Publications

Gold(I)-Catalyzed Propargyl Claisen Rearrangement

Homoallenic alcohols are prepared from propargyl vinyl ethers using a trinuclear gold(I)-oxo complex, [(Ph3PAu)3O]BF4, as a catalyst for propargyl Claisen rearrangement at room temperature. The gold(I)-catalyzed reaction is effective for a diverse collection of propargyl vinyl ethers, including substrates containing aryl and alkyl groups at the propargylic position, and hydrogen, aryl, and alkyl substituents at the alkyne terminus. Tertiary propargyl vinyl ethers can be employed in the reaction, at slightly elevated temperatures, to afford tetrasubstituted allenes. Importantly, the rearrangement of 1,2-disubstituted vinyl ethers proceeds with excellent diastereoselectivity, and the rearrangement of chiral nonracemic propargyl vinyl ethers proceeds with excellent chirality transfer to furnish enantioenriched allenes.

Neural packet classification

Packet classification is a fundamental problem in computer networking. This problem exposes a hard tradeoff between the computation and state complexity, which makes it particularly challenging. To navigate this tradeoff, existing solutions rely on complex hand-tuned heuristics, which are brittle and hard to optimize.

Bacterial Killing by Dry Metallic Copper Surfaces

ABSTRACT Metallic copper surfaces rapidly and efficiently kill bacteria. Cells exposed to copper surfaces accumulated large amounts of copper ions, and this copper uptake was faster from dry copper than from moist copper. Cells suffered extensive membrane damage within minutes of exposure to dry copper. Further, cells removed from copper showed loss of cell integrity. Acute contact with metallic copper surfaces did not result in increased mutation rates or DNA lesions. These findings are important first steps for revealing the molecular sensitive targets in cells lethally challenged by exposure to copper surfaces and provide a scientific explanation for the use of copper surfaces as antimicrobial agents for supporting public hygiene.

CCDC 1938287: Experimental Crystal Structure Determination

The supernova delay function: recovery method and application to the Lick Observatory Supernova Search

TeraPipe: Token-Level Pipeline Parallelism for Training Large-Scale Language Models

Model parallelism has become a necessity for training modern large-scale deep language models. In this work, we identify a new and orthogonal dimension from existing model parallel approaches: it is possible to perform pipeline parallelism within a single training sequence for Transformer-based language models thanks to its autoregressive property. This enables a more fine-grained pipeline compared with previous work. With this key idea, we design TeraPipe, a high-performance token-level pipeline parallel algorithm for synchronous model-parallel training of Transformer-based language models. We develop a novel dynamic programming-based algorithm to calculate the optimal pipelining execution scheme given a specific model and cluster configuration. We show that TeraPipe can speed up the training by 5.0x for the largest GPT-3 model with 175 billion parameters on an AWS cluster with 48 p3.16xlarge instances compared with state-of-the-art model-parallel methods. The code for reproduction can be found at https://github.com/zhuohan123/terapipe

Permeability‐Engineered Compartmentalization Enables In Vitro Reconstitution of Sustained Synthetic Biology Systems

Abstract In nature, biological compartments such as cells rely on dynamically controlled permeability for matter exchange and complex cellular activities. Likewise, the ability to engineer compartment permeability is crucial for in vitro systems to gain sustainability, robustness, and complexity. However, rendering in vitro compartments such a capability is challenging. Here, a facile strategy is presented to build permeability‐configurable compartments, and marked advantages of such compartmentalization are shown in reconstituting sustained synthetic biology systems in vitro. Through microfluidics, the strategy produces micrometer‐sized layered microgels whose shell layer serves as a sieving structure for biomolecules and particles. In this configuration, the transport of DNAs, proteins, and bacteriophages across the compartments can be controlled an guided by a physical model. Through permeability engineering, a compartmentalized cell‐free protein synthesis system sustains multicycle protein production; ≈100 000 compartments are repeatedly used in a five‐cycle synthesis, featuring a yield of 2.2 mg mL −1 . Further, the engineered bacteria‐enclosing compartments possess near‐perfect phage resistance and enhanced environmental fitness. In a complex river silt environment, compartmentalized whole‐cell biosensors show maintained activity throughout the 32 h pollutant monitoring. It is anticipated that permeability‐engineered compartmentalization should pave the way for practical synthetic biology applications such as green bioproduction, environmental sensing, and bacteria‐based therapeutics.

