Skip to main content

miguel pineda

Followers

9

Following

1

Public Views

Address: San Salvador, San Salvador, El Salvador

less

Universitat de Girona

Gustau Aguilella

Pablo Garcia Borja

Universitat Jaume I de Castelló

Pablo Garcia Borja

Joan J. Fornós

Universitat de les Illes Balears

Interests

Uploads

Papers by miguel pineda

El Fartet (Aphanius iberus) al Baix Ter (NE de Catalunya): Mètodes de monitoratge, ús de l'hàbitat i impacte de la gambúsia

Dins d'un projecte Life-Natura es van construir a la costa baixempordanesa nous hàbitats (llacune... more Dins d'un projecte Life-Natura es van construir a la costa baixempordanesa nous hàbitats (llacunes de la Pletera) per a l'expansió del fartet (Aphanius iberus), els quals van ser repoblats a partir d'individus procedents de la bassa de Fra Ramon a finals del 2002. Dos anys després es va detectar la presència de gambúsia (Gambusia holbrooki) a les noves llacunes, però no a Fra Ramon. S'han comparat diferents mètodes de captura passiva per al monitoratge de poblacions de fartet. Tot i que les nanses de malla petita van ser el mètode més eficient, només es van agafar individus immadurs amb ampolles de plàstic, que, a més a més, van capturar un rang més ampli de mides. Els fartets van seleccionar positivament posicions properes al fons dins de la columna d'aigua, així com microhàbitats amb presència de refugis (com ara herbassars de Ruppia). Mentre que els individus immadurs es van trobar sobretot en zones somes, els adults es van distribuir de manera homogènia a les diferents profunditats. L'abundància de fartet va augmentar de l'abril al setembre del 2005 a Fra Ramon, per la incorporació de reclutes de l'any. En canvi, a les llacunes de la Pletera, on les gambúsies van suposar el 95 % de les captures, es va detectar una davallada de la població en aquest període. Aquestes observacions apunten l'existència de problemes durant el període reproductiu del fartet i un procés de desplaçament ecològic com a conseqüència d'un increment de la població de gambúsia.

Automatic nonuniform random variate generation

Computational Statistics, 2004

Random variate generation is an important tool in statistical computing. Many programms for simul... more Random variate generation is an important tool in statistical computing. Many programms for simulation or statistical computing (e.g. R) provide a collection of random variate generators for many standard distributions. However, as statistical modeling has become more sophisticated there is demand for larger classes of distributions. Adding generators for newly required distribution seems not to be the solution to this problem. Instead so called automatic (or black-box) methods have been developed in the last decade for sampling from fairly large classes of distributions with a single piece of code. For such algorithms a data about the distributions must be given; typically the density function (or probability mass function), and (maybe) the (approximate) location of the mode. In this contribution we show how such algorithms work and suggest an interface for R as an example of a statistical library.

The Total Survey Error Approach: a Guide to the New Science of Survey Research by H. F. Weisberg

Journal of The Royal Statistical Society Series A-statistics in Society, 2006

This book is concerned with medical diagnostic and prognostic tests, in particular those relying ... more This book is concerned with medical diagnostic and prognostic tests, in particular those relying on a single measurement. It mainly addresses the questions 'What are the test's characteristics?', 'How does it compare with the existing test?' and 'To what extent is its accuracy affected by external factors?'. The scene is set nicely in the opening chapter, with descriptions of some studies where diagnostic tests have been assessed and preliminary discussion about the design of such studies. The next two chapters are concerned with tests with binary outcomes, i.e. the subject simply tests positively or negatively. The various criteria for assessing tests are introduced: the true and false positive fraction (which the author prefers to sensitivity and specificity), positive and negative predictive values and likelihood ratios. Inference results are given for individual tests and for comparing tests (both paired and unpaired designs). Regression models are introduced for assessing how external factors (e.g. the age of the patient) may affect the characteristics of a test. The next three chapters are concerned with tests having quantitative or ordinal outcomes. The receiver operating characteristic curve is introduced along with variants such as the parametric binormal curve. There is again an extensive discussion of inference and the modelling of the effects of external factors. Later chapters include how to deal with situations where the 'gold standard' (for determining disease or no disease) is only used on a subset of patients or where it is fallible, the phases that are involved in the development of a test (up to five separate studies being recommended) and brief mention of meta-analysis, incorporating the time till disease develops into the analysis and combining test results. There are accompanying Web pages which include the data sets, Stata programs and errata, but not, unfortunately, solutions to the exercises at the end of chapters. This is a well-written book, my only concern being that some chapters resemble review papers, with a wide range of techniques being mentioned but none being fully developed. For this reason, I would not recommend the text for students. This aside, it is a clear and authoritative work which will be invaluable for anyone trying to establish a new diagnostic test.

