The interaction of the eta carinae primary wind with a century old slow equatorial ejecta     

Noam Soker  Amit Kashi 《New Astronomy》2012,17(7):616-623

We argue that the asymmetric morphology of the blue and red shifted components of the outflow at hundreds of AU from the massive binary system η Carinae can be understood from the collision of the primary stellar wind with the slowly expanding dense equatorial gas. Recent high spatial observations of some forbidden lines, e.g. [Fe III] λ4659, reveal the outflowing gas within about one arcsecond (2300AU) from η Car. The distribution of the blue and red shifted components are not symmetric about the center, and they are quite different from each other. The morphologies of the blue and red shifted components correlate with the location of dense slowly moving equatorial gas (termed the Weigelt blob environment; WBE), that is thought to have been ejected during the 1887–1895 Lesser Eruption (LE). In our model the division to the blue and red shifted components is caused by the postshock flow of the primary wind on the two sides of the equatorial plane after it collides with the WBE. The fast wind from the secondary star plays no role in our model for these components, and it is the freely expanding primary wind that collides with the WBE. Because the line of sight is inclined to the binary axis, the two components are not symmetric. We show that the postshock gas can also account for the observed intensity in the [Fe III] λ4659 line.  相似文献   

Characterization of suspended sediment in Meltwater from Glaciers of Garhwal Himalaya          下载免费PDF全文

Deepak Srivastava  Amit Kumar  Akshaya Verma  Siddharth Swaroop 《水文研究》2014,28(3):969-979

Glacierised basins are significant sources of sediments generated by glacial retreat. Estimation of suspended sediment transfer from glacierised basins is very important in reservoir planning for hydropower projects in Himalaya. The present study indicates that storage and release of sediment in proglacial streams may categorise the pattern of suspended sediment transfer from these basins. Assessment of suspended sediment concentration (SSC), suspended sediment load (SSL) and yield has been undertaken for Dunagiri Glacier basin located in Garhwal Himalaya (30^o33'20”N, 79^o53'36”E), and its results are compared with the Gangotri and Dokriani glaciers sharing close proximity. Out of the total drainage basin area, about 14.3 % of the area is glacierised. Data were collected for five ablation seasons (1984–1989, barring 1986). The mean daily SSCs for July, August and September were 333.9, 286.0 and 147.15 mg/l, respectively, indicating highest concentration of mean daily suspended sediment in July followed by August. SSL trends were estimated to be 93.0, 57.0 and 21.3 tonnes. About 59% of the total SSL of the melt period was transported during the months of August and September. Sediment yield for the study basin was computed to be 296.3 t km^?2 yr ^?1. It is observed that the cumulative proportion of SSC precedes the discharge throughout the melt season except in the year 1987. Release of SSL in terms of total load is less in the early part of melt season than in the later stage as compared to that of discharge. Diurnal variations in SSC reach their maximum at 2400 h, and therefore, SSC was found to be high during night (2000–0400 h). There was a good relationship between SSC and SSL with discharge for the ablation seasons (1988 and 1989). Mean monthly SSC and mean monthly SSL provide a good exponentional relationship with mean monthly temperature. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

An Integrated Moral Obligation Model for Landowner Conservation Norms     

Amit K. Pradhananga  Mae A. Davenport  David C. Fulton  Geoffrey M. Maruyama  Dean Current 《社会与自然资源》2017,30(2):212-227

This study applies an integrated moral obligation model to examine the role of environmental and cultural values, and beliefs in the activation of landowner conservation norms. Data for this study were collected through a self-administered survey of riparian landowners in two Minnesota watersheds: Sand Creek and Vermillion River watersheds. Study findings suggest that collectivistic and biospheric–altruistic values form the bases for the activation of personal norms. Further, beliefs about local responsibility and ability to act influence personal norms to protect water resources. Findings suggest that landowners’ personal norms of water conservation are more likely to be activated by conservation strategies that appeal to biospheric–altruistic and collectivistic values, emphasize adverse consequences of water pollution, highlight water resource protection as a local responsibility, and provide the resources needed to protect water resources.  相似文献   

Downscaling future climate change projections over Puerto Rico using a non-hydrostatic atmospheric model     

Amit Bhardwaj  Vasubandhu Misra  Akhilesh Mishra  Adrienne Wootten  Ryan Boyles  J. H. Bowden  Adam J. Terando 《Climatic change》2018,147(1-2):133-147

