An Atypical Survey of Typical-Case Heuristic Algorithms

Heuristic approaches often do so well that they seem to pretty much always give the right answer. How close can heuristic algorithms get to always giving the right answer, without inducing seismic complexity-theoretic consequences? This article first discusses how a series of results by Berman, Buhrman, Hartmanis, Homer, Longpr\'{e}, Ogiwara, Sch\"{o}ening, and Watanabe, from the early 1970s through the early 1990s, explicitly or implicitly limited how well heuristic algorithms can do on NP-hard problems. In particular, many desirable levels of heuristic success cannot be obtained unless severe, highly unlikely complexity class collapses occur. Second, we survey work initiated by Goldreich and Wigderson, who showed how under plausible assumptions deterministic heuristics for randomized computation can achieve a very high frequency of correctness. Finally, we consider formal ways in which theory can help explain the effectiveness of heuristics that solve NP-hard problems in practice.Comment: This article is currently scheduled to appear in the December 2012 issue of SIGACT New

The informal politics of rural livelihoods in Northern Thailand: A case study of Chiang Mai’s songthaeo drivers

This thesis adopts a livelihoods perspective to explore the historical transition and contemporary lives of a group of northern Thai villagers who exited village-based farm work in the 1970s and 1980s to enter the emerging public transport sector of Thailand’s northern capital – Chiang Mai. Through an ethnographic study of these songthaeo drivers, the thesis draws on the story of the drivers’ shift from farm to urban-based, wage labour to interrogate dominant portraits of rural Thai history and to explore the politics through which the drivers have forged and consolidated comparatively healthy livings. In so doing, the thesis contends that rather than a monochromatic history of peasant economic passivity or political resistance to state intervention, the drivers demonstrate an adaptive, aspiration-oriented agency in pursuing enhanced livelihoods. Further, they symbolise a rural politics of actively seeking to cultivate connections with state actors identified as supporting desired exit options away from the land and into more productive labour fields. The thesis proceeds to describe the labour-world ‘invented’ by Chiang Mai’s songthaeo drivers, in terms of both its relatively stable economic dimensions and its familiar rural cultural sociality. It notes that despite the generation of modestly healthy incomes, the drivers remain discontent with their economic position. Describing their livelihoods in desultory terms, the drivers’ pessimistic outlook reflects the ‘status games’ in which they are implicated, indicative of comparisons with men from the professional ranks, and demonstrative of anxieties arising from a new historical epoch marked by the potentially disruptive realities of the Asian Economic Community. To negotiate the new economic era now dawning upon them, and to defend their livelihoods and familiar way of life, the drivers engage in a largely informal mode of politics. Reflective of what Partha Chatterjee has termed ‘political society’, this politics draws on traditional masculine modes of rural Thai power, now deployed within a modern setting of bureaucracy and electoral competition. Centred on the figures of the Presidents of the two largest driving Cooperatives, this politics operates in a murky world of connections, influence, threats, administrative innovations and legal exceptions. Rather than seeking to transform the broader political environment however, this politics is narrowly and parochially focussed, attempting to maintain the status quo rather than fundamentally change it. For the drivers, defending their livelihoods takes precedence over competing political visions of modernising the city or appeasing the city’s growing middle-class residents. As such, the drivers are representative of multiple facets of contemporary Thailand, bridging the formal and informal, rural and the urban, the traditional and the emerging modern within a city itself caught within these often competing dynamics

Polyphase-Coded FM Waveform Optimization within a LINC Transmit Architecture

Linear amplification using nonlinear components (LINC) is a design approach that can suppress the effects of the nonlinear distortion introduced by the transmitter. A typical transmitter design requirement is for the high power amplifier to be operated in saturation. The LINC approach described here employs a polyphase-coded FM (PCFM) waveform that is able to overcome this saturated amplifier distortion to greatly improve the spectral containment of the transmitted waveform. A two stage optimization process involving simulation and hardware-in-the-loop routines is used to create the final PCFM waveform code

A Stark-Effect Modulator for CO\u3csub\u3e2\u3c/sub\u3e Laser Free-Space Communications

