排序方式： 共有25条查询结果，搜索用时 406 毫秒
1.
Highly sensitive microstructural probes subjected to noise disturbances are free of these in laboratory tests. This leads necessarily to the working out of methods for complex testsin situ. The paper reports on the successful use for this purpose of a grate (net) suspended from a free-falling probe. The grate sets up turbulence with reproducible structure in the area of sensor location.UDK 551.46.085 相似文献
2.
Richard Herrington Valeriy Maslennikov Victor Zaykov Igor Seravkin Alexander Kosarev Bernd Buschmann Jean-Jacques Orgeval Nicola Holland Svetlana Tesalina Paolo Nimis Robin Armstrong 《Ore Geology Reviews》2005,27(1-4):203
VMS deposits of the South Urals developed within the evolving Urals palaeo-ocean between Silurian and Late Devonian times. Arc-continent collision between Baltica and the Magnitogorsk Zone (arc) in the south-western Urals effectively terminated submarine volcanism in the Magnitogorsk Zone with which the bulk of the VMS deposits are associated. The majority of the Urals VMS deposits formed within volcanic-dominated sequences in deep seawater settings. Preservation of macro and micro vent fauna in the sulphide bodies is both testament to the seafloor setting for much of the sulphides but also the exceptional degree of preservation and lack of metamorphic overprint of the deposits and host rocks. The deposits in the Urals have previously been classified in terms of tectonic setting, host rock associations and metal ratios in line with recent tectono-stratigraphic classifications. In addition to these broad classes, it is clear that in a number of the Urals settings, an evolution of the host volcanic stratigraphy is accompanied by an associated change in the metal ratios of the VMS deposits, a situation previously discussed, for example, in the Noranda district of Canada.Two key structural settings are implicated in the South Urals. The first is seen in a preserved marginal allochthon west of the Main Urals Fault where early arc tholeiites host Cu–Zn mineralization in deposits including Yaman Kasy, which is host to the oldest macro vent fauna assembly known to science. The second tectonic setting for the South Urals VMS is the Magnitogorsk arc where study has highlighted the presence of a preserved early forearc assemblage, arc tholeiite to calc-alkaline sequences and rifted arc bimodal tholeiite sequences. The boninitc rocks of the forearc host Cu–(Zn) and Cu–Co VMS deposits, the latter hosted in fragments within the Main Urals Fault Zone (MUFZ) which marks the line of arc-continent collision in Late Devonian times. The arc tholeiites host Cu–Zn deposits with an evolution to more calc-alkaline felsic volcanic sequences matched with a change to Zn–Pb–Cu polymetallic deposits, often gold-rich. Large rifts in the arc sequence are filled by thick bimodal tholeiite sequences, themselves often showing an evolution to a more calc-alkaline nature. These thick bimodal sequences are host to the largest of the Cu–Zn VMS deposits.The exceptional degree of preservation in the Urals has permitted the identification of early seafloor clastic and hydrolytic modification (here termed halmyrolysis sensu lato) to the sulphide assemblages prior to diagenesis and this results in large-scale modification to the primary VMS body, resulting in distinctive morphological and mineralogical sub-types of sulphide body superimposed upon the tectonic association classification.It is proposed that a better classification of seafloor VMS systems is thus achievable using a three stage classification based on (a) tectonic (hence bulk volcanic chemistry) association, (b) local volcanic chemical evolution within a single edifice and (c) seafloor reworking and halmyrolysis. 相似文献
3.
