Showing papers by "Instituto Tecnológico Autónomo de México published in 2012"

Changes to dryland rainfall result in rapid moss mortality and altered soil fertility

Abstract: Arid and semi-arid ecosystems cover ∼40% of Earth’s land surface, but little is known about how climate change will affect these areas. Now experimental research shows that altered precipitation (more small events) can result in a negative moss carbon balance leading to dramatic moss mortality. These findings indicate the potential sensitivity of drylands to subtle climatic changes.

Money-Back Guarantees: Helping the Low-Quality Retailer

Abstract: Existing literature, based on signaling theory, suggests that money-back guarantees (MBGs) will be utilized by high-quality firms, where high quality is defined as a low likelihood of product return. However, in today's world, MBGs are ubiquitous among major retailers, even when the likelihood of product return varies greatly between them. To understand this phenomenon, we explore a competitive environment between high-and low-quality retailers where consumers are fully informed and risk neutral, and retailers realize a salvage value for returned products. When MBGs are profitable, under continuous demand it is Nash equilibrium for both retailers to offer MBGs, and the low-quality retailer gains while the high-quality retailer loses relative to when MBGs are not offered. In contrast, if demand is lumpy, retailers can act monopolistically over their respective market segments, allowing both retailers to gain from MBGs, although the low-quality retailer still gains more. This paper was accepted by J. Miguel Villas-Boas, marketing.

Increased temperature and altered summer precipitation have differential effects on biological soil crusts in a dryland ecosystem

Abstract: Biological soil crusts (biocrusts) are common and ecologically important members of dryland ecosystems worldwide, where they stabilize soil surfaces and contribute newly fixed C and N to soils. To test the impacts of predicted climate change scenarios on biocrusts in a dryland ecosystem, the effects of a 2–3 °C increase in soil temperature and an increased frequency of smaller summer precipitation events were examined in a large, replicated field study conducted in the cold desert of the Colorado Plateau, USA. Surface soil biomass (DNA concentration), photosynthetically active cyanobacterial biomass (chlorophyll a concentration), cyanobacterial abundance (quantitative PCR assay), and bacterial community composition (16S rRNA gene sequencing) were monitored seasonally over 2 years. Soil microbial biomass and bacterial community composition were highly stratified between the 0–2 cm depth biocrusts and 5– 10 cm depth soil beneath the biocrusts. The increase in temperature did not have a detectable effect on any of the measured parameters over 2 years. However, after the second summer of altered summer precipitation pattern, significant declines occurred in the surface soil biomass (avg. DNA concentration declined 38%), photosynthetic cyanobacterial biomass (avg. chlorophyll a concentration declined 78%), cyanobacterial abundance (avg. gene copies g 1 soil declined 95%), and proportion of Cyanobacteria in the biocrust bacterial community (avg. representation in sequence libraries declined 85%). Biocrusts are important contributors to soil stability, soil C and N stores, and plant performance, and the loss or reduction of biocrusts under an altered precipitation pattern associated with climate change could contribute significantly to lower soil fertility and increased erosion and dust production in dryland ecosystems at a regional scale.

Warming and increased precipitation frequency on the Colorado Plateau: Implications for biological soil crusts and soil processes

Abstract: Changes in temperature and precipitation are expected to influence ecosystem processes worldwide. Despite their globally large extent, few studies to date have examined the effects of climate change in desert ecosystems, where biological soil crusts are key nutrient cycling components. The goal of this work was to assess how increased temperature and frequency of summertime precipitation affect the contributions of crust organisms to soil processes. With a combination of experimental 2°C warming and altered summer precipitation frequency applied over 2 years, we measured soil nutrient cycling and the structure and function of crust communities. We saw no change in crust cover, composition, or other measures of crust function in response to 2°C warming and no effects on any measure of soil chemistry. In contrast, crust cover and function responded to increased frequency of summer precipitation, shifting from moss to cyanobacteria-dominated crusts; however, in the short timeframe we measured, there was no accompanying change in soil chemistry. Total bacterial and fungal biomass was also reduced in watered plots, while the activity of two enzymes increased, indicating a functional change in the microbial community. Taken together, our results highlight the limited effects of warming alone on biological soil crust communities and soil chemistry, but demonstrate the substantially larger effects of altered summertime precipitation.

