Optimised search heuristic combining valid inequalities and tabu search

This paper presents an Optimised Search Heuristic that combines a tabu search method with the verification of violated valid inequalities. The solution delivered by the tabu search is partially destroyed by a randomised greedy procedure, and then the valid inequalities are used to guide the reconstruction of a complete solution. An application of the new method to the Job-Shop Scheduling problem is presented.

Iterated local search

Iterated Local Search has many of the desirable features of a metaheuristic: it is simple, easy to implement, robust, and highly effective. The essential idea of Iterated Local Search lies in focusing the search not on the full space of solutions but on a smaller subspace defined by the solutions that are locally optimal for a given optimization engine. The success of Iterated Local Search lies in the biased sampling of this set of local optima. How effective this approach turns out to be depends mainly on the choice of the local search, the perturbations, and the acceptance criterion. So far, in spite of its conceptual simplicity, it has lead to a number of state-of-the-art results without the use of too much problem-specific knowledge. But with further work so that the different modules are well adapted to the problem at hand, Iterated Local Search can often become a competitive or even state of the artalgorithm. The purpose of this review is both to give a detailed description of this metaheuristic and to show where it stands in terms of performance.

Assigning proctors to exams with scatter search

In this paper we present an algorithm to assign proctors toexams. This NP-hard problem is related to the generalized assignmentproblem with multiple objectives. The problem consists of assigningteaching assistants to proctor final exams at a university. We formulatethis problem as a multiobjective integer program (IP) with a preferencefunction and a workload-fairness function. We then consider also a weightedobjective that combines both functions. We develop a scatter searchprocedure and compare its outcome with solutions found by solving theIP model with CPLEX 6.5. Our test problems are real instances from aUniversity in Spain.

Costly search and design

Firms compete by choosing both a price and a design from a family of designs thatcan be represented as demand rotations. Consumers engage in costly sequential searchamong firms. Each time a consumer pays a search cost he observes a new offering. Anoffering consists of a price quote and a new good, where goods might vary in the extentto which they are good matches for the consumer. In equilibrium, only two design-styles arise: either the most niche where consumers are likely to either love or loathethe product, or the broadest where consumers are likely to have similar valuations. Inequilibrium, different firms may simultaneously offer both design-styles. We performcomparative statics on the equilibrium and show that a fall in search costs can lead tohigher industry prices and profits and lower consumer surplus. Our analysis is relatedto discussions of how the internet has led to the prevalence of niche goods and the"long tail" phenomenon.

Optimal information transmission in organizations: Search and congestion

We propose a stylized model of a problem-solving organization whoseinternal communication structure is given by a fixed network. Problemsarrive randomly anywhere in this network and must find their way to theirrespective specialized solvers by relying on local information alone.The organization handles multiple problems simultaneously. For this reason,the process may be subject to congestion. We provide a characterization ofthe threshold of collapse of the network and of the stock of foatingproblems (or average delay) that prevails below that threshold. We buildupon this characterization to address a design problem: the determinationof what kind of network architecture optimizes performance for any givenproblem arrival rate. We conclude that, for low arrival rates, the optimalnetwork is very polarized (i.e. star-like or centralized ), whereas it islargely homogenous (or decentralized ) for high arrival rates. We also showthat, if an auxiliary assumption holds, the transition between these twoopposite structures is sharp and they are the only ones to ever qualify asoptimal.

Intergenerational mobility and the informative content of surnames

We propose an alternative method for measuring intergenerational mobility. Measurements obtained fromtraditional methods (based on panel data) are scarce, difficult to compare across countries and almost impossible to get across time. In particular, this means that we do not know how intergenerational mobility is correlated with growth, income or the degree of inequality.Our proposal is to measure the informative content of surnames in one census. The more information thesurname has on the income of an individual, the more important is her background in determining her outcomes; and thus, the less mobility there is.The reason is that surnames provide information about family relationships because the distribution ofsurnames is necessarily very skewed. A large percentage of the population is bound to have a very unfrequent surname. For them the partition generated by surnames is very informative on family linkages.First, we develop a model whose endogenous variable is the joint distribution of surnames and income.There, we explore the relationship between mobility and the informative content of surnames. We allow for assortative mating to be a determinant of both.Second, we use our methodology to show that in large Spanish region the informative content of surnamesis large and consistent with the model. We also show that it has increased over time, indicating a substantial drop in the degree of mobility. Finally, using the peculiarities of the Spanish surname convention we show that the degree of assortative mating has also increased over time, in such a manner that might explain the decrease in mobility observed.Our method allows us to provide measures of mobility comparable across time. It should also allow us tostudy other issues related to inheritance.

