Formal and Informal Credit Markets and Rural Credit Demand in China

Credit markets are an essential economic institution. In developing countries, particularly in countries undergoing rapid social and economic transition, it is important to identify emerging credit demand and institute credit supply in a timely manner to facilitate economic transformation. This research focuses on the evolving rural credit market in China, where borrowing from the social network has been common but the recent economic transition has made this informal credit market inadequate in addressing rural credit needs. This research is aimed at identifying the social and economic factors that explain the farmers’ credit constraint and influence farmers’ decisions to switch from informal to formal credit markets. Using data from a household survey, we estimated both binary choice probit models and a multinomial probit model to explore the determinants of credit market choice and credit constraints. We found that the credit demand is significantly affected by household’s production capacity as supported by the fact that household size, land size, head’s education all significantly increase household’s probability to borrow, but the impact of these factors varies considerably by credit market. Transaction costs have a significant, negative effect on formal credit demand. The credit constraints analysis suggest that off-farm employment, land size and the cost of the credit are the three most important factors that increase the probability of being constrained.Formal Credit, Informal Credit, Credit Markets, Rural Credit, China, Agricultural Finance, Farm Management,

Relative Stability and Local Curvature Analysis in Carbon Nanotori

We introduce a concise formalism to characterize nanometer-sized tori based on carbon nanotubes and to determine their stability by combining {\em ab initio} density functional calculations with a continuum elasticity theory approach that requires only shape information. We find that the high strain energy in nanotori containing only hexagonal rings is significantly reduced in nanotori containing also other polygons. Our approach allows to determine local curvature and link it to local strain energy, which is correlated with local stability and chemical reactivity

A deletion-contraction formula and monotonicity properties for the polymatroid Tutte polynomial

The Tutte polynomial is a crucial invariant of matroids. The polymatroid Tutte polynomial $\mathscr{T}_{P}(x,y)$, introduced by Bernardi et al., is an extension of the classical Tutte polynomial from matroids to polymatroids $P$. In this paper, we first obtain a deletion-contraction formula for $\mathscr{T}_{P}(x,y)$. Then we prove two natural monotonicity properties, for containment and for minors of the interior polynomial $x^{n}\mathscr{T}_{P}(x^{-1},1)$ and the exterior polynomial $y^{n}\mathscr{T}_{P}(1,y^{-1})$, for polymatroids $P$ over $[n]$. We show by a counter-example that these monotonicity properties do not extend to $\mathscr{T}_{P}(x,y)$. Using deletion-contraction, we obtain formulas for the coefficients of terms of degree $n-1$ in $\mathscr{T}_{P}(x,y)$. Finally, for all $k\geq 0$, we characterize hypergraphs $\mathcal{H}=(V,E)$ so that the coefficient of $y^{k}$ in the exterior polynomial of the associated polymatroid $P_{\mathcal{H}}$ attains its maximal value $\binom{|V|+k-2}{k}$.Comment: 27 pages, 2 figure