Studies on the Application of Steady State Assumption in 1DV Model for the Estimation of Settling Velocity of Suspended Sediments in a Shallow Estuary     

K. L. Priya 《Ocean Science Journal》2018,53(3):449-459

Settling velocity is one of the important parameters in sediment transport modeling of estuaries. The methods adopted for its determination vary from theoretical equations to experimental methods. The theoretical equation generally adopted in the 1DV model include assumptions in order to simplify the solution. It is generally assumed that either the condition is steady or the vertical diffusion is negligible. This study evaluated the relative importance of the two assumptions made for the estimation of settling velocity. Two approaches were adopted: unsteady and negligible vertical diffusion (NS-NVD) and steady with vertical diffusion (S-VD) to estimate the settling velocity. The Muthupet Estuary in the Coromandal coast of India was selected for the study. The S-VD approach estimated settling velocity fairly well at the two locations with appreciable vertical diffusion. The NS-NVD approach was observed to be superior for estimating settling velocity at shallow reaches of the estuary having low flow velocity. The calculated settling velocity was further applied in 1DV model to predict the suspended sediment concentration. The S-VD approach predicted suspended sediment concentration at those locations with appreciable vertical diffusion with an R² value of 0.82 against 0.67 for the NS-NVD approach. At the other shallow reach of the estuary with low flow velocity, the NS-NVD approach gave an R² value of 0.822 against 0.71 for the S-VD approach. The vertical diffusion was observed to play a secondary role at those locations which are shallow with a water depth of 0.6 m and with a low flow velocity of the order of 0.01 m/s. The study demonstrated that localized hydrodynamic conditions influence the method adopted for the estimation of settling velocity.  相似文献   

Exact solution of anisotropic compact stars via mass function     

S. K. Maurya  Ayan Banerjee  Y. K. Gupta 《Astrophysics and Space Science》2018,363(10):208

Studying relativistic compact objects is important in modern astrophysics to understand several astrophysical issues. It is therefore natural to ask for an internal structure and physical properties of specific classes of compact stars from astrophysical observations. We obtain a class of new relativistic solutions with anisotropic distribution of matter for compact stars. More specifically, stellar models, described by an anisotropic fluid, establishing a relation between metric potentials and generating a specific form of mass function, are explicitly constructed within the framework of General Relativity. New solutions can be used to model compact objects, which adequately describe compact strange star candidates like SMC X-1, Her X-1 and 4U 1538-52, with observational data taken from Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431:3216, 2013). As a possible astrophysical application the obtained solutions could explain the physics of selfgravitating objects, and might be useful for strong-field regimes where data are currently inadequate.  相似文献   

Determination of Non-gravitational Effects in the Motion of Near-Sun Objects 321P, 322P, 323P,and 342P     

V.?V.?Emel’yanenkoEmail author  S.?A.?Naroenkov 《Solar System Research》2018,52(1):64-68

At the beginning of this century, the SOHO space observatory discovered near-Sun comets with perihelion distances q ≈ 0.05 AU, which remained observable over several close encounters with the Sun. This became one of the surprises in studying the small bodies of the Solar System. Currently, there are objects that have already been observed in four (342P) and five (321P, 322P, and 323P) apparitions. In the present work, the estimates of nongravitational effects are obtained for these objects based on the pair-wise linkage of the apparitions. The calculations show that the observations of these objects are poorly represented if solely the gravitational forces are considered. The magnitude of nongravitational effects in the semimajor axis noticeably changes with time. The motion of all comets is significantly affected by the components of nongravitational forces that are perpendicular to the orbital plane.  相似文献   

Colorful Planets,Cometary Tail,and Nuclear Winter     

A.?S.?GinzburgEmail author 《Izvestiya Atmospheric and Oceanic Physics》2018,54(3):265-274

After the 1967 flight of the Venera-4 automatic interplanetary station (AIS), the study of planetary atmospheres became one of the key areas of scientific research at the Institute of Atmospheric Physics (IAPh), USSR Academy of Sciences. The goal of the Venera-4 mission was to deliver a descent vehicle into the atmosphere of Venus and study the physical parameters and chemical composition of the atmosphere. IAPh scientists published several articles on the analysis of these measurements, with A.M. Obukhov himself directly involved in writing some of these articles. An analysis of the properties of the Martian surface and atmosphere from the data of the Mars-2, Mars-3, and Mariner-9 missions in November–December 1971 set the stage for a series of studies on the atmospheric effects of Martian dust storms. Based on the study of the atmospheres of terrestrial planets, IAPh scientists developed a simple model for the nuclear winter phenomenon, i.e., a long-term cooling due to massive fires caused by nuclear explosions. Obukhov took a keen interest in this subject and participated in the publication of review articles on the possible atmospheric and climatic effects of a nuclear war. In another publication, Obukhov and his coauthors provided a theoretical analysis of the possible causes for the tail from Halley’s comet ripping off, as was observed in January 1986. The present article gives a brief overview of the IAPh works on Solar System research and on the possible consequences of a nuclear conflict, which were published in the 1960s–1980s while Obukhov was alive.  相似文献   

