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Under the generalizability-theory (G-theory) framework, the estimation precision of variance components (VCs) is of significant importance in that they serve as the foundation of estimating reliability. Zhang and Lin advanced the discussion of nonadditivity in data from a theoretical perspective and showed the adverse effects of nonadditivity on the estimation precision of VCs in 2016. Contributing to this line of research, the current article directs the discussion of nonadditivity from a theoretical perspective to a practical application and highlights the importance of detecting nonadditivity in G-theory applications. To this end, Tukey's test for nonadditivity is the only method to date that is appropriate for the typical single-facet G-theory design, in which a single observation is made per element within a facet. The current article evaluates the Type I and Type II error rates of Tukey's test. Results show that Tukey's test is satisfactory in controlling for falsely detecting nonadditivity when the data are actually additive and that it is generally powerful in detecting nonadditivity when it exists. Finally, the article demonstrates an application of Tukey's test in detecting nonadditivity in a judgmental study of educational standards and shows how Tukey's test results can be used to correct imprecision in the estimated VC in the presence of nonadditivity.

With multiple options to choose from, there is always a chance of lucky guessing by examinees on multiple-choice (MC) items, thereby potentially introducing bias in item difficulty estimates. Correct responses by random guessing thus pose threats to the validity of claims made from test performance on an MC test. Under the Rasch framework, the current study investigates the effects of removing responses with likely guessing on item difficulty estimates, person ability measures, and test information function (i.e., a function of measurement precision for person ability) on an MC language proficiency test. Results show that removing responses with likely guessing leads to difficult items becoming more difficult and high-performing examinees receiving higher ability measures, because lucky guesses are more likely to appear in responses to difficult items than to easy items; therefore, removing responses with likely guessing results in lower proportion correct (i.e., higher item difficulty) for difficult items. More importantly, the current study shows that the measurement precision for high-performing examinees increases after accounting for likely random guessing, while the measurement precision for low- and medium-performing examinees remains similar with and without likely guessing. Implications for operational scoring of examinees are discussed.

Sparse-rated data are common in operational performance-based language tests, as an inevitable result of assigning examinee responses to a fraction of available raters. The current study investigates the precision of two generalizability-theory methods (i.e., the rating method and the subdividing method) specifically designed to accommodate the technical complexity involved in estimating score reliability from sparse-rated data. Examining the estimation precision of reliability is of great importance because the utility of any performance-based language test depends on its reliability. Results suggest that when some raters are expected to have greater score variability than other raters (e.g., a mixture of novice and experienced raters being deployed in a rating session), the sub-dividing method is recommended as it yields more precise reliability estimates. When all raters are expected to exhibit similar variability in their scoring, both the rating and sub-dividing methods are equally precise in estimating score reliability, and the rating method is recommended for operational use, as it is easier to implement in practice. Informed by these methodological results, the current study also demonstrates a step-by-step analysis for investigating the score reliability from sparse-rated data taken from a large-scale English speaking proficiency test. Implications for operational performance-based language tests are discussed.

Since the 1980s, China has represented one of the major growth areas in the world for English language education, and studying English has been a priority among its foreign language educational policies. As English has gained more popularity in China, some have noted the potential value of English as a means to greater educational access and social mobility. Others, however, see cause for concern by claiming that English language instruction is not always effective or that learning English is a waste of time and resources because the majority of English learners will most probably not use English after they graduate from college. In considering these issues and their implications for policy and practice, this article reports findings from a research study of 1,613 Chinese undergraduates to understand how learners of English view and experience English Language Teaching (ELT) in China. Data were collected using an online survey questionnaire. Major findings indicate that the majority of respondents have strong motivations to learn English, based on the belief that English has been--and will continue to be--useful and important in their studies and future work, as they perceive themselves becoming more connected to the global economy and global affairs. Despite their motivations to learn and use English, the majority of English learners in China indicated that they lacked opportunities to use English both in and outside of school. The survey also investigated learner perceptions of their own strengths and weaknesses as learners of English in various skill areas. The majority of respondents reported reading and writing as their strengths and noted speaking and listening as their areas of weaknesses. Additionally, statistical analyses of data were conducted to examine the association between learner perceptions and learner characteristics such as gender, major, hometown, home dialect, extramural studies, and parents' level of education. The association between students' self-reported proficiency and their majors, hometown, and parents' level of education was statistically significant.

