Time filter

Source Type

Ghaffar A.,University of Agriculture at Faisalabad
Journal of Electromagnetic Waves and Applications | Year: 2011

In this paper, the focussing of electromagnetic fields from a cylindrical plano convex lens composed of chiral media is analyzed using Maslov's method. The chiral medium is described electromagnetically by the constitutive relations D = εE + jγB and H = jγE + 1/μB. In this study, the propagation of electromagnetic waves through a cylindrical plano convex lens of chiral medium is formulated for normal incidence. The effects of the chirality on the polarization and the intensity of the refracted field from a chiral cylindrical plano convex lens around the caustic region are discussed. Numerical computations are made using Maslov's method to illustrate the effects of the chirality on the intensity of the refracted field from the chiral lens. The results are also compared using Kirchhoff's approximation which are in good agreement. © 2011 VSP.

Ahmad M.S.A.,University of Agriculture at Faisalabad
Reviews of Environmental Contamination and Toxicology | Year: 2011

Nickel is one of 23 metal pollutants of great concern to the environment and to human health (Sunderman 1992; Jarup 2003; Duda-Chodak and Baszczyk 2008). Nickel is the 24th most abundant element (twice as Cu) and comprises approximately 0.008% of the content of the earth's crust; hence, it is a natural component of soil (parent material) and water (Alloway 1995; Hostýnek and Maibach 2002; Hedfi et al. 2007). Most of the earth's nickel, however, is inaccessible, as it is locked in the iron-nickel molten core, which constitutes approximately 10% nickel. The second largest Ni deposits of the earth rest in the sea. It is estimated that the sea contains approximately eight billion tons of Ni, either dissolved in seawater or deposited in the seabed (Birch 1964; Stixrude et al. 1997). Soils may contain nickel levels as low as 0.2 mg kg -1 or as high as 450 mg kg -1. The average nickel content in soil is approximately 20 mg kg -1; however, the content level may vary greatly depending upon the mode of origin of the soil's parent material (Assembly of Life Sciences 1975; Aubert and Pinta 1978; Wilson and Kordybach 2000). Because organic matter strongly absorbs some metals, particularly nickel, fossil fuels such as coal and oil may contain considerable amounts of nickel (Sigel et al. 2005). Moreover, Ni naturally occurs in a few plants (legumes) where it functions as an essential component of some enzymes (e.g., ureases) that are involved in nitrogen assimilation (Eskew et al. 1984; Brown et al. 1987a; Sakamoto and Bryant 2001). © 2011 Springer Science+Business Media, LLC.

Ashraf M.,University of Agriculture at Faisalabad
Biotechnology Advances | Year: 2010

Undoubtedly, drought is one of the prime abiotic stresses in the world. Crop yield losses due to drought stress are considerable. Although a variety of approaches have been used to alleviate the problem of drought, plant breeding, either conventional breeding or genetic engineering, seems to be an efficient and economic means of tailoring crops to enable them to grow successfully in drought-prone environments. During the last century, although plant breeders have made ample progress through conventional breeding in developing drought tolerant lines/cultivars of some selected crops, the approach is, in fact, highly time-consuming and labor- and cost-intensive. Alternatively, marker-assisted breeding (MAB) is a more efficient approach, which identifies the usefulness of thousands of genomic regions of a crop under stress conditions, which was, in reality, previously not possible. Quantitative trait loci (QTL) for drought tolerance have been identified for a variety of traits in different crops. With the development of comprehensive molecular linkage maps, marker-assisted selection procedures have led to pyramiding desirable traits to achieve improvements in crop drought tolerance. However, the accuracy and preciseness in QTL identification are problematic. Furthermore, significant genetic × environment interaction, large number of genes encoding yield, and use of wrong mapping populations, have all harmed programs involved in mapping of QTL for high growth and yield under water limited conditions. Under such circumstances, a transgenic approach to the problem seems more convincing and practicable, and it is being pursued vigorously to improve qualitative and quantitative traits including tolerance to biotic and abiotic stresses in different crops. Rapid advance in knowledge on genomics and proteomics will certainly be beneficial to fine-tune the molecular breeding and transformation approaches so as to achieve a significant progress in crop improvement in future. Knowledge of gene regulation and signal transduction to generate drought tolerant crop cultivars/lines has been discussed in the present review. In addition, the advantages and disadvantages as well as future prospects of each breeding approach have also been discussed. © 2009 Elsevier Inc. All rights reserved.

