Publications

CCDC 257951: Experimental Crystal Structure Determination

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Effect of Polyphosphate Metabolism on the Escherichia coli Phosphate-Starvation Response

A previously developed dynamic model of the Escherichia coli Pho regulon was extended to investigate the effect of polyphosphate synthesis and degradation on this control system. Differential equations for ATP and polyphosphate were formulated, and the model was applied to the growth of cells containing the ppk and ppx genes under control of separate, inducible promoters. In agreement with recent experimental observations, the degradation of polyphosphate by PPX during a period of phosphate limitation could repress the phosphate-starvation response. This is attributed to the release of phosphate from the cell into the periplasm, where it can be detected by the external phosphate sensor. A segregated model was then developed to account for differences in K(I), the dissociation constant for the repression complex, among cells of the population. Since K(I) is the key parameter in determining whether the Pho response is induced or repressed at a particular surface phosphate concentration, this permitted the induction of some cells while others remained repressed. The induction profiles resulting from the population-averaged values more closely matched experimental results than did those with the nonsegregated model.

The impact of inadequate sleep on children's daytime cognitive function

Asymmetric additions to dienes catalysed by a dithiophosphoric acid

Poly-Autoregressive Prediction for Modeling Interactions

Development of the Squaramide Scaffold for High Potential and Multielectron Catholytes for Use in Redox Flow Batteries

Nonaqueous organic redox flow batteries (N-ORFBs) are a promising technology for grid-scale storage of energy generated from intermittent renewable sources. Their primary benefit over traditional aqueous RFBs is the wide electrochemical stability window of organic solvents, but the design of catholyte materials, which can exploit the upper range of this window, has proven challenging. We report herein a new class of N-ORFB catholytes in the form of squaric acid quinoxaline (SQX) and squaric acid amide (SQA) materials. Mechanistic investigation of decomposition in battery-relevant conditions via NMR, HRMS, and electrochemical methods enabled a rational design approach to optimizing these scaffolds. Three lead compounds were developed: a highly stable one-electron SQX material with an oxidation potential of 0.51 V vs Fc/Fc⁺ that maintained 99% of peak capacity after 102 cycles (51 h) when incorporated into a 1.58 V flow battery; a high-potential one-electron SQA material with an oxidation potential of 0.81 V vs Fc/Fc⁺ that demonstrated negligible loss of redox active material as measured by pre- and postcycling CV peak currents when incorporated in a 1.63 V flow battery for 110 cycles over 29 h; and a proof-of-concept two-electron SQA catholyte material with oxidation potentials of 0.48 and 0.85 V vs Fc/Fc⁺ that demonstrated a capacity fade of just 0.56% per hour during static H-cell cycling. These findings expand the previously reported space of high-potential catholyte materials and showcase the power of mechanistically informed synthetic design for N-ORFB materials development.

CCDC 1938285: Experimental Crystal Structure Determination

Self-Assembly, Molecular Ordering, and Charge Mobility in Solution-Processed Ultrathin Oligothiophene Films

Symmetrical α,ω-substituted quarter-(T4), penta-(T5), sexi-(T6), and heptathiophene (T7) oligomers containing thermally removable aliphatic ester solubilizing groups were synthesized, and their UV−vis and thermal characteristics were compared. Spun-cast thin films of each oligomer were examined with atomic force microscopy and near-edge X-ray absorption fine structure spectroscopy to evaluate the ability of the material to self-assemble from a solution-based process while maintaining complete surface coverage. Films of the T5−T7 oligomers self-assemble into crystalline terraces after thermal annealing with higher temperatures required to affect this transformation as the size of the oligomers increases. A symmetrical α,ω-substituted sexithiophene (T6-acid) that reveals carboxylic acids after thermolysis was also prepared to evaluate the effect of the presence of hydrogen-bonding moieties. The charge transport properties for these materials evaluated in top-contact thin film transistor devices were found to correlate with the observed morphology of the films. Therefore, the T4 and the T6-acid performed poorly because of incomplete surface coverage after thermolysis, while T5−T7 exhibited much higher performance as a result of molecular ordering. Increases in charge mobility correlated to increasing conjugation length with measured mobilities ranging from 0.02 to 0.06 cm2/(V·s). The highest mobilities were measured when films of each oligomer had an average thickness between one and two monolayers, indicating that the molecules become exceptionally well-ordered during the thermolysis process. This unprecedented ordering of the solution-cast molecules results in efficient charge mobility rarely seen in such ultrathin films.

A model for surface diffusion of trans-membrane proteins on lipid bilayers

The DNA Damage Response Arouses the Immune System

Abstract Although there is considerable knowledge of how DNA damage triggers cell cycle arrest, DNA repair, and apoptosis, little was known about its potential role in immune responses. Recently, we showed that genotoxic stress and stalled DNA replication forks induce the expression of ligands for the NKG2D receptor found in natural killer cells and certain T cells, cell types that are able to attack tumor cells. Chronic activation of this response in tumor cells may contribute to immune recognition, but it also imposes a selection mechanism for immune escape and malignant progression. This unique arm of the DNA damage response may have implications for understanding therapeutic responses, many of which induce the DNA damage response, and for designing more effective regimens to treat cancer. (Cancer Res 2006; 66(8): 3959-62)

The effect of hospital control strategies on physician satisfaction and physician-hospital conflict.