Research on the relationship between English language proficiency standards and academic content standards serves to provide information about the extent to which English language learners (ELLs) are expected to encounter academic language use that facilitates their content learning, such as in mathematics and science. Standards-to-standards correspondence thus contributes to validity evidence regarding ELL achievements in a standard-based assessment system. The current study aims to examine the reliability of reviewer judgments about language performance indicators associated with academic disciplines in standards-to-standards correspondence studies in the US K-12 settings. Ratings of cognitive complexity germane to the language performance indicators were collected from 20 correspondence studies with over 500 reviewers, consisting of content experts and ESL specialists. Using generalizability theory, we evaluate reviewer reliability and standard errors of measurement in their ratings with respect to the number of reviewers. Results show that depending on the particular grades and subject areas, 3-6 reviewers are needed to achieve acceptable reliability and to control for reasonable measurement errors in their judgments.

The appearance of multiple bands in the N–H stretching region of the infrared spectra of the neutral methylamine dimer and trimer is a sign of NH bend–stretch anharmonic coupling. Ab initio anharmonic calculations were carried out in a step-wise manner to reveal the origin of various bands observed in the spectrum of the methylamine dimer. A seven-dimensional potential energy surface involving symmetric and asymmetric stretching and bending vibrations of both the hydrogen bond donor and the acceptor along intermolecular-translational modes was constructed using the discrete variable representation approach. The resulting spectrum of the dimer shows five bands that can be attributed to the symmetric stretching ( ν sym D ), asymmetric stretchin ( ν asym D ), and bending overtone (2 ν bend D ) of the donor moiety. These appear along with the combination band arising out of bending vibrations of the donor and acceptor ( ν bend D + ν bend A ) and with the combination of the intermolecular translational mode over the donor bending overtone ( ν trans + 2 ν bend D ). The spectrum of the trimer essentially consists of all the features seen in the dimer with marginal changes in band positions. The analysis of the experimental spectra based on the two-state deperturbation model and ab initio anharmonic calculations yield a matrix element of about 40 cm−1 for the N–H bend–stretch Fermi resonance coupling. In general, the IR spectra of the hydrogen-bonded amino group depict three sets of bands that arise due to bend–stretch Fermi resonance coupling. [ABSTRACT FROM AUTHOR]

In this work, starting from the general theory of sum-frequency generation (SFG), we proposed a computational strategy utilizing density functional theory with periodic boundary conditions to simulate the vibrational SFG of molecules/solid surface adsorption system. The method has been applied to the CH3OH/TiO2(110) system successfully. Compared with the isolated molecule model, our theoretical calculations showed that the TiO2 substrate can significantly alter the second-order susceptibilities of a methanol molecule which is directly related to the SFG intensity. In addition, the SFG spectra have obvious changes while the methanol coverage increases, especially for the OH vibration peaks. Our theoretical spectra agree reasonably well with experimental measurements at 1 ML coverage, and an interesting peak which is absent in the theoretical spectra is tentatively assigned to some CH3 stretch vibration of methanol adsorbed on the oxygen vacancy of TiO2. [ABSTRACT FROM AUTHOR]

