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1.
(Fe4Cr4Ni)9C4 is a metal carbide mineral formed by combination of Fe, Cr and Ni with C. It occurs in a chromite deposit in
the Luobusha ophiolite, Tibet. Based on the determination of its crystal structure, the empirical formula is (Fe4.12Cr3.84Ni0.96)8.92C3.70
and the simplified formula is (Fe4Cr4Ni)4C9. The mineral is hexagonal with a = 1.38392(2) nm, c = 0.44690(9) nm, pace group P63 m c, Z=6 and the calculated specific gravity Dx = 7.089 g/cm3. Fe, Cr and Ni occupy different crystallographic sites and their coordination numbers are approximately 12,
forming an alternate stacking sequence of flat and puckered layers along the c axis. Some metallic atoms have a defect structure. The interatomic distances of Fe, Cr and Ni are 0.2525-0.2666 nm, and the
distances between Fe, Cr, Ni and C are 0.1893-0.2169 nm. The coordination number of carbon is 6. It occurs in interstices
of the metallic atoms Fe, Cr and Ni to form trigonalprismatically coordinated polyhedra. These coordination polyhedra are
linked with each other via shared corners or shared edges into a new type of metal carbide structure. 相似文献
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Martin B. C. Brandt 《Journal of Seismology》2016,20(2):439-447
Quality factor Q, which describes the attenuation of seismic waves with distance, was determined for South Africa using data recorded by the South African National Seismograph Network. Because of an objective paucity of seismicity in South Africa and modernisation of the seismograph network only in 2007, I carried out a coda wave decay analysis on only 13 tectonic earthquakes and 7 mine-related events for the magnitude range 3.6?≤?M L ?≤?4.4. Up to five seismograph stations were utilised to determine Q c for frequencies at 2, 4, 8 and 16 Hz resulting in 84 individual measurements. The constants Q 0 and α were determined for the attenuation relation Q c(f)?=?Q 0 f α . The result was Q 0?=?396?±?29 and α?=?0.72?±?0.04 for a lapse time of 1.9*(t s???t 0) (time from origin time t 0 to the start of coda analysis window is 1.9 times the S-travel time, t s) and a coda window length of 80 s. This lapse time and coda window length were found to fit the most individual frequencies for a signal-to-noise ratio of at least 3 and a minimum absolute correlation coefficient for the envelope of 0.5. For a positive correlation coefficient, the envelope amplitude increases with time and Q c was not calculated. The derived Q c was verified using the spectral ratio method on a smaller data set consisting of nine earthquakes and one mine-related event recorded by up to four seismograph stations. Since the spectral ratio method requires absolute amplitudes in its calculations, site response tests were performed to select four appropriate stations without soil amplification and/or signal distortion. The result obtained for Q S was Q 0?=?391?±?130 and α?=?0.60?±?0.16, which agrees well with the coda Q c result. 相似文献
5.
Marvin Lanphere Duane Champion Leone Melluso Vincenzo Morra Annamaria Perrotta Claudio Scarpati Dario Tedesco Andrew Calvert 《Bulletin of Volcanology》2007,69(3):259-263
The Italian volcano, Vesuvius, erupted explosively in AD 79. Sanidine from pumice collected at Casti Amanti in Pompeii and Villa Poppea in Oplontis yielded a weighted-mean 40Ar/39Ar age of 1925±66 years in 2004 (1σ uncertainty) from incremental-heating experiments of eight aliquants of sanidine. This is the calendar age of the eruption. Our results together with the work of Renne et al. (1997) and Renne and Min (1998) demonstrate the validity of the 40Ar/39Ar method to reconstruct the recent eruptive history of young, active volcanoes. 相似文献
6.