The neutral gas environment of a comet is largely influenced by dissociation of parent molecules created at the surface of the comet and collisions of all the involved species. We compare the results from a kinetic model of the neutral cometary environment with measurements from the Neutral Mass Spectrometer and the Dust Impact Detection System onboard the Giotto spacecraft taken during the fly-by at Comet 1P/Halley in 1986. We also show that our model is in good agreement with contemporaneous measurements obtained by the International Ultraviolet Explorer, sounding rocket experiments, and various ground based observations.The model solves the Boltzmann equation with a Direct Simulation Monte Carlo technique (Tenishev, V., Combi, M., Davidsson, B. [2008]. Astrophys. J. 685, 659-677) by tracking trajectories of gas molecules and dust grains under the influence of the comet’s weak gravity field with momentum exchange among particles modeled in a probabilistic manner. The cometary nucleus is considered to be the source of dust and the parent species (in our model: H2O, CO, H2CO, CO2, CH3OH, C2H6, C2H4, C2H2, HCN, NH3, and CH4) in the coma. Subsequently our model also tracks the corresponding dissociation products (H, H2, O, OH, C, CH, CH2, CH3, N, NH, NH2, C2, C2H, C2H5, CN, and HCO) from the comet’s surface all the way out to 106 km.As a result we are able to further constrain cometary the gas production rates of CO (13%), CO2 (2.5%), and H2CO (1.5%) relative to water without invoking unknown extended sources. 相似文献
4.
A. I. Efimov T. Imamura K. -I. Oyama K. Noguchi L. N. Samoznaev A. S. Nabatov M. K. Bird I. V. Chashei 《Astronomy Reports》2010,54(11):1032-1041
Radio-sounding experiments using signals from the Japanese NOZOMI spacecraft to probe the circum solar plasma were performed from December 2000 through January 2001. They can be used to obtain information about the properties of the solar wind plasma in the region where it is accelerated at heliocentric distances of 12.8–36.9R s (where R s is the radius of the Sun). Measurements of the intensity and frequency of the received signals were carried out with high time resolution (～0.05 s for the frequency and ～0.0064 s for the intensity), making it possible to investigate the anisotropy of inhomogeneities and the spatial spectrum of the turbulence of the circum solar plasma. Analysis of these radio-sounding data has shown that the scintillation index and intensity of the frequency fluctuations decrease approximately according to a power law with increasing distance of the line of sight from the Sun. Measurements of the amplitude fluctuations and estimates of the solar wind velocity derived from spatially separated observations indicate the presence of small-scale inhomogeneities with sizes of the order of 50 km at heliocentric distances less than 25R s , which are elongated in the radial direction with anisotropy coefficients from 2.3 to 3.0. The inhomogeneities at heliocentric distances exceeding 30R s become close to isotropic. 相似文献
5.
Vladimir B. Aizen Elena M. Aizen Valeriy A. Kuzmichenok 《Global and Planetary Change》2007,56(3-4):341
This study simulates water resources in the Tien Shan alpine basins to forecast how global and regional climate changes would affect river runoff. The model employed annual mean values for the major characteristics of the water cycle: annual air temperature, precipitation, evapotranspiration and river runoff. The simulation was based on 304 hydro-meteorological stations, 23 precipitation sites, 328 high altitudinal points with glaciological measurements, 123 stream-gauges, and 54 evaporation sites, and it took into account topography. The findings were simulated over Tien Shan relief using a 1:500,000 scale 100 m grid resolution Digital Elevation Model. An applicable GIS-based distributed River Runoff Model was implemented in regional conditions and tested in the Tien Shan basins. The annual evapotranspiration exceeds the river runoff in the Tien Shan watersheds particularly up to 3700 m. Hypothetical climate-change scenarios in the Tien Shan predict that by 2100 river runoff will increase by 1.047 times with an increase in air temperature averaging 3 °C and an increase in precipitation averaging 1.2 times the current levels. Change in precipitation, rather than temperature, is the main parameter determining river runoff in the Tien Shan. The maximum ratio for predicted river runoff could reach up to 2.2 and the minimum is predicted to be 0.55 times current levels. This possibly dramatic change in river runoff indicates on non-linear system response caused mainly by the non-linear response of evapotranspiration from air temperature and precipitation changes. In the frame of forecasted possible climate change scenarios the probability of river runoff growth amounts 83–87% and probability of this decline is 17–13% by 2100 in the Tien Shan River basins. 相似文献
6.
