New class of regular and well behaved exact solutions in general relativity     

Neeraj Pant  R. N. Mehta  Mamta Joshi Pant 《Astrophysics and Space Science》2010,330(2):353-359

We present a new class of spherically symmetric regular and well behaved solutions of the general relativistic field equations in isotropic coordinates. These solutions describe perfect fluid balls with positively finite central pressure and positively finite central density; their ratio is less than one and causality condition is obeyed at the centre. The solutions of this class, the outmarch of pressure, density pressure-density ratio and the ratio of sound speed to light is monotonically decreasing. Keeping in view of well behaved nature in terms of central red shift and surface red shift and by assuming the surface density ρ _b =2×10¹⁴ g/cm³, we constructed a Neutral star model for k=2, resulting into maximum mass ≈6.36M _Θ, linear dimension ≈48.08 km, surface red shift ≈1.132 and central red shift ≈17.1314.  相似文献   

Changes in concentration and size distribution of aerosols during fog over the south Indian Ocean     

Vimlesh Pant  C. G. Deshpande  A. K. Kamra 《Journal of Earth System Science》2010,119(4):479-487

Measurements of the concentration and size distribution of aerosol particles in the size-ranges of 0.5–20 μm and 16–700 nm diameters were made during six fog episodes over the south Indian Ocean. Observations show that concentrations of particles of all sizes start decreasing 1–2 hours before the occurrence of fog. This decrease is more prominent for coarse particles of >1 μm diameter and continues until 10–20 minutes before the onset of fog when particle concentrations in all size ranges rapidly increase by one/two orders of magnitude in ∼20 minutes. Thereafter, concentrations of particles of all sizes gradually decrease until the dissipation of fog. After the fog dissipation, concentrations of coarse mode particles rapidly increase and restore to their pre-fog levels but concentrations of the Aitken mode particles decrease slowly and reach their pre-fog levels only after 1–2 hours. The net effect of fog is to change the bimodal size distributions of aerosols with a coarse mode at 1.0 μm and an accumulation mode at 40–60 nm to a power law size distribution. It is proposed that the preferential growth and sedimentation of the coarse mode hygroscopic particles in the initial phase cause a large decrease in the aerosol surface area. As a result, the low vapour pressure gases which were initially being used for the growth of coarse mode particles, now accelerate the growth rates of the accumulation and Aitken mode particles.  相似文献   

The lunar gravity mission MAGIA: preliminary design and performances     

Marco?Fermi  Marco?Gregnanin  Marco?MazzolenaEmail author  Massimiliano?Chersich  Mirko?Reguzzoni  Fernando?Sansò 《Experimental Astronomy》2011,32(1):1-18

The importance of an accurate model of the Moon gravity field has been assessed for future navigation missions orbiting and/or landing on the Moon, in order to use our natural satellite as an intermediate base for next solar system observations and exploration as well as for lunar resources mapping and exploitation. One of the main scientific goals of MAGIA mission, whose Phase A study has been recently funded by the Italian Space Agency (ASI), is the mapping of lunar gravitational anomalies, and in particular those on the hidden side of the Moon, with an accuracy of 1 mGal RMS at lunar surface in the global solution of the gravitational field up to degree and order 80. MAGIA gravimetric experiment is performed into two phases: the first one, along which the main satellite shall perform remote sensing of the Moon surface, foresees the use of Precise Orbit Determination (POD) data available from ground tracking of the main satellite for the determination of the long wavelength components of gravitational field. Improvement in the accuracy of POD results are expected by the use of ISA, the Italian accelerometer on board the main satellite. Additional gravitational data from recent missions, like Kaguya/Selene, could be used in order to enhance the accuracy of such results. In the second phase the medium/short wavelength components of gravitational field shall be obtained through a low-to-low (GRACE-like) Satellite-to-Satellite Tracking (SST) experiment. POD data shall be acquired during the whole mission duration, while the SST data shall be available after the remote sensing phase, when the sub-satellite shall be released from the main one and both satellites shall be left in a free-fall dynamics in the gravity field of the Moon. SST range-rate data between the two satellites shall be measured through an inter-satellite link with accuracy compliant with current state of art space qualified technology. SST processing and gravitational anomalies retrieval shall benefit from a second ISA accelerometer on the sub-satellite in order to decouple lunar gravitational signal from other accelerations. Experiment performance analysis shows that the stated scientific requirements can be achieved with a low mass and low cost sub-satellite, with a SST gravimetric mission of just few months.  相似文献   

Long-lead prediction of Indian summer monsoon rainfall from global SST evolution   总被引：1，自引：0，他引：1  

A. K. Sahai  A. M. Grimm  V. Satyan  G. B. Pant 《Climate Dynamics》2003,20(7-8):855-863

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Space-wise approach to satellite gravity field determination in the presence of coloured noise   总被引：2，自引：2，他引：2  

