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Various Sets (various + set)

Distribution by Scientific Domains
Polymers and Materials Science25%
Chemistry25%

Selected Abstracts

Dealing with Timing and Synchronization in Opportunities for Joint Activity Participation

GEOGRAPHICAL ANALYSIS, Issue 3 2010
Tijs Neutens
The ability of people to access opportunities offered by the built environment is circumscribed by various sets of space,time constraints, including the requirements to meet other persons at particular times and places to undertake activities together. While models of space,time accessibility recognize that joint activities may constrain the performance of activities in space and time, their specifications do not explicitly acknowledge the opportunities that individuals of a group have for joint activity participation. Therefore, this article focuses on joint activity participation and argues that collective activity decisions are the outcome of a complex process involving various aspects of timing, synchronization, and social hierarchy. The utility-theoretic model proposed here quantifies the extent to which opportunities can be jointly accessed by a particular group of people within a specific time period. Central to the approach are three key variables: the attractiveness of an opportunity, the time available for activity participation, and the travel time to an activity location. Because of the multiperson character of joint activities, the determination of these variables is subject to individual preferences, privileges, and power differentials within a group. Specific attention is given to how time-of-day and synchronization effects influence the opportunities accessible to a group of individuals. The impact of these factors on joint accessibility is illustrated by a real-world example of an everyday rendezvous scenario. The outcomes of a simulation exercise suggest that time-of-day and synchronization effects significantly affect the benefits that can be gained from opportunities for joint activities. La capacidad de acceso a las oportunidades que los entornos construidos (como las ciudades) ofrecen a las personas, está limitada por un conjunto diverso de restricciones espacio-temporales. Entre ellas se incluyen los requisitos para coincidir y encontrarse con otras personas en determinados momentos y lugares con el fin de realizar actividades conjuntas. Los modelos de accesibilidad comunes reconocen que las actividades conjuntas pueden limitar el ejercicio de actividades en el espacio y el tiempo. Sin embargo, sus especificaciones no reconocen explícitamente las oportunidades disponibles a todos los individuos de un grupo para participar de una actividad conjunta. Es en este contexto y dadas las limitaciones descritas que este artículo se centra en la participación de individuos en actividades conjuntas y propone el argumento que la toma de decisiones relacionadas con dichas actividades son el resultado de un proceso complejo que involucra varios aspectos de temporización (programación temporal), sincronización, y jerarquía social. El modelo teórico de utilidad que se propone aquí cuantifica el grado en que las oportunidades pueden ser evaluadas en forma conjunta por un grupo de personas particular dentro de un período de tiempo específico. El marco general propuesto por los autores se basa en tres variables fundamentales: el atractivo de una oportunidad, el tiempo disponible para la participación de la actividad, y el tiempo de desplazamiento al lugar donde se lleva a cabo actividad. Debido al carácter particular de estas actividades (que involucran múltiples participantes), la determinación de estas variables está sujeta a preferencias individuales, a privilegios y a diferencias de poder dentro de un grupo. El presente estudio además presta atención especial a la forma en la que la hora del día y los efectos de sincronización pueden influenciar la disponibilidad de oportunidades para un grupo determinado de individuos. El impacto de estos factores sobre la accesibilidad agregada de actividades conjuntas es ejemplificado por los autores mediante un caso del mundo real que utiliza escenarios de encuentros diarios entre personas. Los resultados de este ejercicio de simulación sugieren que los efectos de la hora del día y la sincronización afectan significativamente los beneficios que se pueden obtener a partir las oportunidades disponibles para acceder a y realizar actividades conjuntas. [source]

Richness patterns, species distributions and the principle of extreme deconstruction

