Publications

Iridium-Catalyzed Allylic Substitution

Space Telescope and Optical Reverberation Mapping Project. VI. Reverberating Disk Models for NGS 5548

We conduct a multi-wavelength continuum variability study of the Seyfert 1 galaxy NGC 5548 to investigate the temperature structure of its accretion disk. The 19 overlapping continuum light curves (1158 Angstrom to 9157 Angstrom) combine simultaneous Hubble Space Telescope, Swift, and ground-based observations over a 180 day period from 2014 January to July. Light-curve variability is interpreted as the reverberation response of the accretion disk to irradiation by a central time-varying point source. Our model yields the disk inclination i = 36deg +/- 10deg, temperature T(sub 1) = (44+/-6) times 10 (exp 3)K at 1 light day from the black hole, and a temperature radius slope (T proportional to r (exp -alpha)) of alpha = 0.99 +/- 0.03. We also infer the driving light curve and find that it correlates poorly with both the hard and soft X-ray light curves, suggesting that the X-rays alone may not drive the ultraviolet and optical variability over the observing period. We also decompose the light curves into bright, faint, and mean accretion-disk spectra. These spectra lie below that expected for a standard blackbody accretion disk accreting at L/L(sub Edd) = 0.1.

Selective Nanocatalysis of Organic Transformation by Metals: Concepts, Model Systems, and Instruments

Monodispersed transition metal (Pt, Rh, Pd) nanoparticles (NP) in the 0.8–15 nm range have been synthesized and are being used to probe catalytic selectivity in multipath organic transformation reactions. For NP systems, the turnover rates and product distributions depend on their size, shape, oxidation states, and their composition in case of bimetallic NP systems. Dendrimer-supported platinum and rhodium NPs of less than 2 nm diameter usually have high oxidation states and can be utilized for catalytic cyclization and hydroformylation reactions which previously were produced only by homogeneous catalysis. Transition metal nanoparticles in metal core (Pt, Co)––inorganic shell (SiO2) structure exhibit exceptional thermal stability and are well-suited to perform catalytic reactions at high temperatures (>400 °C). Instruments developed in our laboratory permit the atomic and molecular level study of NPs under reaction conditions (SFG, ambient pressure XPS and high pressure STM). These studies indicate continuous restructuring of the metal substrate and the adsorbate molecules, changes of oxidation states with NP size and surface composition variations of bimetallic NPs with changes of reactant molecules. The facile rearrangement of NP catalysts required for catalytic turnover makes nanoparticle systems (heterogeneous, homogeneous and enzyme) excellent catalysts and provides opportunities to develop hybrid heterogeneous-homogeneous, heterogeneous-enzyme and homogeneous-enzyme catalyst systems.

Density Functional Theory Study of Proton Mobility in Zeolites:  Proton Migration and Hydrogen Exchange in ZSM-5

Acidic protons in zeolites are known to be mobile at elevated temperatures. In this study, density functional theory was used to identify the reaction pathways for proton migration in a model that represents the zeolite ZSM-5. In the absence of water, the acidic proton "hops" or migrates between two of the four O atoms surrounding an aluminum center with an activation barrier of 28 kcal/mol. During proton transfer, the O atoms stretch closer together in order to stabilize the transition state. This is revealed by a 13.4° decrease in the O−Al−O bond angle. Adsorbed water bridges the proton donor and acceptor sites, reducing the barrier height by 24 kcal/mol. Hence proton migration depends heavily on the local geometry and conditions of the zeolite. We show that experimentally undetectable amounts of water can greatly influence the measured rates and apparent activation barriers. We broaden the scope of our study to consider hydrogen exchange with other gas-phase species of the form RO−H (RO = CH3O, CH3CH2O) and R−H (R = H, CH3, C2H5, C3H7, C6H5). It is evident that to a first approximation the activation barrier increases with an increase in the polarizability of the species RO−H. For the chemical series R−H, the activation energy increases with the deprotonation energy of the interacting species R−H. We also calculate the overall reaction rate constants for proton hopping and hydrogen exchange.

Elastic surface—substrate interactions

A theory for three–dimensional finite deformations of elastic solids with conforming elastic films attached to their bounding surfaces is described. The Gurtin–Murdoch theory incorporating elastic resistance of the film to strain is generalized to account for the effects of intrinsic flexural resistance. This modification yields a model that can be used to describe equilibrium deformations in the presence of compressive–surface stress fields. An associated variational theory is given and material symmetry considerations are discussed. The theory is illustrated by examples.