A sequential quadratic programming algorithm with an additional equality constrained phase

Abstract: A sequential quadratic programming (SQP) method is presented that aims to overcome some of the drawbacks of contemporary SQP methods It avoids the diculties associated with indefinite quadratic programming subproblems by defining this subproblem to be always convex The novel feature of the approach is the addition of an equality constrained phase that promotes fast convergence and improves performance in the presence of ill conditioning This equality constrained phase uses exact second order information and can be implemented using either a direct solve or an iterative method The paper studies the global and local convergence properties of the new algorithm and presents a set of numerical experiments to illustrate its practical performance

Students’ understanding of the general notion of a function of two variables

Abstract: In this study we analyze students’ understanding of two-variable function; in particular we consider their understanding of domain, possible arbitrary nature of function assignment, uniqueness of function image, and range. We use APOS theory and semiotic representation theory as a theoretical framework to analyze data obtained from interviews with thirteen students who had taken a multivariable calculus course. Results show that few students were able to construct an object conception of function of two variables. Most students showed difficulties finding domains of functions, in particular, when they were restricted to a specific region in the xy plane. They also showed that they had not fully coordinated their R3, set, and function of one variable schemata. We conclude from the analysis that many of the interviewed students’ notion of function can be considered as pre-Bourbaki.

Gauge Transformations, Twisted Poisson Brackets and Hamiltonization of Nonholonomic Systems

Abstract: In this paper we study the problem of Hamiltonization of nonholonomic systems from a geometric point of view. We use gauge transformations by 2-forms (in the sense of Severa and Weinstein in Progr Theoret Phys Suppl 144:145 154 2001) to construct different almost Poisson structures describing the same nonholonomic system. In the presence of symmetries, we observe that these almost Poisson structures, although gauge related, may have fundamentally different properties after reduction, and that brackets that Hamiltonize the problem may be found within this family. We illustrate this framework with the example of rigid bodies with generalized rolling constraints, including the Chaplygin sphere rolling problem. We also see through these examples how twisted Poisson brackets appear naturally in nonholonomic mechanics.

Dynamic Stock Selection Strategies: A Structured Factor Model Framework

Abstract: We propose a novel framework for estimating the time-varying covariation among stocks. Our work is inspired by asset pricing theory and associated developments in Financial Index Models. We work with a family of highly structured dynamic factor models that seek the extraction of the latent structure responsible for the cross-sectional covariation in a large set of financial securities. Our models incorporate stock specific information in the estimation of commonalities and deliver economically interpretable factors that are used both, as a vehicle to estimate large time-varying covariance matrix, and as a potential tool for stock selection in portfolio allocation problems. In an empirically oriented, high-dimensional case study, we showcase the use of our methodology and highlight the flexibility and power of the dynamic factor model framework in financial econometrics.

Board versus TMT international experience: a study of their joint effects

Abstract: Purpose – The purpose of this paper is to test the relationship between board and top management team (TMT) members' international experience and CEO multinationality, with their firm's degree of internationalization. Through the lenses of upper echelon theory, on a sample of 108 European and US firms, the author tests the variables “international experience” and “CEO multinationality”, at the board and at the TMT levels.Design/methodology/approach – A longitudinal research design is used to examine director's individual attributes in 2001 and firm's degree of internationalization in 2003‐2008. The sample comprised directors of the 108 largest European and US service and industrial firms by market capitalization, as listed in the Financial Times (FT) Global index of 2007.Findings – A positive effect is found on internationalization for international experience of both boards and TMTs; also a positive relationship is found between CEO multinationality of TMTs and internationalization.Research limitations/i...

