The temperature of the warm neutral medium in the Milky Way     

Nissim Kanekar  Ravi Subrahmanyan  Jayaram N Chengalur  Vicky Safouris 《Monthly notices of the Royal Astronomical Society》2003,346(4):L57-L61

We report high-spectral-resolution Australia Telescope Compact Array (ATCA) H  i 21-cm observations resulting in the detection of the warm neutral medium (WNM) of the Galaxy in absorption against two extragalactic radio sources, PKS 1814−637 and PKS 0407−658. The two lines of sight were selected on the basis of the simplicity of their absorption profiles and the strength of the background sources; the high velocity resolution of the spectra then enabled us to estimate the kinetic temperatures of the absorbing gas by fitting multiple Gaussians to the absorption profiles. Four separate WNM components were detected towards the two sources, with peak optical depths  τ_max= (1.0 ± 0.08) × 10⁻², (1.4 ± 0.2) × 10⁻³, (2.2 ± 0.5) × 10⁻³  and  (3.4 ± 0.5) × 10⁻³  and kinetic temperatures   T _k= 3127 ± 300, 3694 ± 1595, 3500 ± 1354  and  2165 ± 608 K  , respectively. All four components were thus found to have temperatures in the thermally unstable range  500 < T _k < 5000 K  ; this suggests that thermal equilibrium has not been reached throughout the WNM.  相似文献   

Satellite luminosities in galaxy groups     

Ramin A. Skibba  Ravi K. Sheth  Matthew C. Martino 《Monthly notices of the Royal Astronomical Society》2007,382(4):1940-1946

  相似文献   

Non-Gaussian cosmic microwave background temperature fluctuations from peculiar velocities of clusters     

Naoki Yoshida †  Ravi K. Sheth  Antonaldo Diaferio 《Monthly notices of the Royal Astronomical Society》2001,328(2):669-677

We use numerical simulations of a (480 Mpc  h ⁻¹)³ volume to show that the distribution of peak heights in maps of the temperature fluctuations from the kinematic and thermal Sunyaev–Zeldovich (SZ) effects will be highly non-Gaussian, and very different from the peak-height distribution of a Gaussian random field. We then show that it is a good approximation to assume that each peak in either SZ effect is associated with one and only one dark matter halo. This allows us to use our knowledge of the properties of haloes to estimate the peak-height distributions. At fixed optical depth, the distribution of peak heights resulting from the kinematic effect is Gaussian, with a width that is approximately proportional to the optical depth; the non-Gaussianity comes from summing over a range of optical depths. The optical depth is an increasing function of halo mass and the distribution of halo speeds is Gaussian, with a dispersion that is approximately independent of halo mass. This means that observations of the kinematic effect can be used to put constraints on how the abundance of massive clusters evolves, and on the evolution of cluster velocities. The non-Gaussianity of the thermal effect, on the other hand, comes primarily from the fact that, on average, the effect is larger in more massive haloes, and the distribution of halo masses is highly non-Gaussian. We also show that because haloes of the same mass may have a range of density and velocity dispersion profiles, the relation between halo mass and the amplitude of the thermal effect is not deterministic, but has some scatter.  相似文献   

Megacities – megarisks     

Friedemann Wenzel  Fouad Bendimerad  Ravi Sinha 《Natural Hazards》2007,42(3):481-491

We review the definitions, population trends, and characteristics of megacities. Characteristics of megacities are, apart from their size, their complexity in terms of administration, infrastructure, traffic, etc., and at the same time the speed of change. Vulnerabilities and risk potential are discussed using the examples of Mexico City and Mumbai. We present the experience accumulated in the 6 years work of the Earthquakes and Megacities Initiative (EMI, ) with more than 20 large cities around the world, mostly located in the developing world. On this background we analyze obstacles that keep megacities from developing an efficient approach towards disaster mitigation and define a strategy that might overcome these problems. The key element of this strategy is the development of a Disaster Risk Management Master Plan (DRMMP) for cities. Currently the Istanbul Earthquake Master Plan (IEMP) serves as best example for an appropriate strategy for disaster reduction in megacities.  相似文献   

An improved practical approach for estimating catchment-scale response functions through wavelet analysis     

Ravindra Dwivedi  Christopher Eastoe  John F. Knowles  Lejon Hamann  Thomas Meixner  Paul A. “Ty” Ferre  Christopher Castro  William E. Wright  Guo-Yue Niu  Rebecca Minor  Greg A. Barron-Gafford  Nathan Abramson  Bhaskar Mitra  Shirley A. Papuga  Michael Stanley  Jon Chorover 《水文研究》2021,35(3):e14082

  相似文献   

Development of hyperspectral model for rapid monitoring of soil organic carbon under precision farming in the Indo-Gangetic Plains of Punjab,India     

