Discovery of orbital ordering in Bi2Sr2CaCu2O8+x.

The primordial ingredient of cuprate superconductivity is the CuO2 unit cell. Theories usually concentrate on the intra-atom Coulombic interactions dominating the 3d9 and 3d10 configurations of each copper ion. However, if Coulombic interactions also occur between electrons of the 2p6 orbitals of each planar oxygen atom, spontaneous orbital ordering may split their energy levels. This long-predicted intra-unit-cell symmetry breaking should generate an orbitally ordered phase, for which the charge transfer energy ε separating the 2p6 and 3d10 orbitals is distinct for the two oxygen atoms. Here we introduce sublattice-resolved ε(r) imaging to CuO2 studies and discover intra-unit-cell rotational symmetry breaking of ε(r). Spatially, this state is arranged in disordered Ising domains of orthogonally oriented orbital order bounded by dopant ions, and within whose domain walls low-energy electronic quadrupolar two-level systems occur. Overall, these data reveal a Q = 0 orbitally ordered state that splits the oxygen energy levels by ~50 meV, in underdoped CuO2.

'The area I'm from is very rough': Drug users' views on the role of social and economic factors in their experiences of drug-related harm.

Over the last thirty-five years, academic researchers in Ireland have consistently demonstrated the relationship between social deprivation and the most severe instances of drug-related harm. More recently, researchers have begun to include the voices of drug users with lived experiences of harm in these discussions. However, these studies have more often tended to focus on drug users' views on alternative drug policy options, rather than their views on the social and economic factors relevant to their experiences of drug-related harm. Therefore, the current study conducted 12 in-depth interviews with drug users experiencing harm in an Irish city, in order to elicit their views on the specific role they believe social and economic factors played in conditioning their later experiences of drug--related harm. The study participants highlight harms experienced in the education system, the family home, and the local community as more relevant to their later experiences of drug-related harm than their social deficits in education, a lack of resources in the local community or in their families. Many participants also discuss meaningful relationships as the last defence against these harms and argue that the loss of such relationships coincided with their most severe incidences of drug-related harm. The study concludes with a discussion of the conceptual framework of structural violence in terms of its potential for interpreting the participants' views and suggests several avenues for further research.

On the electron pairing mechanism of copper-oxide high temperature superconductivity.

The elementary CuO2 plane sustaining cuprate high-temperature superconductivity occurs typically at the base of a periodic array of edge-sharing CuO5 pyramids. Virtual transitions of electrons between adjacent planar Cu and O atoms, occurring at a rate t/ℏ and across the charge-transfer energy gap [Formula: see text], generate "superexchange" spin-spin interactions of energy [Formula: see text] in an antiferromagnetic correlated-insulator state. However, hole doping this CuO2 plane converts this into a very-high-temperature superconducting state whose electron pairing is exceptional. A leading proposal for the mechanism of this intense electron pairing is that, while hole doping destroys magnetic order, it preserves pair-forming superexchange interactions governed by the charge-transfer energy scale [Formula: see text]. To explore this hypothesis directly at atomic scale, we combine single-electron and electron-pair (Josephson) scanning tunneling microscopy to visualize the interplay of [Formula: see text] and the electron-pair density nP in Bi2Sr2CaCu2O8+x. The responses of both [Formula: see text] and nP to alterations in the distance δ between planar Cu and apical O atoms are then determined. These data reveal the empirical crux of strongly correlated superconductivity in CuO2, the response of the electron-pair condensate to varying the charge-transfer energy. Concurrence of predictions from strong-correlation theory for hole-doped charge-transfer insulators with these observations indicates that charge-transfer superexchange is the electron-pairing mechanism of superconductive Bi2Sr2CaCu2O8+x.

Identification of a nematic pair density wave state in Bi2Sr2CaCu2O8+x.

Electron-pair density wave (PDW) states are now an intense focus of research in the field of cuprate correlated superconductivity. PDWs exhibit periodically modulating superconductive electron pairing that can be visualized directly using scanned Josephson tunneling microscopy (SJTM). Although from theory, intertwining the d-wave superconducting (DSC) and PDW order parameters allows a plethora of global electron-pair orders to appear, which one actually occurs in the various cuprates is unknown. Here, we use SJTM to visualize the interplay of PDW and DSC states in Bi2Sr2CaCu2O8+x at a carrier density where the charge density wave modulations are virtually nonexistent. Simultaneous visualization of their amplitudes reveals that the intertwined PDW and DSC are mutually attractive states. Then, by separately imaging the electron-pair density modulations of the two orthogonal PDWs, we discover a robust nematic PDW state. Its spatial arrangement entails Ising domains of opposite nematicity, each consisting primarily of unidirectional and lattice commensurate electron-pair density modulations. Further, we demonstrate by direct imaging that the scattering resonances identifying Zn impurity atom sites occur predominantly within boundaries between these domains. This implies that the nematic PDW state is pinned by Zn atoms, as was recently proposed [Lozano et al., Phys. Rev. B 103, L020502 (2021)]. Taken in combination, these data indicate that the PDW in Bi2Sr2CaCu2O8+x is a vestigial nematic pair density wave state [Agterberg et al. Phys. Rev. B 91, 054502 (2015); Wardh and Granath arXiv:2203.08250].

