Phase-matchable nonlinear optical interactions in periodic thin films

A proposal for a new method of phase matching in nonlinear optical interactions is made. A periodic perturbation of the surface of a thin-film waveguide generates space harmonics with new propagation constants which can be phase matched. An analysis of this proposal shows it to be particularly interesting for a class of thin-film nonlinear devices using the cubic optically isotropic semiconductors (such as GaAs, GaP, etc.) which possess high nonlinear optical coefficients but are not phase matchable by the conventional birefringent techniques

Understanding Space in Proof Complexity: Separations and Trade-offs via Substitutions

For current state-of-the-art DPLL SAT-solvers the two main bottlenecks are the amounts of time and memory used. In proof complexity, these resources correspond to the length and space of resolution proofs. There has been a long line of research investigating these proof complexity measures, but while strong results have been established for length, our understanding of space and how it relates to length has remained quite poor. In particular, the question whether resolution proofs can be optimized for length and space simultaneously, or whether there are trade-offs between these two measures, has remained essentially open. In this paper, we remedy this situation by proving a host of length-space trade-off results for resolution. Our collection of trade-offs cover almost the whole range of values for the space complexity of formulas, and most of the trade-offs are superpolynomial or even exponential and essentially tight. Using similar techniques, we show that these trade-offs in fact extend to the exponentially stronger k-DNF resolution proof systems, which operate with formulas in disjunctive normal form with terms of bounded arity k. We also answer the open question whether the k-DNF resolution systems form a strict hierarchy with respect to space in the affirmative. Our key technical contribution is the following, somewhat surprising, theorem: Any CNF formula F can be transformed by simple variable substitution into a new formula F' such that if F has the right properties, F' can be proven in essentially the same length as F, whereas on the other hand the minimal number of lines one needs to keep in memory simultaneously in any proof of F' is lower-bounded by the minimal number of variables needed simultaneously in any proof of F. Applying this theorem to so-called pebbling formulas defined in terms of pebble games on directed acyclic graphs, we obtain our results.Comment: This paper is a merged and updated version of the two ECCC technical reports TR09-034 and TR09-047, and it hence subsumes these two report

Capital Market Integration and Wages

For three years after the typical developing country opens its stock market to inflows of foreign capital, the average annual growth rate of the real wage in the manufacturing sector increases by a factor of seven. No such increase occurs in a control group of developing countries. The temporary increase in the growth rate of the real wage drives up the level of average annual compensation for each worker in the sample by 609 US dollars—an increase equal to 25 percent of their annual pre-liberalization salary. The increase in the growth rate of labor productivity in the aftermath of liberalization exceeds the increase in the growth rate of the real wage so that the increase in workers’ incomes actually coincides with a rise in manufacturing sector profitability. Overall, the results suggest that trade in capital may have a larger impact on wages than trade in goods.Developing countries, Wages, Labor Productivity, Captial Market

Experimental study of implications of SFAS 131: The effects of the new standard on the informativeness of segment reporting

This paper analyzes whether the new business segment reporting disclosure rules, SFAS 131, will actually provide capital market participants with more predictive ability than the previous rules. For this we conduct three experiments. Two experiments with advanced accounting students as subjects, where the experiments differ in the firm the subjects analyze, and the third with professional financial analysts. In each experiment we provide one group of subjects with accounting reports based on the new standard (New Rules Group, NRG), and another group with reports based on the old standard (Old Rules Group, ORG). We ask both groups to forecast several accounting and market values of a firm. We then compare the performance predictions and analyses of the two groups. Most of the forecasts of the NRG are neither significantly different from those of the ORG, nor significantly more accurate. Subjects also report the variables that they consider important in their analysis. 25% of the NRG students in Experiment I mention the segment data as being central in their decisions and 33% say they used segment or sector data. Among the analysts in Experiment II the corresponding percentages are 0% and 60%, respectively. Also in experiment III, where the subjects rank the top 4 variables they use in their predictions according to importance, segment repots receive a mediocre rank. It therefore appears that the reports according to the new rules, whereas noticeable by the subjects, do not have a major positive impact on their responses. The subjects also exhibit a considerable degree of overconfidence. --segment reporting,FASB 131,experimental economics,overconfidence

An airline fleet planning model

Imperial Users onl

Risk, Institutions and Growth: Why England and Not China?

We analyze the role of risk-sharing institutions in transitions to modern economies. Transitions requires individual-level risk-taking in pursuing productivity-enhancing activities including using and developing new knowledge. Individual-level, idiosyncratic risk implies that distinct risk-sharing institutions – even those providing the same level of insurance – can lead to different growth trajectories if they differently motivate risk-taking. Historically, risk sharing institutions were selected based on their cultural and institutional compatibility and not their unforeseen growth implications. We simulate our growth model incorporating England’s and China’s distinct pre-modern risk-sharing institutions. The model predicts a transition in England and not China even with equal levels of risk sharing. Under the clan-based Chinese institution, the relatively risk-averse elders had more control over technological choices implying lower risk-taking. Focusing on non-market institutions expands on previous growth-theoretic models to highlight that transitions can transpire even in the absence of exogenous productivity shocks or time-dependent state variables. Recognizing the role of non-market institutions in the growth process bridges the view that transitions are due to luck and the view that transitions are inevitable. Transitions transpire when ‘luck’ creates the conditions under which economic agents find it beneficial to make the choices leading to positive rates of technological change. Luck came in the form of historical processes leading to risk-sharing institutions whose unintended consequences encouraged productivity-enhancing risk-taking.institutions, risk, growth, development

Subspace Polynomials and Cyclic Subspace Codes

Subspace codes have received an increasing interest recently due to their application in error-correction for random network coding. In particular, cyclic subspace codes are possible candidates for large codes with efficient encoding and decoding algorithms. In this paper we consider such cyclic codes and provide constructions of optimal codes for which their codewords do not have full orbits. We further introduce a new way to represent subspace codes by a class of polynomials called subspace polynomials. We present some constructions of such codes which are cyclic and analyze their parameters