Grains of Nonferrous and Noble Metals in Iron–Manganese Formations and Igneous Rocks of Submarine Elevations of the Sea of Japan     

O. N. Kolesnik  N. V. Astakhova 《Oceanology》2018,58(1):71-78

Iron–manganese formations and igneous rocks of submarine elevations in the Sea of Japan contain overlapping mineral phases (grains) with quite identical morphology, localization, and chemical composition. Most of the grains conform to oxides, intermetallic compounds, native elements, sulfides, and sulfates in terms of the set of nonferrous, noble, and certain other metals (Cu, Zn, Sn, Pb, Ni, Mo, Ag, Pd, and Pt). The main conclusion that postvolcanic hydrothermal fluids are the key sources of metals is based upon a comparison of the data of electron microprobe analysis of iron–manganese formations and igneous rocks dredged at the same submarine elevations in the Sea of Japan.  相似文献   

Study of some chaotic inflationary models in $$ gravity     

M. Sharif  Iqra Nawazish 《Astrophysics and Space Science》2018,363(4):73

In this paper, we discuss an inflationary scenario via scalar field and fluid cosmology for an anisotropic homogeneous universe model in \(f(R)\) gravity. We consider an equation of state which corresponds to a quasi-de Sitter expansion and investigate the effect of the anisotropy parameter for different values of the deviation parameter. We evaluate potential models like linear, quadratic and quartic models which correspond to chaotic inflation. We construct the observational parameters for a power-law model of \(f(R)\) gravity and construct the graphical analysis of tensor–scalar ratio and spectral index which indicates the consistency of these parameters with Planck 2015 data.  相似文献   

Light Chemical Elements in Stars: Mysteries and Unsolved Problems     

L. S. Lyubimkov 《Astrophysics》2018,61(2):262-285

  相似文献   

Projections of the impacts of climate change on the water deficit and on the precipitation erosive indexes in Mantaro River Basin,Peru     

Sly C. Wongchuig  Carlos R. Mello  Sin C. Chou 《山地科学学报》2018,15(2):264-279

Projections of climate change are essential to guide sustainable development plans in the tropical Andean countries such as Peru. This study assessed the projections of precipitation and potential evaporation, rain erosive potential, and precipitation concentration in the Mantaro River Basin, in the Peruvian Andes, which is important for agriculture and energy production in Peru. We assumed the Intergovernmental Panel on Climate Change (IPCC) A1B greenhouse gas emission scenario and simulated the global climate change by the HadCM3 global climate model. Due to the steepness of the mountain slopes and the narrowness of the river valley, this study uses the downscaling of the global model simulations by the regional Eta model down to 20-km resolution. The downscaling projections show decrease in the monthly precipitation with respect to the baseline period, especially during the rainy season, between February and April, until the end of the 21st century. Meanwhile, a progressive increase in the monthly evaporation from the baseline period is projected. The Modified Fournier Index (MFI) shows a statistically significant downward trend in the Mantaro River Basin, which suggests a possible reduction in the rain erosive potential. The Precipitation Concentration Index (PCI) shows a statistically significant increasing trend, which indicates increasingly more irregular temporal distribution of precipitation towards the end of the century. The results of this study allow us to conclude that there should be a gradual increase in water deficit and precipitation concentration. Both changes can be negative for agriculture, power generation, and water supply in the Mantaro River Basin in Peru.  相似文献   

Underway Research Aboard the R/V <Emphasis Type="Italic">Akademik Boris Petrov</Emphasis>     

I. A. Nemirovskaya  A. M. Titova 《Oceanology》2018,58(5):760-762

  相似文献   

Steady Lateral Growth of Three-Dimensional Particle Laden Density Currents     

M.R. Moossavi Hekmati  M. Najafi  N. Ashrafi khorasani 《中国海洋工程》2018,32(4):467-475

In this paper the steady lateral growth of three-dimensional turbulent inclined turbidity current is investigated. To simulate the current, an experimental setup is developed to analyze the turbidity current for different regimes in the particle laden density currents environment. The Buckingham's π theorem together with a dimensional analysis is implemented to derive the appropriate non-dimensional variables. The experimental results were normalized and plotted in the form of non-dimensional graphs from which a theoretical model is developed and analyzed. Based on the results obtained for the steady lateral growth, three different regimes, namely, inertia-viscous one as the first regime, buoyancy-viscous and gravity-viscous as the second and third regimes are distinguished within the current.In these regimes, the force balance is between the driving and resisting forces. Namely, in the first regime, the force balance is between the inertia and viscous forces, in the second regime, the buoyancy and viscous forces, and in the third regime, gravity and viscous forces are balanced. The experimental results indicate that the lateral growth rate in the first regime is smaller than that in the second and third regimes due to the magnitude and type of the forces involved in those regimes. According to the graphical results, the three different lateral growth rates appear when the normalized current length is smaller than about 3, between about 3 and 10, and larger than about 10. In those regions,the slopes of the data are different with respect to one another.  相似文献