Optimal estimation of population variance using equilibrated stratified sampling from infinite populations

Journal of The Korean Statistical Society, 2008

A class of unbiased estimators of the population variance is proposed when the coefficient of var... more A class of unbiased estimators of the population variance is proposed when the coefficient of variation is known for each stratum. The technique of equilibrated stratification is used. It is shown that, with optimum allocation, the variance of the suggested estimator for sufficiently large sample size is less than that of the classical minimum variance unbiased estimator under distributionfree setting. Other classes of estimators are also given with similar or better practical properties.

Estimation in Surveys With Nonresponse. Carl-Erik Sarndal and Sixten Lundstrom

The performance of a γ-Al 2O 3 catalyst for the Claus reaction at low temperature in a fixed bed reactor

Applied Catalysis A-general, 1996

Using a kinetic equation derived from results obtained in a differential reactor, a grain model w... more Using a kinetic equation derived from results obtained in a differential reactor, a grain model with variable properties was applied to calculate the global reaction rate for a particle. Furthermore, the theoretical model was developed to explain the performance of alumina as a catalyst for the Claus reaction at low temperature in an integral fixed bed reactor. The results were in good agreement with the experimental ones. The theoretical model was used to study the influence of the most significative parameters involved and to predict the catalyst performance in conditions of practical interest. It was shown that high H2S conversions and efficiencies of the catalyst were to be expected using highly porous materials and small particle sizes. These are the most important parameters for practical utilization.

Modelling of performance of zinc ferrites as high-temperature desulfurizing sorbents in a fixed-bed reactor

Fuel, 1997

... (Keywords: hydrogen sulfide removal; zinc ... Both experimental (Figure 6) and theoretical re... more

The effect of surface and thermal treatments on γ-Al 2O 3 as a catalyst of the claus reaction at low temperature

Applied Catalysis A-general, 1997

y-AI203 was chemically or heat treated to modify its behavior as a catalyst of the Claus reaction... more y-AI203 was chemically or heat treated to modify its behavior as a catalyst of the Claus reaction at low temperature. The treatment by P or La impregnation altered substantially the surface donor properties, as revealed by NH 3 adsorption, with no significant changes in the textural properties. However, the heat treatment by calcination at temperatures above 550°C mostly affected the textural properties through sintering and crystallization. Using a model described in detail in a previous study the global reaction rate was calculated and the H2S conversion curves in a fixed bed reactor were theoretically predicted. The experimental results showed that the surface treatment increased largely the catalytic activity of alumina although the effects on the H2S conversion in the reactor were small since it is a diffusion controlled process. Changes in performance due to heat treatment were much more pronounced allowing to conclude that the alumina performance could be substantially improved by optimization of the textural properties.

