Diego G. Lambas†‡ 《Monthly notices of the Royal Astronomical Society》2004,348(4):1236-1240

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Active galactic nuclei and galaxy interactions   总被引：1，自引：0，他引：1  

M. Sol Alonso  Diego G. Lambas  Patricia Tissera  Georgina Coldwell 《Monthly notices of the Royal Astronomical Society》2007,375(3):1017-1024

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Dark matter influence on velocity dispersion profiles of clusters of galaxies     

Julio F. Navarro  Diego García Lambas 《Astrophysics and Space Science》1987,133(2):241-252

We have performed a series ofN-body experiments including the effects of a massive dominant background which follows Schuster's density law in order to simulate clusters of galaxies in which a smoothly distributed dark component is present. The existence of this background is inferred from the weak luminosity segregation observed in clusters which, however, show several characteristics of well-relaxed systems. The comparison of the velocity dispersion profiles of three clusters of galaxies (Coma, Perseus, and Virgo) with those obtained in the numerical experiments allows us to place some constraints on both the distribution and amount of distributed dark material in these clusters. The profiles are rather insensitive to variations in the ratio of the background mass to the mass attached to galaxies (M _b/M_g), but exhibit a strong dependence on their relative concentration. We conclude that highly concentrated background models are not consistent with observations. We find a maximum value for the ratio of the gravitational radius of the galaxies and the background (R _g/R_b) (approximately 0.6) and using previous results (Navarroet al., 1986) we conclude that virial theorem masses underestimate the total mass (M _b+M _g) of the clusters. As a final result, we derive a minimum value for theM _b/M_g ratio. All these conclusions could apply in general if Coma, Perseus, and Virgo constitute a fair sample of the rich clusters of galaxies in the Universe.  相似文献