Blubber samples of Baikal seals pups (Phoca sibirica) collected in 2001 and 2002 were analyzed for persistent organochlorines (OCs) such as PCBs (polychlorinated biphenyls), DDTs (dichlorodiphenyltrichloroethane and its metabolites), HCHs (hexachlorocyclohexane isomers), CHLs (chlordane related compounds), TCPMe [tris(4-chlorophenyl)methane] and TCPMOH [tris(4-chlorophenyl)methanol]. The distribution pattern of OCs was in the following order: DDTs>PCBs>CHLs>HCHs>TCPMOH>TCPMe. Organochlorine concentrations and composition patterns in eight pup blubber samples (2002) analyzed in the present study were compared with the corresponding levels in juvenile Baikal seals from 1992 survey, and it was found that residue levels of OC compounds have declined during the 10 year period. In particular, concentrations of PCBs, HCHs and CHLs in seals collected in 2002 were approximately two times lower, while DDTs levels were three times lower than the corresponding levels in 1992. Furthermore, higher ratios of beta-HCH/HCHs and p,p(')-DDE/DDTs were found in 2002 samples. While comparing the OC levels with those in other seal pups it appeared that all the OC concentrations were lower than the levels in seals from coastal California known as one of the most polluted areas. PCB and DDT concentrations in the present specimens were higher than that in Arctic seal pups. The proportions of tri-, tetra-, penta- and hexachlorobiphenyls in pups captured in 2002 were higher than those in 1992. TEQ concentrations of non- and mono-ortho coplanar PCBs in Baikal seals collected in 2002 were higher than those in seals collected from some locations in the world, where human and industrial activities are extensive, suggesting potential for toxic implications of coplanar PCBs in Baikal seals. 相似文献
7.
Gennadiy V. Ryabinin Valeriy A. Gavrilov Yuriy S. Polyakov Serge F. Timashev 《Acta Geophysica》2012,60(3):874-893
We propose a new type of earthquake precursor based on the analysis of correlation dynamics between geophysical signals of
different nature. The precursor is found using a two-parameter cross-correlation function introduced within the framework
of flicker-noise spectroscopy, a general statistical physics approach to the analysis of time series. We consider an example
of cross-correlation analysis for water salinity time series, an integral characteristic of the chemical composition of groundwater,
and geoacoustic emissions recorded at the G-1 borehole on the Kamchatka peninsula in the time frame from 2001 to 2003, which
is characterized by a sequence of three groups of significant seismic events. We found that cross-correlation precursors took
place 27, 31, and 35 days ahead of the strongest earthquakes for each group of seismic events, respectively. At the same time,
precursory anomalies in the signals themselves were observed only in the geoacoustic emissions for one group of earthquakes. 相似文献
8.
Jongho Kim Valeriy Y. Ivanov Simone Fatichi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(3):923-944
Predictions of a warmer climate over the Great Lakes region due to global change generally agree on the magnitude of temperature changes, but precipitation projections exhibit dependence on which General Circulation Models and emission scenarios are chosen. To minimize model- and scenario-specific biases, we combined information provided by the 3rd phase of the Coupled Model Intercomparison Project database. Specifically, the results of 12 GCMs for three emission scenarios B1, A1B, and A2 were analyzed for mid- (2046–2065) and end-century (2081–2100) intervals, for six locations of a hydroclimatic transect of Michigan. As a result of Bayesian Weighted Averaging, total annual precipitation averaged over all locations and the three emission scenarios increases by 7 % (mid-)–10 % (end-century), as compared to the control period (1961–1990). The projected changes across seasons are non-uniform and precipitation decreases by 3 % (mid-)–5 % (end-) for the months of August and September are likely. Further, average temperature is very likely to increase by 2.02–2.85 °C by the mid-century and 2.58–4.73 °C by the end-century. Three types of non-additive uncertainty sources due to climate models, anthropogenic forcings, and climate internal variability are addressed. When compared to the emission uncertainty, the relative magnitudes of the uncertainty types for climate model ensemble and internal variability are 149 and 225 % for mean monthly precipitation, and they are respectively 127 and 123 % for mean monthly temperature. A decreasing trend of the frost days and an increasing trend of the growing season length are identified. Also, a significant increase in the magnitude and frequency of heavy rainfall events is projected, with relatively more pronounced changes for heavy hourly rainfall as compared to daily events. Quantifying the inherent natural uncertainty and projecting hourly-based extremes, the study results deliver useful information for water resource stakeholders interested in impacts of climate change on hydro-morphological processes. 相似文献
9.