Culture does account for variation in game behavior

Abstract: Lamba and Mace's critique (1) of our research (2–4) is based on incorrect claims about our experiments and several misunderstandings of the theory underpinning our efforts. Their findings are consistent with our previous work and lead to no unique conclusions.

The KAMET II methodology: Knowledge acquisition, knowledge modeling and knowledge generation

Abstract: The knowledge acquisition (KA) process is not ''mining from the expert's head'' and writing rules for building knowledge-based systems (KBS), as it was 20years ago when KA was often confused with knowledge elicitation activity, and modern engineering tools did not exist. The KA process has definitely changed. Today knowledge acquisition is considered a cognitive process that involves both dynamic modeling and knowledge generation activities. KA should be seen as a spiral of epistemological and ontological content that grows upward by transforming tacit knowledge into explicit knowledge, which in turn becomes the basis for a new spiral of knowledge generation. This paper presents some of our attempts to build a new knowledge acquisition methodology that brings together and includes all of these ideas. KAMET II, the evolution of KAMET (Cairo, 1998), represents a modern approach to creating diagnosis-specialized knowledge models that can be run by Protege 2000, the open source ontology editor and knowledge-based framework.

Co-opting the environment: an empirical test of resource-dependence theory

Abstract: Through the lens of resource-dependence theory, we use the boards of 108 US and European firms to test the following variables: percentage of women, outsiders, government experience, and international members on firm internationalization. We find that the percentage of females and international members both have a positive effect on firm international diversification. Contrary to our expectations, we find that it is the percentage of insiders – and not outsiders as hypothesized – that is related to internationalization.

A Time-Series DDP for Functional Proteomics Profiles

Abstract: Using a new type of array technology, the reverse phase protein array (RPPA), we measure time-course protein expression for a set of selected markers that are known to co-regulate biological functions in a pathway structure. To accommodate the complex dependent nature of the data, including temporal correlation and pathway dependence for the protein markers, we propose a mixed effects model with temporal and protein-specific components. We develop a sequence of random probability measures (RPM) to account for the dependence in time of the protein expression measurements. Marginally, for each RPM we assume a Dirichlet process (DP) model. The dependence is introduced by defining multivariate beta distributions for the unnormalized weights of the stick breaking representation. We also acknowledge the pathway dependence among proteins via a conditionally autoregressive (CAR) model. Applying our model to the RPPA data, we reveal a pathway-dependent functional profile for the set of proteins as well as marginal expression profiles over time for individual markers.

Rubbery Polya Tree.

Abstract: Polya trees (PT) are random probability measures which can assign probability 1 to the set of continuous distributions for certain specifications of the hyperparameters. This feature distinguishes the PT from the popular Dirichlet process (DP) model which assigns probability 1 to the set of discrete distributions. However, the PT is not nearly as widely used as the DP prior. Probably the main reason is an awkward dependence of posterior inference on the choice of the partitioning subsets in the definition of the PT. We propose a generalization of the PT prior that mitigates this undesirable dependence on the partition structure, by allowing the branching probabilities to be dependent within the same level. The proposed new process is not a PT anymore. However, it is still a tail-free process and many of the prior properties remain the same as those for the PT.

Multitasking and interruptions: a SIG on bridging the gap between research on the micro and macro worlds

Abstract: Within the CHI community there has been sustained interest in interruptions and multitasking behaviour. Research in the area falls into two broad categories: the micro world of perception and cognition; and the macro world of organisations, systems and long-term planning. Although both kinds of research have generated insights into behaviour, the data generated by the two kinds of research have been effectively incommensurable. Designing safer and more efficient interactions in interrupted and multitasking environments requires that researchers in the area attempt to bridge the gap between these worlds. This SIG aims to stimulate discussion of the tools and methods we need as a community in order to further our understanding of interruptions and multitasking.

Two-Sided Charts for Monitoring Nonconforming Parts per Million

Abstract: In this article the author shows how to design, analyze, and evaluate the perfomance of two-sided geometric-based control charts.

