Edge detection by selection of pieces of level lines

We propose an edge detector based on the selection of wellcontrasted pieces of level lines, following the proposal ofDesolneux-Moisan-Morel (DMM) [1]. The DMM edge detectorhas the problem of over-representation, that is, everyedge is detected several times in slightly different positions.In this paper we propose two modifications of the originalDMM edge detector in order to solve this problem. The firstmodification is a post-processing of the output using a generalmethod to select the best representative of a bundle of curves.The second modification is the use of Canny’s edge detectorinstead of the norm of the gradient to build the statistics. Thetwo modifications are independent and can be applied separately.Elementary reasoning and some experiments showthat the best results are obtained when both modifications areapplied together.

The effects of structural reforms on productivity and profitability enhancing reallocation: Evidence from Colombia

Estimates for the U.S. suggest that at least in some sectors productivity enhancing reallocationis the dominant factor in accounting for producitivity growth. An open question, particularlyrelevant for developing countries, is whether reallocation is always productivity enhancing. Itmay be that imperfect competition or other barriers to competitive environments imply that thereallocation process is not fully e?cient in these countries. Using a unique plant-levellongitudinal dataset for Colombia for the period 1982-1998, we explore these issues byexamining the interaction between market allocation, and productivity and profitability.Moreover, given the important trade, labor and financial market reforms in Colombia during theearly 1990's, we explore whether and how the contribution of reallocation changed over theperiod of study. Our data permit measurement of plant-level quantities and prices. Takingadvantage of the rich structure of our price data, we propose a sequential mehodology to estimateproductivity and demand shocks at the plant level. First, we estimate total factor productivity(TFP) with plant-level physical output data, where we use downstream demand to instrumentinputs. We then turn to estimating demand shocks and mark-ups with plant-level price data, usingTFP to instrument for output in the inversedemand equation. We examine the evolution of thedistributions of TFP and demand shocks in response to the market reforms in the 1990's. We findthat market reforms are associated with rising overall productivity that is largely driven byreallocation away from low- and towards highproductivity businesses. In addition, we find thatthe allocation of activity across businesses is less driven by demand factors after reforms. Wefind that the increase in aggregate productivity post-reform is entirely accounted for by theimproved allocation of activity.

Oil price shocks, income and democracy

We examine the effect of oil price fluctuations ondemocratic institutions over the 1960-2007 period. We also exploitthe very persistent response of income to oil price fluctuations tostudy the effect of persistent (oil price-driven) income shocks ondemocracy. Our results indicate that countries with greater net oilexports over GDP see improvements in democratic institutionsfollowing upturns in international oil prices. We estimate that a 1percentage point increase in per capita GDP growth due to apositive oil price shock increases the Polity democracy score byaround 0.2 percentage points on impact and by around 2 percentagepoints in the long run. The effect on the probability of a democratictransition is around 0.4 percentage points.

Turnout, political preferences and information: Experimental evidence from Perú

Electoral institutions that encourage citizens to vote are widely used around the world. Yet littleis known about the effects of such institutions on voter participation and the composition of the electorate.In this paper, I combine a field experiment with a change in Peruvian voting laws to identify theeffect of monetary (dis-)incentives on voting. Using the random variation in the fine for abstention andan objective measure of turnout at the individual level, I estimate the elasticity of voting with respectto cost to be -0.21. Consistent with the theoretical model presented, the reduction in turnout inducedby the reduction in the fine is driven by voters who (i) are in the center of the political spectrum, (ii)are less interested in politics, and (iii) hold less political information. However, voters who respondto changes in the cost of abstention do not have different preferences for policies than those who voteregardless of the cost. Further, involvement in politics, as measured by the decision to acquire politicalinformation, seems to be independent of the level of the fine. Additional results indicate that thereduction in the fine does not affect the incidence of vote buying, but increases the price paid for avote.

Consistent solutions in exchange economies: A characterization of the price mechanism

We characterize the Walrasian allocations correspondence by means offour axioms: consistency, replica invariance, individual rationality andPareto optimality. It is shown that for any given class of exchange economiesany solution that satisfies the axioms is a selection from the Walrasianallocations with slack. Preferences are assumed to be smooth, but may besatiated and non--convex. A class of economies is defined as all economieswhose agents' preferences belong to an arbitrary family (finite or infinite)of types. The result can be modified to characterize equal budget Walrasianallocations with slack by replacing individual rationality with individualrationality from equal division. The results are valid also for classes ofeconomies in which core--Walras equivalence does not hold.