This article examines several strategies that hospitals use to control their medical staffs. Such strategies include placing physicians on salary, developing exclusive hospital affiliations with physicians, and involving physicians in decision-making bodies. Using regression techniques, we investigate which hospitals are more likely to utilize these strategies and whether such strategies are effective in promoting physician-hospital integration. Contrary to our expectations, corporate hospital structures (e.g., for-profit hospitals, membership in multihospital systems) generally do not employ these strategies more often and oftentimes employ them less. There is also little evidence that control strategies are effective levers for increasing physician satisfaction or decreasing physician-hospital conflict. We suggest that control strategies are useful for purposes other than promoting physician-hospital integration. Finally, hospital ownership appears to exert the biggest effect on physician satisfaction and conflict.

[Skeletal myorhythmias due to lesions of the dentate nucleus and superior cerebellar peduncle in decortication].

Switchable and Tunable Radiative Cooling: Mechanisms, Applications, and Perspectives

The cost of annual energy consumption in buildings in the United States exceeds 430 billion dollars ( <i>Science</i> 2019, 364 (6442), 760-763), of which about 48% is used for space thermal management (https://www.iea.org/reports/global-status-report-for-buildings-and-construction-2019), revealing the urgent need for efficient thermal management of buildings and dwellings. Radiative cooling technologies, combined with the booming photonic and microfabrication technologies ( <i>Nature</i> 2014, 515 (7528), 540-544), enable energy-free cooling by radiative heat transfer to outer space through the atmospheric transparent window ( <i>Nat. Commun.</i> 2024, 15 (1), 815). To pursue all-season energy savings in climates with large temperature variations, switchable and tunable radiative coolers (STRC) have emerged in recent years and quickly gained broad attention. This Perspective introduces the existing STRC technologies and analyzes their benefits and challenges in future large-scale applications, suggesting ways for the development of future STRCs.

Shape contexts enable efficient retrieval of similar shapes

In this paper we demonstrate that a recently introduced shape descriptor, the "shape context", can be used to quickly prune a search for similar shapes. Our representation for a shape is a discrete set of n points sampled from its internal and external contours. For each of these points, the shape context is a histogram of the relative positions of the n - 1 remaining points. We present two methods for rapid shape retrieval: one that does comparisons based on a small number of shape contexts and another that uses vector quantization in the space of shape contexts. We verify the discriminative power of these methods with tests on the Columbia (COIL-100) 3D object database and the Snodgrass and Vanderwart line drawings. The shape context-based methods are shown to quickly produce an accurate shortlist of candidates suitable for a more exact matching engine in spite of pose variation and occlusion.

Food webs and resource sheds : towards spatially delimiting trophic interactions

Automated Tuberculosis Diagnosis Using Fluorescence Images from a Mobile Microscope

CO Oxidation Mechanisms on CoO_<i>x</i>-Pt Thin Films

The reaction of CO and O₂ with submonolayer and multilayer CoO_<i>x</i> films on Pt(111), to produce CO₂, was investigated at room temperature in the mTorr pressure regime. Using operando ambient pressure X-ray photoelectron spectroscopy and high pressure scanning tunneling microscopy, as well as density functional theory calculations, we found that the presence of oxygen vacancies in partially oxidized CoO_<i>x</i> films significantly enhances the CO oxidation activity to form CO₂ upon exposure to mTorr pressures of CO at room temperature. In contrast, CoO films without O-vacancies are much less active for CO₂ formation at RT, and CO only adsorbed in the form of carbonate species that are stable up to 260 °C. On submonolayer CoO_<i>x</i> islands, the carbonates form preferentially at island edges, deactivating the edge sites for CO₂ formation, even while the reaction proceeds inside the islands. These results provide a detailed understanding of CO oxidation pathways on systems where noble metals such as Pt interact with reducible oxides.

Faculty Opinions recommendation of Global change biology: A primer.

Because of human action, the Earth has entered an era where profound changes in the global environment are creating novel conditions that will be discernable far into the future. One consequence may be a large reduction of the Earth's biodiversity, potentially representing a sixth mass extinction. With effective stewardship, the global change drivers that threaten the Earth's biota could be alleviated, but this requires clear understanding of the drivers, their interactions, and how they impact ecological communities. This review identifies 10 anthropogenic global change drivers and discusses how six of the drivers (atmospheric CO2 enrichment, climate change, land transformation, species exploitation, exotic species invasions, eutrophication) impact Earth's biodiversity. Driver impacts on a particular species could be positive or negative. In either case, they initiate secondary responses that cascade along ecological lines of connection and in doing so magnify the initial impact. The unique nature of the threat to the Earth's biodiversity is not simply due to the magnitude of each driver, but due to the speed of change, the novelty of the drivers, and their interactions. Emphasizing one driver, notably climate change, is problematic because the other global change drivers also degrade biodiversity and together threaten the stability of the biosphere. As the main academic journal addressing global change effects on living systems, GCB is well positioned to provide leadership in solving the global change challenge. If humanity cannot meet the challenge, then GCB is positioned to serve as a leading chronicle of the sixth mass extinction to occur on planet Earth.© 2019 John Wiley & Sons Ltd. PMID: 31663217 Funding information This work was supported by: Natural Science and Engineering Research Council of Canada, International Grant ID: RGPIN-2017-06476