Thermogravimetric study of regenerable sulphur sorbents for H 2S retention at high temperature

Thermochimica Acta, 1997

... t'J ELSEVIER Thermochimica Acta 306 (1997) 2330 therm0chimica acta Thermogravimetric stu... more

Kinetic study of high-temperature removal of HâS by novel metal oxide sorbents

Industrial & Engineering Chemistry Research, 1997

The behavior of different mixed oxides, including zinc titanates (ZT) and zinc ferrites modified ... more

Characterization of zinc oxide and zinc ferrite doped with Ti or Cu as sorbents for hot gas desulphurization

Applied Surface Science, 1997

GAF-domains as novel cAMP-sensor autoactivate a bacterial adenylyl cyclase

CONDICIONES DE LA CREATIVIDAD

El Fartet (Aphanius iberus) al Baix Ter (NE de Catalunya): Mètodes de monitoratge, ús de l'hàbitat i impacte de la gambúsia

Dins d'un projecte Life-Natura es van construir a la costa baixempordanesa nous hàbitats (llacune... more Dins d'un projecte Life-Natura es van construir a la costa baixempordanesa nous hàbitats (llacunes de la Pletera) per a l'expansió del fartet (Aphanius iberus), els quals van ser repoblats a partir d'individus procedents de la bassa de Fra Ramon a finals del 2002. Dos anys després es va detectar la presència de gambúsia (Gambusia holbrooki) a les noves llacunes, però no a Fra Ramon. S'han comparat diferents mètodes de captura passiva per al monitoratge de poblacions de fartet. Tot i que les nanses de malla petita van ser el mètode més eficient, només es van agafar individus immadurs amb ampolles de plàstic, que, a més a més, van capturar un rang més ampli de mides. Els fartets van seleccionar positivament posicions properes al fons dins de la columna d'aigua, així com microhàbitats amb presència de refugis (com ara herbassars de Ruppia). Mentre que els individus immadurs es van trobar sobretot en zones somes, els adults es van distribuir de manera homogènia a les diferents profunditats. L'abundància de fartet va augmentar de l'abril al setembre del 2005 a Fra Ramon, per la incorporació de reclutes de l'any. En canvi, a les llacunes de la Pletera, on les gambúsies van suposar el 95 % de les captures, es va detectar una davallada de la població en aquest període. Aquestes observacions apunten l'existència de problemes durant el període reproductiu del fartet i un procés de desplaçament ecològic com a conseqüència d'un increment de la població de gambúsia.

Automatic nonuniform random variate generation

Computational Statistics, 2004

Random variate generation is an important tool in statistical computing. Many programms for simul... more Random variate generation is an important tool in statistical computing. Many programms for simulation or statistical computing (e.g. R) provide a collection of random variate generators for many standard distributions. However, as statistical modeling has become more sophisticated there is demand for larger classes of distributions. Adding generators for newly required distribution seems not to be the solution to this problem. Instead so called automatic (or black-box) methods have been developed in the last decade for sampling from fairly large classes of distributions with a single piece of code. For such algorithms a data about the distributions must be given; typically the density function (or probability mass function), and (maybe) the (approximate) location of the mode. In this contribution we show how such algorithms work and suggest an interface for R as an example of a statistical library.

The Total Survey Error Approach: a Guide to the New Science of Survey Research by H. F. Weisberg

Journal of The Royal Statistical Society Series A-statistics in Society, 2006

This book is concerned with medical diagnostic and prognostic tests, in particular those relying ... more This book is concerned with medical diagnostic and prognostic tests, in particular those relying on a single measurement. It mainly addresses the questions 'What are the test's characteristics?', 'How does it compare with the existing test?' and 'To what extent is its accuracy affected by external factors?'. The scene is set nicely in the opening chapter, with descriptions of some studies where diagnostic tests have been assessed and preliminary discussion about the design of such studies. The next two chapters are concerned with tests with binary outcomes, i.e. the subject simply tests positively or negatively. The various criteria for assessing tests are introduced: the true and false positive fraction (which the author prefers to sensitivity and specificity), positive and negative predictive values and likelihood ratios. Inference results are given for individual tests and for comparing tests (both paired and unpaired designs). Regression models are introduced for assessing how external factors (e.g. the age of the patient) may affect the characteristics of a test. The next three chapters are concerned with tests having quantitative or ordinal outcomes. The receiver operating characteristic curve is introduced along with variants such as the parametric binormal curve. There is again an extensive discussion of inference and the modelling of the effects of external factors. Later chapters include how to deal with situations where the 'gold standard' (for determining disease or no disease) is only used on a subset of patients or where it is fallible, the phases that are involved in the development of a test (up to five separate studies being recommended) and brief mention of meta-analysis, incorporating the time till disease develops into the analysis and combining test results. There are accompanying Web pages which include the data sets, Stata programs and errata, but not, unfortunately, solutions to the exercises at the end of chapters. This is a well-written book, my only concern being that some chapters resemble review papers, with a wide range of techniques being mentioned but none being fully developed. For this reason, I would not recommend the text for students. This aside, it is a clear and authoritative work which will be invaluable for anyone trying to establish a new diagnostic test.

