Evaluating the impacts of watershed management on runoff storage and peak flow in Gav-Darreh watershed,Kurdistan, Iran     

Ata Amini  Pezhman Taherei Ghazvinei  Mitra Javan  Bahram Saghafian 《Arabian Journal of Geosciences》2014,7(8):3271-3279

Recently, water and soil resource competition and environmental degradation due to inadequate management practices have been increased and pose difficult problems for resource managers. Numerous watershed practices currently being implemented for runoff storage and flood control purposes have improved hydrologic conditions in watersheds and enhanced the establishment of riparian vegetation. The assessment of proposed management options increases management efficiency. The purpose of this study is to assess the impact of watershed managements on runoff storage and peak flow, and determine the land use and cover dynamics that it has induced in Gav-Darreh watershed, Kurdistan, Iran. The watershed area is 6.27 km² which has been subjected to non-structural and structural measures. The implemented management practices and its impact on land use and cover were assessed by integrating field observation and geographic information systems (GIS). The data were used to derive the volume of retained water and determine reduction in peak flow. The hydrology of the watershed was modeled using the Hydrologic Engineering Center–Hydrologic Modeling System (HEC–HMS) model, and watershed changes were quantified through field work. Actual storms were used to calibrate and validate HEC–HMS rainfall–runoff model. The calibrated HEC–HMS model was used to simulate pre- and post-management conditions in the watershed. The results derived from field observation and HEC–HMS model showed that the practices had significant impacts on the runoff storage and peak flow reduction.  相似文献   

Active Region Formation through the Negative Effective Magnetic Pressure Instability     

Koen Kemel  Axel Brandenburg  Nathan Kleeorin  Dhrubaditya Mitra  Igor Rogachevskii 《Solar physics》2013,287(1-2):293-313

The negative effective magnetic-pressure instability operates on scales encompassing many turbulent eddies, which correspond to convection cells in the Sun. This instability is discussed here in connection with the formation of active regions near the surface layers of the Sun. This instability is related to the negative contribution of turbulence to the mean magnetic pressure that causes the formation of large-scale magnetic structures. For an isothermal layer, direct numerical simulations and mean-field simulations of this phenomenon are shown to agree in many details, for example the onset of the instability occurs at the same depth. This depth increases with increasing field strength, such that the growth rate of this instability is independent of the field strength, provided the magnetic structures are fully contained within the domain. A linear stability analysis is shown to support this finding. The instability also leads to a redistribution of turbulent intensity and gas pressure that could provide direct observational signatures.  相似文献   

Book reviews     

Charles E. Chamberlin  Anil Mitra 《Marine Georesources & Geotechnology》2013,31(1):117-118

Mechanics of Sediment Transport. Edited by B. Mutlu Sumer and A. Muller. Proceedings of Euromech 156, Istanbul, 12–14 July 1982. Rotterdam: A. A. Balkema, 1983. 285 pp. $45.00.

Gear Drive Systems: Design and Application, Peter Lynwander, New York and Basel: Marcel Dekker, Inc., 1983. Price: $49.50.  相似文献   

The matter in the Big-Bang model is dust and not any arbitrary perfect fluid!     

Abhas Mitra 《Astrophysics and Space Science》2011,333(1):351-356

We consider a spherically symmetric general relativistic perfect fluid in its comoving frame. It is found that, by integrating the local energy momentum conservation equation, a general form of g ₀₀ can be obtained. During this study, we get a cue that an adiabatically evolving uniform density isolated sphere having ρ(r,t)=ρ ₀(t), should comprise “dust” having p ₀(t)=0; as recently suggested by Durgapal and Fuloria (J. Mod. Phys. 1:143, 2010) In fact, we offer here an independent proof to this effect. But much more importantly, we find that for the homogeneous and isotropic Friedmann-Robertson-Walker (FRW) metric having p(r,t)=p ₀(t) and ρ(r,t)=ρ ₀(t), \(g_{00} = e^{-2p_{0}/(p_{0} +\rho_{0})}\). But in general relativity (GR), one can choose an arbitrary t→t _?=f(t) without any loss of generality, and thus set g ₀₀(t _?)=1. And since pressure is a scalar, this implies that p ₀(t _?)=p ₀(t)=0 in the Big-Bang model based on the FRW metric. This result gets confirmed by the fact the homogeneous dust metric having p(r,t)=p ₀(t)=0 and ρ(r,t)=ρ ₀(t) and the FRW metric are exactly identical. In other words, both the cases correspond to the same Einstein tensor \(G^{a}_{b}\) because they intrinsically have the same energy momentum tensor \(T^{a}_{b}=\operatorname {diag}[\rho_{0}(t), 0,0, 0]\).  相似文献   

An application of regional time and magnitude predictable model for long-term earthquake prediction in the vicinity of October 8, 2005 Kashmir Himalaya earthquake   总被引：2，自引：2，他引：0  

R. B. S. Yadav  D. Shanker  S. Chopra  A. P. Singh 《Natural Hazards》2010,54(3):985-1014

A regional time and magnitude predictable model has been applied to estimate the recurrence intervals for large earthquakes in the vicinity of 8 October 2005 Kashmir Himalaya earthquake (25°–40°N and 65°–85°E), which includes India, Pakistan, Afghanistan, Hindukush, Pamirs, Mangolia and Tien-Shan. This region has been divided into 17 seismogenic sources on the basis of certain seismotectonics and geomorphological criteria. A complete earthquake catalogue (historical and instrumental) of magnitude Ms ≥ 5.5 during the period 1853–2005 has been used in the analysis. According to this model, the magnitude of preceding earthquake governs the time of occurrence and magnitude of future mainshock in the sequence. The interevent time between successive mainshocks with magnitude equal to or greater than a minimum magnitude threshold were considered and used for long-term earthquake prediction in each of seismogenic sources. The interevent times and magnitudes of mainshocks have been used to determine the following predictive relations: logT _t = 0.05 M _min + 0.09 M _p − 0.01 log M ₀ + 01.14; and M _f = 0.21 M _min − 0.01 M _p + 0.03 log M ₀ + 7.21 where, T _t is the interevent time of successive mainshocks, M _min is minimum magnitude threshold considered, M _p is magnitude of preceding mainshock, M _f is magnitude of following mainshock and M ₀ is the seismic moment released per year in each seismogenic source. It was found that the magnitude of following mainshock (M _f) does not depend on the interevent time (T _t), which indicates the ability to predict the time of occurrence of future mainshock. A negative correlation between magnitude of following mainshock (M _f) and preceding mainshock (M _p) indicates that the larger earthquake is followed by smaller one and vice versa. The above equations have been used for the seismic hazard assessment in the considered region. Based on the model applicability in the studied region and taking into account the occurrence time and magnitude of last mainshock in each seismogenic source, the time-dependent conditional probabilities (PC) for the occurrence of next shallow large mainshocks (Ms ≥ 6.5), during next 20 years as well as the expected magnitudes have been estimated.  相似文献   

The helicity constraint in spherical shell dynamos     

A. Brandenburg  P. J. Käpylä  D. Mitra  D. Moss  R. Tavakol 《Astronomische Nachrichten》2007,328(10):1118-1121

The motivation for considering distributed large scale dynamos in the solar context is reviewed in connection with the magnetic helicity constraint. Preliminary accounts of 3-dimensional direct numerical simulations (in spherical shell segments) and simulations of 2-dimensional mean field models (in spherical shells) are presented. Interesting similarities as well as some differences are noted. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献