Representative abundances of a few positive ions in the innermost coma of comet Halley     

P. P. Saxena  Alka Misra 《Earth, Moon, and Planets》1993,60(1):59-68

The production rate of H₂O molecules at a heliocentric distance of 1 AU for comet Halley and the abundance ratio with respect to water (H₂O) of parent molecules at the cometary nucleus from the paper of Yamamoto (1987) have been used to compute the number densities of positive ions viz. H₃O⁺, H₃S⁺, H₂CN⁺, H₃CO⁺, CH₃OH ₂ ⁺ and NH ₄ ⁺ at various cometocentric distances within 600 kms from the nucleus.The role of proton transfer reactions in producing major ionic species is discussed. A major finding of the present investigation is that NH ₄ ⁺ ion which may be produced through proton transfer reactions is the most abundant ion near the nucleus of a comet unless the abundance of NH₃ as a parent is abnormally low. Using the quoted value of Q(NH₃)/Q(H₂O) for comet Halley and the life times of NH₃ and H₂O molecules, the abundance ratio N(NH₃)/N(H₂O) is found to be one-third of that used in the present paper. The consequent proportionate decrease in the NH ₄ ⁺ ions does not, however, affect its superiority in number density over other ions near the nucleus.The number density of the next most abundant ion viz. H₃O⁺ is found to be 4 × 10⁴ cm^-3 at the nucleus of comet Halley and decreases by a factor of two only upto a distance of 600 K ms from the nucleus. The ionic mass peak recorded by VEGA and GIOTTO spacecrafts atm/q = 18 is most probably composite of the minor ionic species H₂O⁺, as its number density = 10² cm^-3 remains virtually constant in the inner coma and of NH ₄ ⁺ , the number density of which at large cometocentric distances may add to the recorded peak atmlq = 18. The number densities of other major ions produced through proton transfer from H₃O⁺ are also discussed in the region within 600 K ms from the nucleus of comet Halley.  相似文献   

Eclipse observations of coronal emission lines. I. [Fex] 6374Å profiles at the eclipse of 16 February 1980     

Jagdev Singh  M. K. V. Bappu  A. K. Saxena 《Journal of Astrophysics and Astronomy》1982,3(3):249-266

Coronal spectra during the total solar eclipse of 1980 February 16, were obtained in the 6374Å [Fex] line using a multislit spectrograph. These spectra have a dispersion of 2.5 Å mm^-1. The observed line profiles from 1.1 to 1.7 R_⊙ with a spatial resolution of 10 × 22 arcsec², give half-widths that vary between 0.6 Å and 2.4Å. A large number of locations have half-widths around 1.3 Å corresponding to a temperature of 4.6 × 10⁶ K. If temperature of the order of 1.3 × 10⁶ K are typical of the regions that emit [Fex], then turbulent velocities of ~ 30 km s^-1 need to be invoked for the enhanced line broadening. The line-of-sight velocities measured range between +14 km s^-1 to -17 km s^-1. Most of the locations have velocities less than ±5 km s^-1. From these observations we conclude that corona does not show any localized differential mass motion and that it co-rotates with the photospheric layers deeper down.  相似文献   

Melting of wüstite and iron up to pressures of 600 kbar     

Guoyin Shen  Peter Lazor  Surendra K. Saxena 《Physics and Chemistry of Minerals》1993,20(2):91-96

The effect of pressure on melting temperature of wüstite and iron has been measured with laser-heated diamond anvil cell. The temperature was determined by measuring the thermal radiation emitted by the sample as a function of wavelength in the range from 600 nm to 900 nm to which Planck's radiation function was fitted; the pressure was measured by ruby-fluorescence technique. The melting curve of wüstite in this study when extrapolated to low pressures agrees with Lindsley's (1966) data. Our data are similar to the recent data of Boehler (1992) and close to that of Ringwood and Hibberson (1990) at pressure of 160 kbar, but the melting temperature does not rise as rapidly with increasing pressure as reported by Knittle and Jeanloz (1991). If tungsten emissivity is used in the temperature calculation, the melting curve of iron matches those of Boehler et al. (1990). Use of emissivity of iron in the temperature calculation results in somewhat higher temperatures than those reported by Boehler et al. (1990).  相似文献   

Assessment of land degradation hazards,etah district,uttar pradesh using landsat data     

