Graphical LASSO Based Model Selection for Time Series

We propose a novel graphical model selection (GMS) scheme for high-dimensional stationary time series or discrete time process. The method is based on a natural generalization of the graphical LASSO (gLASSO), introduced originally for GMS based on i.i.d. samples, and estimates the conditional independence graph (CIG) of a time series from a finite length observation. The gLASSO for time series is defined as the solution of an l1-regularized maximum (approximate) likelihood problem. We solve this optimization problem using the alternating direction method of multipliers (ADMM). Our approach is nonparametric as we do not assume a finite dimensional (e.g., an autoregressive) parametric model for the observed process. Instead, we require the process to be sufficiently smooth in the spectral domain. For Gaussian processes, we characterize the performance of our method theoretically by deriving an upper bound on the probability that our algorithm fails to correctly identify the CIG. Numerical experiments demonstrate the ability of our method to recover the correct CIG from a limited amount of samples

Concurrent evolution of feature extractors and modular artificial neural networks

Artificial Neural Networks (ANNs) are commonly used in both academia and industry as a solution to challenges in the pattern recognition domain. However, there are two problems that must be addressed before an ANN can be successfully applied to a given recognition task: ANN customization and data pre-processing. First, ANNs require customization for each specific application. Although the underlying mathematics of ANNs is well understood, customization based on theoretical analysis is impractical because of the complex interrelationship between ANN behavior and the problem domain. On the other hand, an empirical approach to the task of customization can be successful with the selection of an appropriate test domain. However, this latter approach is computationally intensive, especially due to the many variables that can be adjusted within the system. Additionally, it is subject to the limitations of the selected search algorithm used to find the optimal solution. Second, data pre-processing (feature extraction) is almost always necessary in order to organize and minimize the input data, thereby optimizing ANN performance. Not only is it difficult to know what and how many features to extract from the data, but it is also challenging to find the right balance between the computational requirements for the preprocessing algorithm versus the ANN itself. Furthermore, the task of developing an appropriate pre-processing algorithm usually requires expert knowledge of the problem domain, which may not always be available. This paper contends that the concurrent evolution of ANNs and data pre-processors allows the design of highly accurate recognition networks without the need for expert knowledge in the application domain. To this end, a novel method for evolving customized ANNs with correlated feature extractors was designed and tested. This method involves the use of concurrent evolutionary processes (CEPs) as a mechanism to search the space of recognition networks. In a series of controlled experiments the CEP was applied to the digit recognition domain to show that the efficacy of this method is in-line with results seen in other digit recognition research, but without the need for expert knowledge in image processing techniques for digit recognition

The Effects of Community-Building on Achievement, Motivation, and Engagement in Undergraduate Mathematics

This 2 x 2 quasi-experimental study examined the effects of pedagogical method (i.e., direct instruction vs. 5E inquiry) and intentional community-building (i.e., absence or presence) on undergraduate student (N = 103) motivation, engagement, and achievement in mathematics. Conditions were randomly assigned to one of four different College Algebra classes with a one-time occurrence and taught by a trained expert teacher. Findings indicated that intentional community-building – regardless of pedagogical method – had the strongest effects on students’ motivation, engagement, and achievement. Although no differing pedagogical effects were discovered (most likely due to the one-time implementation of the lesson formats), the findings provide evidence for the necessity of community-building efforts -- an aspect of education that is often overlooked in the undergraduate STEM classroom

Xorbit/CLASP links dynamic microtubules to chromosomes in the Xenopus meiotic spindle

A family of microtubule (MT)-binding proteins, Orbit/multiple asters/cytoplasmic linker protein–associated protein, has emerged as an important player during mitosis, but their functional mechanisms are poorly understood. In this study, we used meiotic egg extracts to gain insight into the role of the Xenopus laevis homologue Xorbit in spindle assembly and function. Xorbit immunodepletion or its inhibition by a dominant-negative fragment resulted in chromosome alignment defects and aberrant MT structures, including monopolar and small spindles. Xorbit-depleted extracts failed to nucleate MTs around chromatin-coated beads, indicating its essential requirement for spindle assembly in the absence of centrosomes and kinetochores. Xorbit's MT stabilizing effect was most apparent during anaphase, when spindle MTs depolymerized rapidly upon Xorbit inhibition. Biochemical interaction between a COOH-terminal Xorbit fragment and the kinetochore-associated kinesin centromeric protein E may contribute to Xorbit's role in chromosome congression. We propose that Xorbit tethers dynamic MT plus ends to kinetochores and chromatin, providing a stabilizing activity that is crucial for spindle assembly and chromosome segregation

An Agent-based Model to Evaluate Interventions on Online Dating Platforms to Decrease Racial Homogamy

