Improving the power of hypothesis tests in sparse contingency tables

When analyzing data in contingency tables it is frequent to deal with sparse data, particularly when the sample size is small relative to the number of cells. Most analyses of this kind are interpreted in an exploratory manner and even if tests are performed, little attention is paid to statistical power. This paper proposes a method we call redundant procedure, which is based on the union–intersection principle and increases test power by focusing on specific components of the hypothesis. This method is particularly helpful when the hypothesis to be tested can be expressed as the intersections of simpler models, such that at least some of them pertain to smaller table marginals. This situation leads to working on tables that are naturally denser. One advantage of this method is its direct application to (chain) graphical models. We illustrate the proposal through simulations and suggest strategies to increase the power of tests in sparse tables. Finally, we demonstrate an application to the EU-SILC dataset

Systematic literature reviews. Case of study: Modeling of a rubbing pair for wear purpose

El daño progresivo que se produce en la superficie de un componente como resultado de su movimiento relativo a las partes adyacentes de trabajo, tiene profundas consecuencias económicas que implican no sólo los costes de sustitución, sino también los gastos relacionados con la inactividad de la máquina y pérdida de producción. En este artículo se presenta la implementación de un método para la revisión sistemática de literatura con el fin de establecer las metodologías con las que se aborda el modelamiento del proceso de desgaste entre sólidos deslizantes y el estado actual de dicha temática de investigación. La revisión sistemática de literatura es una nueva opción en la recopilación y análisis de bibliografía en ingeniería. Con esta metodología de búsqueda, recopilación, clasificación y análisis de información se logra reducir el tiempo y el esfuerzo para el planteamiento de una problemática de investigación. En el presente artículo se analizaron 50 estudios que cumplían las restricciones de la metodología de búsqueda, además se concluye que el modelamiento de las dinámicas termomecánicas presentes en un par deslizante no es aún un tema consolidado, que no se identifican con claridad cuáles son las variables que relacionan de forma directa la generación de fenómenos térmicos en el proceso y la variación de la tasa de desgaste.Abstract: The progressive damage which appears at a component surface as a result of its relative motion with respect to the adjacent working parts, has deep economic consequences which imply not only the replacement costs, but also the expenses related to the stopping of the machine and the losses of the manufacturing process. This paper presents the implementation of a method for systematic reviewing of the literature aimed to stablishing the suitable methodologies for abording the modelling of the wearing process between sliding pieces, and the current state of the research related to such a subject. Systematic literature reviewing is an alternative for collecting and analyzing of engineering-related bibliography. With such a methodology, which is aimed to searching, collecting, classification, and analysis of information, it is possible to reduce time and effort when posing a research problem. This work surveyed about fifty papers, which meet the constraints related to the searching methodology. Besides, it is concluded that the modeling of the thermodynamic phenomena related to sliding pieces is far from being a consolidated subject, and that the identification of the involved variables and the relationship between the thermal phenomena and the changing of the wearing rate is not clear yet

Energy Consumption Analysis Of Machining Centers Using Bayesian Analysis And Genetic Optimization

Responding to the current urgent need for low carbon emissions and high efficiency in manufacturing processes, the relationships between three different machining factors (depth of cut, feed rate, and spindle rate) on power consumption and surface finish (roughness) were analysed by applying a Bayesian seemingly unrelated regressions (SUR) model. For the analysis, an optimization criterion was established and minimized by using an optimization algorithm that combines evolutionary algorithm methods with a derivative-based (quasi-Newton) method to find the optimal conditions for energy consumption that obtains a good surface finish quality. A Bayesian ANOVA was also performed to identify the most important factors in terms of variance explanation of the observed outcomes. The data were obtained from a factorial experimental design performed in two computerized numerical control (CNC) vertical machining centers (Haas UMC-750 and Leadwell V-40iT). Some results from this study show that the feed rate is the most influential factor in power consumption, and the depth of cut is the factor with the stronger influence on roughness values. An optimal operational point is found for the three factors with a predictive error of less than 0.01% and 0.03% for the Leadwell V-40iT machine and the Haas UMC-750 machine, respectively

On the tuning of the lagrangian parameters in a uniform structure in adaptative robot control

