A strong flare of the H<Subscript>2</Subscript>O maser in Sagittarius B2(M)     

O. Ramírez Hernández  E. E. Lekht  A. M. Tolmachev 《Astronomy Reports》2005,49(10):777-782

Results of a study of a strong flare of H₂O maser emission in the star-forming region Sgr B2(M) in 2004 are reported. The observations were carried out on the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. The main emission, with its flux density reaching 3800 Jy, was concentrated in a narrow radial-velocity interval (about 3 km/s) and was most likely associated with the compact group r, while the emission at V_LSR > 64 km/s came from group q. After 1994, the variations of the H₂O maser emission in Sgr B2(M) became cyclic with a mean period of 3 years.  相似文献   

Ambient air quality of Kathmandu valley as reflected by atmospheric particulate matter concentrations (PM10)     

D. Giri  K. V. Murthy  P. R. Adhikary  S. N. Khanal 《International Journal of Environmental Science and Technology》2006,3(4):403-410

This paper presents the analysis and interpretation of ambient particulate matter concentrations measured as PM₁₀ at a network of six air monitoring stations in Kathmandu valley during the years, 2003 through 2005. The purpose was to understand the pollution trends associated with different areas considering levels particulate matter concentrations representing the ambient air quality of Kathmandu valley. The study indicate that particulate concentrations (PM₁₀) measured are persistently higher at air sampling sites representing roadside areas compared to the background sites. The inter-station network variability with respect the particulate pollution suggests optimizing resources. The comparison of annual average PM₁₀ concentration observed at six air-monitoring sites in Kathmandu Valley with standard annual average concentration prescribed by World Health Organization as well as Europe Union indicates serious PM₁₀ pollution in Kathmandu valley.  相似文献   

The ages of the galactic globular clusters     

Ram Sagar 《Journal of Astrophysics and Astronomy》1997,18(4):295-301

The Galactic globular clusters are believed to be among the most ancient objects for which reliable ages can be determined. As the Universe can not be younger than the oldest object it contains, the oldest Galactic globular clusters provide one of the few most important constraints that one can have on cosmological models. Latest estimates indicate that the absolute age of the oldest globular clusters is 14 ± 3 Gyr. The calibration of absolute ages is still subject to observational and theoretical uncertainties at the ≈ 20% level, and represents a major limitation on our ability to test cosmological models. However, relative ages are starting to be much better known due to the super colour-magnitude diagrams that have been obtained through the use of CCD detectors on large telescopes and the Hubble Space Telescope. The available data are consistent with the majority of Galactic globular clusters being virtually coeval but with a minority having significantly lower ages. The existence of “prehistoric” clusters with ages of around 50 Gyr, as hypothesised in the quasi-steady state cosmology, should be readily recognised.  相似文献   

Fluorescence efficiencies of electrons in second positive bands of N₂ and first negative bands of N_2⁺     

S.P. Khare  A. Kumar 《Planetary and Space Science》1973,21(8):1381-1387

Fluorescence efficiencies of electrons in a large number of bands of N₂ second positive and N_2⁺ first negative groups lying in the 3000–5200 Å region are calculated. At very low pressure where quenching is negligible the present values are within 15 per cent of the experimental data of Hartmann (1968). The efficiencies are found to be independent of the impact energies greater than 200 eV which is in accordance with other theoretical and experimental results. The ratio of the total efficiencies in N₂ second positive and N_2⁺ first negative groups is 1·31 and is about 20 per cent lower than the experimental values. The efficiencies at a higher pressure equal to 600 torr are compared with the experimental data of Davidson and O'Neil (1964a).  相似文献   

The N-th root process applied to seismic array data   总被引：2，自引：0，他引：2  

K. T. Muirhead  Ram Datt 《Geophysical Journal International》1976,47(1):197-210

  相似文献   

Mercury's atmosphere: A perspective after Mariner 10     

Shailendra Kumar 《Icarus》1976,28(4):579-591

Measurements made during the Mariner 10 flybys of Mercury have shown that this planet has a tenuous atmosphere, somewhat similar to that of the Moon, which consists of at least helium and can be classified as an exosphere. The amount of helium observed can be supplied by either the accretion of only a fraction of the solar wind He²⁺ diffusing across the magnetopause, or from outgassing of radiogenic helium from the planetary crust. The role of solar wind in the maintenance and depletion of Mercury's atmosphere is discussed in view of the density upper limits established from Mariner 10. The argon supply rate on Mercury is probably not more than that on the Earth, but it is difficult to say whether Mercury is deficient in potassium or not on the basis of the present data. The global outgassing of CO₂ and H₂O from the planet interior is estimated to be at least four orders of magnitude smaller than for Earth which indicates that either Mercury is deficient in volatiles or that this planet is very inactive.  相似文献   

