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Interfacial electron transfer between sensitizers and semiconducting nanoparticles is a crucial yet poorly understood process. To address this problem, we have used transient absorption (TA) and femtosecond stimulated Raman spectroscopy (FSRS) to investigate the photoexcited dynamics of a series of triphenylamine-coumarin dye/TiO2 conjugates. The TA decay is multiexponential, spanning time scales from 100 fs to 100 ps, while the characteristic transient Raman spectrum of the radical cation decays biexponentially with a dominant ∼3 ps component. To explain these observations, we propose a model in which the decay of the TA is due to hot electrons migrating from surface trap states to the conduction band of TiO 2 while the decay of the Raman signature is due to internal conversion of the dye molecule. Furthermore, the S1 Raman spectrum of TPAC3, a dye wherein a vinyl group separates the triphenylamine and coumarin moieties, is similar to the S1 Raman spectrum of trans-stilbene; we conclude that their S1 potential energy surfaces and reactivity are also similar. This correlation suggests that dyes containing vinyl linkers undergo photoisomerization that competes with electron injection. © 2013 American Chemical Society.
Abstract In these highly uncertain times, flexibility has value.
A theoretical analysis has been conducted on the selective oxidation of methanol to formaldehyde catalyzed by isolated vanadate species supported on silica. The active site was represented by a VO group substituted for a Si−H group in the corner of silsesquioxane, Si8O12H8. Calculations of ground and transition states were carried out using density functional theory, whereas statistical mechanics and absolute rate theory were used to determine equilibrium constants and rate coefficients for each elementary step. The formation of formaldehyde was found to involve two key steps. The first is the reversible adsorption of methanol, which occurs by addition across one of the three V−O−Si bonds of the active site. The rate-limiting step is the transfer of a hydrogen atom from the resulting V−OCH3 species to the VO bond of the active center. The release of formaldehyde and water from the active center leads to a two electron reduction of the vanadium atom in the center. Rapid reoxidation of the reduced vanadium can occur via adsorption of O2 to form a peroxide species and subsequent migration of one of the O atoms associated with the peroxide across the surface of the support. The predicted heat of adsorption and equilibrium constant for methanol adsorption are in good agreement with those found experimentally, as is the infrared spectrum of the adsorbed methanol. The apparent first-order rate coefficient and the apparent activation energy are also in very good agreement with the values determined experimentally.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRhenium-selenium-chlorine solid phases: cluster excision and core substitution reactions of molecular speciesOmar M. Yaghi, Michael J. Scott, and R. H. HolmCite this: Inorg. Chem. 1992, 31, 23, 4778–4784Publication Date (Print):November 1, 1992Publication History Published online1 May 2002Published inissue 1 November 1992https://pubs.acs.org/doi/10.1021/ic00049a013https://doi.org/10.1021/ic00049a013research-articleACS PublicationsRequest reuse permissionsArticle Views488Altmetric-Citations64LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
Despite advances in the treatment of bipolar disorder, a significant proportion of patients experience disabling symptoms between episodes, and relapse rates are high. These circumstances suggest that there is a critical need to achieve a mechanistic understanding of triggers of relapse and to target them with specific, empirically derived treatments. Sleep disturbances are among the most prominent correlates of mood episodes and inadequate recovery, yet sleep has been minimally studied in ways that integrate mechanistic understanding and treatment. In this article, the author seeks to define the limits of current knowledge and to specify preliminary clinical implications. Sleep disturbance is important because it impairs quality of life, contributes to relapse, and has adverse consequences for affective functioning. While sleep disturbance and circadian dysregulation are critical pathophysiological elements in bipolar disorder, many questions about the mechanisms that underpin the association remain. The author presents a model that recognizes a role for genetic vulnerability and suggests that there is a bidirectional relationship between daytime affect regulation and nighttime sleep such that an escalating vicious circle of disturbance in affect regulation during the day interferes with nighttime sleep/circadian functioning, and the effects of sleep deprivation contribute to difficulty in affect regulation the following day.
The paper presents several circuit-theory approaches for analysing the qualitative behaviour of nonlinear networks containing one or two energy-storage elements. The main concept consists in the transformation of a dynamic-network problem into an equivalent resistive-network problem. In particular, it is shown that any 1st-order nonlinear network can be analysed by obtaining the solution waveforms of an associated resistive constant-slope network. For 2nd-order autonomous nonlinear networks, it is shown that their isoclines are identical to the transfer-characteristic plots of an associated resistive isocline network. Many qualitative properties are shown to be derivable from this network. The classical approach for finding singular points, separatrices, and limit cycles is shown to have simple circuit-theory interpretations. The paper concludes with the presentation of three symmetry theorems useful for analysing 2nd-order nonlinear networks.
Instance segmentation aims to detect and segment individual objects in a scene. Most existing methods rely on precise mask annotations of every category. However, it is difficult and costly to segment objects in novel categories because a large number of mask annotations is required. We introduce ShapeMask, which learns the intermediate concept of object shape to address the problem of generalization in instance segmentation to novel categories. ShapeMask starts with a bounding box detection and gradually refines it by first estimating the shape of the detected object through a collection of shape priors. Next, ShapeMask refines the coarse shape into an instance level mask by learning instance embeddings. The shape priors provide a strong cue for object-like prediction, and the instance embeddings model the instance specific appearance information. ShapeMask significantly outperforms the state-of-the-art by 6.4 and 3.8 AP when learning across categories, and obtains competitive performance in the fully supervised setting. It is also robust to inaccurate detections, decreased model capacity, and small training data. Moreover, it runs efficiently with 150ms inference time and trains within 11 hours on TPUs. With a larger backbone model, ShapeMask increases the gap with state-of-the-art to 9.4 and 6.2 AP across categories. Code will be released.
Abstract Hydrosilyl ethers, generated in situ by the dehydrogenative silylation of cyclopropylmethanols with diethylsilane, undergo asymmetric, intramolecular silylation of cyclopropyl C−H bonds in high yields and with high enantiomeric excesses in the presence of a rhodium catalyst derived from a rhodium precursor and the bisphosphine ( S )‐DTBM‐SEGPHOS. The resulting enantioenriched oxasilolanes are suitable substrates for the Tamao–Fleming oxidation to form cyclopropanols with conservation of the ee value from the C−H silylation. Preliminary mechanistic data suggest that C−H cleavage is likely to be the turnover‐limiting and enantioselectivity‐determining step.
There was little effect of TQM and organizational culture on multiple endpoints of care for CABG patients. There is a need to examine further the relationships among individual professional skills and motivations, group and microsystem team processes, specifically tailored interventions, and organization-wide culture, decision support processes, and incentives. Assessing the impact of such multifaceted approaches is an important area for further research.