Dynamic price competition with fixed capacities

Many revenue management (RM) industries are characterized by (a) fixed capacities in theshort term (e.g., hotel rooms, seats on an airline flight), (b) homogeneous products (e.g., twoairline flights between the same cities at similar times), and (c) customer purchasing decisionslargely influenced by price. Competition in these industries is also very high even with just twoor three direct competitors in a market. However, RM competition is not well understood andpractically all known implementations of RM software and most published models of RM donot explicitly model competition. For this reason, there has been considerable recent interestand research activity to understand RM competition. In this paper we study price competitionfor an oligopoly in a dynamic setting, where each of the sellers has a fixed number of unitsavailable for sale over a fixed number of periods. Demand is stochastic, and depending on howit evolves, sellers may change their prices at any time. This reflects the fact that firms constantly,and almost costlessly, change their prices (alternately, allocations at a price in quantity-basedRM), reacting either to updates in their estimates of market demand, competitor prices, orinventory levels. We first prove existence of a unique subgame-perfect equilibrium for a duopoly.In equilibrium, in each state sellers engage in Bertrand competition, so that the seller withthe lowest reservation value ends up selling a unit at a price that is equal to the equilibriumreservation value of the competitor. This structure hence extends the marginal-value conceptof bid-price control, used in many RM implementations, to a competitive model. In addition,we show that the seller with the lowest capacity sells all its units first. Furthermore, we extendthe results transparently to n firms and perform a number of numerical comparative staticsexploiting the uniqueness of the subgame-perfect equilibrium.

Relative price riddles in international business cycle theory: Are transport costs the explanation?

We study relative price behavior in an international business cyclemodel with specialization in production, in which a goods marketfriction is introduced through transport costs. The transporttechnology allows for flexible transport costs. We analyze whetherthis extension can account for the striking differences betweentheory and data as far as the moments of terms of trade and realexchange rates are concerned. We find that transport costs increaseboth the volatility of the terms of trade and the volatility of thereal exchange rate. However, unless the transport technology isspecified by a Leontief technology, transport costs do not resolvethe quantitative discrepancies between theory and data. Asurprising result is that transport costs may actually lower thepersistence of the real exchange rate, a finding that is in contrastto much of the emphasis of the empirical literature.

Real wage rigidities and the new Keynesian model

Most central banks perceive a trade-off between stabilizing inflation and stabilizing the gap between output and desired output. However, the standard new Keynesian framework implies no such trade-off. In that framework, stabilizing inflation is equivalent to stabilizing the welfare-relevant output gap. In this paper, we argue that this property of the new Keynesian framework, which we call the divine coincidence, is due to a special feature of the model: the absence of non trivial real imperfections.We focus on one such real imperfection, namely, real wage rigidities. When the baseline new Keynesian model is extended to allow for real wage rigidities, the divine coincidence disappears, and central banks indeed face a trade-off between stabilizing inflation and stabilizing the welfare-relevant output gap. We show that not only does the extended model have more realistic normative implications, but it also has appealing positive properties. In particular, it provides a natural interpretation for the dynamic inflation-unemployment relation found in the data.

Price increase and stability with new entries in Cournot markets

It is widely accepted in the literature about the classicalCournot oligopoly model that the loss of quasi competitiveness is linked,in the long run as new firms enter the market, to instability of the equilibrium. In this paper, though, we present a model in which a stableunique symmetric equilibrium is reached for any number of oligopolistsas industry price increases with each new entry. Consequently, the suspicion that non quasi competitiveness implies, in the long run, instabilityis proved false.

Targeting fertility and female participation through the income tax

We evaluate the effect of a 2003 reform in the Spanish income tax on fertility and the employment of mothers with small children. The reform introduced a tax credit for working mothers with children under the age of three, while also increasing child deductions for all households with children. Theoretically, given the interplay of these two components, the expected effect of the reform is ambiguous on both outcomes. We find that the combined reforms significantly increased both fertility (by almost five percent) and the employment rate of mothers with children under three (by two percent). These effects were more pronounced among less-educated women. In addition, to disentangle the impact of the two reform components, we use an earlier reform that increased child deductions in 1999. We find that the child deductions affect mothers employment negatively, which implies that the 2003 tax credit would have increased employment even more (up to five percent) in the absence of the change in child deductions.