GLOBAL ECOLOGY, Issue 2 2009
Levi Carina Terribile
ABSTRACT Aim, To analyse the global patterns in species richness of Viperidae snakes through the deconstruction of richness into sets of species according to their distribution models, range size, body size and phylogenetic structure, and to test if environmental drivers explaining the geographical ranges of species are similar to those explaining richness patterns, something we called the extreme deconstruction principle. Location, Global. Methods, We generated a global dataset of 228 terrestrial viperid snakes, which included geographical ranges (mapped at 1° resolution, for a grid with 7331 cells world-wide), body sizes and phylogenetic relationships among species. We used logistic regression (generalized linear model; GLM) to model species geographical ranges with five environmental predictors. Sets of species richness were also generated for large and small-bodied species, for basal and derived species and for four classes of geographical range sizes. Richness patterns were also modelled against the five environmental variables through standard ordinary least squares (OLS) multiple regressions. These subsets are replications to test if environmental factors driving species geographical ranges can be directly associated with those explaining richness patterns. Results, Around 48% of the total variance in viperid richness was explained by the environmental model, but richness sets revealed different patterns across the world. The similarity between OLS coefficients and the primacy of variables across species geographical range GLMs was equal to 0.645 when analysing all viperid snakes. Thus, in general, when an environmental predictor it is important to model species geographical ranges, this predictor is also important when modelling richness, so that the extreme deconstruction principle holds. However, replicating this correlation using subsets of species within different categories in body size, range size and phylogenetic structure gave more variable results, with correlations between GLM and OLS coefficients varying from ,0.46 up to 0.83. Despite this, there is a relatively high correspondence (r = 0.73) between the similarity of GLM-OLS coefficients and R2 values of richness models, indicating that when richness is well explained by the environment, the relative importance of environmental drivers is similar in the richness OLS and its corresponding set of GLMs. Main conclusions, The deconstruction of species richness based on macroecological traits revealed that, at least for range size and phylogenetic level, the causes underlying patterns in viperid richness differ for the various sets of species. On the other hand, our analyses of extreme deconstruction using GLM for species geographical range support the idea that, if environmental drivers determine the geographical distribution of species by establishing niche boundaries, it is expected, at least in theory, that the overlap among ranges (i.e. richness) will reveal similar effects of these environmental drivers. Richness patterns may be indeed viewed as macroecological consequences of population-level processes acting on species geographical ranges. [source]

Artificial neural network modeling of RF MEMS resonators

INTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 4 2004
Yongjae Lee
Abstract In this article, a novel and efficient approach for modeling radio-frequency microelectromechanical system (RF MEMS) resonators by using artificial neural network (ANN) modeling is presented. In the proposed methodology, the relationship between physical-input parameters and corresponding electrical-output parameters is obtained by combined circuit/full-wave/ANN modeling. More specifically, in order to predict the electrical responses from a resonator, an analytical representation of the electrical equivalent-network model (EENM) is developed from the well-known electromechanical analogs. Then, the reduced-order, nonlinear, dynamic macromodels from 3D finite-element method (FEM) simulations are generated to provide training, validating, and testing datasets for the ANN model. The developed ANN model provides an accurate prediction of an electrical response for various sets of driving parameters and it is suitable for integration with an RF/microwave circuit simulator. Although the proposed approach is demonstrated on a clamped-clamped (C-C) beam resonator, it can be readily adapted for the analysis of other micromechanical resonators. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14: 302,316, 2004. [source]

Determination of rank by median absolute deviation (DRMAD): a simple method for determining the number of principal factors responsible for a data matrix,

JOURNAL OF CHEMOMETRICS, Issue 1 2009
Edmund R. Malinowski
Abstract Median absolute deviation (MAD) is a well-established statistical method for determining outliers. This simple statistic can be used to determine the number of principal factors responsible for a data matrix by direct application to the residual standard deviation (RSD) obtained from principal component analysis (PCA). Unlike many other popular methods the proposed method, called determination of rank by MAD (DRMAD), does not involve the use of pseudo degrees of freedom, pseudo F -tests, extensive calibration tables, time-consuming iterations, nor empirical procedures. The method does not require strict adherence to normal distributions of experimental uncertainties. The computations are direct, simple to use and extremely fast, ideally suitable for online data processing. The results obtained using various sets of chemical data previously reported in the chemical literature agree with the early work. Limitations of the method, determined from model data, are discussed. An algorithm, written in MATLAB format, is presented in the Appendix. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Empirical-likelihood-based difference-in-differences estimators

