Recommendation for consideration in the development of Nepal's Irrigation Master Plan. Part 1 - Management of irrigation systems for effective O & M and resource mobilization; Part 2 - Farmer managed irrigation systems. Occasional paper

Irrigation management / Farmer managed irrigation systems / Resource management / Agricultural production / Nepal

Irrigation development: The management and use of irrigation in the mountains of Nepal

Irrigation systems / Irrigation management / Policy / Nepal

Probability distribution of residence-times of grains in sandpile models

We show that the probability distribution of the residence-times of sand grains in sandpile models, in the scaling limit, can be expressed in terms of the survival probability of a single diffusing particle in a medium with absorbing boundaries and space-dependent jump rates. The scaling function for the probability distribution of residence times is non-universal, and depends on the probability distribution according to which grains are added at different sites. We determine this function exactly for the 1-dimensional sandpile when grains are added randomly only at the ends. For sandpiles with grains are added everywhere with equal probability, in any dimension and of arbitrary shape, we prove that, in the scaling limit, the probability that the residence time greater than t is exp(-t/M), where M is the average mass of the pile in the steady state. We also study finite-size corrections to this function.Comment: 8 pages, 5 figures, extra file delete

Sferno simetrični nesingularni modeli s promjenljivim članom λ u relativističkoj kozmologiji

We discuss a class of nonsingular spherically-symmetric cosmological models with radial heat flux and variable cosmological term Λ(t). Three different exact solutions of the Einstein’s field equations are obtained for both perfect fluid and fluid with bulk viscosity. It turns out that the cosmological term Λ(t) is a decreasing function of time, what is consistent with recent observations of type Ia supernovae.Raspravljamo niz nesingularnih sferno-simetričnih kozmoloških modela s radijalnim tokom topline i promjenljivim kozmološkim članom Λ(t). Postigli smo tri različita egzaktna rješenja Einsteinovih jednadžbi polja za perfektnu tekućinu i tekućinu s volumnim trenjem. Ishodi računa pokazuju da je kozmološki član padajuća funkcija vremena što je u suglasju s nedavnim opažanjima supernova tipa Ia

Failure due to fatigue in fiber bundles and solids

We consider first a homogeneous fiber bundle model where all the fibers have got the same stress threshold beyond which all fail simultaneously in absence of noise. At finite noise, the bundle acquires a fatigue behavior due to the noise-induced failure probability at any stress. We solve this dynamics of failure analytically and show that the average failure time of the bundle decreases exponentially as the stress increases. We also determine the avalanche size distribution during such failure and find a power law decay. We compare this fatigue behavior with that obtained phenomenologically for the nucleation of Griffith cracks. Next we study numerically the fatigue behavior of random fiber bundles having simple distributions of individual fiber strengths, at stress less than the bundle's strength (beyond which it fails instantly). The average failure time is again seen to decrease exponentially as the stress increases and the avalanche size distribution shows similar power law decay. These results are also in broad agreement with experimental observations on fatigue in solids. We believe, these observations regarding the failure time are useful for quantum breakdown phenomena in disordered systems.Comment: 13 pages, 4 figures, figures added and the text is revise