Giovanni Chiodini Stefano Caliro Alessandro Aiuppa Rosario Avino Domenico Granieri Roberto Moretti Francesco Parello 《Bulletin of Volcanology》2011,73(5):531-542
We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic
composition of CO2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct
sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are
in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at
volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method
to Mount Etna where we derived a δ13C of volcanic CO2 between −0.9 ± 0.27‰ and −1.41 ± 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported
in previous work highlights a temporal trend of systematic increase of δ13C values of Etna CO2 from ~ −4‰, in the 1970’s and the 1980’s, to ~ −1‰ at the present time (2009). This shift toward more positive δ13C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss
such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to
magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the
carbon isotopic composition of the CO2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity. 相似文献
7.
C. R. COLLIN A. SALVI D. LEMERCIER P. LEMERCIER F. ROBACH 《Geophysical Prospecting》1973,21(4):704-715
The aim of this article is to describe the double resonance magnetometer system designed and built by the Division de Magnétométrie of the C.E.N. Grenoble, and used by the Département des Recherches Minières du CE.A. For the measurement of magnetic anomalies of geological origin it is necessary to make differential measurements between a mobile instrument which scans the region of interest and a fixed compensatory instrument. The apparatus described here features the following main characteristics: — it gives a direct numerical measurement of the differential magnetic field between the two instruments with an accuracy of 0.01 gamma (10-7 Oe). — it is designed to be easily operated in geological field work (light weight, low power, possibility to make continuous measurements along a given profile, the measuring signals being radio-linked there are no wires connecting the instruments). Firstly we describe the components of the magnetometer itself namely: double resonance magnetometer heads and differential numerical magnetometer. Secondly we describe the measuring technique. 相似文献
8.
Meteorological conditions, biochemical processes in water bodies and anthropogenic pressure of a region are the main factors to determine the atmosphere water-body gas exchange. Research on oxygen outflows in the Dnjepr estuary region has shown that though gas exchange with atmosphere permanently exists its intensity varies throughout a day, vegetation period, year. The process of evasion is the most active in the flood plain pools of the river. Oxygen exchange between the atmosphere and a river is to be determined with physical characteristics of water outflow and with the anthropogenic influence. Oxygen absorption from the atmosphere is dominating for the liman water area in spite of differences between its parts. The obtained results have shown that gas exchange between river estuary pools and the atmosphere is of great importance for the oxygen balance of these pools. 相似文献
9.
Michel Cara Marylin Denieul Olivier Sèbe Bertrand Delouis Yves Cansi Antoine Schlupp 《Journal of Seismology》2017,21(3):551-565
The recent seismicity catalogue of metropolitan France Sismicité Instrumentale de l’Hexagone (SI-Hex) covers the period 1962–2009. It is the outcome of a multipartner project conducted between 2010 and 2013. In this catalogue, moment magnitudes (M w) are mainly determined from short-period velocimetric records, the same records as those used by the Laboratoire de Détection Géophysique (LDG) for issuing local magnitudes (M L) since 1962. Two distinct procedures are used, whether M L-LDG is larger or smaller than 4. For M L-LDG >4, M w is computed by fitting the coda-wave amplitude on the raw records. Station corrections and regional properties of coda-wave attenuation are taken into account in the computations. For M L-LDG ≤4, M w is converted from M L-LDG through linear regression rules. In the smallest magnitude range M L-LDG <3.1, special attention is paid to the non-unity slope of the relation between the local magnitudes and M w. All M w determined during the SI-Hex project is calibrated according to reference M w of recent events. As for some small events, no M L-LDG has been determined; local magnitudes issued by other French networks or LDG duration magnitude (M D) are first converted into M L-LDG before applying the conversion rules. This paper shows how the different sources of information and the different magnitude ranges are combined in order to determine an unbiased set of M w for the whole 38,027 events of the catalogue. 相似文献
10.
本文利用保角映射方法对两种二维地形作了推导:一种是半圆弧形的边界,另一种是拋物线形的边界。并作了一些数值计算。 相似文献
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A. Chovanec 《洁净——土壤、空气、水》1997,25(5):233-241
Pesticides in Austrian Running Waters – a Country-wide Overview The analyses of pesticides in Austrian running waters are major part of the country-wide water quality monitoring system which has been established in 1991. This paper summarizes the data which were collected for 29 substances between December 1991 and June 1995. The monitoring activities focus on herbicides because they are the most important pesticide group in Austria. Substances of the triazines and phenoxyalkanecarboxylic acid group analyzed within the programme represent the major part of the total amount of herbicides applied. The most detected pesticides were atrazine and its metabolite deethylatrazine. Peak concentrations were obtained in rivers situated in the eastern and southern regions of Austria with intensive agriculture. Other substances play a minor role as contaminants in running waters. These findings correspond to the data obtained by investigations of groundwater in porous media. 相似文献
13.