Bajwa A.A.,University of Agriculture at Faisalabad
Crop Protection | Year: 2014

Sustainable crop production is necessary to ensure global food security and environmental safety. Conservation agriculture (CA) is gaining popularity around the globe due to its sustainable approaches such as permanent soil cover, minimal soil disturbance, planned crop rotations and integrated weed management. Weed control is the biggest challenge to CA adoption. Weed ecology and management is different in CA than in conventional agriculture. In CA, weeds expression, seed bank status, distribution, dispersal mechanisms, diversification, growing patterns and competition trends are complex and differ from conventional systems. It is due to reduced tillage of the soil and the flora that thrives in CA. Reduced tillage systems affect the efficacy of herbicides and mechanical weed control measures. So, it is an important task to find out the differences and to fabricate new management options. In this review, changing weed dynamics have been framed. A novel aspect of this review is the comprehensive account of sustainable weed management strategies in relation to CA. Modified tillage operations, improved cultural practices, bioherbicides, chemical herbicides, allelopathy, and crop nutrition have been identified as suitable weed management tools. None of these offers complete control but the integration of these tools in suitable combinations works efficiently. Weeds dominating CA and their responses to CA components are highlighted. For example, small seeded and perennial weeds are more abundant in CA. The role of herbicide resistance in weeds and herbicide tolerant (HT) crops in CA is also highlighted. Allelopathy and crop nutrition are discussed as modern weed management tools for CA. A detailed account of weed responses to fertilizer management options is also given. Integrated weed management compatible to cropping patterns and climatic conditions offers the best results in CA. Future efforts must be directed towards the optimization and integration of these weed management practices. © 2014 Elsevier Ltd.

Wakeel A.,University of Agriculture at Faisalabad
Journal of Plant Nutrition and Soil Science | Year: 2013

About 7% of the total land around the globe is salt-affected causing a great loss to agriculture. Salt stress refers to the excessive amount of soluble salts in the root zone which induce osmotic stress and ion toxicity in the growing plant. Among toxic ions, sodium (Na+) has the most adverse effects on plant growth by its detrimental influence on plant metabolism in inhibiting enzyme activities. An optimal potassium (K+) : Na+ ratio is vital to activate enzymatic reactions in the cytoplasm necessary for maintenance of plant growth and yield development. Although most soils have adequate amounts of K+, in many soils available K+ has become insufficient because of large amounts of K+ removal by high-yielding crops. This problem is exacerbated under sodic or saline-sodic soil conditions as a consequence of K+-Na+ antagonism. Here K+ uptake by plants is severely affected by the presence of Na+ in the nutrient medium. Due to its similar physicochemical properties, Na+ competes with K+ in plant uptake specifically through high-affinity potassium transporters (HKTs) and nonselective cation channels (NSCCs). Membrane depolarization caused by Na+ makes it difficult for K+ to be taken up by K+ inward-rectifying channels (KIRs) and increases K+ leakage from the cell by activating potassium outward-rectifying channels (KORs). Minimizing Na+ uptake and preventing K+ losses from the cell may help to maintain a K+ : Na+ ratio optimum for plant metabolism in the cytoplasm under salt-stress conditions. It would seem a reasonable assumption therefore that an increase in the concentration of K+ in salt-affected soils may support enhanced K+ uptake and reduce Na+ influx via HKTs and NCCSs. Although very useful information is available regarding K+-Na+ homeostasis indicating their antagonistic effect in plants, current knowledge in applied research is still inadequate to recommend application of potassium fertilizers to alleviate Na+ stress in plants under sodic and saline-sodic conditions. Nevertheless some encouraging results regarding alleviation of Na+ stress by potassium fertilization provide the motivation for conducting further studies to improve our understanding and perspectives for potassium fertilization in sodic and saline-sodic environments. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Discover hidden collaborations