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491.
Mauro Gemmi Marco Merlini Alessandro Pavese Nadia Curetti 《Physics and Chemistry of Minerals》2008,35(7):367-379
Phengite samples (2M
1 and 3T politypes) and a synthetic end-member muscovite specimen were studied by in situ high-temperature synchrotron radiation X-ray
diffraction. The measured volume thermal expansion of 2M
1 phengite (<α
V> ≈ 36.6 × 10−6 K−1) was systematically greater than <α
V> of the 3T polytype (≈33.3 × 10−6 K−1). A positive linear correlation between the average thermal expansion on (001) plane and the mean tetrahedral rotation angle
at ambient condition is proposed on the ground of new measurements and literature data. Dehydroxylation processes were observed
in 2M
1, starting at 1,000 K in 3T at 800 and 945 K in synthetic muscovite. Rietveld refinements allowed a determination of structural variations upon heating
of phengite samples and their dehydroxylate phases. The phengite structure expands by regularizing the tetrahedral sheet and
by reducing the bond length differences between the outer and inner coordination shell of the interlayer site. The dehydroxylate
phase derived from 2M
1 is characterized by fivefold polyhedra in the low temperature form as a consequence of two OH groups reacting to form H2O + O (residual). The dehydroxylate exhibits an increase of the cation–cation distances along the M–Or–M bonds with respect
to low-temperature phengite structures. For the 3T phase, we were unable to achieve completion of dehydroxylation. The refined structural model of the dehydroxylate phase shows
two hydroxyl sites, but at a short distance from one another. This result suggests that the dehydroxylation reaction did not
proceed to completion.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
492.
493.
Sarah Aciego Bernard Bourdon Jakob Schwander Heinrich Baur Alessandro Forieri 《Quaternary Science Reviews》2011,30(19-20):2389-2397
Ice sheets and deep ice cores have yielded a wealth of paleoclimate information based on continuous dating methods while independent radiometric ages of ice have remained elusive. Here we demonstrate the application of (234U/238U) measurements to dating the EPICA Dome C ice core based on the accumulation of 234U in the ice matrix from recoil during 238U decay out of dust bound within the ice. Measured (234U/238U) activity ratios within the ice generally increase with depth while the surface areas of the dust grains are relatively constant. Using a newly designed device for measuring surface area for small samples, we were able to estimate reliably the recoil efficiency of nuclides from dust to ice. The resulting calculated radiometric ages range between 80 ka and 870 ka. Measured samples in the upper 3100 m fall on the previously published age-depth profile. Samples in the 3200–3255 m section show a marked change from 723–870 ka to 85 ka indicating homogenization of the deep ice prior to resetting of the (234U/238U) age in the basal layers. The mechanism for homogenization is likely enhanced lateral ice flow due to high basal melting and geothermal heat flux. 相似文献
494.
495.
Alessandro Patruno Luca Zampieri 《Monthly notices of the Royal Astronomical Society》2008,386(1):543-552
We present evolutionary tracks of binary systems with high-mass companion stars and stellar-through-intermediate mass black holes (BHs). Using Eggleton's stellar evolution code, we compute the luminosity produced by accretion from the donor during its entire evolution. We compute also the evolution of the optical luminosity and colours of the binary system taking the disc contribution and irradiation effects into account. The calculations presented here can be used to constrain the properties of the donor stars in ultraluminous X-ray sources by comparing their position on the Hertzsprung–Russell or colour–magnitude diagrams with the evolutionary tracks of massive BH binaries. This approach may actually provide interesting clues also on the properties of the binary system itself, including the BH mass. We found that, on the basis of their position on the colour–magnitude diagram, some of the candidate counterparts considered can be ruled out and more stringent constraints can be applied to the donor masses. 相似文献
496.
Fabrice Doveil Alessandro Macor Anass Aïssi 《Celestial Mechanics and Dynamical Astronomy》2008,102(1-3):255-272
The motion of charged particle in longitudinal waves is a paradigm for the transition to large scale chaos in Hamiltonian systems. Recently a test cold electron beam has been used to observe its non-self-consistent interaction with externally excited wave(s) in a specially designed Traveling Wave Tube (TWT). The velocity distribution function of the electron beam is recorded with a trochoidal energy analyzer at the output of the TWT. An arbitrary waveform generator is used to launch a prescribed spectrum of waves along the slow wave structure (a 4 m long helix) of the TWT. The resonant velocity domain associated to a single wave is observed, as well as the transition to large scale chaos when the resonant domains of two waves and their secondary resonances overlap. This transition exhibits a “devil’s staircase” behavior when increasing the excitation amplitude in agreement with numerical simulation. A new strategy for control of chaos by building barriers of transport which prevent electrons to escape from a given velocity region as well as its robustness are also successfully tested. Thus generic features of Hamiltonian chaos have been experimentally observed. 相似文献
497.
Antonio Emolo Matteo Picozzi Gaetano Festa Claudio Martino Simona Colombelli Alessandro Caruso Luca Elia Aldo Zollo Piero Brondi Nicola Miranda 《Bulletin of Earthquake Engineering》2016,14(9):2513-2529
We present the results of a feasibility study of an earthquake early warning system (EEWS) for the Campania region (southern Italy) using schools as specific targets. The study considered the seismogenic zones as sources of potential earthquakes for the area, the Italian accelerometric network as the recording network for seismic event occurrence, and the performances of the software platform PRESTo Plus for data analysis and processing. We analyze the distribution of lead-times for all possible threatening seismic sources for each municipality in the region under study by extracting the lead-time value corresponding to the 5th, 10th and 25th percentiles of the distributions. We discuss the results for the 5th percentile in order to analyze the worst-case scenario: in the case of a single site, the lead-time is expected to be larger than this value in the 95 % of the cases. Since the population distribution in Campania is uneven and most of the people live nearby the coast, whilst the most destructive earthquakes occur along the Apennine chain, we can conclude that an efficient EEWS can allow most of the schools in the area to undertake some mitigating actions. The testing of the EEWS was carried out in the high school ITIS ‘E. Majorana’, located at Somma Vesuviana, about 80 km from the seismogenic Irpinia region. For this purpose, the Sentinel, an actuator made up of low-cost hardware (i.e., Arduino®), was developed in close cooperation with students and teachers of the school to receive alert messages from the PRESTo Plus platform and warn the school users in case of a seismic event. The EEWS and the Sentinel were successfully tested during some blind drills performed during normal school activities. 相似文献
498.
Rajesh P. Dhakal Atefeh Pourali Ali Sahin Tasligedik Trevor Yeow Andrew Baird Gregory MacRae Stefano Pampanin Alessandro Palermo 《地震工程与工程振动(英文版)》2016,15(1):1-17
This paper summarizes the research on non-structural elements and building contents being conducted at University of Canterbury in New Zealand. Since the 2010-2011 series of Canterbury earthquakes, in which damage to non-structural components and contents contributed heavily to downtime and overall financial loss, attention to seismic performance and design of non-structural components and contents in buildings has increased exponentially in NZ. This has resulted in an increased allocation of resources to research leading to development of more resilient non-structural systems in buildings that would incur substantially less damage and cause little downtime during earthquakes. In the last few years, NZ researchers have made important developments in understanding and improving the seismic performance of secondary building elements such as partitions, facades, ceilings and contents. 相似文献
499.
The authors thank the discusser for the additional information,which is provided related to the historical interventions of the church through the centuries.This information was known to the authors,however they decided not to include it in the paper because of lack of space.Additional details regarding the retrofit interventions of the church can also be found in the MCEER report regarding the L'Aquila earthquake (Cimellaro et al.,2010). 相似文献
500.