Urea from natural and anthropogenic sources is one of the most interesting nitrogen compounds in an aquatic environment. Results of experimental investigations are presented for the successive biochemical urea transformation into nitrates via ammonium and nitrite species. Kinetic models based on a combination of Michaelis-Menten and Monod equations have been derived which describe reasonably well the course of the enzymatic reactions and the concentration-time profiles of different N oxydation states. Main factors affecting the rates of nitrogen metabolization are the initial concentration of ureolytic bacteria, the physical state of the nitrifying microorganisms, and the concentration of toxic organics added to the system under study. 相似文献
14.
Starting from the classical empirical magnitude-energy relationships, in this article, the derivation of the modern scales
for moment magnitude M
w and energy magnitude M
e is outlined and critically discussed. The formulas for M
w and M
e calculation are presented in a way that reveals, besides the contributions of the physically defined measurement parameters
seismic moment M
0 and radiated seismic energy E
S, the role of the constants in the classical Gutenberg–Richter magnitude–energy relationship. Further, it is shown that M
w and M
e are linked via the parameter Θ = log(E
S/M
0), and the formula for M
e can be written as M
e = M
w + (Θ + 4.7)/1.5. This relationship directly links M
e with M
w via their common scaling to classical magnitudes and, at the same time, highlights the reason why M
w and M
e can significantly differ. In fact, Θ is assumed to be constant when calculating M
w. However, variations over three to four orders of magnitude in stress drop Δσ (as well as related variations in rupture velocity V
R and seismic wave radiation efficiency η
R) are responsible for the large variability of actual Θ values of earthquakes. As a result, for the same earthquake, M
e may sometimes differ by more than one magnitude unit from M
w. Such a difference is highly relevant when assessing the actual damage potential associated with a given earthquake, because
it expresses rather different static and dynamic source properties. While M
w is most appropriate for estimating the earthquake size (i.e., the product of rupture area times average displacement) and
thus the potential tsunami hazard posed by strong and great earthquakes in marine environs, M
e is more suitable than M
w for assessing the potential hazard of damage due to strong ground shaking, i.e., the earthquake strength. Therefore, whenever
possible, these two magnitudes should be both independently determined and jointly considered. Usually, only M
w is taken as a unified magnitude in many seismological applications (ShakeMap, seismic hazard studies, etc.) since procedures
to calculate it are well developed and accepted to be stable with small uncertainty. For many reasons, procedures for E
S and M
e calculation are affected by a larger uncertainty and are currently not yet available for all global earthquakes. Thus, despite
the physical importance of E
S in characterizing the seismic source, the use of M
e has been limited so far to the detriment of quicker and more complete rough estimates of both earthquake size and strength
and their causal relationships. Further studies are needed to improve E
S estimations in order to allow M
e to be extensively used as an important complement to M
w in common seismological practice and its applications. 相似文献
15.