I. D. Litovchenko O. S. Bayandina A. V. Alakoz I. E. Val’tss G. M. Larionov D. V. Mukha A. S. Nabatov A. A. Konovalenko V. V. Zakharenko E. V. Alekseev V. S. Nikolaenko V. F. Kulishenko S. A. Odintsov 《Astronomy Reports》2012,56(7):536-552
A sample of Class I methanol masers (MMI) has been surveyed at 1720 MHz to search for possible associations between MMI and 1720-MHz OH masers, which should be formed by the same collisional pumping mechanism. If the model for methanol masers is correct, the sample should contain a statistically significant number of 1720-MHz OH masers at the positions of MMI. The observations were conducted on the 70-meter radio telescope of the National Academy of Sciences of Ukraine (NASU). The results show that ??50% of 72 MMI are associated with OH emission at 1720 MHz. In many sources, strong absorption lines are also observed. In most cases, the OH (1720) lines are narrow (linewidths of <2 km/s) suggesting they may be maser lines. The OH column densities obtained from Gaussian fitting of these narrow OH lines are, on average, 1.5 × 1017 cm?2. TheH2 density in the emitting medium reaches 107 cm?3 if the region of the OH (1720) emission has been subject to interaction with a bipolar-outflow front. This is sufficient to excite MMI, and the presence of narrow, possibly masing OH (1720) lines at the MMI velocities indicates the likely presence of shocks from bipolar outflows in the vicinity of the maser condensations, supporting models in which these molecules are collisionally pumped. 相似文献
10.
Distributed hydrologic models based on triangulated irregular networks (TIN) provide a means for computational efficiency in small to large‐scale watershed modelling through an adaptive, multiple resolution representation of complex basin topography. Despite previous research with TIN‐based hydrology models, the effect of triangulated terrain resolution on basin hydrologic response has received surprisingly little attention. Evaluating the impact of adaptive gridding on hydrologic response is important for determining the level of detail required in a terrain model. In this study, we address the spatial sensitivity of the TIN‐based Real‐time Integrated Basin Simulator (tRIBS) in order to assess the variability in the basin‐averaged and distributed hydrologic response (water balance, runoff mechanisms, surface saturation, groundwater dynamics) with respect to changes in topographic resolution. Prior to hydrologic simulations, we describe the generation of TIN models that effectively capture topographic and hydrographic variability from grid digital elevation models. In addition, we discuss the sampling methods and performance metrics utilized in the spatial aggregation of triangulated terrain models. For a 64 km2 catchment in northeastern Oklahoma, we conduct a multiple resolution validation experiment by utilizing the tRIBS model over a wide range of spatial aggregation levels. Hydrologic performance is assessed as a function of the terrain resolution, with the variability in basin response attributed to variations in the coupled surface–subsurface dynamics. In particular, resolving the near‐stream, variable source area is found to be a key determinant of model behaviour as it controls the dynamic saturation pattern and its effect on rainfall partitioning. A relationship between the hydrologic sensitivity to resolution and the spatial aggregation of terrain attributes is presented as an effective means for selecting the model resolution. Finally, the study highlights the important effects of terrain resolution on distributed hydrologic model response and provides insight into the multiple resolution calibration and validation of TIN‐based hydrology models. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献