Matrix models without scaling limit

In the context of hermitean one--matrix models we show that the emergence of the NLS hierarchy and of its reduction, the KdV hierarchy, is an exact result of the lattice characterizing the matrix model. Said otherwise, we are not obliged to take a continuum limit to find these hierarchies. We interpret this result as an indication of the topological nature of them. We discuss the topological field theories associated with both and discuss the connection with topological field theories coupled to topological gravity already studied in the literature.Comment: Latex, SISSA-ISAS 161/92/E

The (N,M)-th KdV hierarchy and the associated W algebra

We discuss a differential integrable hierarchy, which we call the (N, M)$--th KdV hierarchy, whose Lax operator is obtained by properly adding$M$pseudo--differential terms to the Lax operator of the N--th KdV hierarchy. This new hierarchy contains both the higher KdV hierarchy and multi--field representation of KP hierarchy as sub--systems and naturally appears in multi--matrix models. The N+2M-1 coordinates or fields of this hierarchy satisfy two algebras of compatible Poisson brackets which are {\it local} and {\it polynomial}. Each Poisson structure generate an extended W_{1+\infty} and W_\infty algebra, respectively. We call W(N, M) the generating algebra of the extended W_\infty algebra. This algebra, which corresponds with the second Poisson structure, shares many features of the usual$W_N$ algebra. We show that there exist M distinct reductions of the (N, M)--th KdV hierarchy, which are obtained by imposing suitable second class constraints. The most drastic reduction corresponds to the (N+M)--th KdV hierarchy. Correspondingly the W(N, M) algebra is reduced to the W_{N+M} algebra. We study in detail the dispersionless limit of this hierarchy and the relevant reductions.Comment: 40 pages, LaTeX, SISSA-171/93/EP, BONN-HE-46/93, AS-IPT-49/9

Disentangling the Demand-enhancing Effect and Trade-cost Effect of Technical Measures in Agricultural Trade among OECD countries

Domestic technical measures such as SPS and TBTs can enhance import demand via information disclosure and quality improvement, or hamper foreign export supply via imposing sizeable compliance costs, or both. The traditional gravity equation model estimates the net effect of these measures on international trade with a loss of useful inference on separate effects. We stipulate a generalized gravity equation model to disentangle the two effects. We apply the augmented approach to agricultural trade among OECD countries in 2004. We find that technical measures in agriculture often jointly enhance import demand and hinder export supply with the net effect of promoting the propensity to trade. Further disaggregated data analysis reveals heterogeneity across sectors in terms of net effects of technical measures, despite common demand-enhancing and supply-hindering effects. These measures in the net decrease the probability of intra-OECD trade in dairy products, whereas they increase that of intra-OECD trade in cereal preparations.sanitary and phytosanitary, SPS, technical measures, NTM, TBT, standards, gravity equation, protectionism, OECD, International Relations/Trade,

Does European Aflatoxin Regulation Hurt Groundnut Exporters from Africa?

We provide an ex-post econometric examination of the harmonization and tightening of the EU Maximum Residues Limit (MRL) on aflatoxins in 2002, and its impact on African exports of groundnut products. We show that the MRL set by the EU has no significant trade impact on groundnut exports from Africa across various methods of estimation. African domestic supply plays an important role in the determination of the volumes of trade and the propensity to trade. Our findings suggest that the trade potential of African groundnut exporters is more constrained by domestic supply issues rather than by limited market access.food safety; standards; aflatoxin; MRL; groundnut; Africa; EU; market access

Aflatoxin Redux: Does European Aflatoxin Regulation Hurt Groundnut Exporters from Africa?

Replaced with revised version of paper 07/02/10.food safety, standards, aflatoxin, Maximum Residues Limit, groundnut, gravity equation, Africa, market access, EU, Agricultural and Food Policy, Community/Rural/Urban Development, Crop Production/Industries, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, International Development, International Relations/Trade, Q17, F13,