Measuring on Farm Diversity and Determinants of Barley Diversity in Tigray, Northern Ethiopia

Maintaining on-farm diversity of crop varieties has received increasing attention as a strategy for mitigating production risk and protecting food security in resource-poor farming systems with few opportunities for insurance or trade. Barley is grown under a wide range of environmental conditions and in marginal areas or seasons where the production of other cereals is limited. Food consumption preferences and variable tolerance to biotic and abiotic stresses influence the mixture and number of varieties to be grown. Phenotypic diversity was determined using Shannon diversity index. An econometric approach has been applied to identify the social and economic factors that influence levels of diversity maintained on-farm. A high phenotypic diversity index (0.79) was recorded from sampled barley varieties. Censored regression indicates that physical characteristics of the farm (land fragmentation index, farm size), agro climatic features of the site (altitude, rainfall, temperature) and household characteristics (only number of children) had a significant and positive impact on diversity and area allocation of barley. The significant negative relation of number of extension contact with barley diversity implies further attention and analysis. Key words: On farm diversity, Determinants of diversity, On farm conservation, Diversity inde

Separation of complexity classes in Koiran's weak model

AbstractWe continue the study of complexity classes over the weak model introduced by P. Koiran. In particular we provide several separations of complexity classes, the most remarkable being the strict inclusion of P in NP. Other separations concern classes defined by weak polynomial time over parallel or alternating machines as well as over nondeterministic machines whose guesses are required to be 0 or 1

Bowen Measure From Heteroclinic Points

We present a new construction of the entropy-maximizing, invariant probability measure on a Smale space (the Bowen measure). Our construction is based on points that are unstably equivalent to one given point, and stably equivalent to another: heteroclinic points. The spirit of the construction is similar to Bowen's construction from periodic points, though the techniques are very different. We also prove results about the growth rate of certain sets of heteroclinic points, and about the stable and unstable components of the Bowen measure. The approach we take is to prove results through direct computation for the case of a Shift of Finite type, and then use resolving factor maps to extend the results to more general Smale spaces

Six Years of ScoX-1 Monitoring with BeppoSAX Wide Field Cameras

We performed a systematic analysis of 54 Wide Field Camera (WFC) observations of ScoX-1 available in the BeppoSAX public archive. Observations span over the six years of BeppoSAX mission lifetime and include 690 hr of data. We searched for shifts and shape changes of the Z pattern in the color-color diagrams. We find that the Z pattern occupies most of the time the same locus in the color-color diagram. There are however a few exceptions, which are discussed in detail.Comment: 4 Pages, 4 figures. To appear in Proc. of the BeppoSAX Symposium: "The Restless High-Energy Universe", E.P.J. van den Heuvel, J.J.M. in 't Zand, and R.A.M.J. Wijers (Eds

Strong Field Gravity and X-Ray Observations of 4U1820-30

The behavior of quasi-periodic oscillations (QPOs) at frequencies near 1 kHz in the x-ray emission from the neutron star x-ray binary 4U1820-30 has been interpreted as evidence for the existence of the marginally stable orbit, a key prediction of strong-field general relativity. The signature of the marginally stable orbit is a saturation in QPO frequency, assumed to track inner disk radius, versus mass accretion rate. Previous studies of 4U1820-30 have used x-ray count rate as an indicator of mass accretion rate. However, x-ray count rate is known to not correlate robustly with mass accretion rate or QPO frequency in other sources. Here, we examine the QPO frequency dependence on two other indicators of mass accretion rate: energy flux and x-ray spectral shape. Using either of these indicators, we find that the QPO frequency saturates at high mass accretion rates. We interpret this as strong evidence for the existence of the marginally stable orbit.Comment: accepted to the Astrophysical Journal Letters, 7 page

Hodge Theory on Metric Spaces

Hodge theory is a beautiful synthesis of geometry, topology, and analysis, which has been developed in the setting of Riemannian manifolds. On the other hand, spaces of images, which are important in the mathematical foundations of vision and pattern recognition, do not fit this framework. This motivates us to develop a version of Hodge theory on metric spaces with a probability measure. We believe that this constitutes a step towards understanding the geometry of vision. The appendix by Anthony Baker provides a separable, compact metric space with infinite dimensional \alpha-scale homology.Comment: appendix by Anthony W. Baker, 48 pages, AMS-LaTeX. v2: final version, to appear in Foundations of Computational Mathematics. Minor changes and addition

Hubble flow variance and the cosmic rest frame

We characterize the radial and angular variance of the Hubble flow in the COMPOSITE sample of 4534 galaxies, on scales in which much of the flow is in the nonlinear regime. With no cosmological assumptions other than the existence of a suitably averaged linear Hubble law, we find with decisive Bayesian evidence (ln B >> 5) that the Hubble constant averaged in independent spherical radial shells is closer to its asymptotic value when referred to the rest frame of the Local Group, rather than the standard rest frame of the Cosmic Microwave Background. An exception occurs for radial shells in the range 40/h-60/h Mpc. Angular averages reveal a dipole structure in the Hubble flow, whose amplitude changes markedly over the range 32/h-62/h Mpc. Whereas the LG frame dipole is initially constant and then decreases significantly, the CMB frame dipole initially decreases but then increases. The map of angular Hubble flow variation in the LG rest frame is found to coincide with that of the residual CMB temperature dipole, with correlation coefficient -0.92. These results are difficult to reconcile with the standard kinematic interpretation of the motion of the Local Group in response to the clustering dipole, but are consistent with a foreground non-kinematic anisotropy in the distance-redshift relation of 0.5% on scales up to 65/h Mpc. Effectively, the differential expansion of space produced by nearby nonlinear structures of local voids and denser walls and filaments cannot be reduced to a local boost. This hypothesis suggests a reinterpretation of bulk flows, which may potentially impact on calibration of supernovae distances, anomalies associated with large angles in the CMB anisotropy spectrum, and the dark flow inferred from the kinematic Sunyaev-Zel'dovich effect. It is consistent with recent studies that find evidence for a non-kinematic dipole in the distribution of distant radio sources.Comment: 37 pages, 9 tables, 13 figures; v2 adds extensive new analysis (including additional subsections, tables, figures); v3 adds a Monte Carlo analysis (with additional table, figure) which further tightens the statistical robustness of the dipole results; v4 adds further clarifications, small corrections, references and discussion of Planck satellite results; v5 typos fixed, matches published versio