General nonparametric ROC curve comparison

Martinez-Camblor, Pablo,Carleos, Carlos,Corral, Norberto 한국통계학회 2013 Journal of the Korean Statistical Society Vol.42 No.1

Although the equality among two or more ROC (receiver operating characteristic) curves is usually contrasted from the respective AUCs (area under the ROC curve), two different ROC curves can share the same AUC and, in order to compare the ROC curves equality, most general criteria must be considered. In this paper, the authors deal with the general ROC curve comparison problem on paired design. They extend the tests for the classical cumulative distribution functions (CDF) comparison to the ROC curves context. To approximate the statistic distribution, two different resampling plans are considered; the usual one based on permutations and a new bootstrap procedure which does not require the exchangeability assumption. As usual, from Monte Carlo simulations, the performance of the proposed methodology is studied for two traditional tests; one based on the Kolmogorov-Smirnov criteria and the other one on the $L_2$-measure. The observed results suggest that the proposed bootstrap provides a good statistic distribution approximation for medium sample size. Therefore the studied methodology allows us to compare the equality of ROC curves by defining a criteria according to the needs of the problem.

General nonparametric ROC curve comparison

Pablo Martínez-Camblor,Carlos Carleos,Norberto Corral 한국통계학회 2013 Journal of the Korean Statistical Society Vol.42 No.1

Although the equality among two or more ROC (receiver operating characteristic) curves is usually contrasted from the respective AUCs (area under the ROC curve), two different ROC curves can share the same AUC and, in order to compare the ROC curves equality,most general criteria must be considered. In this paper, the authors deal with the general ROC curve comparison problem on paired design. They extend the tests for the classical cumulative distribution functions (CDF) comparison to the ROC curves context. To approximate the statistic distribution, two different resampling plans are considered; the usual one based on permutations and a new bootstrap procedure which does not require the exchangeability assumption. As usual, from Monte Carlo simulations, the performance of the proposed methodology is studied for two traditional tests; one based on the Kolmogorov–Smirnov criteria and the other one on the L2-measure. The observed results suggest that the proposed bootstrap provides a good statistic distribution approximation for medium sample size. Therefore the studied methodology allows us to compare the equality of ROC curves by defining a criteria according to the needs of the problem.

Area under the ROC curve comparison in the presence of missing data

Pablo Martínez-Camblor 한국통계학회 2013 Journal of the Korean Statistical Society Vol.42 No.4

The area under the receiver operating characteristic (ROC) curve (AUC) is broadly acceptedand often used as a diagnostic accuracy index. Moreover, the equality among the predictivecapacity of two or more diagnostic systems is frequently checked from the comparison oftheir respective AUCs. In paired designs, this comparison is usually performed by using onlythe subjects who have collected all the necessary information, in the so-called availablecaseanalysis. On the other hand, the presence of missing data is a frequent problem,especially in retrospective and observational studies. The loss of statistical power andthe misuse of the available information (with the resulting ethical implications) are themain consequences. In this paper a non-parametric method is developed to exploit allavailable information. In order to approximate the distribution for the proposed statistic,the asymptotic distribution is computed and two different resampling plans are studied. In addition, the methodology is applied to a real-world medical problem. Finally, sometechnical issues are also reported in the Appendix.

PST-1: A Synthetic Small-Pore Zeolite that Selectively Adsorbs H₂

Shin, Jiho,Camblor, Miguel A.,Woo, Hee Chul,Miller, Stuart R.,Wright, Paul A.,Hong, Suk Bong WILEY-VCH Verlag 2009 Angewandte Chemie Vol.48 No.36

<B>Graphic Abstract</B> <P>No gas too small: A synthetic potassium gallosilicate natrolite with Si/Ga=1.28 (denoted PST-1; see picture, Ga/Si gray, O red, K pink) was found to selectively adsorb small gases, especially H<SUB>2</SUB>, and hence to discriminate them from slightly larger molecules such as Ar or CO<SUB>2</SUB>. The remarkable ease of its dehydration and great (hydro)thermal stability make PST-1 a potential candidate for fast, selective H<SUB>2</SUB> or He separation processes. <img src='wiley_img/14337851-2009-48-36-ANIE200903336-content.gif' alt='wiley_img/14337851-2009-48-36-ANIE200903336-content'> </P>