We analyze the anelasticity of the earth using group delays of P-body waves of deep (>200 km) events in the period range 4–32 s for epicentral distances of 5–85 degrees. We show that Time Frequency Analysis (TFA), which is usually applied to very dispersive surface waves, can be applied to the much less dispersive P-body waves to measure frequency-dependent group delays with respect to arrival times predicted from the CMT centroid location and PREM reference model. We find that the measured dispersion is due to: (1) anelasticity (described by the P-wave quality factor Q
p
), (2) ambient noise, which results in randomly distributed noise in the dispersion measurements, (3) interference with other phases (triplications, crustal reverberations, conversions at deep mantle boundaries), for which the total dispersion depends on the amplitude and time separation between the different phases, and (4) the source time function, which is dispersive when the wavelet is asymmetrical or contains subevents. These mechanisms yield dispersion ranging in the order of one to 10 seconds with anelasticity responsible for the more modest dispersion. We select 150 seismograms which all have small coda amplitudes extending to ten percent of the main arrival, minimizing the effect of interference. The main P waves have short durations, minimizing effects of the source. We construct a two-layer model of Q
p
with an interface at 660 km depth and take Q
p
constant with period. Our data set is too small to solve for a possible frequency dependence of Q
p
. The upper mantle Q
1 is 476 [299–1176] and the lower mantle Q
2 is 794 [633–1064] (the bracketed numbers indicate the 68 percent confidence range of Q
p
–1). These values are in-between the AK135 model (Kennett et al., 1995) and the PREM model (Dziewonski and Anderson, 1981) for the lower mantle and confirm results of Warren and Shearer (2000) that the upper mantle is less attenuating than PREM and AK135. 相似文献
16.
Zafeiria Roumelioti Anastasia Kiratzi Christoforos Benetatos 《Journal of Seismology》2010,14(2):309-337
We use 576 earthquakes of magnitude, M
w, 3.3 to 6.8 that occurred within the region 33° N–42.5° N, 19° E–30° E in the time period 1969 to 2007 to investigate the
stability of the relation between moment magnitude, M
w, and local magnitude, M
L, for earthquakes in Greece and the surrounding regions. We compare M
w to M
L as reported in the monthly bulletins of the National Observatory of Athens (NOA) and to M
L as reported in the bulletins of the Seismological Station of the Aristotle University of Thessaloniki. All earthquakes have
been analyzed through regional or teleseismic waveform inversion, to obtain M
w, and have measured maximum trace amplitudes on the Wood–Anderson seismograph in Athens, which has been in operation since
1964. We show that the Athens Wood–Anderson seismograph performance has changed through time, affecting the computed by NOA
M
L by at least 0.1 magnitude units. Specifically, since the beginning of 1996, its east–west component has been recording systematically
much larger amplitudes compared to the north–south component. From the comparison between M
w and M
L reported by Thessaloniki, we also show that the performance of the sensors has changed several times through time, affecting
the calculated M
L’s. We propose scaling relations to convert the M
L values reported from the two centers to M
w. The procedures followed here can be applied to other regions as well to examine the stability of magnitude calculations
through time. 相似文献
17.
785 traces of vertical components from shallow earthquakes recorded by 10 CDSN (Chinese Digital Seismographic Network) stations
and 5 GSN (Global Seismographic Network) stations were collected to study the attenuation characteristics ofL
g coda in the Chinese continent and its adjacent regions. The records were processed first using the stack spectral ratio method
to obtain the average values ofQ
0 (Q at 1Hz) and η, the frequency dependence, ofL
g coda in the ellipses corresponding to the paths. The back-projection technique was then employed to obtain the tomographic
maps ofQ
0 and η values, and the distribution of their errors. Results indicate that in the studied areaQ
0 varies between 200 and 500. The lowest value ofQ
0 exists in the Yun-nan-Tibetan region, while the highest value ofQ
0 occurs in the southern edge of Siberian platform. η varies between 0.3 and 0.8. For most part of the studied area η varies
inversely withQ
0. 相似文献
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19.
Ample observational evidence shows that there is a northward crustal subduction zone underneath the Yarlung Zangbo suture between India and Eurasia. It penetrates Moho to a depth of about 100 km. There are probably multiple such crustal subductions under the Himalayas. They are different from lithosphere subduction during oceanic collisions. The detected slabs in the upper mantle north of the Yarlung Zangbo suture can be interpreted as remains of the Indian Plate’s mantle lithosphere. In contrary to ocean-continent subduction, the mantle lithosphere is delaminated from the crust as the Indian Plate subducts underneath Eurasia. Existing structural images of the crust and upper mantle of the Tibetan Plateau reveal that there were both northward and southward subductions over different geological periods, causing some seismic velocity anomalies around those subduction zones. 相似文献