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1.
The paper presents an efficient finite difference based 2D-inversion algorithm, EM2INV, for geoelectromagnetic data. The special features of the algorithm are
–  • optimal grid generation based on grid design thumb rules,
–  • finite domain boundary conditions,
–  • interpolation matrix that permits generation of response at observation points different from grid points,
–  • Gaussian elimination forward matrix solver, that enables reuse of already decomposed coefficient matrix,
–  • super-block notion that reduces the number of blocks with unknown resistivities and, in turn, the size of Jacobian matrix and
–  • bi-conjugate gradient matrix solver for inverse problem which circumvents the need of explicit Jacobian matrix computation.
The algorithm is tested rigorously by setting up exercises of diverse nature and of practical significance. The stability of the algorithm is established by inverting the synthetic response corrupted with Gaussian noise. The inversion experiments are aimed at studying
–  • relative performance of response functions,
–  • inversion quality of E- and B-polarization data,
–  • efficacy of single and multi-frequency data inversion,
–  • minimum number of frequencies and observation points needed for successful data inversion.
It has been observed that the Magneto-telluric data deciphers better the vertical position of the target and Geomagnetic Depth Sounding data deciphers the horizontal variations in a better way. The conductive and resistive bodies are better resolved by inversion of E- and B-polarization data respectively. The results of multi-frequency inversion imply that the increase in the number of frequencies does not necessarily enhance the inversion quality especially when the spread of observation points is sufficiently large to sense the target. The study of a minimum number of observation points highlights the importance of single point inversion that furnishes useful information about the inhomogeneity.  相似文献   

2.
The notion of remote element synthesis has recently been modified to explain the presence of nucleogenetic isotopic anomalies and decay products of short-lived nuclides by injection of a small amount ofexotic nucleogenetic material. Even with this modification, remote element synthesis seems inconsistent with the following observations:
–  Evidence of coupled variations in the chemical and isotopic compositions of the source material for meteorites.
–  Residual coupling of chemical and isotopic heterogeneities across planetary distances in the solar system today.
–  The mass-fractionation relationship seen across isotopes of elements in the planetary system, in the solar wind, and in solar flares.
–  Linkage of short-lived radioactivities with isotopic anomalies and with physical properties of their host grains, as expected for early condensate of fresh stellar debris.
–  Temporal and spatial distributions of short-live nuclides and their decay products.
–  Mirror-image (+ and −) isotopic anomalies in meteorite grains that sum to “normal” isotopic ratios, as expected of unmixed products of the same nuclear reactions that produced our bulk elements.
–  The lac supporting evidence for “presolar” grains or nearby stars that injectedexotic material into the early solar nebula.
  相似文献   

3.
Petrographic observations of two Vindhyan black shales (Rampur Shale of the Semri Group and Bijaigarh Shale of the Kaimur Group) revealed the following features:
–  •general wavy lamination,
–  •contorted and folded thin shreds of organic matter,
–  •wavy pyritic laminae,
–  •‘teeth and socket’ structure.
These features are indirect evidence of microbial mat colonization during the Proterozoic. The microbial mats probably fixed carbon at the sediment surface, stabilized sediment and recycled organic matter and were the primary producers, unlike during the Phanerozoic time.  相似文献   

4.
Scientific objectives and payloads of Chang’E-1 lunar satellite   总被引：1，自引：0，他引：1  
China plans to implement its first lunar exploration mission Chang’E-1 by 2007. The mission objectives are
–  • to obtain a three-dimensional stereo image of the lunar surface,
–  • to determine distribution of some useful elements and to estimate their abundance
–  • to survey the thickness of lunar soil and to evaluate resource of3He and
–  • to explore the environment between the Moon and Earth.
To achieve the above mission goals, five types of scientific instruments are selected as payloads of the lunar craft. These include stereo camera and spectrometer imager, laser altimeter, microwave radiometer, gamma and X-ray spectrometers and space environment monitor system. In order to collect, process, store and transmit the scientific data of various payloads a special payload data management system is also included. In this paper the goals of Chang’E-1 and its payloads are described  相似文献   

