Integrating farmers’ preferences into the breeding and dissemination of new genotypes is a effective approach to enhance their successful adoption by farmers. In the case of sweet potato, a staple crop in many parts of West Africa, there is a need for more research on the selection criteria used by farmers when choosing which varieties to grow. This study aims to highlight farmers’ selection criteria for sweet potato varieties in the main production areas in Benin. A total of 480 farmers from the top three sweet potato production areas were surveyed. The relative importance of various traits for sweet potato farmers was evaluated using best-worst scaling methods. Latent class analysis was applied to find groups of farmers with similar preferences. Best-Worst Scaling analysis revealed that high root yield, root size, marketability, and early maturing were the most important variety selection criteria. Latent class analysis revealed three farmers’ groups referred to as ‘Yield potential’, ‘Market value’, and ‘Plant resilience’ classes. ‘Yield potential’ farmers were more likely to be from Atlantique and Alibori departments; they significantly committed more acreage to sweet potato production. The ‘Market value’ farmers highlighted the variety of root size and commercial value as the main selection criteria and consisted of farmers with primary education levels from the Ouémé department. ‘Plant resilience’ refers to a group of Alibori farmers who prioritize environmental issues and primarily grow sweet potatoes for self-consumption. Our findings shed light on farmers’ preferences and suggested that heterogeneity in sweet potato selection criteria was highly influenced by various socio-economic factors and location.

Sesame is an oilseed crop and source of income for small-scale farmers, particularly in developing countries. In Benin, sesame production is poorly developed and the underlying reasons are still unknown. In this study, we investigated the sesame management practices, socio-demographic factors and ethnobotanical knowledge associated with sesame production, as well as the production constraints across four agroecological zones in Benin. In total, 370 farmers were surveyed based on a structured interview. Qualitative and quantitative data including socio-demographic parameters, management practices and knowledge associated with the crop, were recorded. A binary logistic regression was performed to explain the effects of socio-demographic parameters on management practices. The farm typology was generated through a principal component analysis followed by a cluster analysis. Cultivars were classified based on the seed coat colour and size. To assess the ethnobotanical knowledge related to sesame, use value, plant part used value and fidelity level were calculated. Our results showed that older farmers were more likely to practice intercropping than young farmers. In addition, male farmers applied more fertilisers and used more pesticide than female. Five distinct farm typologies were recorded in the four agroecological zones. Five different cultivars were recorded across the four agroecological zones. Sesame is mostly produced for local consumption as sauce and seed appetiser (mentioned by at least 73.23% of respondents). The seeds were the most used part of the crop. The lack of improved seeds, road impassability to the field, rarity of rain, non-availability of cultivable land for sesame production, lack of cash for farm operations were the main constraints to wide sesame production. We discussed the differences among farm typology and their productivity and proposed future research actions for expanding sesame production in Benin.

A large nosocomial outbreak of keratoconjunctivitis due to adenovirus type 8 is described. Two hundred cases were identified, 123 by isolation of the virus and 77 by detecting HI antibodies in convalescent sera. Infection usually presented as a severe keratoconjunctivitis, and 107 (54%) of infected patients developed sub-epithelial corneal opacities. The majority (66%) of infections were acquired at the accident and emergency department attached to a large urban eye hospital when patients attended for other reasons; trauma to the eye, especially corneal foreign bodies, was the most frequent cause for the initial attendance. Transmission of virus within the family occurred in 13% of cases, but there was little spread outside family or hospital environments. The outbreak lasted from May to September, 1982, but it was not confirmed by isolation of the virus until the end of June when control measures were instituted. Delay in applying control measures was probably the major factor accounting for this large, prolonged outbreak of epidemic keratoconjunctivitis.

In this article we study injective representations of infinite quivers. We classify the indecomposable injective representations of trees and describe Gorenstein injective and projective representations of barren trees.

We describe the structure of finitely generated cotorsion modules over commutative noetherian rings. Also we characterize the so-called covering morphisms between finitely generated modules over these rings.

AMS 2000 Mathematics subject classification: Primary 16D10. Secondary 13C11

CoGalois groups appear in a natural way in the study of covers. They generalize the well-known group of covering automorphisms associated with universal covering spaces. Recently, it has been proved that each quasi-coherent sheaf over the projective line $\bm{P}^1(R)$ ($R$ is a commutative ring) admits a flat cover and so we have the associated coGalois group of the cover. In general the problem of computing coGalois groups is difficult. We study a wide class of quasi-coherent sheaves whose associated coGalois groups admit a very accurate description in terms of topological properties. This class includes finitely generated and cogenerated sheaves and therefore, in particular, vector bundles.

Given a left Noetherian ring $R$, we give a necessary and sufficient condition in order that a complex of $R$-modules be DG-injective. Using this result we prove that if $(K_i)_{i\in I}$ is a family of DG-injective complexes of left $R$-modules and $K$ is the $\aleph_1$-product of $(K_i)_{i\in I}$ (i.e. $K\subset\prod_{i\in I}K_i$ is such that, for each $n$, $K^n\subset\prod_{i\in I}K_i^n$ consists of all $(x_i)_{i\in I}$ such that $\{i\mid x_i\neq0\}$ is at most countable), then $K$ is DG-injective.