JOURNAL OF THE ROYAL STATISTICAL SOCIETY: SERIES B (STATISTICAL METHODOLOGY), Issue 2 2008
Jing Qin
Summary., Recently there has been a surge in econometric and epidemiologic works focusing on estimating average treatment effects under various sets of assumptions. Estimation of average treatment effects in observational studies often requires adjustment for differences in pretreatment variables. Rosenbaum and Rubin have proposed the propensity score method for estimating the average treatment effect by adjusting pretreatment variables. In this paper, the empirical likelihood method is used to estimate average treatment effects on the treated under the difference-in-differences framework. The advantage of this approach is that the common marginal covariate information can be incorporated naturally to enhance the estimation of average treatment effects. Compared with other approaches in the literature, the method proposed can provide more efficient estimation. A simulation study and a real economic data analysis are presented. [source]

Studies of Adjacent Re-Entry Folds of Chains of Syndiotactic l,2-Poly(1,3-butadiene) by Molecular Mechanics Calculations

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 2 2007
Roberto Napolitano
Abstract The mode of packing and the adjacent re-entry folds of chains of syndiotactic 1,2-poly(1,3-butadiene) have been studied by molecular mechanics calculations with the use of various sets of potential functions. The results of the packing analysis indicate that the crystal grows preferentially along the [100] and [110] directions. Models of fold have been built up on an infinite ab surface completely covered by adjacent re-entry folds in the (100) and (110) planes. The results of energy minimizations show that several almost isoenergetic folds, constituted by four monomeric units, can be realized in the (100) planes, while the fold in the (110) planes has higher energy. The calculated value of the work of fold is in satisfactory agreement with that derived by crystallization kinetics reported in literature. [source]

Closed form solution of resin flow from multiple line gates in liquid composite molding

POLYMER COMPOSITES, Issue 8 2010
B. Markicevic
The resin flow from multiple line injection into a fibrous porous medium is investigated analytically and experimentally. The flow in a rectangular porous medium is created by placing two inlets: a channel along one of the domain edges, and a manifold placed in the center of the domain perpendicular to the first inlet on the top surface of the porous medium. It is demonstrated that two distinct sub-regions of the porous medium exist: inner sub-region which is filled by the liquid from the manifold, and outer sub-region that is filled by fluid from the channel. In the experiments, the following geometric parameters are varied: channel cross-sectional area, mold width, and thickness to investigate how the processing parameters influence which part of the overall domain is filled by fluid from a specific inlet. Neither fluid nor porous medium are varied throughout the study. For nonconstrained flow, an analytical model is formulated to predict the interface between the two sub-regions which is called the inner sub-region thickness. Both, implicit and explicit solutions are found, where the explicit solution is represented as inverse Lambert function. The solution relies on one physical constant which is a function of the pressure gradients and the directional permeabilities of the fibrous preform. Comparisons between experimental and analytical results reveal an excellent agreement for various sets of geometric parameters. This research should prove useful in understanding the flow in composites manufacturing when resin is injected simultaneously from multiple gates and channels. POLYM. COMPOS., 31:1434,1441, 2010. © 2009 Society of Plastics Engineers [source]

Color difference formulas: An unsatisfactory state of affairs

COLOR RESEARCH & APPLICATION, Issue 4 2008
Rolf G. Kuehni
Abstract Color difference formulas are of considerable importance in production control of colored materials, as they offer a kind of quantitative numerical method to predict perceived differences. Current formulas are based on various sets of empirical difference perception data established with different kinds of materials, under different evaluation conditions, and with different observer panels. The best current formulas predict the average of these perceptual data only with an accuracy of about 65%, a PF/3 value of about 35 (zero being optimal). This article argues that this is an unsatisfactory state of affairs and proposes the development of new uniformly established perceptual data and a new formula/system that predicts the visual results, statistically verified to represent the world-average observer, with an accuracy of 95%, a PF/3 value (or appropriate improved measure) of 5 or lower. Such a multiyear effort requires a solid experimental plan and a consortium supported by Government and industry to achieve its goal. © 2008 Wiley Periodicals, Inc. Col Res Appl, 33, 324,329, 2008. [source]