5.
The aeolian sedimentation record of the Thar desert   总被引：1，自引：0，他引：1  
A review of the aeolian sedimentary record of the Thar desert is presented. This includes a regional survey of the major dune forms, their genesis and their relationship to climate and other regional landforms. A key aspect of this work is the chronometry of the dunes using luminescence methods. Luminescence dating of sand has enabled quantification of the duration of the phases of sand aggradation and quiescence, time scales of dune migration and the dating of pedogenic carbonates. We demonstrate that the conventional wisdom of synchronicity of dune aggradation with glacial epoch is not true in the context of Thar sands and here only a short durationwindow of opportunity existed for dune aggradation. Luminescence ages further suggest that this window occurred during a transitional climatic regime from glacial to interglacial about 4–10 ka after the glacial epoch. Other inferences included are that:
–  • the aeolian activity in the Thar began over > 150 ka, resolving that Thar is not of anthropogenic origin as suggested previously;
–  • the present spatial extent of the aeolian activity in the Thar is in a contracted stage compared to that in the geological past, which refutes the arguments on its rapid north-eastward expansion;
–  • the current dune migration rates in areas of significant human-induced disturbances are much higher than during the geological past;
–  • the monsoon activity in the Thar varied significantly, from being minimal during the isotopic marine stages 4 and 2 to being close to the present during stage 3;
–  • on shorter time scales the dune activities correlated with the lacustrine records of the region with a phase difference of a few centuries and a periodicity of ∼ 1500 years;
–  • the sand aggradation climate in the southern margin in Gujarat gradually shrank northwards such that in general dunes older than 10 ka are seen in the extreme southern margin and dunes younger than 2ka ages occur mostly in the western part of Rajasthan.
  相似文献   

6.
Optimal trajectory design of a probe for soft landing on the Moon from a lunar parking orbit by minimizing the fuel required is obtained. The problem is formulated as an optimal control problem with the thrust direction being the control variable. Using the maximum principle of Pontryagin, the control variable is expressed as a function of co-state variables and the problem is converted into a two-point boundary value problem. The two-point boundary value problem is solved using an optimization technique, i.e., controlled random search. The strategies such as
–  • direct landing from a lunar parking orbit using powered braking
–  • direct landing from an intermediate orbit using powered braking
–  • by executing powered braking in two phases: through horizontal braking and vertical landing
are analyzed and an optimal strategy that achieves the goals is suggested. Also, appropriate design parameters are selected using this analysis  相似文献   

7.
Petrographic studies of samples of the Rajmahal basalt reveal a variety of microscopic joints within phenocrysts, which seem to have developed under the influence of thermal stresses during cooling. The theoretical analysis shows that:
–  •thermal stresses develop in a system only under unsteady state of cooling,
–  •the stresses responsible for the development of joints are tensile in nature, and
–  •the magnitude of stresses increases with increasing rates of cooling.
In order to understand the effects of cooling rate on the mode of jointing, analogue model experiments were performed by quenching melt films of organic, crystalline materials under varying cooling conditions. In experiments, non-branching linear joints developed at relatively lower rates of cooling by a process of sub-critical crack propagation. On the other hand, at higher rates of cooling the mechanism of crack propagation was essentially supercritical leading to the development of branching joints.  相似文献   