Sex Differences in the Effects of Pubertal Development on Responses to a Corticotropin‐Releasing Hormone Challenge: The Pittsburgh Psychobiologic Studies

A bstract : We propose that sex differences in HPA regulation may emerge during puberty and help to explain sex differences in depression. In this study, we examined sex differences in cortisol responses to CRH challenge across pubertal stages in carefully screened control subjects from the Pittsburgh Psychobiologic Studies. Participants were 7‐16 years of age, physically healthy, and had no personal or family history of psychiatric disorder. Physician‐rated Tanner staging was conducted, followed by CRH challenge sessions including 30‐40 minutes pre‐infusion baseline, 1 μg/kg CRH infusion, 90‐180 minutes of post‐infusion measures, and 9‐10 plasma cortisol samples. Girls showed increasing total cortisol responses to CRH across Tanner stages, explained by slower recovery from peak cortisol levels, while boys showed similar total responses across Tanner stages. Results show subtle sex differences in the influence of puberty on HPA regulation at the pituitary level, which may represent one factor underlying the emergence of girls' greater rates of depression during this time.

Supernova 2005af in NGC 4945

3D Covalent Organic Frameworks of Interlocking 1D Square Ribbons

A new mode of mechanical entanglement in extended structures is described where 1D organic ribbons of corner-sharing squares are mutually interlocked to form 3D woven covalent organic framework-500, COF-500. Reaction of aldehyde-functionalized tetrahedral Cu(PDB)₂PO₂Ph₂ complexes (PDB = 4,4'-(1,10-phenanthroline-2,9-diyl)dibenzaldehyde) with rectangular tetratopic ETTBA (4',4‴,4''''',4''''‴-(ethene-1,1,2,2-tetrayl)tetrakis([1,1'-biphenyl]-4-amine)) linkers through imine condensation, yielded a crystalline porous metalated COF, COF-500-Cu, with pts topology. Upon removal of the Cu(I) ions, the individual 1D square ribbons in the demetalated form (COF-500) are held together only by mechanical interlocking of rings, which allows their collective movement to produce a narrow-pore form, as evidenced by nitrogen adsorption and solid-state photoluminescence studies. When exposed to tetrahydrofuran vapor, the interlocking ribbons can dynamically move away from each other to reopen up the structure. The structural integrity of COF-500 is maintained during its dynamics because the constituent square ribbons cannot part company due to spatial confinement imparted by their interlocking nature.

Understanding the Structural Evolution of IrFeCoNiCu High-Entropy Alloy Nanoparticles under the Acidic Oxygen Evolution Reaction

High-entropy alloy (HEA) nanoparticles are promising catalyst candidates for the acidic oxygen evolution reaction (OER). Herein, we report the synthesis of IrFeCoNiCu-HEA nanoparticles on a carbon paper substrate via a microwave-assisted shock synthesis method. Under OER conditions in 0.1 M HClO₄, the HEA nanoparticles exhibit excellent activity with an overpotential of ∼302 mV measured at 10 mA cm^-2 and improved stability over 12 h of operation compared to the monometallic Ir counterpart. Importantly, an active Ir-rich shell layer with nanodomain features was observed to form on the surface of IrFeCoNiCu-HEA nanoparticles immediately after undergoing electrochemical activation, mainly due to the dissolution of the constituent 3d metals. The core of the particles was able to preserve the characteristic homogeneous single-phase HEA structure without significant phase separation or elemental segregation. This work illustrates that under acidic operating conditions, the near-surface structure of HEA nanoparticles is susceptible to a certain degree of structural dynamics.