RK Saxena  KS Verma  AK Barthwal 《Journal of the Indian Society of Remote Sensing》1991,19(2):83-94

To understand the nature of land degradation and factors responsible for it, investigations were carried out in Etah district with an area of 4.45 lakh hectares. For identification of soil/land degradation problems, multidate Landsat, TM spectral bands and FCC were used. It is observed that salt-affected soils are sharply depicted by light and dark gray mixed tone on band 3, while they are not clear on band 4. Flood plain and waterlogged soils are clearly observed on band 4. Band 6 (10.3 – 12.5 µm) helps in separation of broad zones of coarse and fine-textured soils, active flood plain of rivers, and eroded and gullied lands. The confusion between coarse-textured droughty soils and salt-affected areas in TM FCC (2, 3, 4) could be eliminated by use of band-6 data in combination with FCC. For delineation of problematic areas, two approaches were followed viz. (i) physiographic approach, and (ii) direct approach. In the physiographic approach landscape map associated with image characteristics was prepared. Further the image interpretation units were interpreted for land degradation hazards. With this approach physiography and soil relationship and the degradation problems vis-a-vis soil units could be established and ameliorative measures as per soil condition can be suggested. In direct approach, the problematic areas as per predetermined key were demarcated. Out of 4.45 lakh ha of the area, 1.99 lakh ha is affected by various soil degradation problems, like droughty soils, flooding hazard and salinity and alkalinity which cover 22.1%, 50.0% and 27.9%, respectively. To study the distribution of a salt-affected lands, major physiographic boundaries were superimposed over the land degradation map prepared by direct approach. It is observed that 81.5% of the salt-affected areas lie in the old alluvial plain while 18.5% is in recent flood plain.  相似文献   

X-ray diffraction study of Fe2+-Mg order-disorder in orthopyroxene. Some kinetic results     

S. K. Saxena  M. C. Domeneghetti  G. M. Molin  V. Tazzoli 《Physics and Chemistry of Minerals》1989,16(5):421-427

Kinetic rates of Fe²⁺-Mg disordering in three orthopyroxenes (mean value of X_Fe = Fe²⁺/(Fe²⁺+Mg) = 0.175,0.482,0.770 respectively) have been determined employing heating experiments and single crystal X-ray structural refinements. Disordering rate constants \((\vec K)\) (550800° C) for two pyroxenes are given by: ln \((\vec K)\) = 27.107(±5.177)?32062(±783)T^?1(X_Fe = 0.175) ln \((\vec K)\) = 16.142(±0.057)?18227(±423)T^?1(X_Fe = 0.770) The distribution coefficients K_D (representing a steady state of disordering Fe_M2 + Mg_M1 ? Fe_M1 + Mg_M2) are given by: ln K_D = 5.016(±0.223)-7033(±1473) T^?1(X_Fe = 0.175) ln K_D = 1.988(±0.122)-3809(±913)T^?1(X_Fe = 0.770) These distribution coefficients provide the constraint of the disordering reaction on the value of the equilibrium constant for Fe²⁺-Mg order-disorder. Until the low temperature dependence of K_D is well constrained, the calculation of cooling rates of pyroxenes and host rocks cannot be done reliably.  相似文献   

Remote sensing techniques in establishing geomorphic-soil relationships     

R. S. Murthy  R. M. Pofali  R. K. Saxena 《Journal of the Indian Society of Remote Sensing》1982,10(2):1-11

Landform constitutes one of the important factors in establishing a firm relationship between soil development and pertinent morphological characteristics. Therefore, an understanding of the geomorphological processes helps to initiate studies in the characterisation of soil scapes. Landscape-soil relationships also assist in mapping soils rapidly and accurately. Remote sensing data products like aerial photographs and satelite imagery help in the recognition, delineation and satellite imagery help in the recognition, delineation and classification of landforms for genetical studies. Five sample areas selected from heterogeneous climatic environments distinctly reveal geomorphic-soil linkages. In the humid, highly weathered, sedimentary hilly terrain of Tripura, Udalfs, Ochrepts and Orthents are common while in the valleys Aqualfs, and Aquepts occur dominantly. In the arid and hilly terrain of Kutch, shallow Orthents and Orthids form the dominant soils but in the plains, deep Salorthids and Natrargids take a dominant place. The semihumid Malwa plateau and Nagpur consists of Ochrepts and Usterts.  相似文献   

