On Cr−C^r-closing for flows on 2-manifolds

For some full measure subset B of the set of iet's (i.e. interval exchange transformations) the following is satisfied: Let X be a $C^r$, $1\le r\le \infty$, vector field, with finitely many singularities, on a compact orientable surface M. Given a nontrivial recurrent point $p\in M$ of X, the holonomy map around p is semi-conjugate to an iet $E :[0,1) \to [0,1).$ If $E\in B$ then there exists a $C^r$ vector field Y, arbitrarily close to X, in the $C^r-$topology, such that Y has a closed trajectory passing through p.Comment: 7 pages, 1 figur

Analysis of Yelp Reviews

In the era of Big Data and Social Computing, the role of customer reviews and ratings can be instrumental in predicting the success and sustainability of businesses. In this paper, we show that, despite the apparent subjectivity of user ratings, there are also external, or objective factors which help to determine the outcome of a business's reviews. The current model for social business review sites, such as Yelp, allows data (reviews, ratings) to be compiled concurrently, which introduces a bias to participants (Yelp Users). Our work examines Yelp Reviews for businesses in and around college towns. We demonstrate that an Observer Effect causes data to behave cyclically: rising and falling as momentum (quantified in user ratings) shifts for businesses.Comment: 24 pages, 20 figures and 5 table

Understanding the impact of economic shocks on labor market outcomes in developing countries : an application to Indonesia and Mexico

In this paper the authors use a search and matching model of multi-sector labor markets, to understand the channels through which economic shocks affect labor market outcomes in developing countries. In the model workers can be employed in agriculture, formal or informal urban jobs, or unemployed. Economic shocks are manifested as either increased turbulence in the formal/informal sectors or a decrease in overall sectoral productivity. By calibrating the model to Indonesia and Mexico, the authors are able to understand how the 1998 Indonesian crisis and the 2001 Mexican recession translated into labor market outcomes. They then venture to simulate how the current financial crisis might affect the allocation of labor and earnings across sectors, in these countries. The results suggest that in both countries past crises have increased the degree of turbulence of the formal sector, increasing job destruction. However, while in Indonesia the crisis affected the overall formal sector productivity, this was not the case in Mexico. This explains the larger blow to formal wages -- relative to the size of the shock- witnessed by Indonesian workers. The response of the informal sector was also different: In both countries the informal sector was able to act as a buffer, as relative earnings increased. However, while in Mexico it became much harder to find informal sector opportunities and easier to keep the job once found; in Indonesia turbulence in the informal sector increased substantially increasing the job destruction rate of informal jobs andlimiting the cushioning role that the informal sector might have played. The agricultural sector was spared from the shock in both countries. In Indonesia, it actually benefited from an unusual exogenous increase in the price of rise. The simulations show that if either the informal or agricultural sectors are spared from the shocks, large reallocations of labor might occur, and the overall effect of the shock is smaller. Instead, if these sectors can’t buffer the shock, the reallocation of labor is much smaller, but earnings in the formal sector drop substantially. The authors also explore the impact of alternative policies. They find that in relatively flexible markets where informality can be seen more as a choice rather than as queuing, unemployment benefits and informal employment subsidies may have paradoxical effects, by discouraging formal search. Instead, policies targeted at creating informal employment and boosting formal TFP growth have the desired effects.Labor Markets,Labor Policies,Markets and Market Access,Banks&Banking Reform,Economic Theory&Research

Electron transport in carbon nanotube-metal systems: contact effects

Carbon nanotubes (CNT) have a very large application potential in the rapid developing field of molecular electronics. Infinite single-wall metallic CNTs have theoretically a conductance of 4e2/h because of the two electronic bands crossing the Fermi level. For finite size CNTs experiments have shown that other values are also possible, indicating a very strong influence of the contacts. We study electron transport in single- and double-wall CNTs contacted to metallic electrodes within the Landauer formalism combined with Green function techniques. We show that the symmetry of the contact region may lead to blocking of a transport channel. In the case of double-wall CNTs with both inner and outer shells being metallic, non-diagonal self energy contributions from the electrodes may induce channel mixing, precluding a simple addition of the individual shell conductances

Tribalism as a Minimax-Regret Strategy: Evidence of Voting in the 2007 Kenyan Elections

Although many studies find that voting in Africa approximates an ethnic census in that voting is primarily along ethnic lines, hardly any of the studies have sought to explain ethnic voting following a rational choice framework. Using data of voter opinions from a survey conducted two weeks before the December 2007 Kenyan elections, we find that the expected benefits associated with a win by each of the presidential candidates varied significantly across voters from different ethnic groups. We hypothesize that decision to participate in the elections was influenced by the expected benefits as per the minimax-regret voting model. We test the predictions of this model using data of voter turnout in the December 2007 elections and find that turnout across ethnic groups varied systematically with expected benefits. The results suggest that individuals participated in the elections primarily to avoid the maximum regret should a candidate from another ethnic group win. The results therefore offer credence to the minimax regret model as proposed by Ferejohn and Fiorina (1974) and refute the Downsian expected utility model.