8.
This study presents a review of published geological data, combined with original observations on the tectonics of the Simplon massif and the Lepontine gneiss dome in the Western Alps. New observations concern the geometry of the Oligocene Vanzone back fold, formed under amphibolite facies conditions, and of its root between Domodossola and Locarno, which is cut at an acute angle by the Miocene, epi- to anchizonal, dextral Centovalli strike-slip fault. The structures of the Simplon massif result from collision over 50 Ma between two plate boundaries with a different geometry: the underthrusted European plate and the Adriatic indenter. Detailed mapping and analysis of a complex structural interference pattern, combined with observations on the metamorphic grade of the superimposed structures and radiometric data, allow a kinematic model to be developed for this zone of oblique continental collision. The following main Alpine tectonic phases and structures may be distinguished:
1.  NW-directed nappe emplacement, starting in the Early Eocene (~50 Ma);
2.  W, SW and S-verging transverse folds;
3.  transpressional movements on the dextral Simplon ductile shear zone since ~32 Ma;
4.  formation of the Bergell – Vanzone backfolds and of the southern steep belt during the Oligocene, emplacement of the mantle derived 31–29 Ma Bergell and Biella granodiorites and porphyritic andesites as well as intrusions of 29–25 Ma crustal aplites and pegmatites;
5.  formation of the dextral discrete Rhone-Simplon line and the Centovalli line during the Miocene, accompanied by the pull-apart development of the Lepontine gneiss dome – Dent Blanche (Valpelline) depression.
It is suggested that movements of shortening in fan shaped NW, W and SW directions accompanied the more regular NW- to WNW-directed displacement of the Adriatic indenter during continental collision.
Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Editorial Handling: Stefan Bucher  相似文献   

9.
A study of the synoptic situation which produced the catastrophic floods of November 1988 in Catalonia (in the northeast of the Iberian Peninsula) is presented. Analyses of the vertical structure, potential instability, precipitable water, and instability index are made through the radiosounding data from Palma, Majorca. It is found that the 1988 situation is included in type I intense convective events in Catalonia (classification obtained from all the events since 1950, (Llasat, 1989)). It was characterized by:
(a)  -pattern in the middle and high troposphere, the ridge axis east of Catalonia.
(b)  High pressure over Europe.
(c)  South-easterly winds in the lower troposphere with warm and moist humid air advection and south-westerlies aloft over Catalonia.
(d)  Strong instability (convective and latent).
(e)  Penetration of Atlantic air.
  相似文献   

10.
It seems that beyond differences among the drawings several generalisations may be made, relating to the ethno-spatial relations in Israeli Palestinian adolescents' perceptions, two years after the emergence of the uprising.
–  - Israeli Palestinian adolescents tend to adopt a nationalistic identity that to a large extent denies its Israeli civilian component, and thus tends to deny any shared identity with the Jewish sector. This is a shift from the Israeli Palestinians' political consensus which stresses the struggle for civilian and social equality.
–  - The Israeli Palestinian adolescents fully identify themselves with the Palestinians in the Occupied Territories, perceiving the uprising there as the major source of stimulation for the formation of a Palestinian identity.
–  - The PLO is perceived as the only political leadership which supports the Palestinians, including Israeli Palestinians, and offer a tangible sense of control over their destiny.
–  - The Palestinian identity crises (incuding the Israeli Palestinians) will be solved through the PLO military struggle for independence and peaceful compromise with the Jewish state.
–  - The elder adolescents, who have developed more sophisticated spatial abilities and have crystalised their collective identity, tend to attribute Palestinians and Jews with separate territorial bases, while the younger ones tend to ignore the territorial aspects of identity and inter-group relations.
–  - The compromise will lead to coexistence between two separate political identities which split the territory west of the Jordan river equally.
–  - The adolescents at the age of 13–14 represent strong awareness of the Palestinian national struggle and they clearly identify with a tendency to separate themselves from the Israeli state and join a Palestinian identity led by the PLO. If this is the milieu in which they form their identity for the future, one may conclude that the uprising succeeded in increasing unity and solidarity at least between the Israeli Palestinians and the Palestinians of the Occupied Territories around a more crystalised and determined national identity.
  相似文献   