We present results from 20-year “high-resolution” regional climate model simulations of precipitation change for the sub-tropical island of Puerto Rico. The Japanese Meteorological Agency Non-Hydrostatic Model (NHM) operating at a 2-km grid resolution is nested inside the Regional Spectral Model (RSM) at 10-km grid resolution, which in turn is forced at the lateral boundaries by the Community Climate System Model (CCSM4). At this resolution, the climate change experiment allows for deep convection in model integrations, which is an important consideration for sub-tropical regions in general, and on islands with steep precipitation gradients in particular that strongly influence local ecological processes and the provision of ecosystem services. Projected precipitation change for this region of the Caribbean is simulated for the mid-twenty-first century (2041–2060) under the RCP8.5 climate-forcing scenario relative to the late twentieth century (1986–2005). The results show that by the mid-twenty-first century, there is an overall rainfall reduction over the island for all seasons compared to the recent climate but with diminished mid-summer drought (MSD) in the northwestern parts of the island. Importantly, extreme rainfall events on sub-daily and daily time scales also become slightly less frequent in the projected mid-twenty-first-century climate over most regions of the island.  相似文献   

Cosmic-ray positrons: are there primary sources?     

Stphane Coutu  Steven W. Barwick  James J. Beatty  Amit Bhattacharyya  Chuck R. Bower  Christopher J. Chaput  Georgia A. de Nolfo  Michael A. DuVernois  Allan Labrador  Shawn P. McKee  Dietrich Müller  James A. Musser  Scott L. Nutter  Eric Schneider  Simon P. Swordy  Gregory Tarl  Andrew D. Tomasch  Eric Torbet 《Astroparticle Physics》1999,11(4):208-435

Galactic cosmic rays consist of primary and secondary particles. Primary cosmic rays are thought to be energized by first order Fermi acceleration processes at supernova shock fronts within our Galaxy. The cosmic rays that eventually reach the Earth from this source are mainly protons and atomic nuclei, but also include electrons. Secondary cosmic rays are created in collisions of primary particles with the diffuse interstellar gas. They are relatively rare but carry important information on the Galactic propagation of the primary particles. The secondary component includes a small fraction of antimatter particles, positrons and antiprotons. In addition, positrons and antiprotons may also come from unusual sources and possibly provide insight into new physics. For instance, the annihilation of heavy supersymmetric dark matter particles within the Galactic halo could lead to positrons or antiprotons with distinctive energy signatures. With the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have measured the abundances of positrons and electrons at energies between 1 and 50 GeV. The data suggest that indeed a small additional antimatter component may be present that cannot be explained by a purely secondary production mechanism. Here we describe the signature of the effect and discuss its possible origin.  相似文献   

Estimation of carbon stock for greenhouse gas emissions from hydropower reservoirs     

Amit?KumarEmail authorView author&#;s OrcID profile  M.?P.?Sharma  Tao?Yang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(11):3183-3193

The identification and accurate quantification of sources or sinks of greenhouse gas (GHG) have become a key challenge for scientists and policymakers working on climate change. The creation of a hydropower reservoir, while damming a river for power generation, converts the terrestrial ecosystems into aquatic and subsequently aerobic and anaerobic decomposition of flooded terrestrial soil organic matter resulting in the emission of significant quantity of GHG to the atmosphere. Tropical/subtropical hydropower reservoirs are more significant sources of GHG compared to boreal or temperate one. This paper aims to estimate the emission factor (gCO₂eq./kWh) and net GHG emission from Koteshwar hydropower reservoir in Uttarakhand, India. Further, estimated GHG are compared with those from global reservoirs located in the same eco-region so that its impact could be timely minimized/mitigated. Results have shown that emission factor and net GHG emission of Koteshwar reservoir are, respectively, estimated as 13.87 gCO₂eq./kWh and 167.70 Gg C year^?1 which are less than other global reservoirs located in the same eco-region. This information could be helpful for the hydropower industries to construct reservoirs in tropical eco-regions.  相似文献   

Computation of ground motion amplification in Kolkata megacity (India) using finite-difference method for seismic microzonation     

