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Yield decline is the major concern in tropical aerobic rice (Oryza sativa L.). Both biotic and abiotic factors were responsible for this phenomenon. No analytical information on actual causes was reported taking into account of responses of root to water stress conditions. In a field experiment at the Central Rice Research Institute, India during 2009 and 2010, five rice genotypes were grown under two soil water conditions, aerobic and semi-aerobic condition, for better understanding of yield penalty vis-à-vis yield stability. Results showed aerobic condition significantly inhibited structural development of root and caused significant variation in biochemical root traits accounting for higher concentration of hydrogen peroxide (24.6%) and proline (20%), and lower concentration of total soluble protein (20%) that resulted in 17% yield decline than semi-aerobic condition. Applying supplementary irrigation at semi-aerobic condition achieved 21% more grain yield compared with aerobic condition due to 21%, 8.3, and 10.4% more root biomass, root volume, and root/shoot ratio, respectively. Interaction of genotypes with soil water conditions revealed that at aerobic condition, better performance could be expected in 'Apo' (4.0 t ha-1) and 'IR 74371-3-1-1' (3.80 t ha-1) with less yield decline (7.0-9.5%); supplementary irrigation enhanced their grain yield (4.3-4.4 t ha-1) at semi-aerobic condition. Therefore, detrimental impact of physical and biochemical root traits' changes on yield decline in aerobic rice could be alleviated with supplementary irrigation at critical growth stages under semi-aerobic condition without compromising with water productivity. [ABSTRACT FROM AUTHOR]

We consider an annular elliptic lightguide of constant radial width (CRWEG), whose guiding region cross section is bounded by two elliptical boundaries. Using Goell's point-matching method, we obtain the characteristic equation and dispersion curves for this waveguide. When the dispersion curves of this waveguide are compared with that of confocal and concentric elliptic lightguides (CFEG and CEG), it is found that they are less steep for CRWEG. It is also found that the cutoff value of the lowest order modes for this waveguide is greater than that for CFEG and CEG. This means that this waveguide supports fewer modes than CFEG and CEG. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 40–43, 2001. [ABSTRACT FROM AUTHOR]

We study the modal characteristics of a waveguide of annular cross section with nonconcentric circular boundaries. In this study, either both or one of the cladding regions is taken as highly conducting. The bipolar coordinate system is introduced for the analysis, and the characteristic equations are derived. Results show that the absence of concentricity of the two boundaries reduces the number of sustained modes. Dispersion curves show that two types of modes are propagated simultaneously through the waveguide in which either of the claddings is metallic. One type shows an anomalous dispersion behavior. For the waveguide with both of the boundaries conducting, dispersion curves have the expected shape as in the case of standard annular waveguides of concentric circular boundaries. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 129–134, 2000. [ABSTRACT FROM AUTHOR]

We make an analytical study of the modal characteristic equation of a step index fiber with a parabolically decreasing refractive index grading in the direction of propagation. We choose the cylindrical polar coordinates (ρ, φ, z) and, assuming that the propagation is along the z-direction, we use the boundary conditions under the weak guidance approximation to obtain the modal characteristic equation. The propagation constant β depends on the z-coordinate, and a typical numerical computation for the azimuthal modal index ν=1 shows local modes with an oscillatory dependence of β with z. The oscillatory behavior of β is expected to be due to a superposition of the forward wave with partially reflected backward waves. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 444–448, 1998. [ABSTRACT FROM AUTHOR]

In this paper, a multiloop curve with a rather simple mathematical description in polar coordinates is chosen to describe the core cross-section boundary of a waveguide. This waveguide is used as a model representing a waveguide in which several cores are embedded in a common cladding. The cutoff equation for the lowest order modes is derived using the scalar wave approximation. Numerical computations are made to determine how the cutoff condition is modified as one increases the number of cores (loops) from three to ten. It is found that a waveguide with a crossection having fewer loops sustains more modes than that with a greater number of loops. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 196–200, 1998. [ABSTRACT FROM AUTHOR]

In this paper, continuing our earlier work on the modal properties of a planar waveguide with a flare, we examine whether unattenuated guided modes can exist in such waveguides. We use the scalar wave approximation and the cylindrical polar coordinates (ρ, φ, z) in a new way. Ordinarily, the guiding region lies between two distinct values of ρ, and the propagation is along the z-axis. In our case, however, we take the propagation in the ρ-direction, and the guiding region is bounded by two planes corresponding to two slightly different values of φ. This represents a planar waveguide with a flare, and we obtain the modal characteristic equation for unattenuated modes. Numerical computation shows the surprising result that global unattenuated modes can be sustained in such a structure for ν=0, where ν is the modal index corresponding to the φ-coordinate. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 77–80, 1998. [ABSTRACT FROM AUTHOR]

We make an analytical study of the modal characteristic equation of a slab waveguide with a flare bounded by two planes. We choose cylindrical polar coordinates (ρ, φ, z), and assume that the two bounding planes are extended infinitely in the z-direction, and are represented by φ=φ1 and φ=φ2 so that φ2-φ1 is very small. The field in the z-direction is assumed to be uniform, and we consider propagation along the ρ-direction. Using the weak guidance approximation, the characteristic equation is obtained. Numerical computations show that only one global mode can be sustained in such a structure for the model ν=0, corresponding to the coordinate φ. There is an attenuation in this supported mode, and this is because of the flare. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 17: 394–398, 1998. [ABSTRACT FROM AUTHOR]

An optical fiber with an annular cross section bounded by two nonconcentric circles is analytically studied with a view to obtaining the modal characteristics. Using the characteristic equation derived from the matching of fields at the core–cladding boundaries expressed in terms of bipolar coordinates, dispersion curves are obtained on the basis of numerical computations. The curves corresponding to some modes are similar to the standard dispersion curves for waveguides. However, the dispersion curves of other modes show some unexpected behavior; one mode even shows no dispersion at all. These points are qualitatively discussed. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 280–283, 1997. [ABSTRACT FROM AUTHOR]

In this paper, we present a theoretical analysis of the propagation of electromagnetic waves through a fiber with a trefoil cross section. This may be regarded as a preliminary study of a waveguide in which three cores are embedded in a common cladding. By choosing an appropriate coordinate system, the scalar wave equation is solved, and thereby the characteristic equation for the guided modes under the weak guidance approximation is derived. To understand the basic modal properties in a simple manner, the cutoff equation is derived, and the modal cutoff properties of some modes are determined numerically. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 85–89, 1997. [ABSTRACT FROM AUTHOR]

We make an analytical study of the modal cutoff behavior of a waveguide with an annular core cross section bounded by two nonconcentric circles. The characteristic and cutoff equations ae obtained with the use of the weak guidance approximation. Numerical computations show that the number of modes sustained is lowered as the concentric annular cross section becomes nonconcentric. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 179–184, 1997. [ABSTRACT FROM AUTHOR]

Presents a correction to the article "Modal Cutoff Behavior of An Optical Waveguide With a Multiloop Core Cross Section Embedded in a Common Cladding," by Alka Sharma, P. Khastgir and O. N. Singh, published in the January 1999 issue of the journal "Microwave & Optical Technology Letters."

Presents a correction to the article "Modal Dispersion Curves of an Optical Waveguide With an Annular Core Cross Section Separated by Two Nonconcentric Circles From Two Cladding Regions," that was previously published in a 1998 issue of "Microwave & Optical Technology Letters."