11.
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12.
The construction of deep railway tunnels requires the prediction of natural temperatures at depth. Geothermal data for the Alps are presented and principles of previously employed methods to predict temperatures, using Andreae's analytical approach, are discussed. We then use a finite element numerical model based on pure conduction to calculate temperatures at depth. This method allows rock heterogeneity and anisotropy to be taken into account.This model is applied to the Maurienne-Ambin tunnel project, a 55 km long tunnel between St-Jean-de-Maurienne (France) and Susa (Italy), which will be the longest tunnel for the planned TGV (high speed train) Lyon-Torino link. Data from several deep boreholes (10 total, with 3>1000 m) are used to provide essential parameters for the model, i.e.:
–  - geological structure;
–  - geothermal gradients;
–  - rock conductivities from cores;
–  - geothermal deep heat flow.
  相似文献   

13.
The Rewa Group of the Vindhyan Supergroup in the Son valley begins with a thick (∼200m) dominantly shaly, shelfal succession, occurring between the Dhandraul Formation of the Kaimur Group (fluvial sandstone) below and Drammondganj Formation of the Rewa Group (marginal marine sandstone) above. Such a stratigraphic disposition indicates a sharp rise in relative sea level at the onset of Rewa sedimentation, inducing a shelfal depth to the Vindhyan basin. However, a number of wedge-shaped, sandstone/conglomerate bodies (maximum thickness 23.5 m) occur at multiple stratigraphic levels within the aforesaid deeper water shale succession, which appear to be of much shallow water origin representing regressive deposits. Though these bodies do not define a single physically continuous unit, either vertically or laterally, they are still designated by a single term ‘Asan Sandstone’ in the literature. On the other hand, the encasing shelfal shales are termed as Panna and Jhiri Shales, in accordance with their occurrence below or above the so-called ‘Asan Sandstone’. The present study reveals that in different sections spread over the Son valley, there are several discrete regressive wedges occurring vertically, and their depositional environment is also variable, ranging between braided fluvial, shoreface fan and braid delta. The features common to most of the regressive coarser clastic bodies are:
–  •invariable presence of deeper water, shelfal shale below (Panna or Jhiri);
–  •the underlying shale at places shows signatures of emergence at the top;
–  •laterally impersistent, wedge-like geometry; and
–  •presence of granular transgressive lags at the top. These coarser clastic wedges record several episodes of regressive deposition during short-term falling stage or lowstand of relative sea level at the early phase of Rewa sedimentation. Each individual phase of regressive deposition was, however, followed by flooding and resumption of shelf mud deposition.
  相似文献   

14.
Within the context of the phase IV (1994–1996) research and development activities at the Grimsel Test Site (GTS), Nagra developed, in collaboration with the Agence Nationale pour la Gestion des Déchets Radioactifs (Andra), an investigation project for the sealing of boreholes drilled from underground. The project had the following goals:
–  sealing of boreholes drilled from underground facilities with a length of up to 500 m,
–  sealing of boreholes with mainly irregular shape (e.g. breakouts of borehole wall),
–  ensuring a hydraulic conductivity of 10−11–10−12 m/s for the seal,
–  ensuring reliable quality control in routine production.
The new concept developed in this project was to use highly compacted bentonite pellets only. The two techniques tested were
(1)  pneumatic injection of pellets into a borehole using a grain size distribution of 4–10 mm,
(2)  emplacement using a modified core barrel for transport and compaction of the pellets.
Both techniques were tested in situ at the GTS to estimate their performance under realistic field conditions. The swelling pressures were monitored for 4 months after seal emplacement until an almost constant value was attained. Finally the hydraulic and mechanical performance of the seal was tested. It was found that the conductivities measured across the seal were equivalent to the matrix properties of the surrounding rock (2–5 × 10−12 m/s). The hydraulic testing also showed no linear preferential flow.  相似文献   