Infrared spectra for a series of asymmetric proton‐bound dimers with protonated trimethylamine (TMA‐H+) as the proton donor were recorded and analyzed. The frequency of the N–H+ stretching mode is expected to red shift as the proton affinity of proton acceptors increases. The observed band, however, shows a peculiar splitting of approximately 300 cm−1 with the intensity shifting pattern resembling a two‐level system. Theoretical investigation reveals that the observed band splitting and its extraordinarily large gap of around 300 cm−1 is a result of strong coupling between the fundamental of the proton stretching mode and overtone states of the two proton bending modes, that is commonly known as Fermi resonance (FR). We also provide a general theoretical model to link the strong FR coupling to the quasi‐two‐level system. Since the model does not depend on the molecular specification of TMA‐H+, the strong coupling we observed is an intrinsic property associated with proton motions. [ABSTRACT FROM AUTHOR]

The electronic spectrum of a cold molecular beam of zirconium dioxide, ZrO2, has been investigated using laser induced fluorescence (LIF) in the region from 17 000 cm-1 to 18 800 cm-1 and by mass-resolved resonance enhanced multi-photon ionization (REMPI) spectroscopy from 17 000 cm-1-21 000 cm-1. The LIF and REMPI spectra are assigned to progressions in the Ã1B2(ν1, ν2, ν3) ← X1A1(0, 0, 0) transitions. Dispersed fluorescence from 13 bands was recorded and analyzed to produce harmonic vibrational parameters for the X1A1 state of ω1 = 898(1) cm-1, ω2 = 287(2) cm-1, and ω3 = 808(3) cm-1. The observed transition frequencies of 45 bands in the LIF and REMPI spectra produce origin and harmonic vibrational parameters for the Ã1B2 state of Te = 16 307(8) cm-1, ω1 = 819(3) cm-1, ω2 = 149(3) cm-1, and ω3 = 518(4) cm-1. The spectra were modeled using a normal coordinate analysis and Franck-Condon factor predictions. The structures, harmonic vibrational frequencies, and the potential energies as a function of bending angle for the Ã1B2 and X1A1 states are predicted using time-dependent density functional theory, complete active space self-consistent field, and related first-principle calculations. A comparison with isovalent TiO2 is made. [ABSTRACT FROM AUTHOR]

The negatively charged nitrogen-vacancy defect center, (NV)–, in diamond has been investigated theoretically for its one- and two-photon absorption properties involving the first excited state with the 3A2→3E transition. Time-dependent density functional theory (TD-DFT), configuration interaction with single excitation (CIS), and complete active space self-consistent field (CASSCF) were employed in this investigation along with the 6-31G(d) basis set. Diamond lattice models containing 24–104 carbon atoms were constructed to imitate the local environment of the defect center. TD-DFT calculations in large molecular cluster models (with 85 or more carbon atoms) predicted the vertical excitation energy quite consistent with the experimental absorption maximum. CASSCF calculations were feasible only for small cluster models (less than 50 carbon atoms) but yielded one-photon absorption (OPA) and two-photon absorption (TPA) cross sections somewhat larger than the experimental values obtained with linearly polarized incident light [T.-L. Wee et al., J. Phys. Chem. A 111, 9379 (2007)]. CIS calculations in larger cluster models showed a systematic overestimation of the excitation energy while just slightly underestimated the OPA cross section and overestimated the TPA cross section. The agreements between calculations and measurements suggest that the computational approaches established in this work are applicable to explore the optical properties of related defect centers in diamond as well. [ABSTRACT FROM AUTHOR]

In studying ultrafast electron transfer from a dye molecule to a nanosized semiconductor particle, pump-probe experiments are commonly used. In this system the electron transfer (ET) rate is faster than vibrational relaxation so that the ET rate should be described by a single-level rate constant and the probing signal (often in the form of time-resolved spectra) contains the contribution from the dynamics of both population and coherence (i.e., wave packet). In this paper, we shall present the theoretical treatments for femtosecond time-resolved pump-probe experiment and the dynamics of population and coherence by the density matrix method, and the calculation of single-level ET rate constant involved in a pump-probe experiment. As an application, we show the theoretical results using parameters extracted from experiments on a specific dye/semiconductor system. [ABSTRACT FROM AUTHOR]

