Water Resources Problems in Developing Countries

Resource /Energy Economics and Policy,

Seasonal Time Series and Autocorrelation Function Estimation

Time series are demeaned when sample autocorrelation functions are computed. By the same logic it would seem appealing to remove seasonal means from seasonal time series before computing sample autocorrelation functions. Yet, standard practice is only to remove the overall mean and ignore the possibility of seasonal mean shifts in the data. Whether or not time series are seasonally demeaned has very important consequences on the asymptotic behavior of autocorrelation functions (henceforth ACF). Hasza (1980) and Bierens (1993) studied the asymptotic properties of the sample ACF of non-seasonal integrated processes and showed how they depend on the demeaning of the data. In this paper we study the large sample behavior of the ACF when the data generating processes are seasonal with or without seasonal unit roots. The effect on the asymptotic distribution of seasonal mean shifts and their removal is investigated and the practical consequences of these theoretical developments are also discussed. We also examine the small sample behavior of ACF estimates through Monte Carlo simulations. Lorsqu'on calcule une fonction d'autocorrélation, il est normal d'enlever d'une série la moyenne non conditionnelle. Cette pratique s'applique également dans le cas des séries saisonnières. Pourtant, il serait plus logique d'utiliser des moyennes saisonnières. Hasza (1980) et Bierens (1993) ont étudié l'effet de la moyenne sur l'estimation d'une fonction d'autocorrélation pour un processus avec racine unitaire. Nous examinons le cas de processus avec racines unitaires saisonnières. Nos résultats théoriques de distribution asymptotique, de même que nos simulations de petits échantillons, démontrent l'importance d'enlever les moyennes saisonnières quand on veut identifier proprement les processus saisonniers.Deterministic/stochastic seasonality, model identification, seasonal unit roots, autocorrelation, Saisonalité stochastique et déterministe, identification de modèles, racines unitaires saisonnières,

AN ANALYSIS OF FACTORS THAT AFFECT THE QUALITY OF FEDERAL LAND BANK LOANS

Financial conditions existing in agriculture are placing severe pressure on lenders as well as borrowers. Data from both good and foreclosed Federal Land Bank loans were analyzed to determine the most important characteristics leading to the failure of loans. The analysis was completed by comparing means through t-tests and the development of a discriminant model. The ratio of total debt service to total income, the debt to asset ratio, the ratio of total loan amount to appraised value, and the ratio of acres in security to acres owned were determined to be the most important discriminating variables.Agricultural Finance,

Opaque or transparent? A link between neutrino optical depths and the characteristic duration of short gamma-ray bursts

Cosmological gamma ray bursts (GRBs) are thought to occur from violent hypercritical accretion onto stellar mass black holes, either following core collapse in massive stars or compact binary mergers. This dichotomy may be reflected in the two classes of bursts having different durations. Dynamical calculations of the evolution of these systems are essential if one is to establish characteristic, relevant timescales. We show here for the first time the result of dynamical simulations, lasting approximately one second, of post--merger accretion disks around black holes, using a realistic equation of state and considering neutrino emission processes. We find that the inclusion of neutrino optical depth effects produces important qualitative temporal and spatial transitions in the evolution and structure of the disk, which may directly reflect upon the duration and variability of short GRBs.Comment: Accepted for publication in ApJ Letter

Halting indigenous biodiversity decline: ambiguity, equity, and outcomes in RMA assessment of significance

In New Zealand, assessment of ‘significance’ is undertaken to give effect to a legal requirement for local authorities to provide for protection of significant sites under the Resource Management Act (1991). The ambiguity of the statute enables different interests to define significance according to their goals: vested interests (developers), local authorities, and non-vested interests in pursuit of protection of environmental public goods may advance different definitions. We examine two sets of criteria used for assessment of significance for biological diversity under the Act. Criteria adapted from the 1980s Protected Natural Areas Programme are inadequate to achieve the maintenance of biological diversity if ranking is used to identify only highest priority sites. Norton and Roper-Lindsay (2004) propose a narrow definition of significance and criteria that identify only a few high-quality sites as significant. Both sets are likely to serve the interests of developers and local authorities, but place the penalty of uncertainty on non-vested interests seeking to maintain biological diversity, and are likely to exacerbate the decline of biological diversity and the loss of landscape-scale processes required for its persistence. When adopting criteria for assessment of significance, we suggest local authorities should consider whose interests are served by different criteria sets, and who will bear the penalty of uncertainty regarding biological diversity outcomes. They should also ask whether significance criteria are adequate, and sufficiently robust to the uncertainty inherent in the assessment of natural values, to halt the decline of indigenous biological diversity

Magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field

A computational investigation of magnetic helicity of the fluctuatingmagnetic fieldHm in ideal and freely decaying three‐dimensional (3‐D) magnetohydrodynamics (MHD) in the presence of a uniform mean magnetic field is performed. It is shown that for ideal 3‐D MHDHm, which is a rugged invariant in the absence of a mean magnetic field [Frisch et al., J. Fluid Mech. 77, 796 (1975)], decays from its initial value and proceeds to oscillate about zero. The decay of Hm is shown to result from the presence of a new ‘‘generalized’’ helicity invariant, which includes contributions from the uniform magnetic field. The loss of invariance of Hm will diminish the effects of inverse transfer of Hm on freely decaying turbulence. This is demonstrated in a discussion of the selective decay relaxation process

THE EFFECTS OF USER PARTICIPATION ON SYSTEM SUCCESS: TOWARD A CONTINGENCY THEORY OF USER SATESFACTION

User participation is an important construct in IS research. It is also a frequently employed practical implementation strategy. However, research findings concerning the effects of user participation on system success are mixed and inconclusive. This study reviews a contingency theory of attitude change, proposes competing models, and empirically tests the models in end-user computing involving multiple end-user groups. Results lend support to the Cognition Fit Model. Other models receive only partial support