In this paper the application of "uniform structures" formerly introduced for the Hamiltonian description of robtos is investigated in the case of a SCARA within the frames of the Lagrangian model. This model does not suffer from measurability problems of the Hamiltonian one. Via simulation it was found that this simple method can improve the control of an imperfectly modeled system under unmodeled environmental interaction. It uses the Lie parameters of the Orthogonal Group and the "Sliding Simplex Algorithm" for the on-line tuning the parameters in the uniform structures. This method is very similar to the learning process of the artificial neural Networks. To evade the problem of local optima tuning starts from the estimtaed vicinity of the Global Optimum at the begining. It is shown that a fast enough tuning can "stick" in this optimum and it propagates together with it in time as the local dynamics of the system is changes in time.N/

An international network to monitor the structure, composition and dynamics of Amazonian forests (RAINFOR)

The Amazon basin is likely to be increasingly affected by environmental changes: higher temperatures, changes in precipitation, CO2 fertilization and habitat fragmentation. To examine the important ecological and biogeochemical consequences of these changes, we are developing an international network, RAINFOR, which aims to monitor forest biomass and dynamics across Amazonia in a co-ordinated fashion in order to understand their relationship to soil and climate. The network will focus on sample plots established by independent researchers, some providing data extending back several decades. We will also conduct rapid transect studies of poorly monitored regions. Field expeditions analysed local soil and plant properties in the first phase (2001–2002). Initial results suggest that the network has the potential to reveal much information on the continental-scale relations between forest and environment. The network will also serve as a forum for discussion between researchers, with the aim of standardising sampling techniques and methodologies that will enable Amazonian forests to be monitored in a coherent manner in the coming decades

Intraoperative frozen section analysis for breast-conserving therapy in 1016 patients with breast cancer

Abstract Objective: We evaluate the number of surgical two-stage procedures after FSA during breast-conserving therapy (clinical false negative result of FSA) and investigate the influence of microcalcifications, small tumour diameter, neoadjuvant therapy and preoperative biopsy on the clinical false negative rate of FSA. Subjects: We retrospectively examined 1016 patients after intraoperative FSA during breast-conserving therapy for breast cancer operated between 1995 and 2001 at the Medical University Vienna. Results: Only 9% of all patients had to undergo a two-stage operation due to a false negative intraoperative FSA result. The annual local recurrence rate was 1.2% in all patients with no difference between one-and two-stage operated patients. In situ and pT1 lesions were similarly distributed between one-stage and two-stage operated patients. The use of neoadjuvant therapy and stereotactic biopsy (reflecting non-palpable lesions and microcalcifications) were significantly predictive for a false negative FSA result. The use of a preoperative core biopsy, however, reduced the necessity of performing a two-stage operation. Conclusion: Our study demonstrates that FSA leads to a low rate of two-stage operations. Small lesions and microcalcifications as well as the occurrence of intraductal cancer cells and neoadjuvant therapy increased while preoperative core biopsy reduced the false negative rate of FSA. Overall local recurrence rates after FSA were acceptable

Diameters in preferential attachment models

In this paper, we investigate the diameter in preferential attachment (PA-) models, thus quantifying the statement that these models are small worlds. The models studied here are such that edges are attached to older vertices proportional to the degree plus a constant, i.e., we consider affine PA-models. There is a substantial amount of literature proving that, quite generally, PA-graphs possess power-law degree sequences with a power-law exponent \tau>2. We prove that the diameter of the PA-model is bounded above by a constant times \log{t}, where t is the size of the graph. When the power-law exponent \tau exceeds 3, then we prove that \log{t} is the right order, by proving a lower bound of this order, both for the diameter as well as for the typical distance. This shows that, for \tau>3, distances are of the order \log{t}. For \tau\in (2,3), we improve the upper bound to a constant times \log\log{t}, and prove a lower bound of the same order for the diameter. Unfortunately, this proof does not extend to typical distances. These results do show that the diameter is of order \log\log{t}. These bounds partially prove predictions by physicists that the typical distance in PA-graphs are similar to the ones in other scale-free random graphs, such as the configuration model and various inhomogeneous random graph models, where typical distances have been shown to be of order \log\log{t} when \tau\in (2,3), and of order \log{t} when \tau>3