Optimal estimation of population variance using equilibrated stratified sampling from infinite populations

Journal of The Korean Statistical Society, 2008

A class of unbiased estimators of the population variance is proposed when the coefficient of var... more A class of unbiased estimators of the population variance is proposed when the coefficient of variation is known for each stratum. The technique of equilibrated stratification is used. It is shown that, with optimum allocation, the variance of the suggested estimator for sufficiently large sample size is less than that of the classical minimum variance unbiased estimator under distributionfree setting. Other classes of estimators are also given with similar or better practical properties.

Estimation in Surveys With Nonresponse. Carl-Erik Sarndal and Sixten Lundstrom

The performance of a γ-Al 2O 3 catalyst for the Claus reaction at low temperature in a fixed bed reactor

Applied Catalysis A-general, 1996

Using a kinetic equation derived from results obtained in a differential reactor, a grain model w... more Using a kinetic equation derived from results obtained in a differential reactor, a grain model with variable properties was applied to calculate the global reaction rate for a particle. Furthermore, the theoretical model was developed to explain the performance of alumina as a catalyst for the Claus reaction at low temperature in an integral fixed bed reactor. The results were in good agreement with the experimental ones. The theoretical model was used to study the influence of the most significative parameters involved and to predict the catalyst performance in conditions of practical interest. It was shown that high H2S conversions and efficiencies of the catalyst were to be expected using highly porous materials and small particle sizes. These are the most important parameters for practical utilization.

Modelling of performance of zinc ferrites as high-temperature desulfurizing sorbents in a fixed-bed reactor

Fuel, 1997

... (Keywords: hydrogen sulfide removal; zinc ... Both experimental (Figure 6) and theoretical re... more

The effect of surface and thermal treatments on γ-Al 2O 3 as a catalyst of the claus reaction at low temperature

Applied Catalysis A-general, 1997

y-AI203 was chemically or heat treated to modify its behavior as a catalyst of the Claus reaction... more y-AI203 was chemically or heat treated to modify its behavior as a catalyst of the Claus reaction at low temperature. The treatment by P or La impregnation altered substantially the surface donor properties, as revealed by NH 3 adsorption, with no significant changes in the textural properties. However, the heat treatment by calcination at temperatures above 550°C mostly affected the textural properties through sintering and crystallization. Using a model described in detail in a previous study the global reaction rate was calculated and the H2S conversion curves in a fixed bed reactor were theoretically predicted. The experimental results showed that the surface treatment increased largely the catalytic activity of alumina although the effects on the H2S conversion in the reactor were small since it is a diffusion controlled process. Changes in performance due to heat treatment were much more pronounced allowing to conclude that the alumina performance could be substantially improved by optimization of the textural properties.

Thermogravimetric study of regenerable sulphur sorbents for H 2S retention at high temperature

Thermochimica Acta, 1997

... t'J ELSEVIER Thermochimica Acta 306 (1997) 2330 therm0chimica acta Thermogravimetric stu... more

Kinetic study of high-temperature removal of HâS by novel metal oxide sorbents

Industrial & Engineering Chemistry Research, 1997

The behavior of different mixed oxides, including zinc titanates (ZT) and zinc ferrites modified ... more

Characterization of zinc oxide and zinc ferrite doped with Ti or Cu as sorbents for hot gas desulphurization

Applied Surface Science, 1997

GAF-domains as novel cAMP-sensor autoactivate a bacterial adenylyl cyclase

CONDICIONES DE LA CREATIVIDAD