Tetrahedral Atom Ordering in a Zeolite Framework: A Key Factor Affecting Its Physicochemical Properties

Shin, Jiho,Bhange, Deu S.,Camblor, Miguel A.,Lee, Yongjae,Kim, Wha Jung,Nam, In-Sik,Hong, Suk Bong American Chemical Society 2011 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.133 No.27

<P>Three gallosilicate natrolites with closely similar chemical composition but differing in the distribution of Si and Ga over crystallographically different tetrahedral sites (T-sites) show striking differences in their cation exchange performance. The ability to exchange Na<SUP>+</SUP> by the larger alkali metal cations decreases upon increasing the size of the cation, as expected, but also with the degree of T-atom ordering. To seek an insight into this phenomenon, the crystal structures of 11 different zeolites, which show variations in degree of T-atom ordering, nature of countercation, and hydration state, have been refined using synchrotron diffraction data. While the three as-made sodium materials were characterized to have a low, medium, and high degree of ordering, respectively, their pore sizes are close to the size of the bare Na<SUP>+</SUP> cation and much smaller than that of the larger alkali cations, which are nonetheless exchanged into the materials, each one at a different level. Interestingly, large differences are also manifested when the Na<SUP>+</SUP> back-exchange is performed on the dehydrated K<SUP>+</SUP> forms, with crystallographic pore sizes too small even to allow the passage of Na<SUP>+</SUP>. Although the thermodynamic data point to small differences in the enthalpy of the Na<SUP>+</SUP>/K<SUP>+</SUP> exchange in the three materials, comparison of the “static” crystallographic pore sizes and the diameter of the exchanged cations lead us to conclude that during the exchange process these zeolites undergo significant deformations that dynamically open the pores, allowing cation traffic even for Cs<SUP>+</SUP> in the case of the most disordered material. In addition to the very large topological flexibility typical of the natrolite framework, we propose as a hypothesis that there is an additional flexibility mechanism that decreases the rigidity of the natrolite chain itself and is dependent on preferential siting of Si or Ga on crystallographically different T-sites.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2011/jacsat.2011.133.issue-27/ja202739j/production/images/medium/ja-2011-02739j_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja202739j'>ACS Electronic Supporting Info</A></P>

Synthesis and <i>in situ</i> transformation of PST-1: a potassium gallosilicate natrolite with a high Ga content

Shin, Jiho,Kim, Seok Han,Camblor, Miguel A.,Warrender, Stewart J.,Miller, Stuart R.,Zhou, Wuzong,Wright, Paul A.,Hong, Suk Bong Royal Society of Chemistry 2010 Dalton Transactions Vol.39 No.9

<P>The synthetic details of a novel potassium gallosilicate natrolite with Si/Ga = 1.28, denoted PST-1, are described. The presence of K<SUP>+</SUP> and Ga with well-defined levels of concentration in the synthesis mixture is essential for directing its crystallisation. PST-1 transforms rapidly into TNU-6 under hydrothermal conditions, behaviour that contrasts sharply with its very high thermal and hydrothermal stability, which is unusual for a material of such a high Ga content. These stability issues are discussed and rationalized based on chemical composition, likely violations of Loewenstein's rule and the temperature of dehydration of as-made K-PST-1. The crystal structure of TNU-6 has been resolved through the combined use of synchrotron X-ray and electron diffraction data; it has the BaFeGaO<SUB>4</SUB> structure type with an additional √3<I>a</I>×√3<I>a</I>“GeAlO<SUB>4</SUB>” superstructure that arises from tilting of some of the tetrahedral units in all of the 6-rings.</P> <P>Graphic Abstract</P><P>Details of the synthesis and <I>in situ</I> transformation of PST-1, a new potassium gallosilicate natrolite with Si/Ga = 1.28, are described, together with its (hydro)thermal stability. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b920540n'> </P>

Synthesis of Aluminosilicate Natrolites and Control of Their Tetrahedral Atom Ordering

Shin, Jiho,Ahn, Nak Ho,Camblor, Miguel A.,Zicovich-Wilson, Claudio M.,Hong, Suk Bong American Chemical Society 2014 Chemistry of materials Vol.26 No.11