15.
δ18 O and δ13C of G.sacculifer have been measured in five cores from the northern Indian Ocean. In addition, high resolution analysis (1 to 2 cm) was performed on one core (SK-20-185) for both δ18O and gd13C in five species of planktonic foraminifera. CaCO3 variation was measured in two cores. The results, presented here, show that
–  • the summer monsoon was weaker during 18 ka and was stronger during 9 ka, relative to modern conditions;
–  • δ13C variations are consistent with independent evidence that shows that during the last glacial maximum (LGM; 18 ka) the upwelling was reduced while during 9 ka it was vigorous;
–  • calculation of CaCO3 flux shows that the LGM was characterized by low biogenic productivity in the Arabian Sea while during the Holocene productivity increased by ∼65%, as a direct consequence of the changes in upwelling. Similar changes (of lesser magnitude) are also seen in the equatorial Indian Ocean. The amount of terrigenous input into the Arabian Sea doubled during LGM possibly due to the higher erosion rate along the west coast.
–  • δ18O values indicate that the Arabian Sea was saltier by 1 to 2%o during LGM. The northern part was dominated by evaporation while in the equatorial part there was an increased precipitation.
  相似文献   

16.
With the launch of the German Aerospace Agency's (DLR) Modular Opto-electronic Scanner (MOS) sensor on board the Indian Remote Sensing satellite (IRS-P3) launched by the Indian Space Research Organization (ISRO) in March 1996, 13 channel multi-spectral data in the range of 408 to 1010 nm at high radiometric resolution, precision, and with narrow spectral bands have been available for a variety of land, atmospheric and oceanic studies. We found that these data are best for validation of radiative transfer model and the corresponding code developed by one of the authors at Space Applications Centre, and called ATMRAD (abbreviated for ATMospheric RADiation). Once this model/code is validated, it can be used for retrieving information on tropospheric aerosols over ocean or land. This paper deals with two clear objectives, viz.,
1  Validation of ATMRAD model/code using MOS data and synchronously measured atmospheric data, and if found performing well, then to
2  derive relationship between MOS radiances and Aerosol Optical Thickness (AOT).
The data validation procedure essentially involves
–  •near-synchronous measurements of columnar aerosol optical thickness and altitude profiles of aerosol concentration using ground-based multi-filter solar radiometers and Argon-ion Lidar, respectively and
–  •computation of the top-of-the-atmosphere (TOA) radiances from a low reflecting target (near clear water reservoir in the present study) using the ATMRAD model.
The results show that the model performance is satisfactory and a relationship between the spectral parameters of MOS radiances and aerosol optical thickness can be established. In this communication, we present the details of the experiments conducted, database, validation of the ATMRAD model and development of the relationship between AOT and MOS radiance.  相似文献   

17.
The eastern Dharwar Craton of southern India includes at least three ∼ 2700Ma supracrustal belts (schist belts) which have mesothermal, quartz-carbonate vein gold mineralization emplaced within the sheared metabasalts. In the Hutti and the Kolar schist belts, the host rocks are amphibolites and the ore veins have been flanked by only a thin zone of biotitic alteration; in the Ramagiri belt, however, the host rocks to the veins have been affected by more extensive but lower temperature alteration by fluids. The rare earth element (REE) geochemistry of the host metabasalts, alteration zones, ore veins and the bulk sulfides separated from the ore veins and the alteration zones suggest that
–  •the REE chemistry of the immediate host rocks has been modified by fluids which added LREE,
–  •the REE abundance of the ore veins vary with the amount of host rock fragments included in the veins,
–  •the sulfides formed during mineralization have significant REE concentration with patterns nearly identical to the ore veins and alteration zones and
–  •therefore the ore fluids involved in gold mineralization here could be LREE enriched.
Because alteration and mineralization involved addition of REE, more LREE compared to HREE, the fluids could be of higher temperature origin. The initial Nd isotope ratios in the host rocks (εNd calculated at 2700 Ma) showed a large variation (+8 to -4) and a deep crustal source for the fluid REE seems likely. A crustal source for Pb and Os in the ore samples of Kolar belt has previously been suggested (Krogstadet al 1995; Walkeret al 1989). Such a source for ore fluids is consistent with a late Archean (2500Ma) accretionary origin for the terrains of the eastern Dharwar Craton.  相似文献   