A search theory of money and commerce with Neoclassical production

This paper advances a highly tractable model with search theoretic foundations for money and neoclassical growth. In the model, manufacturingand commerce are distinct and separate activities. In manufacturing,goods are efficiently produced combining capital and labor. In commerce,goods are exchanged in bilateral meetings. The model is applied to studythe effects of in��ation on capital accumulation and welfare. With realisticparameters, inflation has large negative effects on welfare even though itraises capital and output. In contrast, with cash-in-advance, a deviceinformally motivated with bilateral trading, inflation depresses capitaland output and has a negligible effect on welfare.

A simple optimised search heuristic for the job-shop scheduling problem

This paper presents a simple Optimised Search Heuristic for the Job Shop Scheduling problem that combines a GRASP heuristic with a branch-and-bound algorithm. The proposed method is compared with similar approaches and leads to better results in terms of solution quality and computing times.

How to recognize opportunities: Heterarchical search in a Wall Street trading room

Our task in this paper is to analyze the organization of trading in the era of quantitativefinance. To do so, we conduct an ethnography of arbitrage, the trading strategy that bestexemplifies finance in the wake of the quantitative revolution. In contrast to value andmomentum investing, we argue, arbitrage involves an art of association - the constructionof equivalence (comparability) of properties across different assets. In place of essentialor relationa l characteristics, the peculiar valuation that takes place in arbitrage is based on an operation that makes something the measure of something else - associating securities to each other. The process of recognizing opportunities and the practices of making novel associations are shaped by the specific socio-spatial and socio-technical configurations of the trading room. Calculation is distributed across persons and instruments as the trading room organizes interaction among diverse principles of valuation.

Non-stationary job search when jobs are not forever: A structural estimation

This paper considers a job search model where the environment is notstationary along the unemployment spell and where jobs do not lastforever. Under this circumstance, reservation wages can be lower thanwithout separations, as in a stationary environment, but they can alsobe initially higher because of the non-stationarity of the model. Moreover,the time-dependence of reservation wages is stronger than with noseparations. The model is estimated structurally using Spanish data forthe period 1985-1996. The main finding is that, although the decrease inreservation wages is the main determinant of the change in the exit ratefrom unemployment for the first four months, later on the only effect comesfrom the job offer arrival rate, given that acceptance probabilities areroughly equal to one.

Unemployment insurance with endogenous search intensity and precautionary saving

A welfare analysis of unemployment insurance (UI) is performed in a generalequilibrium job search model. Finitely-lived, risk-averse workers smooth consumption over time by accumulating assets, choose search effort whenunemployed, and suffer disutility from work. Firms hire workers, purchasecapital, and pay taxes to finance worker benefits; their equity is the assetaccumulated by workers. A matching function relates unemployment, hiringexpenditure, and search effort to the formation of jobs. The model is calibrated to US data; the parameters relating job search effort to the probability of job finding are chosen to match microeconomic studies ofunemployment spells. Under logarithmic utility, numerical simulation shows rather small welfaregains from UI. Even without UI, workers smooth consumption effectivelythrough asset accumulation. Greater risk aversion leads to substantiallylarger welfare gains from UI; however, even in this case much of its welfareimpact is due not to consumption smoothing effects, but rather to decreased work disutility, or to a variety of externalities.

Job search and asset accumulation under borrowing constraints

In this paper I show how borrowing constraints and job search interact.I fit a dynamic model to data from the National Longitudinal Survey(1979-cohort) and show that borrowing constraints are significant. Agentswith more initial assets and more access to credit attain higher wagesfor several periods after high school graduation. The unemployed maintaintheir consumption by running down their assets, while the employed saveto buffer against future unemployment spells. I also show that, unlikein models with exogenous income streams, unemployment transfers, byallowing agents to attain higher wages do not 'crowd out' but increasesaving.