A paleolimnological record of Holocene climate and environmental change in the Temagami region,northeastern Ontario   总被引：3，自引：0，他引：3  

Robert?E.?A.?Boudreau  Jennifer?M.?Galloway  R.?Timothy?PattersonEmail author  Arun?Kumar  Frederick?A.?Michel 《Journal of Paleolimnology》2005,33(4):445-461

The Arcellacean (Thecamoebian) fauna was assessed in five Holocene sediment cores obtained from James and Granite lakes in the Temagami region of northeastern Ontario. In addition, palynological analysis was carried out on two of these cores, one each from James and Granite lakes. The first indication of postglacial colonization by plants was the appearance of rare Cupressaceae pollen, dated to 10,800 yr BP. Plant diversity began to increase by 10,770 yr BP when Pinus spp. and Larix migrated into the area. The first appearance of arcellaceans occurred after 9650 yr BP in assemblages dominated by Centropyxis constricta and opportunistic Centropyxis aculeata. High abundances of charophytes in the cores until 8800 yr BP indicated that macroalgae were proliferating at this time. This deposition is interpreted to have occurred during the draining of an ice-marginal lake following the retreat of the Laurentide Ice Sheet. Based on pollen analysis, warmer conditions associated with the Holocene Hypsithermal prevailed in the area from 6250 to 4115 yr BP. The stable, open Great Lakes – St. Lawrence type forest that developed here at the beginning of the Hypsithermal continues to prevail to the present. The periodic colonization of the lake by beavers (Castor canadensis) acted as a control on water-level and eutrophication through the Holocene. Evidence of eutrophication was indicated in the core samples by the abundance of high levels of the alga Pediastrum and the arcellacean Cucurbitella tricuspis. Eutrophication periodically developed when beavers dammed a site, causing the rate of flow in drainage streams to slow and stagnant conditions occurred. When the site became depleted of the nearby trees, which were preferred by beaver (Betula, Alnus and Populus), the dam would be abandoned, causing the water-level to drop. Stagnant conditions were reduced as flow levels increased, reducing eutrophication and resulting in recovering forest stands. In addition, the lowering water levels would result in encroachment of the forest along the lake shore. This cycle occurred many times in the history of this lake as indicated by fluctuations in the size of arcellacean populations.  相似文献   

Development of micro-scale joints in volcanic rocks under thermal stress     

Susanta Kumar Samanta 《Journal of Earth System Science》2001,110(3):191-203

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   

p Modes in and Away from a Sunspot     

Kumar  Brajesh  Jain  Rajmal  Tripathy  S.C.  Vats  Hari Om  Deshpande  M.R. 《Solar physics》2000,191(2):293-307

A time series of GONG Dopplergrams for the period 10–14 May 1997 from Udaipur and Big Bear sites has been used to measure the velocity fluctuations in a sunspot (NOAA active region 8038) and quiet photosphere simultaneously. We observe that the power of pre-dominant p mode is reduced in the sunspot as compared to quiet photosphere by 39–52% depending on the location of the sunspot region on the solar disk. We also observe a relative peak frequency deviation of p modes in the sunspot, of the order of 80–310 Hz, which shows a linear dependence on the magnetic field gradient in the active region. The maximum frequency deviation of 310 Hz on 12 May appears to be an influence of a long-duration solar flare that occurred in this active region. We interpret this relative peak frequency deviation as either due to power re-distribution of p modes in the sunspot or a consequence of frequency modulation of these modes along the magnetic flux tubes due to rapidly varying magnetic field structure.  相似文献   

Precipitation reconstruction using ring-width chronology of himalayan cedar from western himalaya: Preliminary results     

Ram R Yadav  Won-Kyu Park 《Journal of Earth System Science》2000,109(3):339-345

Himalayan cedar (Cedrus deodara (D. Don) G. Don) due to its long age and wide ecological amplitude in the Himalayan region has strong dendroclimatic potential. A well replicated ring-width chronology of it, derived from the ensemble of tree-ring samples of two adjacent homogeneous sites, has been used to reconstruct precipitation for the non-monsoon months (previous year October to concurrent May) back to AD 1171. This provides the first record of hydrological conditions for the western Himalayan region, India during the whole of the ‘Little Ice Age’ and latter part of the ‘Medieval Warm Period’. The reconstruction revealed the wettest and the driest non-monsoon months during the fourteenth and the thirteenth centuries, respectively. The seventeenth century consistently recorded dry non-monsoon months in the western Himalayan region. Surplus precipitation, especially more pronounced since the 1950s, is recorded in the current century.  相似文献