A Stark-effect modulator prototype has been designed and constructed to transmit an RF signal upon an infrared carrier wave produced by a CO2 laser. The anticipated future use of this prototype will be to integrate it into an all-weather long-wavelength infrared (LWIR) free-space communication link. This communication system is expected to be capable of operation at 2.5 Gbits/sec over a range of \u3e6 kilometers. The Stark-effect modulator prototype is ideal to replace existing microwave and radio communication links used currently. Also, the Stark-effect modulator is a better choice than electro-optic crystal modulators and acousto-optic Bragg cell modulators because it operates at higher frequencies and is less costly. The Stark-effect occurs when an electric field is applied to a gas molecule that has a substantial polarizability. The electric field changes the spacing of the gas molecule energy levels. The gas molecule used is deuterated ammonia (NH2D) because it has a molecular absorption resonance near the 10.59 micron wavelength line of the CO2 laser emission. The modulator is a dielectric waveguide that is constructed of borosilicate glass, measuring 36-cm in length and having an inner diameter of 1.8-mm and an outer diameter of 3-mm. The modulator has been characterized successfully, with an experimental result agreeing with a predicted model. For the first time, an RF signal has been successfully applied to the Stark-effect modulator and successfully transmitted and detected by a nearby receiver

Gun Related Youth Violence: Fear of Victimization versus the Influence of Significant Others

Differential association/social learning theories have received considerable empirical support as an explanation of participation in delinquent acts, including violent delinquency (Heimer 1997). More recently, and primarily as a result of highly publicized school shootings in suburban high schools, fear of crime and victimization have received attention as motivators of gun-carrying and gun violence. These phenomena are generally not examined in unison, however, leaving open the question of their relative role as a cause of gun carrying and violence amongst youth. The current research project addresses this question. A major strength of the current research is the adoption of multiple measures of each perspective. We examine the impact of the attitudes and behaviors of family members and friends on the gun-related behaviors of a sample of male high school age youth. Moreover, we adopt a variety of measures of fear of victimization and actual victimization in schools, on school grounds, and in neighborhoods. The primary goal of this research is to enhance our understanding of the multiplicity of factors that contribute to youthful involvement with firearms and violent delinquency

Gun Related Youth Violence: Fear of Victimization versus the Influence of Significant Others

Differential association/social learning theories have received considerable empirical support as an explanation of participation in delinquent acts, including violent delinquency (Heimer 1997). More recently, and primarily as a result of highly publicized school shootings in suburban high schools, fear of crime and victimization have received attention as motivators of gun-carrying and gun violence. These phenomena are generally not examined in unison, however, leaving open the question of their relative role as a cause of gun carrying and violence amongst youth. The current research project addresses this question. A major strength of the current research is the adoption of multiple measures of each perspective. We examine the impact of the attitudes and behaviors of family members and friends on the gun-related behaviors of a sample of male high school age youth. Moreover, we adopt a variety of measures of fear of victimization and actual victimization in schools, on school grounds, and in neighborhoods. The primary goal of this research is to enhance our understanding of the multiplicity of factors that contribute to youthful involvement with firearms and violent delinquency

Gun Related Youth Violence: Fear of Victimization versus the Influence of Significant Others

Differential association/social learning theories have received considerable empirical support as an explanation of participation in delinquent acts, including violent delinquency (Heimer 1997). More recently, and primarily as a result of highly publicized school shootings in suburban high schools, fear of crime and victimization have received attention as motivators of gun-carrying and gun violence. These phenomena are generally not examined in unison, however, leaving open the question of their relative role as a cause of gun carrying and violence amongst youth. The current research project addresses this question. A major strength of the current research is the adoption of multiple measures of each perspective. We examine the impact of the attitudes and behaviors of family members and friends on the gun-related behaviors of a sample of male high school age youth. Moreover, we adopt a variety of measures of fear of victimization and actual victimization in schools, on school grounds, and in neighborhoods. The primary goal of this research is to enhance our understanding of the multiplicity of factors that contribute to youthful involvement with firearms and violent delinquency

Calibration of Computational Models with Categorical Parameters and Correlated Outputs via Bayesian Smoothing Spline ANOVA

It has become commonplace to use complex computer models to predict outcomes in regions where data does not exist. Typically these models need to be calibrated and validated using some experimental data, which often consists of multiple correlated outcomes. In addition, some of the model parameters may be categorical in nature, such as a pointer variable to alternate models (or submodels) for some of the physics of the system. Here we present a general approach for calibration in such situations where an emulator of the computationally demanding models and a discrepancy term from the model to reality are represented within a Bayesian Smoothing Spline (BSS) ANOVA framework. The BSS-ANOVA framework has several advantages over the traditional Gaussian Process, including ease of handling categorical inputs and correlated outputs, and improved computational efficiency. Finally this framework is then applied to the problem that motivated its design; a calibration of a computational fluid dynamics model of a bubbling fluidized which is used as an absorber in a CO2 capture system