The SPEAK study rationale and design: A linguistic corpus-based approach to understanding thought disorder.

AIM: Psychotic symptoms are typically measured using clinical ratings, but more objective and sensitive metrics are needed. Hence, we will assess thought disorder using the Research Domain Criteria (RDoC) heuristic for language production, and its recommended paradigm of "linguistic corpus-based analyses of language output". Positive thought disorder (e.g., tangentiality and derailment) can be assessed using word-embedding approaches that assess semantic coherence, whereas negative thought disorder (e.g., concreteness, poverty of speech) can be assessed using part-of-speech (POS) tagging to assess syntactic complexity. We aim to establish convergent validity of automated linguistic metrics with clinical ratings, assess normative demographic variance, determine cognitive and functional correlates, and replicate their predictive power for psychosis transition among at-risk youths. METHODS: This study will assess language production in 450 English-speaking individuals in Australia and Canada, who have recent onset psychosis, are at clinical high risk (CHR) for psychosis, or who are healthy volunteers, all well-characterized for cognition, function and symptoms. Speech will be elicited using open-ended interviews. Audio files will be transcribed and preprocessed for automated natural language processing (NLP) analyses of coherence and complexity. Data analyses include canonical correlation, multivariate linear regression with regularization, and machine-learning classification of group status and psychosis outcome. CONCLUSIONS: This prospective study aims to characterize language disturbance across stages of psychosis using computational approaches, including psychometric properties, normative variance and clinical correlates, important for biomarker development. SPEAK will create a large archive of language data available to other investigators, a rich resource for the field.

Structure of the rutile TiO2(011) surface in an aqueous environment.

First principles simulations are carried out to investigate the structure and stability of the rutile TiO2(011) surface in contact with liquid water. Whereas this surface exhibits a (2×1) reconstruction in vacuo, our results show that the interaction with water leads to an inversion of the stabilities of the reconstructed and unreconstructed surfaces. This indicates that surface structures determined in vacuo or at low water coverages are not generally representative of those occurring in the aqueous environments typical of most photocatalytic applications of TiO2.

Electronic structure of metal/molecule//metal junctions: a density functional theory study of the influence of the molecular terminal group.

We report on density functional theory calculations of the electronic structure of Au(111)/molecule//Au(111) junctions in which thiol molecules are chemically bound at one end to a gold electrode (the "substrate"), while the other end has a separation of a few to several angstroms from a second gold electrode (the "tip"). Our goal is to investigate the role of different molecular terminal groups and of the tip-molecule distance either on the spatial dependence of the local density of states (LDOS) at the Fermi energy E(f) or on the energy dependence of the projected density of states onto different molecular subunits. We consider conjugated diphenylthiol (SPh2R) molecules with terminal groups R = H, SH, CH3, or CF3 as well as "mixed" conjugated-saturated phenylthiol-pentane (SPhC4CH3) and butanethiol-toluene (SC4PhCH3) molecules. For SPh2R molecules, the LDOS at E(f) exhibits an oscillatory exponential decay along the molecule, with an average decay constant that depends weakly on the R terminal group. For the mixed aromatic-aliphatic molecules instead, there are large differences in the LDOS at E(f), with SC4PhCH3 showing a much larger LDOS in the proximity of the terminal CH3 group than SPhC4CH3.

First-principles string molecular dynamics: an efficient approach for finding chemical reaction pathways.

A recently proposed approach, called "string method," allows us to find minimum energy pathways connecting two metastable states of a system [W. E et al., Phys. Rev. B 66, 052301 (2002)]. So far this approach has been only used with empirical force field parametrizations of the atomic potential energy surface or in the context of macroscopic continuum models. Here we show that the string method can be efficiently combined with first-principles molecular dynamics to provide an accurate description of chemical reaction pathways and barriers. We illustrate the first-principles string molecular dynamics by applying it to the study of a surface chemical reaction, for which extensive experimental and theoretical works are available, namely, the adsorption of H(2) on the reconstructed Si(100) surface.

Stress-driven reconstruction of an oxide surface: the anatase TiO(2)(001)-(1 x 4) surface.

The recently discovered (1 x 4) reconstruction of the stoichiometric anatase TiO(2)(001) surface is studied via first principles density functional calculations. We propose a new structural model for this reconstruction, which is energetically much more favorable than all the other available models, including the unreconstructed (1 x 1) surface. In this model, rows of TiO(3) species periodically replace rows of surface bridging oxygens of the (1 x 1) surface, thus leading to a relief of the large surface tensile stress present on that surface. The corresponding empty-state charge density distribution correctly describes the experimental scanning tunneling microscopy images.