This paper describes a systematic study on the clathrate structure of H+(H2O)21 using tandem mass spectrometry, vibrational predissociation spectroscopy, Monte Carlo simulations, and density functional theory calculations. We produced H+(H2O)n from a continuous corona-discharged supersonic expansion and observed three anomalies simultaneously at the cluster temperature near 150 K, including (1) the peak at n=21 is more intense than its neighboring ions in the mass spectrum, (2) the size-dependent dissociation fractions show a distinct drop for the 21-mer, and (3) the infrared spectrum of H+(H2O)21 exhibits only a single feature at 3699 cm-1, corresponding to the free-OH stretching of three-coordinated water molecules. Interestingly, the anomalies appear or disappear together with cluster temperature, indicating close correlation of these three observations. The observations, together with Monte Carlo simulations and density functional theory calculations, corroborate the notion for the formation of a distorted pentagonal dodecahedral (512) cage with a H2O molecule in the cage and a H3O+ ion on the surface for this “magic number” water cluster ion. The dodecahedral cage melts at higher temperatures, as evidenced by the emergence of a free-OH stretching feature at 3717 cm-1 for the two-coordinated water in H+(H2O)21 produced in a warmer molecular beam. Extension of this study to larger clusters strongly suggests that the experimentally observed isomer of H+(H2O)28 is most likely to consist of a distorted protonated pentakaidecahedral (51263) cage enclosing two neutral water molecules. [ABSTRACT FROM AUTHOR]

This paper describes a systematic study on the clathrate structure of H+(H2O)21 using tandem mass spectrometry, vibrational predissociation spectroscopy, Monte Carlo simulations, and density functional theory calculations. We produced H+(H2O)n from a continuous corona-discharged supersonic expansion and observed three anomalies simultaneously at the cluster temperature near 150 K, including (1) the peak at n=21 is more intense than its neighboring ions in the mass spectrum, (2) the size-dependent dissociation fractions show a distinct drop for the 21-mer, and (3) the infrared spectrum of H+(H2O)21 exhibits only a single feature at 3699 cm-1, corresponding to the free-OH stretching of three-coordinated water molecules. Interestingly, the anomalies appear or disappear together with cluster temperature, indicating close correlation of these three observations. The observations, together with Monte Carlo simulations and density functional theory calculations, corroborate the notion for the formation of a distorted pentagonal dodecahedral (512) cage with a H2O molecule in the cage and a H3O+ ion on the surface for this “magic number” water cluster ion. The dodecahedral cage melts at higher temperatures, as evidenced by the emergence of a free-OH stretching feature at 3717 cm-1 for the two-coordinated water in H+(H2O)21 produced in a warmer molecular beam. Extension of this study to larger clusters strongly suggests that the experimentally observed isomer of H+(H2O)28 is most likely to consist of a distorted protonated pentakaidecahedral (51263) cage enclosing two neutral water molecules. [ABSTRACT FROM AUTHOR]

Based on the atomic electronic configuration and Ti–Se coordination, a valence bond model for the layered transition metal dichalcogenide (TMDC) 1T-TiSe2 is proposed. 1T-TiSe2 is viewed as being composed of edge-sharing TiSe4-plaquettes as TiSe2-ribbon chains in each layer via a directional valence shell electron distribution as chemical bonds, in contrast to the conventional layer view of face-sharing TiSe6-octahedra. The four valence electrons per Ti in the hybridized dsp2-orbitals of square coordination form σ-bonds with the four nearest neighbor Se atoms in the chain. The electrons in the lone pair of the Se-4pz orbital are proposed to form a dp type π-bond via side-to-side orbital overlap with the empty Ti-3dxz/3dyz orbitals within each chain, which is positively supported by quantum chemistry calculations. A study of electron energy loss spectroscopy (EELS) with transmission electron microscopy (TEM) for 1T-TiSe2 is presented to show an energy loss near ∼7 and ∼20 eV, which confirms the existence of collective plasmon oscillations with the predicted effective electron numbers for the π- and (π + σ)-bond electrons, respectively. [ABSTRACT FROM AUTHOR]