Publications

Exceptional fracture toughness of CrCoNi-based medium- and high-entropy alloys close to liquid helium temperatures

Medium- and high-entropy alloys based on the CrCoNi-system have been shown to display outstanding strength, tensile ductility and fracture toughness (damage-tolerance properties), especially at cryogenic temperatures. Here we examine the JIc and (back-calculated) KJIc fracture toughness values of the face-centered cubic, equiatomic CrCoNi and CrMnFeCoNi alloys at 20 K. At flow stress values of ~1.5 GPa, crack-initiation KJIc toughnesses were found to be exceptionally high, respectively 235 and 415 MPa(square-root)m for CrMnFeCoNi and CrCoNi, with the latter displaying a crack-growth toughness Kss exceeding 540 MPa(square-root)m after 2.25 mm of stable cracking, which to our knowledge is the highest such value ever reported. Characterization of the crack-tip regions in CrCoNi by scanning electron and transmission electron microscopy reveal deformation structures at 20 K that are quite distinct from those at higher temperatures and involve heterogeneous nucleation, but restricted growth, of stacking faults and fine nano-twins, together with transformation to the hexagonal closed-packed phase. The coherent interfaces of these features can promote both the arrest and transmission of dislocations to generate respectively strength and ductility which strongly contributes to sustained strain hardening. Indeed, we believe that these nominally single-phase, concentrated solid-solution alloys develop their fracture resistance through a progressive synergy of deformation mechanisms, including dislocation glide, stacking-fault formation, nano-twinning and eventually in situ phase transformation, all of which serve to extend continuous strain hardening which simultaneously elevates strength and ductility (by delaying plastic instability), leading to truly exceptional resistance to fracture.

Where Did the Euro Go Wrong?

The euro crisis may have been an inevitable result of the ideologically driven arguments for adopting the common currency—or of incompatible national economic philosophies.

Surface chemistry-mechanical property relationship of low density polyethylene: an IR+visible sum frequency generation spectroscopy and atomic force microscopy study

Expressed Emotion in Mothers of Currently Depressed, Remitted, High-Risk, and Low-Risk Youth: Links to Child Depression Status and Longitudinal Course

This study examined expressed emotion in the families of children and adolescents who were (a) in a current episode of Major Depressive Disorder (MDD), (b) in remission from a past episode of MDD, (c) at high familial risk for developing MDD, and (d) low-risk controls. Participants were 109 mother-child dyads (children ages 8-19). Expressed emotion was assessed using the Five Minute Speech Sample, and psychiatric follow-ups were conducted annually. Mothers of children with a current or remitted episode of MDD and at high risk for MDD were more likely to be rated high on criticism than mothers of controls. There were no differences in critical expressed emotion among mothers of children in the current, remitted, or high-risk for depression groups. Higher initial critical expressed emotion was associated with a greater likelihood of having a future onset of a depressive episode in high-risk and depressed participants. Diagnostic groups did not differ in Emotional Overinvolvement.

Current-enabled optical conductivity of superconductors

In most superconductors, optical excitations require impurity scattering or the presence of multiple bands. This is because in clean single-band superconductors, the combination of particle-hole and inversion symmetries prevents momentum-conserving transitions. In this Letter we show how the flow of supercurrent can lead to new contributions to optical conductivity. As the supercurrent breaks inversion symmetry, transitions across the superconducting gap become allowed even in clean superconductors and dominate over impurity-induced contributions for energies comparable to the gap width. Further, the response is dependent on the nature of the underlying normal state as well as on the type of superconducting order. Use of an external magnetic field to produce a screening supercurrent with controllable magnitude and direction, enables a detailed investigation of the superconducting state, allowing determination of the gap symmetry in unconventional superconductors for which other techniques have not been practicable.

