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1.
Esmeralda A. Ramalho 《Computational statistics & data analysis》2010,54(4):987-1001
Theoretical and simulation analysis is performed to examine whether unobserved heterogeneity independent of the included regressors is really an issue in logit, probit and loglog models with both binary and fractional data. It is found that unobserved heterogeneity has the following effects. First, it produces an attenuation bias in the estimation of regression coefficients. Second, although it is innocuous for logit estimation of average sample partial effects, it may generate biased estimation of those effects in the probit and loglog models. Third, it has much more deleterious effects on the estimation of population partial effects. Fourth, it is only for logit models that it does not substantially affect the prediction of outcomes. Fifth, it is innocuous for the size of Wald tests for the significance of observed regressors but, in small samples, it substantially reduces their power. 相似文献
2.
Esmeralda Mendoza-Mendoza Karinjilottu P. Padmasree Sagrario M. Montemayor Antonio F. Fuentes 《Journal of Materials Science》2012,47(16):6076-6085
Lanthanum-based LaBO3 oxides adopting the very stable perovskite structure are currently considered attractive materials for a growing number of applications in the field of solid-state ionics. In particular, LaAlO3-based perovskites are promising electrolyte materials for solid oxide fuel cells because they show almost pure oxygen ion conductivity at low oxygen partial pressures and high temperatures as well as excellent thermal and chemical stability under the standard operating conditions. This article describes a low-temperature synthesis of pure and acceptor-doped perovskite-type LaAlO3 nanopowders via a facile and environmental-friendly molten salts method. Using hydrated metal nitrates and sodium hydroxide as raw materials, the proposed methodology consists of two steps: a mechanically induced metathesis reaction and short firing above NaNO3's melting point. The purpose of the first is twofold: i.e., to generate in situ the NaNO3 flux and to obtain a suitable precursor for the synthesis of the target materials in molten nitrates. Accordingly, pure and Mg- and/or Sr-doped LaAlO3 powders were obtained directly without using any purification step at temperatures ≤500 °C. When preparing the Mg-containing samples, NaNO2 was also added to the reaction mixture to increase melt reactivity. The formation of the target series in the molten salt is thought to proceed through a “dissolution–precipitation” mechanism with LaAlO3 particles precipitating during cooling from a solution oversaturated with reactants. Electrical properties of the as-prepared materials were measured as a function of temperature and frequency by means of impedance spectroscopy and found comparable to those shown by similar materials prepared using more complicated routes. 相似文献
3.
Sebastián López Remedios Castro Esmeralda García Jose S. Pazo Carmelo G. Barroso 《European Food Research and Technology》2001,212(6):671-675
Fining experiments have been conducted on fino sherry wine from the Jerez-Xérès-Sherry region (southern Spain), in which the combined use of activated charcoal with proteinaceous fining agents (casein, potassium caseinate, albumin, and gelatin) has been studied. The effect of these fining agents on the polyphenolic content, the aromatic profile, and the resistance to browning of the treated wine has been determined. The polyphenolic content suffers significant decreases following the use of activated charcoal; these decreases are only increased slightly by the subsequent use of the other fining agents. The aromatic profile was not found to be altered by the clarification agents used. Despite the reduction in the polyphenolic content, the treated wines show a tendency to suffer browning similar to that observed in non-clarified wine. 相似文献
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5.