Aquifer chemistry of the Puga and Chumatang high temperature geothermal systems in India     

V.K. Saxena  Franco D'Amore 《Journal of Volcanology and Geothermal Research》1984,21(3-4)

Results of a chemical study of the fluids from drill holes and hot springs of Puga and Chumatang areas in the northwestern part of the Himalaya are presented and discussed in this paper. The thermal waters of Puga and Chumatang are of Na-HCO₃-Cl and Na-HCO₃ types, respectively. A comparison between these waters, their chemical classification and activity studies suggest a flow path within a quartzitic-schistose basement, containing quartz, K-feldspar and illite, and in clayey terrains containing montmorillonite and illite.The chemistry of thermal waters also indicate their association with magmatic activity. The chemical geothermometers indicate the possible existence of a geothermal reservoir at Puga with temperature ≈250°C. The Chumatang area has a comparatively cooler reservoir with a temperature of 150–180°C.  相似文献   

Kinetics of Fe2+-Mg distribution in aluminous orthopyroxenes     

S. K. Saxena  V. Tazzoli  M. C. Domeneghetti 《Physics and Chemistry of Minerals》1987,15(2):140-147

Kinetic studies of isothermal heating experiments (600–800° C) on aluminous pyroxenes (Mg_0.942Fe _0.880 ²⁺ Fe _0.068 ³⁺ Mn_0.016Ca_0.010Al_0.084) (Si_1.848Al_0.152) permit the determination of rate constant of isothermal disordering as 2.5457 E13(±1.4 E13) min^?1. The activation energy is determined as 278 (±23) kJ/mol. Data on two other aluminous pyroxenes at 700° C indicate that the rate constant decreases significantly with increasing amount of trivalent cations. There is a similar but reverse correlation between the concentration of trivalent cations and the Fe²⁺-Mg equilibrium distribution between sites. The site distribution coefficient increases with increasing concentration of trivalent cations at constant temperature.  相似文献   

Activity-composition relations in feldspars     

S. K. Saxena  P. H. Ribbe 《Contributions to Mineralogy and Petrology》1972,37(2):131-138

Seck's (1971a) compositional data on coexisting feldspars in the Or-Ab-An ternary at 650° C and 1 kb were used to calculate the activity-composition relations in binary alkali feldspar and binary plagioclase. The energy constants in Guggenheim's expression for excess free energy of mixing are A ₀=3920 and A ₁=657 cal/mole for alkali feldspar, in excellent agreement with values obtained by Thompson and Waldbaum (1969), and 1320 and 373 cal/ mole for plagioclase. Using Orville's (1972) data from ion-exchange experiments between plagioclase and Na—Ca chloride solutions at 700° C and 2 kb, we obtained 967 cal/mole for A ₀ and 715 cal/mole for A ₁ in the plagioclase crystalline solution.Activity-composition relations for plagioclase are interpreted in terms of a continuous, random substitution of CaAl for NaSi across the high structural state plagioclase series. This interpretation is consistent with that obtained from a consideration of lattice parameters.  相似文献   

Atmospheric boundary layer studies at Jodhpur during MONTBLEX using sodar and tower     

B. S. Gera  S. P. Singal  Neeraj Saxena  Y. S. Ramakrishna 《Journal of Earth System Science》1996,105(3):261-272

A monostatic sodar was set up at Jodhpur, near the western end of the monsoon trough, to investigate the atmospheric boundary layer dynamics. A 30 m instrumented tower was also located close to the sodar antenna. Data were collected from June to August during the monsoon period of 1990, as also from July 1992 to September 1993. Thermal plumes, surface-based stable layers (both flat or short spiky top and tall spiky top), elevated/multi-layers with or without undulations and dot echo structures were seen; however, erosion of the morning inversion layer in the form of a rising layer with growing thermal plumes under it was rarely seen, and that too only during the winter period. The observed structure of the stable layer with tall spikes and its depth have been found to be correlated with the intensity of the monsoon spell; the dot echoes have been found to be correlated with the approach of a monsoon depression near Jodhpur; and the elevated/multilayers have been attributed to the formation of a subsidence (shear instability).  相似文献