Does Electoral Manipulation Discourage Voter Turnout? Evidence from Mexico

Abstract: Does electoral manipulation reduce voter turnout? The question is central to the study of political behavior in many electoral systems and to current debates on electoral reform. Nevertheless, existing evidence suggests contradictory answers. This paper clarifies the theoretical relationship between electoral manipulation and turnout by drawing some simple conceptual distinctions, and presents new empirical evidence from Mexico. The deep electoral reforms in 1990s Mexico provide a hitherto-unexploited opportunity to estimate the effect of electoral manipulation on turnout. The empirical strategy makes use of variation over time and across the states of Mexico in turnout and in electoral manipulation. The analysis finds that electoral manipulation under the PRI discouraged citizens from voting. Conceptually, the paper shows that true and reported turnout need not move in the same direction, nor respond in the same way to electoral manipulation.

Ethics and Tax Evasion: A Survey of Mexican Opinion

Abstract: Several studies on the ethics of tax evasion have been conducted in recent years. Some of them have been theoretical while others have been empirical. The present study is mostly empirical, although some theory is also discussed.

Factions with clout: Presidential cabinet coalition and policy in the Uruguayan parliament

Abstract: We investigate bill passage by party factions in Uruguay and show that those joining cabinet coalitions earn policy influence. The policy advantage of coalition is therefore not collected by the president alone, as often implied: partners acquire clout in law-making and use it to pass bills of their own and to strike deals with outside factions. Analysis of all bills initiated between 1985 and 2005 reveals that the odds of passing a bill sponsored alone by a majority cabinet faction was about 0.5, up from about 0.15 otherwise. Contingent upon the cabinet status of factions involved, the odds of co-sponsored bills conform well to patterns expected by a view that policy rewards are a fundamental part of the politics of coalition in presidentialism.

Comments on 'The End of Informality in Mexico? Fiscal Reform for Universal Social Insurance' by Arturo Anton, Fausto Hernandez and Santiago Levy

Abstract: This is a review of the paper by Anton, Hernandez and Levy (2012), which is motivated by the analysis by Santiago Levy (2008) on the impact on the labor market of subsidized programs that deviate demand from funded social insurance programs. The paper deals with the evaluation of a fiscal reform and proposes an hypothesis on the determinants of the evolution of social policy. The first issue is amenable to empirical verification, while on the second, the arguments presented are not consistent with history or with a view based on the competition of ideas.

How Serious Is Tax Evasion? A Survey of Mexican Opinion

Abstract: The goal of this study is to determine the relative seriousness of tax evasion compared to other crimes or acts that are considered to be unethical. A few other studies have examined this issue and have used methodologies similar to the one used in the present study. Karlinsky, Burton and Blanthorne (2004) measured the perceptions of students in North Carolina and California as to the seriousness of tax evasion and found that it ranked 11th out of 21 offenses. Burton, Karlinsky and Blanthorne (2005) surveyed MBA and graduate tax students from California and North Carolina as well as a few tax professors from across the USA using the same methodology and list of crimes and found the same result with regard to tax evasion; it ranked 11th out of 21 crimes. Gupta (2007) replicated the 2004 study using a New Zealand student population and found that tax evasion ranked 12th out of 21 crimes.

Photo-based narratives as communication mediators between grandparents and their children and grandchildren living abroad

Abstract: Media-sharing Web sites are facilitating modern versions of storytelling activities. This study investigates the use of photo-based narratives to support young parents who are geographically separated from their aging parents to share stories about their young children. The case analyses Malaysian young mothers living in the UK, communicating regularly with their families back home, sharing experiences living in another country, looking for parenting advice, and opening opportunities for sharing the life and development of their young children. Sixteen families participated in the study by providing access to their social networking and web spaces and participating in exercises for creating photo stories. We identified the characteristics of the mediating system serving to establish the contact between grandparents and grandchildren as well as the characteristics of the photo stories and the practices around sharing them.