Motivation and content Language Integrated Learning : an impulse for Second Language Teaching

���Estudiantes motivados producen profesores motivados y viceversa��� (Lesley Denham)La cita refleja el efecto rec��proco que tiene el comportamiento del profesor en el compromiso de los estudiantes a lo largo del a��o y viceversa. Es sorprendente como, destacando las fortalezas de cada estudiante en lugar de sus debilidades, nunca compar��ndolos entre ellos sino con su propio rendimiento, puede despertar una motivaci��n intr��nseca en el estudiante, y una merecida satisfacci��n personal para el profesor.Sin embargo, no existen botones motivacionales m��gicos que podamos pulsar y hacer que el alumno quiera aprender. Como profesores, tomar la iniciativa ser�� crucial: dar a nuestros estudiantes el espacio suficiente para experimentar, realzar su autonom��a, e intuir las respuestas a trav��s de un proceso inductivo. En definitiva, hacerles protagonistas de su proceso de aprendizaje.Incluir AICLE en la clase de ingl��s es una metodolog��a que nos ayudar�� a conseguirlo. Los estudiantes asocian AICLE con algo interesante y divertido, diferente a las sesiones te��ricas. Como resultado, al utilizar la lengua, lo hacen movidos por sus sentimientos, aprendiendo de forma impl��cita.���Estudiants motivats produeixen professors motivats i viceversa��� (Lesley Denham)La cita reflecteix l'efecte rec��proc que t�� el comportament del professor en el comprom��s dels estudiants al llarg de l'any i viceversa. ��s sorprenent com, destacant les fortaleses de cada estudiant en lloc de les seves debilitats, mai comparant-los entre ells sin�� amb el seu propi rendiment, pot despertar una motivaci�� intr��nseca a l'estudiant, i una merescuda satisfacci�� personal per al professor.No obstant aix��, no existeixen botons motivacionals m��gics que puguem pr��mer i fer que l'alumne vulgui aprendre. Com a professors, prendre la iniciativa ser�� crucial: donar als nostres estudiants l'espai suficient per experimentar, real��ar la seva autonomia, i intuir les respostes a trav��s d'un proc��s inductiu. En definitiva, fer-los protagonistes del seu proc��s d'aprenentatge.Incloure AICLE en la classe d'angl��s ��s una metodologia que ens ajudar�� a aconseguir-ho. Els estudiants consideren AICLE interessant i divertit, diferent a les sessions te��riques. Com a resultat, en utilitzar la llengua, ho fan moguts pels seus sentiments, aprenent de forma impl��cita.

Periodismo y dispositivos m��viles de lecto-escritura. Introducci��n al dise��o de contenidos para tabletas

El lanzamiento de las tabletas, especialmente la iPad de Apple en 2010, abri�� la competencia entre las compa����as de comunicaci��n en el sentido de hacer disponible el contenido para este entorno de medios emergentes. La fuga de lectores de peri��dicos impresos y la consecuente ca��da en las ganancias por publicidad, forz�� a las compa����as period��sticas a que buscaran los otros medios de mantener sus negocios. La diversificaci��n de productos y la penetraci��n de los peri��dicos en dispositivos m��viles constituyen un escenario prometedor para el medio. El vertiginoso volumen de ventas de las tabletas indica que en 2012 ser��n comercializadas m��s de 140 millones de unidades en el mundo. El dise��o de los peri��dicos en tabletas est�� ��ntimamente ligado al dise��o de la versi��n impresa por la fuerza de su met��fora. El desaf��o es encontrar un dise��o de p��ginas propio, aprovechando el potencial multimedia sin interferir negativamente en la legibilidad y en el car��cter intr��nseco de informar.

A search for microquasar candidates at low galactic latitudes

Recent studies of relativistic jet sources in the Galaxy, also known as microquasars, have been very useful in trying to understand the accretion/ejection processes that take place near compact objects. However, the number of sources involved in such studies is still small. In an attempt to increase the number of known microquasars we have carried out a search for new Radio Emitting X-ray Binaries (REXBs). These sources are the ones to be observed later with VLBI techniques to unveil their possible microquasar nature. To this end, we have performed a cross-identification between the X-ray ROSAT all sky survey Bright Source Catalog (RBSC) and the radio NRAO VLA Sky Survey (NVSS) catalogs under very restrictive selection criteria for sources with |b|<5 degrees. We have also conducted a deep observational radio and optical study for six of the selected candidates. At the end of this process two of the candidates appear to be promising, and deserve additional observations aimed to confirm their proposed microquasar nature.