Amit Shiuly  Vinay Kumar  Jay P. Narayan 《Acta Geophysica》2014,62(3):425-450

This paper presents the ground motion amplification scenario along with fundamental frequency (F ₀) of sedimentary deposit for the seismic microzonation of Kolkata City, situated on the world’s largest delta island with very soft soil deposit. A 4th order accurate SH-wave viscoelastic finite-difference algorithm is used for computation of response of 1D model for each borehole location. Different maps, such as for F ₀, amplification at F ₀, average spectral amplification (ASA) in the different frequency bandwidth of earthquake engineering interest are developed for a variety of end-users communities. The obtained ASA of the order of 3–6 at most of the borehole locations in a frequency range of 0.25–10.0 Hz reveals that Kolkata City may suffer severe damage even during a moderate earthquake. Further, unexpected severe damage to collapse of multi-storey buildings may occur in localities near Hoogly River and Salt Lake area due to double resonance effects during distant large earthquakes.  相似文献   

GPR Signatures of Pipes and Walls with Emphasis on the Effect of Inclined Scanning Trajectory     

Mohmad Mohsin Thakur  Amit Prashant 《Geotechnical and Geological Engineering》2017,35(5):1977-1989

This study investigates the effects of some commonly encountered constraints such as inclined scanning trajectory, multiple targets in the vicinity and material variation on GPR responses of pipes and walls. Further, the effects of wall inclination and broken walls are also explored in GPR signatures. Interpretation of such signatures in GPR data for archaeological and geotechnical surveys has been a challenge. A physical model was created to simulate buried pipes and walls under controlled conditions by maintaining density and moisture content of the soil medium. The presence of PVC pipes, plastered brick and stone walls buried in the dry sand have been investigated and major observations have been reported. The inclined scanning trajectory on buried pipes shows a change in curvature of hyperbola-like signatures. Inclined transects near the ends of pipes and walls manifest single limb GPR signatures. The responses of multiple pipes and walls show dependence on separation of targets and footprint of an antenna. One can discern stone walls from brick walls by recognizing the diffraction of waves by irregular stones in GPR responses. The signatures of walls differ from pipes with respect to the width of the apex and variation in the intensity in the limb.  相似文献   

Deterministic seismic microzonation of Kolkata city   总被引：1，自引：0，他引：1  

Amit Shiuly  J. P. Narayan 《Natural Hazards》2012,60(2):223-240

This paper presents the deterministic seismic microzonation of densely populated Kolkata city situated on the world’s largest delta island with very soft and thick soil deposit in the surficial layers. A fourth-order accurate staggered-grid finite-difference algorithm for SH-wave propagation simulation in visco-elastic medium is used for the linear computation of ground motion amplifications in sedimentary deposit. Different maps such as for fundamental frequency (F ₀), peak ground acceleration (PGA), peak ground velocity, and peak ground displacement are developed for variety of end-users communities, including structural and geotechnical engineers for performance-based designs, building officials, emergency managers, land-use planners, private businesses, and the general public. The scenario of simulated amplification factors in the different frequency bands revealed that the Kolkata city is very much prone to severe damage even during a moderate earthquake and very selective damage may occur at some of the localities during local and distant earthquakes. The deterministically predicted PGA at bedrock level is 0.0844 g and the maximum PGA predicted at the free surface is 0.6 g in Kolkata city due to maximum credible earthquake (M _w = 5.4) associated with Eocene Hinge Zone at a depth of 36 km. The seismic microzonation of Kolkata city reveals that the Nager Bazar and Nimtala areas are the safest regions with earthquake point of view.  相似文献   

Evaluating the Long-term Urban Expansion of Ranchi Urban Agglomeration,India Using Geospatial Technology     

Amit Kumar  Arvind Chandra Pandey  Najmul Hoda  A. T. Jeyaseelan 《Journal of the Indian Society of Remote Sensing》2011,39(2):213-224

The present study analyzes the built-up expansion of Ranchi urban agglomeration over a period of about 8 decades from 1927–2005. Satellite images and topographical maps were used to evaluate land use dynamics during these periods. Built-up growth of 473.7% during 1927–2005 was primarily at the expense of agricultural land along with reduction of natural water bodies reflects negative impacts of built-up expansion, which increased many folds in recent decades. The built-up growth is also analyzed with reference to population growth, land consumption rate and land transformation. The land loss due to increasing built-up growth of Ranchi were compared with other capital regions and cities along with population increase to provide insight into the possible scenario of built-up expansion in Ranchi urban area.  相似文献