In this article we extend the results about Gorenstein modules and Foxby duality to a non-commutative setting. This is done in §3 of the paper, where we characterize the Auslander and Bass classes which arise whenever we have a dualizing module associated with a pair of rings. In this situation it is known that flat modules have finite projective dimension. Since this property of a ring is of interest in its own right, we devote §2 of the paper to a consideration of such rings. Finally, in the paper’s final section, we consider a natural generalization of the notions of Gorenstein modules which arises when we are in the situation of §3, i.e. when we have a dualizing module.

AMS 2000 Mathematics subject classification: Primary 16D20

We have undertaken an adaptive optics imaging survey of extra-solar planetary systems and stars showing interesting radial velocity trends from high precision radial velocity searches. Adaptive Optics increases the resolution and dynamic range of an image, substantially improving the detectability of faint close companions. This survey is sensitive to objects less luminous than the bottom of the main sequence at separations as close as 1″. We have detected stellar companions to the planet bearing stars HD 114762 and Tau Boo. We have also detected a companion to the non-planet bearing star 16 Cyg A.

We construct Ks-band light curves for nine field L and T brown dwarfs using the Palomar 60 inch Telescope. Results of a robust statistical analysis indicate that about half the targets show significant evidence for variability. Two of these variable targets have marginally significant peaks in the Lomb-Scargle periodogram. The phased light curves show evidence for periodic behavior on timescales of about 1.5 and 3.0 hours.

In this paper we give two different proofs that the flat cover conjecture is true: that is, every module has a flat cover. The two proofs are of completely different nature, and, we hope, will have different applications. The first of the two proofs (due to the third author) is essentially an application of the work of P. Eklof and J. Trlifaj (work which is more set-theoretic). The second proof (due to the first two authors) is more direct, and has a model-theoretic flavour.

In this paper we extend the concept of the group of covering automorphisms associated to a universal covering space ϕ: U → X (where X is a connected topological manifold), to the case of left (or right) minimal approximations. In the case of torsion-free coverings of abelian groups we exhibit a topology on these groups which makes them into topological groups and we give necessary and sufficient conditions for these groups to be compact. Finally we prove that when these groups are compact they are pronilpotent (Theorem 5·3). We also characterize when these groups are torsion-free (Proposition 5·4).

It is shown that a morphism of quivers having a certain path lifting property has a decomposition that mimics the decomposition of maps of topological spaces into homotopy equivalences composed with fibrations. Such a decomposition enables one to describe the right adjoint of the restriction of the representation functor along a morphism of quivers having this path lifting property. These right adjoint functors are used to construct injective representations of quivers. As an application, the injective representations of the cyclic quivers are classified when the base ring is left noetherian. In particular, the indecomposable injective representations are described in terms of the injective indecomposable $R$-modules and the injective indecomposable $R[\text{x},\,{{\text{x}}^{-1}}]$ -modules.

Touts can be defined as free-lance workers at railway stations, airports, ferry points, and especially motor-parks, who undertake the self-imposed responsibility of recruiting and organising passengers who wish to travel by road, and for this work they receive a fee, or more appropriately, a ‘commission’, that is generally paid by the drivers of the vehicles just before their departure. All the owners are private entrepreneurs, who both compete and collaborate with one another to provide road transport for the public.

Throughout this paper it is assumed that rings are associative, have the identity element, and all modules are left unital. R will denote a ring with identity, R-Mod the category of left R-modules, and for each left R-module M, E(M) (resp. J(M)) will represent the injective hull (resp. Jacobson radical) of M. Also, for a module M, A ⊆' M will mean that A is an essential submodule of M, and Z(M) denotes the singular submodule of M. M is called singular if Z(M) = M, and it is called non-singular in case Z(M) = 0. For fundamental definitions and results related to torsion theories, we refer to [12] and [14]. In this paper we shall deal mainly with Goldie torsion theory. Recall that a pair (G, F) of classes of left R-modules is known as Goldie torsion theory if G is the smallest torsion class containing all modules B/A, where A ⊆' B, and the torsion free class F is precisely the class of non-singular modules.

An associative ring R with identity is said to be c-commutative for c ∈ R if a, b ∈ R and ab = c implies ba = c. Taft has shown that if R is c-commutative where c is a central nonzero divisor]can be omitted. We show that in R[x] is h(x)-commutative for any h(x) ∈ R [x] then so is R with any finite number of (commuting) indeterminates adjoined. Examples adjoined. Examples are given to show that R [[x]] need not be c-commutative even if R[x] is, Finally, examples are given to answer Taft's question for the special case of a zero-commutative ring.

It's well known (see Endo [1]) that for a commutative ring A, if A is semihereditary then w.gl. dim. A ≤ 1. It seems worth recording the noncommutative version of this.