Perhaps the most controversial questions in the study of online platforms today surround the extent to which platforms can intervene to reduce the societal ills perpetrated on them. Up for debate is whether there exist any effective and lasting interventions a platform can adopt to address, e.g., online bullying, or if other, more far-reaching change is necessary to address such problems. Empirical work is critical to addressing such questions. But it is also challenging, because it is time-consuming, expensive, and sometimes limited to the questions companies are willing to ask. To help focus and inform this empirical work, we here propose an agent-based modeling (ABM) approach. As an application, we analyze the impact of a set of interventions on a simulated online dating platform on the lack of long-term interracial relationships in an artificial society. In the real world, a lack of interracial relationships are a critical vehicle through which inequality is maintained. Our work shows that many previously hypothesized interventions online dating platforms could take to increase the number of interracial relationships from their website have limited effects, and that the effectiveness of any intervention is subject to assumptions about sociocultural structure. Further, interventions that are effective in increasing diversity in long-term relationships are at odds with platforms' profit-oriented goals. At a general level, the present work shows the value of using an ABM approach to help understand the potential effects and side effects of different interventions that a platform could take

Gender Differences in Participation and Reward on Stack Overflow

Programming is a valuable skill in the labor market, making the underrepresentation of women in computing an increasingly important issue. Online question and answer platforms serve a dual purpose in this field: they form a body of knowledge useful as a reference and learning tool, and they provide opportunities for individuals to demonstrate credible, verifiable expertise. Issues, such as male-oriented site design or overrepresentation of men among the site's elite may therefore compound the issue of women's underrepresentation in IT. In this paper we audit the differences in behavior and outcomes between men and women on Stack Overflow, the most popular of these Q&A sites. We observe significant differences in how men and women participate in the platform and how successful they are. For example, the average woman has roughly half of the reputation points, the primary measure of success on the site, of the average man. Using an Oaxaca-Blinder decomposition, an econometric technique commonly applied to analyze differences in wages between groups, we find that most of the gap in success between men and women can be explained by differences in their activity on the site and differences in how these activities are rewarded. Specifically, 1) men give more answers than women and 2) are rewarded more for their answers on average, even when controlling for possible confounders such as tenure or buy-in to the site. Women ask more questions and gain more reward per question. We conclude with a hypothetical redesign of the site's scoring system based on these behavioral differences, cutting the reputation gap in half

Group Fairness for Content Creators: the Role of Human and Algorithmic Biases under Popularity-based Recommendations

The Creator Economy faces concerning levels of unfairness. Content creators (CCs) publicly accuse platforms of purposefully reducing the visibility of their content based on protected attributes, while platforms place the blame on viewer biases. Meanwhile, prior work warns about the “rich-get-richer” effect perpetuated by existing popularity biases in recommender systems: Any initial advantage in visibility will likely be exacerbated over time. What remains unclear is how the biases based on protected attributes from platforms and viewers interact and contribute to the observed inequality in the context of popularity-biased recommender systems. The difficulty of the question lies in the complexity and opacity of the system. To overcome this challenge, we design a simple agent-based model (ABM) that unifies the platform systems which allocate the visibility of CCs (e.g., recommender systems, moderation) into a single popularity-based function, which we call the visibility allocation system (VAS). Through simulations, we find that although viewer homophilic biases do alone create inequalities, small levels of additional biases in VAS are more harmful. From the perspective of interventions, our results suggest that (a) attempts to reduce attribute-biases in moderation and recommendations should precede those reducing viewers’ homophilic tendencies, (b) decreasing the popularity-biases in VAS decreases but not eliminates inequalities, (c) boosting the visibility of protected CCs to overcome viewers’ homophily with respect to one fairness metric is unlikely to produce fair outcomes with respect to all metrics, and (d) the process is also unfair for viewers and this unfairness could be overcome through the same interventions. More generally, this work demonstrates the potential of using ABMs to better understand the causes and effects of biases and interventions within complex sociotechnical systems

A snorkel trail based on reef condition and visitor perception as a management tool for a threatened shallow water reef in Dahab (South Sinai, Egypt)

