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We study a general double Dirac delta potential to show that this is the simplest yet versatile solvable potential to introduce double wells, avoided crossings, resonances and perfect transmission (T = 1). Perfect transmission energies turn out to be the critical property of symmetric and antisymmetric cases wherein these discrete energies are found to correspond to the eigenvalues of Dirac delta potential placed symmetrically between two rigid walls. For well(s) or barrier(s), perfect transmission [or zero reflectivity, R(E)] at energy E = 0 is non-intuitive. However, earlier this has been found and called "threshold anomaly". Here we show that it is a critical phenomenon and we can have 0 ≤ R(0) < 1 when the parameters of the double delta potential satisfy an interesting condition. We also invoke zero-energy and zero curvature eigenstate (ψ(x) = Ax + B) of delta well between two symmetric rigid walls for R(0) = 0. We resolve that the resonant energies and the perfect transmission energies are different and they arise differently. * Electronic address: 1:zahmed@barc.gov.in, 2: Sachinv@barc.gov.in, 3: mayank.

Flash floods leading to complete submergence of rice plants for 10-15 days is one of the major constraints for rice production, mainly in rainfed lowland areas. In India, 30% of the rice growing area (12-14 M ha) is prone to flash flooding with average productivity of only 0.5-0.8 t ha −1 .

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