Fichorova RN Richardson-Harman N Alfano M Belec L Carbonneil C Chen S Cosentino L Curtis K Dezzutti CS Donoval B Doncel GF Donaghay M Grivel JC Guzman E Hayes M Herold B Hillier S Lackman-Smith C Landay A Margolis L Mayer KH Pasicznyk JM Pallansch-Cokonis M Poli G Reichelderfer P Roberts P Rodriguez I Saidi H Sassi RR Shattock R Cummins JE 《Analytical chemistry》2008,80(12):4741-4751
The increase of proinflammatory cytokines in vaginal secretions may serve as a surrogate marker of unwanted inflammatory reaction to microbicide products topically applied for the prevention of sexually transmitted diseases, including HIV-1. Interleukin (IL)-1beta and IL-6 have been proposed as indicators of inflammation and increased risk of HIV-1 transmission; however, the lack of information regarding detection platforms optimal for vaginal fluids and interlaboratory variation limit their use for microbicide evaluation and other clinical applications. This study examines fluid matrix variants relevant to vaginal sampling techniques and proposes a model for interlaboratory comparisons across current cytokine detection technologies. IL-1beta and IL-6 standards were measured by 12 laboratories in four countries, using 14 immunoassays and four detection platforms based on absorbance, chemiluminescence, electrochemiluminescence, and fluorescence. International reference preparations of cytokines with defined biological activity were spiked into (1) a defined medium simulating the composition of human vaginal fluid at pH 4.5 and 7.2, (2) physiologic salt solutions (phosphate-buffered saline and saline) commonly used for vaginal lavage sampling in clinical studies of cytokines, and (3) human blood serum. Assays were assessed for reproducibility, linearity, accuracy, and significantly detectable fold difference in cytokine level. Factors with significant impact on cytokine recovery were determined by Kruskal-Wallis analysis of variance with Dunn's multiple comparison test and multiple regression models. All assays showed acceptable intra-assay reproducibility; however, most were associated with significant interlaboratory variation. The smallest reliably detectable cytokine differences ( P < 0.05) derived from pooled interlaboratory data varied from 1.5- to 26-fold depending on assay, cytokine, and matrix type. IL-6 but not IL-1beta determinations were lower in both saline and phosphate-buffered saline as compared to vaginal fluid matrix, with no significant effect of pH. The (electro)chemiluminescence-based assays were most discriminative and consistently detected <2-fold differences within each matrix type. The Luminex-based assays were less discriminative with lower reproducibility between laboratories. These results suggest the need for uniform vaginal sampling techniques and a better understanding of immunoassay platform differences and cross-validation before the biological significance of cytokine variations can be validated in clinical trials. This investigation provides the first standardized analytic approach for assessing differences in mucosal cytokine levels and may improve strategies for monitoring immune responses at the vaginal mucosal interface. 相似文献
6.
Enrique Snchez Mora Estela Gmez Barojas Esmeralda Rojas Rojas Rutilo Silva Gonzlez 《Solar Energy Materials & Solar Cells》2007,91(15-16):1412-1415
Morphological, optical and photocatalytic properties of TiO2, Fe2O3 and TiO2–Fe2O3 samples (formed by 1, 3 and 5 coatings) were studied. The layers were deposited on glass substrate by the sol–gel method. The catalytic activity of the samples was studied by the photodecomposition of methylene blue (MB) under visible light illumination. The FTIR results indicate that all samples present surface OH radicals that are bound either to the Ti or Fe atoms. This effect is better visualized at larger number of coatings in the TiO2–Fe2O3/glass systems. Also, two mechanisms are observed during the photodecomposition of the MB. 相似文献
7.
A solid-phase microextraction (SPME) procedure followed by gas chromatography electron capture detection (GC/ECD) for the
determination of triazole residues was developed. An experimental design with two steps was done. Firstly, a 26−2 fractional factorial design for screening several experimental variables (fiber-coating type, extraction temperature, extraction
time, stirring rate, desorption temperature, and desorption time) was done. After, a two-factor central composite design for
optimizing, the experimental conditions were carried out. The chosen experimental conditions were: fiber, PDMS/DVB; extraction
time, 45 min; extraction temperature, 60 °C; desorption time, 3 min; desorption temperature, 260 °C, and stirring speed, 500 rpm.
Using those conditions the limits of detection obtained for tetraconazole, myclobutanil, and diniconazole were in the order
of few μg L−1 in grape and apple liquid extracts. Recoveries were from 93.6% to 112.1%. Relative standard deviation ranged from 1.2% to
11.6% (apple) and 6.7 to 18.0% (grape). The method was applied to five grape samples and 13 apple samples collected in Navarra,
Rioja, and Basque Country. Quantification was performed by the standard addition method. Three standard additions by duplicate
covering adequate range concentration were used. Myclobutanil was found in three apple samples (110–122 μg L−1) and diniconazole in one grape sample (9.4 μg L−1). 相似文献
8.