Der Küstentourismus am Süd Sinai, im Besonderen in Sharm El-Sheikh, gefolgt von Dahab und Nuweiba, unterliegt einem jährlichen Wachstum von 42%, wobei auch der Anteil an Schnorlern zunimmt (40% in 2003). In dieser Studie wurden die Auswirkungen von Schnorchelaktivitäten auf ein Seichtwasser-Korallenriff am äußeren Rand der ‚Lagune’ in Dahab untersucht. Anhand der Ergebnisse wird der Plan für einen Unterwasserlehrpfad für Schnorchler als Management-Werkzeug für dieses gebiet erstellt. Korallenbedeckung, Substratzusammensetzung, partielle Mortalität und Korallenbruchvorkommen von verzweigt wachsenden Korallen wurden mittels ‚point-intercept-sampling’ Methode sowohl am Riffach als auch am Rückriff erhoben. Wo die meisten Besucher schnorchelten dominierten verzweigt wachsende Korallen das Riff (76,2% von 122 Korallenkolonien). Am Rückriff 81% der gebrochenen Kolonien verzweigt wachsend. Partielle Mortalität wurde bei 50% von Acropora, 80% von Millepora sowie Stylophora und 90% von Pocillopora Kolonien festgestellt. Zusätzlich halfen standardisierte Fragebögen die sozioökonomischen Charakteristika, Bedürfnisse und Meinungen bezüglich riffökologischer Fortbildung und Schnorchel-Training der Besucher zu eruieren. Mit abstand als häufigste Motivation für Schnorcheln und Tauchen wurde ‚Naturerleben’ angegeben (96,5%). Schnorchel- und Tauch- Erfahrung der Besucher zeigte sich als relative gering. 48,7% der Schnorchler stuften sich als Beginner ein, 15,1% der Taucher waren Neuanfänger und 27,7% der Taucher hatten ein Open-Water-Brevet (den Anfängerschein innerhalb der Tauchausbildung). Das Interesse für Fortbildung im bereich Riffökologie und Schnorchelfertigkeiten war groß und die Mehrheit der Befragen war gewillt eine entsprechende Gebühr für den geführten Besuch an einem Unterwasser-Lehrpfad zu zahlen (62,8% waren bereit mehr als 10€ zu zahlen). Die unerfahrenen Schnorchler und Taucher, die eigentliche Zielgruppe für Fortbildung und Training, zeigten die größte Bereitschaft solch ein Managementprojekt auch finanziell zu unterstützen. Somit formt diese Gruppe an Besuchern eine essenzielle Einnahmequelle für einen Rifflehrpfad. Die massiven Riffschäden, hauptsächlich verursacht durch Schnorcheln und destruktive Fischereimethoden, sowie das Interesse am Naturerleben unter den Besuchern unterstreichen den Bedarf von Managementaktionen zum Schutz des Riffs. Eine Strategie ist die Errichtung eines Rifflehrpfades entlang des Rückriffs (als ‚Ökotourismus-Zone’ nutzbar), wobei die Urlaubsaktivitäten auf das Rückriff und weniger sensible Bereiche umgelenkt werden. Die Benutzung des Lehrpfades erfolgt in kleinen geführten gruppen Gruppen, die nach einem ausführlichen Briefing und Schnorcheltraining von professionell ausgebildeten Guides begleitet werden. Gleichzeitig wird das seichte und sensible Riffdach vor destruktiver Fischerei und touristischer Nutzung geschützt. Zusätzlich können Künstliche Riffstrukturen den Pfad ergänzen und Ausweichmöglichkeiten bei Niedrigwasserstand bieten.Coastal tourism in the South Sinai, especially in Sharm El-Sheikh, followed by Dahab and Nuweiba, has experienced a growth of 42% per year (PERSGA, 2001) whereby an increasing number of visitors are snorkelers (40% in 2003). This study investigated the ecological impact of snorkelers visiting a shallow water reef at the outside of the ‘Lagoon’ in Dahab. The results are used to frame a plan for an underwater nature snorkelling trail as a reef management tool in this area. Benthic communities, hard coral cover, partial mortality and breakage frequencies of branching hard corals were examined using the point intercept sampling method on the reef flat (0.5m water depth) and back reef (1.0m water depth). In the area where most snorkelers occurred branching growth forms were in the absolute majority of hard corals with 76.2% of 122 colonies in total. On the back reef, 81% of the broken colonies were branching species. Partial mortality frequency was found in 50% of Acropora, 80% of Millepora and Stylophora and 90% of Pocillopora colonies. In addition standardized questionnaires helped to determine visitor’s socioeconomic and personal characteristics, requirements and perceptions about further education in reef ecology and skill training related to snorkelling, SCUBA-diving and visiting a reef nature trail in Dahab. ‘Nature’ (96.5%) was by far the highest motivation for snorkelling and diving. The sorkel- and dive-experience in tropical seas was relative low (48.7% snorkelling beginners, 15.1% novice SCUBA-divers, 27.7% divers at an Open-Water certification level). The interest in further education about reef ecology and skill training was high, and respondents were willing to pay appropriate fees for a guided snorkel trip at an underwater nature trail (62.8% were prepared to pay more than 10€). The less experienced snorkelers and divers who formed the target group for further information and education about reef ecology, threats to the reef and skill training, were also the ones most prepared to financially support such a management project and therefore form an important source of income. The heavy impact on the shallow water reef, mostly caused by snorkelers and local fishermen, and the high interest in nature amongst the respondents, highlight the need for management action. Two strategies include implementing a reef nature trail at the back reef, restricting the recreational use to the nature trail and less sensitive areas while protecting the shallow reef flat, excluding destructive fishing and recreational use. The nature trail at the back reef can be used as ‘Ecotourism Zone’, where access is restricted to small groups of snorkelers led by certified tour guides. Impacts, like physical contact and sediment resuspension, would be minimized by requiring that all guides provide prior briefings and skill training. In addition artificial structures can complete the trail and offer the possibility to switch to deeper areas when the circumstances do not allow snorkelling along the natural back reef (i.e. during low tide)