Publications

Fatigue crack propagation thresholds for long and short cracks in René 95 Nickel-base superalloy

A study was made of the near-threshold fatigue crack propagation behaviour of a wrought nickel-base superalloy, René 95, with reference to the effect of crack size on the threshold stress intensity ΔK0 no detectable crack growth. Measured threshold ΔK0 values at low load ratios (R = 0.1) for physically short (0.01 – 0.20 mm) cracks were found to be 60% smaller than the corresponding ΔK0 values for long (about 25 mm) cracks. However, short crack threshold values at R = 0.1 were found to be similar to long crack thresholds at R = 0.8. Such behavior is rationalized in terms of fatigue crack closure, specifically involving the role of fracture surface roughness from crystallographic crack growth in nickel-base alloys. The large difference observed between the threshold values for long and physically short cracks serves to illustrate the potential problems in applying conventional (long crack) fatigue data to defect-tolerant lifetime predictions for structural components containing small flaws.

Multiscale Combinatorial Grouping for Image Segmentation and Object Proposal Generation

We propose a unified approach for bottom-up hierarchical image segmentation and object proposal generation for recognition, called Multiscale Combinatorial Grouping (MCG). For this purpose, we first develop a fast normalized cuts algorithm. We then propose a high-performance hierarchical segmenter that makes effective use of multiscale information. Finally, we propose a grouping strategy that combines our multiscale regions into highly-accurate object proposals by exploring efficiently their combinatorial space. We also present Single-scale Combinatorial Grouping (SCG), a faster version of MCG that produces competitive proposals in under five seconds per image. We conduct an extensive and comprehensive empirical validation on the BSDS500, SegVOC12, SBD, and COCO datasets, showing that MCG produces state-of-the-art contours, hierarchical regions, and object proposals.

Spectral statistics across the many-body localization transition

The many-body localization transition (MBLT) between ergodic and many-body\nlocalized phase in disordered interacting systems is a subject of much recent\ninterest. Statistics of eigenenergies is known to be a powerful probe of\ncrossovers between ergodic and integrable systems in simpler examples of\nquantum chaos. We consider the evolution of the spectral statistics across the\nMBLT, starting with mapping to a Brownian motion process that analytically\nrelates the spectral properties to the statistics of matrix elements. We\ndemonstrate that the flow from Wigner-Dyson to Poisson statistics is a\ntwo-stage process. First, fractal enhancement of matrix elements upon\napproaching the MBLT from the metallic side produces an effective power-law\ninteraction between energy levels, and leads to a plasma model for level\nstatistics. At the second stage, the gas of eigenvalues has local interaction\nand level statistics belongs to a semi-Poisson universality class. We verify\nour findings numerically on the XXZ spin chain. We provide a microscopic\nunderstanding of the level statistics across the MBLT and discuss implications\nfor the transition that are strong constraints on possible theories.\n

Tearing down walls: the International Monetary Fund, 1990-1999

This volume--the fifth in a series of histories of the International Monetary Fund--examines the 1990s, a tumultuous decade in which the IMF faced difficult challenges and took on new and expanded roles. Among these were assisting countries that had long operated under central planning to manage transitions toward market economies, helping countries in financial crisis after sudden loss of support from private financial markets, adapting surveillance to reflect the growing acceptance of international standards for economic and financial policies, helping low-income countries grow and begin to eradicate poverty while staying within its mandate as a monetary institution, and providing adequate financial assistance to members in an age of limited official resources. The IMF's successes and setbacks in facing these challenges provide valuable lessons for an uncertain future

On the proposed conservation of the specific name of Australopithecus afarensis Johanson, 1978 (Mammalia, Primates)

Gold and South Africa's Great Depression

South Africa was one of the fastest growing economies of the 1930s. This paper seeks to identify the roots of this macroeconomic outperformance and reconcile it with the country's delayed departure from the gold standard, such departure having typically been the event inaugurating recovery from the slump. It emphasizes South Africa's dependence on gold production, which gave the economy an additional boost from currency depreciation, over and above that felt in other countries, when depreciation finally took place. This highlights the paradox of South African policy makers' resistance to currency depreciation, as epitomized by the report of the Select Committee on the Gold Standard in 1932.

From ethane to SDN and beyond

We briefly describe the history behind the Ethane paper and its ultimate evolution into SDN and beyond.

Extracting Structured Seed-Mediated Gold Nanorod Growth Procedures from Literature with GPT-3

Although gold nanorods have been the subject of much research, the pathways for controlling their shape and thereby their optical properties remain largely heuristically understood. Although it is apparent that the simultaneous presence of and interaction between various reagents during synthesis control these properties, computational and experimental approaches for exploring the synthesis space can be either intractable or too time-consuming in practice. This motivates an alternative approach leveraging the wealth of synthesis information already embedded in the body of scientific literature by developing tools to extract relevant structured data in an automated, high-throughput manner. To that end, we present an approach using the powerful GPT-3 language model to extract structured multi-step seed-mediated growth procedures and outcomes for gold nanorods from unstructured scientific text. GPT-3 prompt completions are fine-tuned to predict synthesis templates in the form of JSON documents from unstructured text input with an overall accuracy of $86\%$. The performance is notable, considering the model is performing simultaneous entity recognition and relation extraction. We present a dataset of 11,644 entities extracted from 1,137 papers, resulting in 268 papers with at least one complete seed-mediated gold nanorod growth procedure and outcome for a total of 332 complete procedures.