Resilience among children and adolescents at risk for depression: Mediation and moderation across social and neurobiological contexts

This article offers a multilevel perspective on resilience to depression, with a focus on interactions among social and neurobehavioral systems involved in emotional reactivity and regulation. We discuss models of cross-contextual mediation and moderation by which the social context influences or modifies the effects of resilience processes at the biological level, or the biological context influences or modifies the effects of resilience processes at the social level. We highlight the socialization of emotion regulation as a candidate process contributing to resilience against depression at the social context level. We discuss several factors and their interactions across levels—including genetic factors, stress reactivity, positive affect, neural systems of reward, and sleep—as candidate processes contributing to resilience against depression at the neurobehavioral level. We then present some preliminary supportive findings from two studies of children and adolescents at high risk for depression. Study 1 shows that elevated neighborhood level adversity has the potential to constrain or limit the benefits of protective factors at other levels. Study 2 indicates that ease and quickness in falling asleep and a greater amount of time in deep Stage 4 sleep may be protective against the development of depressive disorders for children. The paper concludes with a discussion of clinical implications of this approach.

Direct Observation of Vapor−Liquid−Solid Nanowire Growth

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTDirect Observation of Vapor−Liquid−Solid Nanowire GrowthYiying Wu and Peidong YangView Author Information Materials Science Division Lawrence Berkeley National Laboratory Department of Chemistry University of California, Berkeley, California 94720 Cite this: J. Am. Chem. Soc. 2001, 123, 13, 3165–3166Publication Date (Web):March 13, 2001Publication History Received20 December 2000Published online13 March 2001Published inissue 1 April 2001https://pubs.acs.org/doi/10.1021/ja0059084https://doi.org/10.1021/ja0059084rapid-communicationACS PublicationsCopyright © 2001 American Chemical SocietyRequest reuse permissionsArticle Views11573Altmetric-Citations917LEARN 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-Alertsclose SUBJECTS:Alloys,Crystallization,Gold,Metal clusters,Nanowires Get e-Alerts

The Progenitors of Recent Core-Collapse Supernovae

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation N. Elias‐Rosa, S. D. Van Dyk, W. Li, A. V. Filippenko; The Progenitors of Recent Core‐Collapse Supernovae. AIP Conf. Proc. 3 May 2009; 1111 (1): 625–626. https://doi.org/10.1063/1.3141621 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

Microlithographic Assessment of a Novel Family of Transparent and Etch-Resistant Chemically Amplified 193-nm Resists Based on Cyclopolymers

The evaluation and structural optimization of a family of single layer, positive tone, chemically amplified resists for 193-nm lithography is presented. The resists are formulated from cyclopolymeric materials in which the nature, etch properties, and spatial disposition of the substituents are systematically varied. Their lithographic performance is evaluated on the basis of the interplay between chemical structure, molecular weight, and comonomer composition. These materials have good optical clarity at the desired wavelength, excellent resolution to ca. 90 nm with a phase-shifting mask, and outstanding reactive ion etch resistance.

CCDC 2026249: 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.

The Melt Viscosity of Dendritic Poly(benzyl ether) Macromolecules

The zero shear melt viscosity, eta0, for a variety of dendritic poly(benzyl ether) macromolecules has been measured. The viscosity of low generation dendrimers exhibits a strong molecular mass, M, dependence, yet, direct proportionality between eta0 and M is observed at higher generations. The viscosity scales with M for mono- and tridendrons rather than generation number. Hypercore dendrimers continue this scaling although the viscosity is slightly greater. A large deviation from the master curve for the mono- and tridendrons is found for an end-substituted monodendron. The viscosity for the end-substituted monodendron is also much more temperature dependent than virgin dendrimers, and it is concluded that end groups have a much larger effect on the viscosity than the core. Reexamination of literature data for intrinsic viscosity and glass transition temperature is performed, and these quantities also scale with molecular mass. Comparison with free volume theory indicates that the theory is extremely robust although some question of its validity is made when applied to dendrimers.