Rajeev Srivastava  Dipak Sarkar  Siddhartha S. Mukhopadhayay  Anil Sood  Manjeet Singh  Ravindra A. Nasre  Sanjay A. Dhale 《Journal of the Indian Society of Remote Sensing》2015,43(4):751-759

  相似文献   

The M w 6.9 Sikkim–Nepal earthquake of September 2011: a perspective for wrench faulting in the Himalayan thrust zone     

N. Purnachandra Rao  V. M. Tiwari  M. Ravi Kumar  Pinki Hazarika  Dipankar Saikia  R. K. Chadha  Y. J. Bhaskar Rao 《Natural Hazards》2015,77(1):355-366

  相似文献   

Stability evaluation of hill cut slopes along national highway-13 near Hospet,Karnataka, India     

Ravi Kumar Umrao  T. N. Singh 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2015,9(3):158-170

The road networks are backbone of a nation for the economic growth and safe communication. A shortest road design shall always be encouraged, but in hilly terrain, railway crossings and road crossings are constraints for the highway designers. The same problem was faced while planning a new design of National Highway-13 near the Hospet city in Karnataka, India. To resolve that problem, a twin tunnel was proposed to overcome steep gradient, sharp curve and a railway crossing. The field investigation was carried out to measure the joint parameters, lithology and ground water condition to establish the tunnel and tunnel portal stability along with hill cuttings. In the present study, the basic rock mass rating (RMR_Basic) and continuous slope mass rating (CSMR) of the slope outside tunnel portal were computed based on the field investigation for different rocks of Sandur schist belt viz. metabasics, phyllite/chlorite schist and banded iron formation. The support measures were proposed based on the computed CSMR.  相似文献   

Secondary instability as a possible mechanism for clear-air turbulence: a case study     

T. N. Venkatesh  Joseph Mathew  Ravi S. Nanjundiah 《Meteorology and Atmospheric Physics》2014,126(3-4):139-160

Many theories and mechanisms have been proposed to explain the phenomenon of clear-air turbulence (CAT), and some of them have been successful in predicting light, moderate and, in some cases, severe turbulence. It is only recently that skill in the forecasting of the severe form of CAT, which could lead to injuries to passengers and damage to aircraft, has improved. Recent observations and simulations suggest that some severe to extreme turbulence could be caused by horizontal vortex tubes resulting from secondary instabilities of regions of high shear in the atmosphere. We have conducted direct numerical simulations to understand the scale relationship between primary structures (larger-scale structures related to one of the causes mentioned above) and secondary structures (smaller-sized, shear structures of the size of aircraft). From shear layer simulations, we find that the ratio of sizes of primary and secondary vortices is of the right order to generate aircraft-scale vortex tubes from typical atmospheric shear layers. We have also conducted simulations with a mesoscale atmospheric model, to understand possible causes of turbulence experienced by a flight off the west coast of India. Our simulations show the occurrence of primary flow structures related to synoptic conditions around the time of the incident. The evidence presented for this mechanism also has implications for possible methods of detection and avoidance of severe CAT.  相似文献   

The mineralogic transformation of ferrihydrite induced by heterogeneous reaction with bioreduced anthraquinone disulfonate (AQDS) and the role of phosphate     

John M. Zachara  Ravi K. Kukkadapu  Tanya Peretyazhko  Mark Bowden  Chongmin Wang  Dave W. Kennedy  Dean Moore  Bruce Arey 《Geochimica et cosmochimica acta》2011,75(21):6330-6349

Bioreduced anthraquinone-2,6-disulfonate (AH₂DS; dihydro-anthraquinone) was reacted with a 2-line, Si-substituted ferrihydrite under anoxic conditions at neutral pH in PIPES buffer. Phosphate (P) and bicarbonate (C); common adsorptive oxyanions and media/buffer components known to effect ferrihydrite mineralization; and Fe(II)_aq (as a catalytic mineralization agent) were used in comparative experiments. Heterogeneous AH₂DS oxidation coupled with Fe(III) reduction occurred within 0.13-1 day, with mineralogic transformation occurring thereafter. The product suite included lepidocrocite, goethite, and/or magnetite, with proportions varing with reductant:oxidant ratio (r:o) and the presence of P or C. Lepidocrocite was the primary product at low r:o in the absence of P or C, with evidence for multiple formation pathways. Phosphate inhibited reductive recrystallization, while C promoted goethite formation. Stoichiometric magnetite was the sole product at higher r:o in the absence and presence of P. Lepidocrocite was the primary mineralization product in the Fe(II)_aq system, with magnetite observed at near equal amounts when Fe(II) was high [Fe(II)/Fe(III)] = 0.5 and P was absent. P had a greater effect on reductive mineralization in the Fe(II)_aq system, while AQDS was more effective than Fe(II)_aq in promoting magnetite formation. The mineral products of the direct AH₂DS-driven reductive reaction are different from those observed in AH₂DS-ferrihydite systems with metal reducing bacteria, particularly in presence of P.  相似文献