F. Migliaccio  M. Reguzzoni  F. Sansò 《Journal of Geodesy》2004,78(4-5):304-313

For many years, the gravity field of the Earth was only seen by satellite geodesy as the main factor affecting the orbit and consequently it was retrieved together with a number of other orbital perturbations. Since the advent of a new generation of accelerometers, non-gravitational perturbations can be separated from the gravity effects and a new era of gravity field estimates from space has been born. During preparatory data analysis for new missions performed by the geodetic community, three approaches have been proposed and numerically tested: the brute force method (direct approach), the semi-analytical (time-wise) method and the space-wise method. In particular, the time-wise method takes advantage of the incoming time flow of data and, after performing a Fourier transform of the observation equations, exploits the prevailing block diagonal structure of the normal equations to estimate the spherical harmonic coefficients of the gravity field. Complementary to this is the space-wise approach, which goes back to the traditional computation of the harmonic coefficients by an integration technique or by least-squares collocation. Some advantages and disadvantages are peculiar to both methods, particularly the space-wise approach, which has for a long time ignored the marked signature of the noise spectrum due to the specific measuring conditions of space-borne accelerometers. The application of a proper Wiener filter, exploiting the correlation along the orbit, embedded into an iterative scheme, seems to be the answer. The solution to this major problem of the space-wise approach is illustrated and simulation results are discussed.  相似文献   

Pressure dependence of melting of metals     

M.M. Pant 《Physics of the Earth and Planetary Interiors》1978,17(2):P14-P15

A relationship between the melting temperature of a metal and its surface energy is used to predict, in a semi-empirical way, the variation of the melting temperature with pressure for sodium. The agreement of the predicted results with the experiments is very good.  相似文献   

Behaviour of volatiles in the magmatic solutions and energetic implications     

G. Imbò 《Bulletin of Volcanology》1968,32(2):343-351

Energetic investigation on the eruptive activity presupposes the knowledge of the distribution and dynamics of volatiles within the magmatic melt. In this paper balance distributions are studied in case of: an initial constant contents; a variable contents; a volatile pseudo-enrichment caused by crystalline separation; a pseudo-increase with depth in relation to the variation of the equilibrium contents with the external pressure. Diffusion of volatiles causes their migration toward the surface. The emission of free volatiles with the subsequent expansion produces the eruptive phenomena. Computation of the energy of expelled masses can be made if the magmatic pressure at the vent and the mixing ratio are known. Data performed on the occasion of the Vesuvian paroxysm of March, 1944 are 1.8×10¹² joule for the fountain phase and 3.3×10¹⁴ joule for the whole paroxysm. By assuming mean values if the expelled masses (M) (in gr) are known, the energy (E) (in joule) may be calculated by the relationE=48M.  相似文献   

Neodymian goyazite in the bauxite deposit of Vlasenica,Yugoslavia     

Prof. Dr. Z. Maksimović  Dr. Gy. Pantó 《Mineralogy and Petrology》1985,34(2):159-165

Summary Electron probe analysis of a bauxite sample with the highest content of the rare earth elements from the Nazda bauxite deposit in the Vlasenica bauxite-bearing area, revealed the presence of neodymian goyazite, a mineral of the crandallite group. Its composition lies between goyazite, florencite and crandallite, and can be described asCn ₂₄Fc₃₃Gz₄₃. The first analyses of this mineral in bauxites are presented and the genesis is discussed.

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Nd-haltiger Goyazit im Bauxitlager von Vlasenica, Jugoslawien

Zusammenfassung Ein Mineral der Crandallitgruppe, Neodym-Goyazit, wurde mittels Mikrosondenanalysen aus dem mit höchsten Gehalten an Seltenen Erden gekennzeichneten Nazda Bauxitlager im Vlasenica Bauxitgebiet identifiziert. Die Zusammensetzung liegt zwischen Goyazit, Florencit und Crandallit und kann mitCn ₂₄Fc₃₃Gz₄₃ angegeben werden. Ein Überblick über die ersten Analysen dieses Minerals von Bauxitlagerstätten und seinen Ursprung wird hiermit gegeben.

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With 3 Figures  相似文献   

Towards integrated essential variables for sustainability     

Anthony Lehmann  Joan Masò  Stefano Nativi  Gregory Giuliani 《International Journal of Digital Earth》2020,13(2):158-165

ABSTRACT

Measuring the achievement of a sustainable development requires the integration of various data sets and disciplines describing bio-physical and socio-economic conditions. These data allow characterizing any location on Earth, assessing the status of the environment at various scales (e.g. national, regional, global), understanding interactions between different systems (e.g. atmosphere, hydrosphere, biosphere, geosphere), and modeling future changes. The Group on Earth Observations (GEO) was established in 2005 in response to the need for coordinated, comprehensive, and sustained observations related to the state of the Earth. GEO’s global engagement priorities include supporting the UN 2030 Agenda for Sustainable Development, the Paris Agreement on Climate, and the Sendai Framework for Disaster Risk Reduction. A proposition is made for generalizing and integrating the concept of EVs across the Societal Benefit Areas of GEO and across the border between Socio-Economic and Earth systems EVs. The contributions of the European Union projects ConnectinGEO and GEOEssential in the evaluation of existing EV classes are introduced. Finally, the main aim of the 10 papers of the special issue is shortly presented and mapped according to the proposed typology of SBA-related EV classes.  相似文献   

On the aliasing problem in the spherical harmonic analysis     

F. Sansò 《Journal of Geodesy》1990,64(4):313-330

To apply the least squares method for the interpolation of harmonic functions is a common practice in Geodesy. Since the method of least squares can be applied only to overdetermined problem, the interpolation problem which is always under-determined, is often reduced to an overdetermined form by truncating a series of spherical harmonics. When the data points are the knots of a regular grid it is easy to see that the estimated harmonic coefficients converge to the correct theoretical values, but when the observation density is not constant a significant bias is introduced. The result is obtained by assuming that the number of observations tends to infinity with points sampled from a given distribution. Under the same conditions it is shown that quadrature and “collocation-like” formulas displays a statistically consistent behaviour.  相似文献