Esmeralda Ruiz Pujadas Gemma Piella Hans Martin Kjer Miguel Angel González Ballester 《Machine Vision and Applications》2018,29(3):405-414
A cochlear implant is an electronic device which can restore sound to completely or partially deaf patients. For surgical planning, a patient-specific model of the inner ear must be built using high-resolution images accurately segmented. We propose a new framework for segmentation of micro-CT cochlear images using random walks, where a region term estimated by a Gaussian mixture model is combined with a shape prior initially obtained by a statistical shape model (SSM). The region term can then take advantage of the high contrast between the background and foreground, while the shape prior guides the segmentation to the exterior of the cochlea and to less contrasted regions inside the cochlea. The prior is obtained via a non-rigid registration regularized by a statistical shape model. The SSM constrains the inner parts of the cochlea and ensures valid output shapes of the inner ear. 相似文献
9.
Ricardo Acosta Ortiz Aida Esmeralda Garcia Valdez Gustavo Soria Arguello Guadalupe Mendez Padilla Omar Acosta Berlanga 《Journal of Polymer Research》2018,25(7):160
Herein a method is described to prepare photocurable thermally-conductive shape memory epoxy/ graphene composites. By photopolymerizing the epoxy resin diglycidyl ether of bisphenol A with an allyl-functionalized ditertiary amine as the curing agent, jointly with a multifunctional thiol, a crosslinked polyether-polythioether co-network was obtained. The presence of a soft domain like the flexible polythioethers enable the co-network to display shape memory properties. By varying the polyether to polythioether ratio it was possible to modulate the shape memory characteristics of the composite. The effect of the concentration of graphene nanoplatelets (GNP) in the composite was also investigated. Shape memory performances revealed excellent values of shape recovery and shape fixity with maximums of 98 and 99% respectively. The temporary- shaped composites with higher concentration of polythioethers and GNP regained their permanent shapes in 2–3 s when heated above the programming temperature. The thermal conductivity in the composites reached 0.39 W/m°K for the composite with 15% w/w of GNP. The presence of the polythioethers in the co-network enhanced the toughness of the composite as revealed by the impact resistance analysis. 相似文献
10.
Overexpression of Tropomyosin Isoform Tpm3.1 Does Not Alter Synaptic Function in Hippocampal Neurons
Chanchanok Chaichim Tamara Tomanic Holly Stefen Esmeralda Paric Lucy Gamaroff Alexandra K. Suchowerska Peter W. Gunning Yazi D. Ke Thomas Fath John Power 《International journal of molecular sciences》2021,22(17)
Tropomyosin (Tpm) has been regarded as the master regulator of actin dynamics. Tpms regulate the binding of the various proteins involved in restructuring actin. The actin cytoskeleton is the predominant cytoskeletal structure in dendritic spines. Its regulation is critical for spine formation and long-term activity-dependent changes in synaptic strength. The Tpm isoform Tpm3.1 is enriched in dendritic spines, but its role in regulating the synapse structure and function is not known. To determine the role of Tpm3.1, we studied the synapse structure and function of cultured hippocampal neurons from transgenic mice overexpressing Tpm3.1. We recorded hippocampal field excitatory postsynaptic potentials (fEPSPs) from brain slices to examine if Tpm3.1 overexpression alters long-term synaptic plasticity. Tpm3.1-overexpressing cultured neurons did not show a significantly altered dendritic spine morphology or synaptic activity. Similarly, we did not observe altered synaptic transmission or plasticity in brain slices. Furthermore, expression of Tpm3.1 at the postsynaptic compartment does not increase the local F-actin levels. The results suggest that although Tpm3.1 localises to dendritic spines in cultured hippocampal neurons, it does not have any apparent impact on dendritic spine morphology or function. This is contrary to the functional role of Tpm3.1 previously observed at the tip of growing neurites, where it increases the F-actin levels and impacts growth cone dynamics. 相似文献