The Chua Lectures: From Memristors and Cellular Nonlinear Networks to the Edge of Chaos

Marginalité, ethnicité et pénalité dans la ville néolibérale : une cartographie analytique

Cet article dresse une cartographie analytique du programme de recherche poursuivi au fil de mes trois livres Parias urbains (2006), Punishing the Poor : The Neoliberal Government of Social Insecurity (2009), et Deadly Symbiosis : Race and the Rise of the Penal State (2015). Dans cette trilogie, je démêle les rapports triangulaires entre fragmentation de classe, division ethnique et remodelage de l’État dans la ville polarisée au tournant du siècle pour rendre compte de la production politique, de la distribution sociospatiale et de la gestion punitive de la marginalité par le couplage de politiques sociales disciplinaires et de politiques de justice neutralisantes. J’indique comment je déploie des notions clef de Pierre Bourdieu (espace social, champ bureaucratique, pouvoir symbolique) pour clarifier des catégories restées floues (telle celle de ghetto) et forger de nouveaux concepts (stigmatisation territoriale et marginalité avancée, contention punitive et libéral-paternalisme, hyperincarcération et sociodicée négative) comme outils pour une sociologie comparée de la genèse inachevée du précariat post-industriel, de la régulation punitive de la pauvreté à l’ère de l’insécurité sociale diffuse et de la construction du Léviathan néolibéral. Intégrer l’étude des permutations contemporaines de la formation de classes, de la domination ethnoraciale et de l’immigration, et de l’État dans un même cadre montre comment la racisation, la pénalisation et la dépolitisation des turbulences urbaines associées à la marginalité avancée se renforcent circulairement sur le continent européen comme aux États-Unis. Ce cadre confirme que le châtiment n’est pas seulement un indicateur saillant de la solidarité sociale, comme le proposait jadis Durkheim, mais aussi une capacité politique et un site crucial pour mettre en scène la souveraineté de l’État comme instance de classification et stratification. Et il révèle la parenté profonde entre race et sanction judiciaire comme formes germaines du déshonneur officiel qui convergent dans la fabrication de parias publics.

Copper-Mediated Perfluoroalkylation of Heteroaryl Bromides with (phen)CuR_F

The attachment of perfluoroalkyl groups onto organic compounds has been a major synthetic goal over the past several decades. Previously, our group reported phenanthroline-ligated perfluoroalkyl copper reagents, (phen)CuRF, which react with aryl iodides and aryl boronates to form the corresponding benzotrifluorides. Herein the perfluoroalkylation of a series of heteroaryl bromides with (phen)CuCF3 and (phen)CuCF2CF3 is reported. The mild reaction conditions allow the process to tolerate many common functional groups. Perfluoroethylation with (phen)CuCF2CF3 occurs in somewhat higher yields than trifluoromethylation with (phen)CuCF3, creating a method to generate fluoroalkyl heteroarenes that are less accessible from trifluoroacetic acid derivatives.

CCDC 829035: 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.

Modulation of gene expression from the arabinose-inducible araBAD promoter

The arabinose-inducible PBAD promoter suffers from all-or-none gene expression in which cells harboring the natively controlled arabinose transport gene (araE) are either induced or uninduced, the relative fraction of which is controlled by the concentration of arabinose. The population-averaged variation in expression from PBAD as a function of inducer concentration is proportional to the percentage of cells that are fully induced (vs. uninduced) rather than the level of expression in individual cells. Because of its undesirable effects on the expression of heterologous genes, the all-or-none phenomenon was eliminated in Escherichia coli by expression of araE from arabinose-independent (either the Lactococcus lactis constitutive or IPTG-inducible lac) promoters. In these arabinose-transport engineered cells, variation in PBAD expression with arabinose concentration was a result of variation of the expression level in individual cells with all cells in the population having approximately the same induction level. Journal of Industrial Microbiology & Biotechnology (2002) 29, 34–37 doi:10.1038/sj.jim.7000259

Direct Michael Addition of Alkenes via a Cobalt-Dinitrosyl Mediated Vinylic C–H Functionalization Reaction

We report a one-pot, direct C-H functionalization reaction of alkenes mediated by [CpCo(NO)(2)]. All intermediates in the proposed reaction sequence have been characterized. A variety of Michael acceptors can be utilized with the one-pot procedure to give the desired cyclic tetra-alkyl-substituted, γ,δ-unsaturated compounds in good yields. We also provide a preliminary result for catalytic turnover in both base and [CpCo(NO)(2)].