Artificial photosynthesis systems and methods for producing carbon-based chemical compounds

This disclosure provides systems, methods, and apparatus related to artificial photosynthesis. In one aspect a system includes a photoanode chamber including a photoanode assembly, a photocathode chamber including a photocathode assembly, an electrical connection electrically connecting the photoanode assembly and the photocathode assembly, a membrane separating the photoanode chamber and the photocathode chamber, and a microorganism disposed in the photocathode chamber. The photoanode assembly is operable to oxidize water to generate oxygen, protons, and electrons. The membrane is permeable to the protons and operable to allow the protons to travel to the photocathode chamber. The electrical connection provides electrons to the photocathode assembly. The microorganism comprises a metabolic pathway to reduce carbon dioxide and to generate a carbon-based compound using the electrons or hydrogen formed by two protons.

Addressing needs in the public health workforce in Europe

On the Benefits of 3D Pose and Tracking for Human Action Recognition

In this work we study the benefits of using tracking and 3D poses for action recognition. To achieve this, we take the Lagrangian view on analysing actions over a trajectory of human motion rather than at a fixed point in space. Taking this stand allows us to use the tracklets of people to predict their actions. In this spirit, first we show the benefits of using 3D pose to infer actions, and study person-person interactions. Subsequently, we propose a Lagrangian Action Recognition model by fusing 3D pose and contextualized appearance over tracklets. To this end, our method achieves state-of-the-art performance on the AVA v2.2 dataset on both pose only settings and on standard benchmark settings. When reasoning about the action using only pose cues, our pose model achieves +10.0 mAP gain over the corresponding state-of-the-art while our fused model has a gain of +2.8 mAP over the best state-of-the-art model. Code and results are available at: https://brjathu.github.io/LART

CCDC 2079319: 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.

Diffuse Electron Diffraction Intensities in Concentrated Solid Solutions Do Not Necessarily Come from Short-range Order

The observation of diffuse streaking and superlattice intensities by energy-filtered transmission electron microscopy selected area electron diffraction (EFTEM-SAED) and high-resolution STEM (HRSTEM) techniques has been attributed to the presence of chemical short-range order (SRO) in many concentrated solid solutions (Figure 1), most notably in FCC single-phase high and medium entropy alloys (HEA/MEA) [1-5].Recently, alternative interpretations have been offered on the existence of nanoscale planar defects, higher order Laue Zone effects, and atomic surface steps causing these intensities [6].In this study, we examine the plausibility of these interpretations by performing EFTEM-SAED, EF-STEM, HRS/TEM, and multislice diffraction pattern simulations on quenched and slow-cooled CrCoNi MEA.Our theoretical predictions reveal the absence of additional peaks that are expected from SRO, and we discover a large density of stacking faults (SF) and small stacking fault tetrahedra (SFT) in quenched samples (Figure 2) that contribute to the same diffuse intensities as in current experimental observations.However, the diffuse intensities persist in the slow-cooled samples where SFTs were not observed [7].

Fatigue crack propagation in oil environments—I. Crack growth behavior in silicone and paraffin oils

The influence of dehumidified silicone and paraffin oils with kinematic viscosities varying from 5 to 60,000 cS has been examined on fatigue crack propagation in a lower strength bainitic steel. Crack growth data at both low and high load ratios are compared with previous results for environments of moist air, dry gaseous hydrogen and dry gaseous helium. It is found that at low load ratios, growth rates in oil exceed those in moist air below 10−6 mm/cycle, yet are lower than in moist air above 10−6 mm/cycle. Furthermore there is a small but definite trend of higher growth rates in the higher viscosity oils. Such observations are discussed and interpreted in terms of three mutually competitive mechanisms specific to dry viscous environments, namely suppression of moisture-induced hydrogen embrittlement and/or metal dissolution, minimization of oxide-induced crack closure, and the hydrodynamic wedging action of the oil inside the crack. A quantitative analysis for the effect of crack closure induced by a viscous medium is developed in Part II of this paper.

Urban Desolation and Symbolic Denigration in the Hyperghetto

This paper is based on the ethnographic description of a devastated corridor of Chicago’s collapsing black ghetto at the end of the century and examines the links between the urban environment, the social structure, and collective psychology. It stresses the need for a theoretical and empirical foundation for studying the connections between urban desolation and symbolic denigration of poor neighborhoods in the polarized metropolises of advanced societies. It also discusses how the everyday experience of material shortages, ethnoracial seclusion, and socioeconomic marginality corrodes the self, stresses interpersonal ties, and skews public policy driven by the negative perceptions of these infamous places.