Response and Discrimination Performance of Arrays of Organothiol-Capped Au Nanoparticle Chemiresistive Vapor Sensors

The response and discrimination performance of an array that consisted of 20 different organothiol-capped Au nanoparticle chemiresistive vapor sensors was evaluated during exposure to 13 different organic vapors. The passivating organothiol ligand library consisted of collections of straight-chain alkanethiols, branched alkanethiols, and aromatic thiols. A fourth collection of sensors was formed from composites of 2-phenylethanethiol-capped Au nanoparticles and nonpolymeric aromatic materials that were coembedded in a sensor film. The organic vapors consisted of six hydrocarbons (n-hexane, n-heptane, n-octane, isooctane, cyclohexane, and toluene), three polar aprotic vapors (chloroform, tetrahydrofuran, and ethyl acetate), and four alcohols (methanol, ethanol, isopropanol, and 1-butanol). Trends in the resistance response of the sensors were consistent with expected trends in sorption due to the properties of the test vapor and the molecular structure of the passivating ligands in the sensor films. Classification algorithms including principal components analysis and Fisher’s linear discriminant were used to evaluate the discrimination performance of an array of such sensors. Each collection of sensors produced accurate classification of most vapors, with misclassification occurring primarily for vapors that had mutually similar polarity. The classification performance for an array that contained all of the sensor collections produced nearly perfect discrimination for all vapors studied. The dependence of the array size (i.e., the number of sensors) and the array chemical diversity on the discrimination performance indicated that, for an array of 20 sensors, an array size of 13 sensors or more produced the maximum discrimination performance

Response versus Chain Length of Alkanethiol-Capped Au Nanoparticle Chemiresistive Chemical Vapor Sensors

Au nanoparticles capped with a homologous series of straight chain alkanethiols (containing 4−11 carbons in length) have been investigated as chemiresistive organic vapor sensors. The series of alkanethiols was used to elucidate the mechanisms of vapor detection by such capped nanoparticle chemiresistive films and to highlight the molecular design principles that govern enhanced detection. The thiolated Au nanoparticle chemiresistors demonstrated rapid and reversible responses to a set of test vapors (n-hexane, n-heptane, n-octane, iso-octane, cyclohexane, toluene, ethyl acetate, methanol, ethanol, isopropanol, and 1-butanol) that possessed a variety of analyte physicochemical properties. The resistance sensitivity to nonpolar and aprotic polar vapors systematically increased as the chain length of the capping reagent increased. Decreases in the nanoparticle film resistances, which produced negative values of the differential resistance response, were observed upon exposure of the sensor films to alcohol vapors. The response signals became more negative with higher alcohol vapor concentrations, producing negative values of the sensor sensitivity. Sorption data measured on Au nanoparticle chemiresistor films using a quartz crystal microbalance allowed for the measurement of the partition coefficients of test vapors in the Au nanoparticle films. This measurement assumed that analyte sorption only occurred at the organic interface and not the surface of the Au core. Such an assumption produced partition coefficient values that were independent of the length of the ligand. Furthermore, the value of the partition coefficient was used to obtain the particle-to-particle interfacial effective dielectric constant of films upon exposure to analyte vapors. The values of the dielectric constant upon exposure to alcohol vapors suggested that the observed resistance response changes observed were not significantly influenced by this dielectric change, but rather were primarily influenced by morphological changes and by changes in the interparticle spacing

Invarianza de medida transcultural en la Escala de Satisfacción con la Vida en estudiantes universitarios de Chile y España

Introducción: La Escala de Satisfacción con la Vida (SWLS) es un instrumento ampliamente utilizado para la evaluación cognitiva del bienestar subjetivo de los individuos. La SWLS ha sido validada en numerosos contextos y poblaciones, pero la invarianza de medida a nivel transcultural en adultos emergentes ha sido poco explorada. El propósito de este artículo fue evaluar la invarianza de medida de la SWLS en estudiantes universitarios de Chile y España y según género. Método: Una muestra no probabilística de 165 estudiantes universitarios de Chile (66.7% mujeres, edad promedio = 21.9, DE = 2.35) y 109 estudiantes de España (48.6% mujeres, edad promedio = 22.9, DE = 2.4) completaron la SWLS. Resultados: Por medio de un análisis factorial confirmatorio multigrupo, los resultados mostraron que la SWLS exhibió invarianza configural, métrica y escalar en la comparación entre las muestras de estudiantes chilenos y españoles y según género. Conclusión: Este hallazgo muestra que la SWLS permite comparaciones significativas de medias latentes entre muestras transculturales universitarias. Además, este estudio aporta evidencia de la SWLS como un instrumento válido que puede guiar la creación de políticas para mejorar el bienestar subjetivo de los estudiantes universitarios de ambos géneros, tanto en países desarrollados como en desarrollo de habla hispana.Introduction: The Satisfaction with Life Scale (SWLS) is a widely used measure of an individuals’ cognitive assessment of subjective well-being. The SWLS has been validated in several contexts and populations, but its cross-cultural measurement invariance in emerging adult samples remains barely explored. The purpose of this study was to evaluate the measurement invariance of the SWLS in university students from Chile and Spain and according to gender. Method: A non-probabilistic sample of 165 university students from Chile (66.7% women, Mage = 21.9, SD = 2.35), and 109 students from Spain (48.6% women; Mage = 22.9, SD = 2.4) completed the SWLS. Results: Using multi-group confirmatory factor analysis, results showed that the SWLS exhibited configural, metric and scalar invariance in the comparison between the Chilean and Spanish student samples and also according to gender. Conclusions: This finding allows for significant latent mean comparisons between cross-cultural samples. Moreover, this study supports the SWLS as a valid instrument which provides data that can inform policies in order to improve the subjective well-being of university students of both genders, both in developed and developing Spanish-speaking countries.This work was supported by Fondecyt Project 1160005 and Project AGL2015-65897-C3-1 of the Ministry of Economics and Competitivity of the Government of Spain

Design and Construction of Absorption Cells for Precision Radial Velocities in the K Band using Methane Isotopologues

We present a method to optimize absorption cells for precise wavelength calibration in the near-infrared. We apply it to design and optimize methane isotopologue cells for precision radial velocity measurements in the K band. We also describe the construction and installation of two such cells for the CSHELL spectrograph at NASA's IRTF. We have obtained their high-resolution laboratory spectra, which we can then use in precision radial velocity measurements and which can also have other applications. In terms of obtainable RV precision methane should out-perform other proposed cells, such as the ammonia cell ($^{14}$NH$_{3}$) recently demonstrated on CRIRES/VLT. The laboratory spectra of Ammonia and the Methane cells show strong absorption features in the H band that could also be exploited for precision Doppler measurements. We present spectra and preliminary radial velocity measurements obtained during our first-light run. These initial results show that a precision down to 20-30 m s$^{-1}$ can be obtained using a wavelength interval of only 5 nm in the K band and S/N$\sim$150. This supports the prediction that a precision down to a few m s$^{-1}$ can be achieved on late M dwarfs using the new generation of NIR spectrographs, thus enabling the detection of terrestrial planets in their habitable zones. Doppler measurements in the NIR can also be used to mitigate the radial velocity jitter due to stellar activity enabling more efficient surveys on young active stars.Comment: accepted PASP, Apr 2012 (in press). Preprint version with 36 pages, 9 Figures, 2 Table