Brønsted Acidity in Metal–Organic Frameworks

ADVERTISEMENT RETURN TO ISSUEPREVReviewBrønsted Acidity in Metal–Organic FrameworksJuncong Jiang*† and Omar M. Yaghi*†§View Author Information† Department of Chemistry, University of California—Berkeley, Materials Sciences Division, Lawrence Berkeley National Laboratory, and Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720, United States§ King Fahd University of Petroleum and Minerals, Dhahran 34464, Saudi Arabia*J.J. e-mail: [email protected]*O.M.Y e-mail: [email protected]Cite this: Chem. Rev. 2015, 115, 14, 6966–6997Publication Date (Web):June 19, 2015Publication History Received13 April 2015Published online19 June 2015Published inissue 22 July 2015https://pubs.acs.org/doi/10.1021/acs.chemrev.5b00221https://doi.org/10.1021/acs.chemrev.5b00221review-articleACS PublicationsCopyright © 2015 American Chemical SocietyRequest reuse permissionsArticle Views15329Altmetric-Citations476LEARN 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 SUBJECTS:Acidity,Ammonia,Brønsted acid,Metal organic frameworks,Molecules Get e-Alerts

A Modal Pushover Analysis Procedure to Estimate Seismic Demands for Buildings: Theory and Preliminary Evaluation

CCDC 1473706: 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.

<i>gem</i>‐Difluoroallylation of Aryl Halides and Pseudo Halides with Difluoroallylboron Reagents in High Regioselectivity

Abstract We report the palladium‐catalyzed gem ‐difluoroallylation of aryl halides and pseudo halides with 3,3‐difluoroallyl boronates in high yield with high regioselectivity, and we report the preparation of the 3,3‐difluoroallyl boronate reactants by a copper‐catalyzed defluorinative borylation of inexpensive gaseous 3,3,3‐trifluoropropene with bis(pinacolato)diboron. The gem ‐difluoroallylation of aryl and heteroaryl bromides proceeds with low catalyst loading (0.1 mol % [Pd]) and tolerates a wide range of functional groups, including primary alcohols, secondary amines, ethers, ketones, esters, amides, aldehydes, nitriles, halides, and nitro groups. This protocol extends to aryl iodides, chlorides, and triflates, as well as substituted difluoroallyl boronates, providing a versatile synthesis of gem ‐difluoroallyl arenes that we show to be valuable intermediates to a series of fluorinated building blocks.

Equivalence of coupled parametric oscillator dynamics to Lagrange multiplier primal-dual optimization

There has been a recent surge of interest in physics-based solvers for combinatorial optimization problems. We present a dynamical solver for the Ising problem that is comprised of a network of coupled parametric oscillators and show that it implements Lagrange multiplier constrained optimization. We show that the pump depletion effect, which is intrinsic to parametric oscillators, enforces binary constraints and enables the system's continuous analog variables to converge to the optimal binary solutions to the optimization problem. Moreover, there is an exact correspondence between the equations of motion for the coupled oscillators and the update rules in the primal-dual method of Lagrange multipliers. Though our analysis is performed using electrical LC oscillators, it can be generalized to any system of coupled parametric oscillators. We simulate the dynamics of the coupled oscillator system and demonstrate that the performance of the solver on a set of benchmark problems is comparable to the best-known results obtained by digital algorithms in the literature.

Effect of <i>l</i> <i>acY</i> Expression on Homogeneity of Induction from the P _t _ac and P _trc Promoters by Natural and Synthetic Inducers

Abstract The role of the Escherichia coli lactose permease (LacY) in the homogeneous induction of the lactose‐inducible promoters P tac and P trc by the natural inducer lactose and the synthetic inducer isopropyl‐β‐ d ‐thiogalactopyranoside (IPTG) was investigated. Lactose requires active transport by LacY, whereas IPTG can freely penetrate the cell wall. In E. coli strains lacking a functional LacY, IPTG is required for induction of P tac and P trc . In E. coli strains carrying a functional LacY, induction of P trc and P tac with intermediate concentrations of lactose gave rise to two subpopulations, one fully induced and one uninduced, whereas a single, fully induced population resulted when high inducer concentrations were used. In contrast, induction with IPTG gave rise to a single population of cells at all inducer concentrations in both lacY and lacY + strains.

Supplementary Table 2 from Intestinal Bacteria Modify Lymphoma Incidence and Latency by Affecting Systemic Inflammatory State, Oxidative Stress, and Leukocyte Genotoxicity

&lt;p&gt;PDF file - 61K, Relative Abundance of Phyla of CM and RM Mice by Genotype and Intestinal Region.&lt;/p&gt;