Faculty Opinions recommendation of The human footprint in the carbon cycle of temperate and boreal forests.

Temperate and boreal forests in the Northern Hemisphere cover an area of about 2 x 10(7) square kilometres and act as a substantial carbon sink (0.6-0.7 petagrams of carbon per year). Although forest expansion following agricultural abandonment is certainly responsible for an important fraction of this carbon sink activity, the additional effects on the carbon balance of established forests of increased atmospheric carbon dioxide, increasing temperatures, changes in management practices and nitrogen deposition are difficult to disentangle, despite an extensive network of measurement stations. The relevance of this measurement effort has also been questioned, because spot measurements fail to take into account the role of disturbances, either natural (fire, pests, windstorms) or anthropogenic (forest harvesting). Here we show that the temporal dynamics following stand-replacing disturbances do indeed account for a very large fraction of the overall variability in forest carbon sequestration. After the confounding effects of disturbance have been factored out, however, forest net carbon sequestration is found to be overwhelmingly driven by nitrogen deposition, largely the result of anthropogenic activities. The effect is always positive over the range of nitrogen deposition covered by currently available data sets, casting doubts on the risk of widespread ecosystem nitrogen saturation under natural conditions. The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly (through forest management) or indirectly (through nitrogen deposition). PMID: 17568744

CCDC 837471: 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.

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

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Rationalization of the tensile creep behavior of the Nb45Ta25Ti15Hf15 bcc refractory complex concentrated alloy using Rao-Suzuki screw dislocation glide model

Transient analysis of nonlinear transmission lines by hybrid harmonic balance method

The authors discuss a transient analysis of transmission lines terminated by nonlinear subnetworks. In this analysis, the circuit is partitioned into the transmission line and nonlinear subnetwork by using a substitution source. The transmission line is solved by the phasor technique or perturbation method, and the nonlinear subnetwork by a numerical integration technique. The substitution source giving rise to the transient response is calculated by application of the relaxation hybrid harmonic balance method.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Forest Canopy Temperature: a comparison between an isotopic measurement approach and photosynthesis-weighted air temperature

PTF10nvg: An Outbursting Class I Protostar in the Pelican/North American Nebula

During a synoptic survey of the North American Nebula region, the Palomar Transient Factory (PTF) detected an optical outburst (dubbed PTF10nvg) associated with the previously unstudied flat or rising spectrum infrared source IRAS 20496+4354. The PTF R-band light curve reveals that PTF10nvg brightened by more than 5 mag during the current outburst, rising to a peak magnitude of R PTF ≈ 13.5 in 2010 September. Follow-up observations indicate that PTF10nvg has undergone a similar ~5 mag brightening in the K band and possesses a rich emission-line spectrum, including numerous lines commonly assumed to trace mass accretion and outflows. Many of these lines are blueshifted by ~175 km s–1 from the North American Nebula's rest velocity, suggesting that PTF10nvg is driving an outflow. Optical spectra of PTF10nvg show several TiO/VO band heads fully in emission, indicating the presence of an unusual amount of dense (&gt;1010 cm–3), warm (1500-4000 K) circumstellar material. Near-infrared spectra of PTF10nvg appear quite similar to a spectrum of McNeil's Nebula/V1647 Ori, a young star which has undergone several brightenings in recent decades, and 06297+1021W, a Class I protostar with a similarly reached near-infrared emission line spectrum. While further monitoring is required to fully understand this event, we conclude that the brightening of PTF10nvg is indicative of enhanced accretion and outflow in this Class-I-type protostellar object, similar to the behavior of V1647 Ori in 2004-2005.