N\'eron-Severi group of a general hypersurface

In this paper we extend the well known theorem of Angelo Lopez concerning the Picard group of the general space projective surface containing a given smooth projective curve, to the intermediate N\'eron-Severi group of a general hypersurface in any smooth projective variety.Comment: 14 pages, to appear on Communications in Contemporary Mathematic

Plucker-Clebsch formula in higher dimension

Let S\subset\Ps^r ($r\geq 5$) be a nondegenerate, irreducible, smooth, complex, projective surface of degree $d$. Let $\delta_S$ be the number of double points of a general projection of $S$ to \Ps^4. In the present paper we prove that $\delta_S\leq{\binom {d-2} {2}}$, with equality if and only if $S$ is a rational scroll. Extensions to higher dimensions are discussed.Comment: 12 page

On the topology of a resolution of isolated singularities

Let $Y$ be a complex projective variety of dimension $n$ with isolated singularities, $\pi:X\to Y$ a resolution of singularities, $G:=\pi^{-1}{\rm{Sing}}(Y)$ the exceptional locus. From Decomposition Theorem one knows that the map $H^{k-1}(G)\to H^k(Y,Y\backslash {\rm{Sing}}(Y))$ vanishes for $k>n$. Assuming this vanishing, we give a short proof of Decomposition Theorem for $\pi$. A consequence is a short proof of the Decomposition Theorem for $\pi$ in all cases where one can prove the vanishing directly. This happens when either $Y$ is a normal surface, or when $\pi$ is the blowing-up of $Y$ along ${\rm{Sing}}(Y)$ with smooth and connected fibres, or when $\pi$ admits a natural Gysin morphism. We prove that this last condition is equivalent to say that the map $H^{k-1}(G)\to H^k(Y,Y\backslash {\rm{Sing}}(Y))$ vanishes for any $k$, and that the pull-back $\pi^*_k:H^k(Y)\to H^k(X)$ is injective. This provides a relationship between Decomposition Theorem and Bivariant Theory.Comment: 18 page

Conditional cash transfers, adult work incentives, and poverty

Conditional cash transfer (CCT) programs aim to alleviate poverty through monetary and in-kind benefits, as well as reduce future levels of poverty by encouraging investments in education, health, and nutrition. The success of CCT programs at reducing poverty depends on whether, and the extent to which, cash transfers affect adult work incentives. The authors examine whether the PROGRESA program of Mexico affects adult participation in the labor market and overall adult leisure time, and they link these effects to the impact of the program on poverty. Using the experimental design of PROGRESA's evaluation sample, the authors find that the program does not have any significant effect on adult labor force participation and leisure time. Their findings on adult work incentives are reinforced further by the result that PROGRESA leads to a substantial reduction in poverty. The poverty reduction effects are stronger for the poverty gap and severity of poverty measures.Rural Poverty Reduction,Population Policies,Poverty Monitoring&Analysis,Health Monitoring&Evaluation