نتایج جستجو برای: genetic erosion

تعداد نتایج: 644003  

Ali Ashraf Jafari Parvin Salehi Shanjani Roya Hoseinzadeh

Secale montanum is one of the important perennial grasses growingnaturally in arid to semiarid pastures and rangelands, with a typical Mediterraneanclimate, in northern and western Iran at altitudes of 800-2900 m. In this paper, seedstorage protein profiles of nine wild populations of S. montanum from differentregions of Iran and their phenotypically superior progenies as well as a multi-origin...

2003
DAVID D. BRESHEARS JEFFREY J. WHICKER MATHEW P. JOHANSEN JOHN E. PINDER

Soil erosion is an important process in dryland ecosystems, yet measurements and comparisons of wind and water erosion within and among such ecosystems are lacking. Here we compare wind erosion and transport field measurements with water erosion and transport from rainfall-simulation for three different semi-arid ecosystems: a shrubland near Carlsbad, New Mexico; a grassland near Denver, Colora...

2013
George Ashiagbor Eric K Forkuo Prosper Laari Raymond Aabeyir

Soil erosion involves detachment and transport of soil particles from top soil layers, degrading soil quality and reducing the productivity of affected lands. Soil eroded from the upland catchment causes depletion of fertile agricultural land and the resulting sediment deposited at the river networks creates river morphological change and reservoir sedimentation problems. However, land managers...

2011
Hari Prasad Neopane Ole Gunnar Dahlhaug Michel Cervantes

Sediment erosion not only reduces efficiency and life of hydropower turbines but also causes problems in operation and maintenance. Several factors are responsible for this erosion in hydro turbine components. This paper presents the sediment erosion types in hydraulic turbines and their components based upon an extensive literature review and the field observation at Cahua hydropower plant, Pe...

2012
Jessica L Ward Mike J Blum David M Walters Brady A Porter Noel Burkhead Byron Freeman

The erosion of species boundaries can involve rapid evolutionary change. Consequently, many aspects of the process remain poorly understood, including the formation, expansion, and evolution of hybrid swarms. Biological invasions involving hybridization present exceptional opportunities to study the erosion of species boundaries because timelines of interactions and outcomes are frequently well...

2011
Dirk Goossens Brenda Buck

Wind erosion measurements were carried out in Nellis Dunes Recreation Area, southern Nevada, USA. Gross erosion (the total mass of sediment effectively blown away from a surface), gross deposition (the total mass of sediment effectively depositing on a surface) and net erosion (the difference in sediment mass before and after an event) were measured for 1 year, on 17 different types of surfaces...

Journal: :Environmental Modelling and Software 2004
Robert Scott Van Pelt Ted M. Zobeck

In the United States, the USDA Natural Resources Conservation Service (NRCS) is the primary agency charged with the task of reducing wind erosion associated with production agriculture. The NRCS has used the Wind Erosion Equation (WEQ) (Woodruff and Siddoway, 1965) to assess the effects of field management on the potential for wind erosion for the last two and a half decades. The WEQ uses input...

2016
Jianlin Zhao Kristof Van Oost Longqian Chen Gerard Govers

Despite a multitude of studies, overall erosion rates as well as the contribution of different erosion processes on Chinese Loess Plateau (CLP) remain uncertain, which hampers a correct assessment of the impact of soil erosion on carbon and nutrient cycling as well as on crop productivity. In this paper we used a novel approach, based on field evidence, to reassess erosion rates on the CLP befo...

پایان نامه :وزارت علوم، تحقیقات و فناوری - دانشگاه پیام نور - دانشگاه پیام نور استان تهران - دانشکده مهندسی برق و کامپیوتر 1392

با وجود حجم بالای اطلاعات متنی، نیازمند سیستمی کارا جهت دسته بندی خودکار متون داریم. بنابراین، باید دسته بندی را طوری انجام داد که ضمن افزایش دقت، سبب کاهش زمان و هزینه شود. فرایند دسته بندی متون دارای گام‎های پیش پردازش، وزن دهی، کاهش ویژگی و دسته بندی است که برای هر گام روش‎های مختلفی تا کنون ارائه شده است. یکی از گام‎های تعیین کننده در دسته بندی، کاهش ویژگی‎ها است. این موضوع در زبان فارسی به...

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