<P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2014/cmatex.2014.26.issue-11/cm5013763/production/images/medium/cm-2014-013763_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5013763'>ACS Electronic Supporting Info</A></P>

Unseeded hydroxide-mediated synthesis and CO₂ adsorption properties of an aluminosilicate zeolite with the RTH topology

Jo, Donghui,Lim, Jong Bin,Ryu, Taekyung,Nam, In-Sik,Camblor, Miguel A.,Hong, Suk Bong The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.38

<▼1><P>Unseeded hydroxide-mediated synthesis and CO2 adsorption properties of an aluminosilicate zeolite with the RTH topology.</P></▼1><▼2><P>We have synthesized an aluminosilicate RTH-type zeolite with Si/Al = 10 using 1,2,3-trimethylimidazolium (123TMI<SUP>+</SUP>) as an organic structure-directing agent (OSDA) together with Na<SUP>+</SUP> or K<SUP>+</SUP> in hydroxide media and without the use of seed crystals. The zeolite obtained is characterized by a cuboid morphology made of very small ill-defined crystallites, largely different from the plank-like morphology typically observed for RTH-type zeolite crystals thus far. More interestingly, we show experimental evidence demonstrating that two 123TMI<SUP>+</SUP> ions are located within each [4<SUP>6</SUP>5<SUP>8</SUP>6<SUP>4</SUP>8<SUP>4</SUP>] cavity of the RTH framework, forming antiparallel dimers, as found by Rietveld refinement. When hydrothermally aged at 1023 K, Cu-RTH is much less active for NO reduction with NH3 than Cu-SSZ-13, the best catalyst known for this reaction to date. However, while the CO2 uptake (3.2 mmol g<SUP>−1</SUP>) on Na-RTH at 298 K and 1.0 bar is lower than that (4.5 mmol g<SUP>−1</SUP>) on zeolite Na-Rho, a well-studied small-pore zeolite that selectively adsorbs CO2, it exhibits much faster CO2 sorption kinetics. This renders our RTH zeolite potentially useful as a selective CO2 adsorbent.</P></▼2>

Zeolite Synthesis in FluorideMedia: Structure Directiontoward ITW by Small Methylimidazolium Cations

Rojas, Alex,Martí,nez-Morales, Evangelina,Zicovich-Wilson, Claudio M.,Camblor, Miguel A. American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.4

<P>Pure silica ITW zeolite can be synthesized using 1,2,3-trimethylimidazoliumand 1,3-dimethylimidazolium cations and fluoride anions as structure-directingagents (SDAs). Similarly to the previously reported 1,3,4-trimethylimidazolium,the dimethyl cation can also produce the zeolite TON, but this higherframework density phase finally transforms <I>in situ</I> into ITW. The structures of the as-made and calcined phases preparedwith the new cations show a unit cell doubling along <I>z</I>, and the refined structures are reported. Periodic Density FunctionalTheory calculations provide the energies of the six SDA-ITW and SDA-TONzeolites, and their relative stabilities fully agree with the experimentalobservations. Structure-direction in this system is discussed fromexperimental and theoretical results that give strong support to theidea that strained silica frameworks are made possible in fluoridemedia by decreasing the covalent character of the Si–O bond.This decreased covalency is enhanced with the 1,2,3-trimethyl isomer,which is shown to be the strongest SDA for ITW and, at the same time,is the more hydrophilic of the three SDAs tested. Our observationswith the three SDAs agree with the so-called Villaescusa’srule, i.e., the low framework density phase is favored at higher concentrations,but at the same time question the supersaturation hypothesis thathas been proposed to explain this rule, since here the low-densityphase is the most stable one.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-4/ja209832y/production/images/medium/ja-2011-09832y_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja209832y'>ACS Electronic Supporting Info</A></P>

Compositionally Enhanced Flexibility in a Ga-Rich Zeolite Affords Unusual Structural Changes via Alkali Ion Exchange

Seo, Sung Man,Ahn, Nak Ho,Shin, Jiho,Cho, Sung June,Camblor, Miguel A.,Hong, Suk Bong American Chemical Society 2015 Chemistry of materials Vol.27 No.18

<P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-18/acs.chemmater.5b02741/production/images/medium/cm-2015-027416_0004.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5b02741'>ACS Electronic Supporting Info</A></P>