CCDC 119758: 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.

Radiative cooling, what’s next?

Iridium‐Catalyzed Regio‐ and Enantioselective Allylic Substitution of Trisubstituted Allylic Electrophiles

Abstract The first Ir‐catalyzed enantioselective allylation of trisubstituted allylic electrophiles has been developed. Through modification of the leaving group of allylic electrophiles, we found that trisubstituted allylic phosphates are suitable electrophiles for asymmetric allylation. The reaction of allylic phosphates with enol silanes derived from dioxinones gave allylated products in good yields with high enantioselectivities.

A polyketide-based biosynthetic platform for diols, amino alcohols and hydroxyacids

Abstract Medium- and branched-chain diols and amino alcohols are important industrial solvents, polymer building blocks, cosmetics and pharmaceutical ingredients, yet biosynthetically challenging to produce. Here, we present a novel approach utilising a modular polyketide synthase (PKS) platform for the efficient production of these compounds. This platform takes advantage of a versatile loading module from the rimocidin PKS and NADPH-dependent terminal thioreductases (TRs), previously untapped in engineered PKSs. Reduction of the terminal aldehyde with specific alcohol dehydrogenases enables production of diols, oxidation enables production of hydroxy acids, and transamination with specific transaminases enables production of various amino alcohols. Furthermore, replacement of the malonyl-coenzyme A (CoA)–specific acyltransferase (AT) in the extension module with methyl- or ethylmalonyl- CoA–specific ATs enables production of branched-chain diols and amino alcohols. In total, we demonstrated production of nine 1,3-diols (including the difficult-to-produce insect repellent and cosmetic ingredient 2-ethyl-1,3-hexanediol), six amino alcohols, and two carboxylic acids using our PKS platform in Streptomyces albus . Finally, tuning production of the PKS acyl-CoA substrates enabled production of high titers of specific diols and amino alcohols (1 g/L diol titer in shake flasks), demonstrating high tunability and efficiency of the platform.

CCDC 845038: 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.

How Different Is California? A Comparison Of U.S. Physician Organizations

Data from a national study of medical groups and independent practice associations are used to examine the extent to which California physician organizations are different from physician organizations in the rest of the United States. California physician organizations are different in many ways: most notably, they are more likely to have external incentives to improve quality and more likely to use recommended care management processes for treating patients with chronic illnesses. The implications of these differences for policy and practice are discussed.

An Empirical Study of Autoregressive Pre-training from Videos

We empirically study autoregressive pre-training from videos. To perform our study, we construct a series of autoregressive video models, called Toto. We treat videos as sequences of visual tokens and train transformer models to autoregressively predict future tokens. Our models are pre-trained on a diverse dataset of videos and images comprising over 1 trillion visual tokens. We explore different architectural, training, and inference design choices. We evaluate the learned visual representations on a range of downstream tasks including image recognition, video classification, object tracking, and robotics. Our results demonstrate that, despite minimal inductive biases, autoregressive pre-training leads to competitive performance across all benchmarks. Finally, we find that scaling our video models results in similar scaling curves to those seen in language models, albeit with a different rate. More details at https://brjathu.github.io/toto/

Data-Centric Storage in Sensornets with GHT, a Geographic Hash Table

UV-NIR Observations of the Probable Luminous Supernova CSS 081009:002151-163204

Pierre Bourdieu and democratic politics : the mystery of ministry

Contributors.Introduction: Symbolic Power and Democratic Practice.1 Pointers on Pierre Bourdieu and Democratic Politics.(Loic Wacquant).2 From the King's House to the Reason of State: A Model of the Genesis of the Bureaucratic Field.(Pierre Bourdieu).3 The Mystery of Ministry: From Particular Wills to the General Will.(Pierre Bourdieu).4 Scholarship with Commitment: On the Political Engagements of Pierre Bourdieu.(Franck Popupeau and Thierry Discepolo).5 Ancien Regime Ballots: A Double Historicization of Electoral Practices.(Olivier Christin).6 Making the People Speak: On the Social Uses of and Reactions to Opinion Polls.(Patrick Champagne).7 Symbolic Power in the Rule of the State Nobility.(Loic Wacquant).8 The Making and Breaking of the Czechoslovak Political Field.(Gil Eyal).9 The Cunning of Imperialist Reason.(Pierre Bourdieu and Loic Wacquant).Key Writings of Pierre Bourdieu on Democratic Politics.Index