18.
The study shows that in the scenario of global warming temperature gradient (TG) between Indian landmass and Arabian Sea/Bay of Bengal is significantly decreasing in the lower troposphere with maxima around 850 hPa. TG during pre-monsoon (March to May) is reducing at a significant rate of 0.036°/year (Arabian Sea) and 0.030°/year (Bay of Bengal). The above alarming results are based on sixty years (1948–2007) of daily temperature and wind data extracted from CDAS-NCEP/NCAR reanalysis datasets. TG based on ERA-40 data also indicates a decreasing trend of 0.0229°/year and 0.0397°/year for Arabian Sea and Bay of Bengal respectively. As TG is not governed by any type of significant oscillation, there is a possibility of TG tending to zero. It is further observed that the rate of warming over the oceans is more than that over the land which has resulted into the weakening of TG. Pre-monsoon TG has significant correlations with
•  All India Seasonal Monsoon Rainfall (AISMR)
•  kinetic energy of waves 1 and 2 at 850 hPa
•  kinetic energy, and
•  stream function at 850 hPa over Indian landmass during monsoon season.
Except AISMR, the decreasing trends observed in all the above parameters are significant. All India rainfall for July and August together shows a significant decreasing trend of 0.995mm/year. Reducing number of depressions and cyclonic storms and increasing number of break days during monsoon over India are the reflections of the weakening of TG.  相似文献   

19.
Systematic and random error and their growth rate and different components of growth rate budget in energy/variance form are investigated at wavenumber domain for medium range tropical (30‡S-30‡N) weather forecast using daily horizontal wind field of 850 hPa up to 5-day forecast for the month of June, 2000 of NCEP (MRF) model. Part I of this paper deals with the study at physical domain. The following are the major findings in this paper:
–  •Tropical systematic error is associated with large scale wave of wavenumber 2, unlike the tropical random error, in which case dominant spectra of random error are observed at higher spectral band of wavenumbers 4–7 in comparison to that of systematic error.
–  •Systematic error growth rate peak is observed at wavenumber 2 up to 4-day forecast then the peak is shifted to wavenumber 1 at 5-day forecast. Random error energy shows maximum growth at wavenumber 4 for 2-day forecast, wavenumber 6 for 3–4 day forecasts and at wavenumber 7 for 1-day and 5-day forecasts.
–  •In the error growth rate budget, flux of systematic error shows the net increase of error energy at wavenumber 1 through the triad interactions with the pairs of waves of other wavenumbers. Flux and pure generation of random error energy are found to be accumulated at wavenumber 4. Resolving the possible triads in wavenumber 4 associated with these terms, it is shown that the wave receives more energy from the pairs of waves of different wavenumbers than it loses, leading to the error energy peak at wavenumber 4. However, the significant triad interaction occurs among the wavenumber 2 and higher wavenumbers in systematic error energy flux.
  相似文献   

20.
The ppaer re-examines three suggestions previously made concerning the colonization of the Krakatau islands since the extirpating 1883 eruption that involve the more recently emergent volcanic island Anak Krakatau, which itself suffered a devastating eruption in 1952. The suggestions re-addressed in the light of recent comments by other workers are:
(1)  Anak Krakatau offers, in general terms, an analogy of the early successional processes that occurred on the three older islands in the first decades after the 1883 extirpating eruption.
(2)  Anak Krakatau (with the Sertung spit) may have acted as an ecological refuge for open country species whose habitat on the three older islands declined as a result of vegetation succession.
(3)  Mainland open country species that did not colonize the archipelago when the appropriate vegetational successional stage occurred on the three older islands may now do so through a reopened early-successional window — Anak Krakatau (and the Sertung spit).
  相似文献   

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