Covid-19 in Critically Ill Patients in the Seattle Region - Case Series.

BACKGROUND: Community transmission of coronavirus 2019 (Covid-19) was detected in the state of Washington in February 2020. METHODS: We identified patients from nine Seattle-area hospitals who were admitted to the intensive care unit (ICU) with confirmed infection with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Clinical data were obtained through review of medical records. The data reported here are those available through March 23, 2020. Each patient had at least 14 days of follow-up. RESULTS: We identified 24 patients with confirmed Covid-19. The mean (±SD) age of the patients was 64±18 years, 63% were men, and symptoms began 7±4 days before admission. The most common symptoms were cough and shortness of breath; 50% of patients had fever on admission, and 58% had diabetes mellitus. All the patients were admitted for hypoxemic respiratory failure; 75% (18 patients) needed mechanical ventilation. Most of the patients (17) also had hypotension and needed vasopressors. No patient tested positive for influenza A, influenza B, or other respiratory viruses. Half the patients (12) died between ICU day 1 and day 18, including 4 patients who had a do-not-resuscitate order on admission. Of the 12 surviving patients, 5 were discharged home, 4 were discharged from the ICU but remained in the hospital, and 3 continued to receive mechanical ventilation in the ICU. CONCLUSIONS: During the first 3 weeks of the Covid-19 outbreak in the Seattle area, the most common reasons for admission to the ICU were hypoxemic respiratory failure leading to mechanical ventilation, hypotension requiring vasopressor treatment, or both. Mortality among these critically ill patients was high. (Funded by the National Institutes of Health.).

Ultrafast Relaxation of Symmetry-Breaking Photo-Induced Atomic Forces.

We present a first-principles method for the calculation of the temperature-dependent relaxation of symmetry-breaking atomic driving forces in photoexcited systems. We calculate the phonon-assisted decay of the photoexcited force on the low-symmetry E_{g} mode following absorption of an ultrafast pulse in Bi, Sb, and As. The force decay lifetimes for Bi and Sb are of the order of 10 fs and in agreement with recent experiments, demonstrating that electron-phonon scattering is the primary mechanism relaxing the symmetry-breaking forces. Calculations for a range of absorbed photon energies suggest that larger amplitude, symmetry-breaking atomic motion may be induced by choosing a pump photon energy which maximizes the product of the initial E_{g} force and its lifetime. The high-symmetry A_{1g} force undergoes a partial decay to a nonzero constant on similar timescales, which has not yet been measured in experiments. The average imaginary part of the electron self-energy over the photoexcited carrier distribution provides a crude indication of the decay rate of symmetry-breaking forces.

Direct Measurement of Anharmonic Decay Channels of a Coherent Phonon.

We report channel-resolved measurements of the anharmonic coupling of the coherent A_{1g} phonon in photoexcited bismuth to pairs of high wave vector acoustic phonons. The decay of a coherent phonon can be understood as a parametric resonance process whereby the atomic displacement periodically modulates the frequency of a broad continuum of modes. This coupling drives temporal oscillations in the phonon mean-square displacements at the A_{1g} frequency that are observed across the Brillouin zone by femtosecond x-ray diffuse scattering. We extract anharmonic coupling constants between the A_{1g} and several representative decay channels that are within an order of magnitude of density functional perturbation theory calculations.

The length but not the sequence of peptide linker modules exerts the primary influence on the conformations of protein domains in cellulosome multi-enzyme complexes.

Cellulosomes are large multi-protein catalysts produced by various anaerobic microorganisms to efficiently degrade plant cell-wall polysaccharides down into simple sugars. X-ray and physicochemical structural characterisations show that cellulosomes are composed of numerous protein domains that are connected by unstructured polypeptide segments, yet the properties and possible roles of these 'linker' peptides are largely unknown. We have performed coarse-grained and all-atom molecular dynamics computer simulations of a number of cellulosomal linkers of different lengths and compositions. Our data demonstrates that the effective stiffness of the linker peptides, as quantified by the equilibrium fluctuations in the end-to-end distances, depends primarily on the length of the linker and less so on the specific amino acid sequence. The presence of excluded volume - provided by the domains that are connected - dampens the motion of the linker residues and reduces the effective stiffness of the linkers. Simultaneously, the presence of the linkers alters the conformations of the protein domains that are connected. We demonstrate that short, stiff linkers induce significant rearrangements in the folded domains of the mini-cellulosome composed of endoglucanase Cel8A in complex with scaffoldin ScafT (Cel8A-ScafT) of Clostridium thermocellum as well as in a two-cohesin system derived from the scaffoldin ScaB of Acetivibrio cellulolyticus. We give experimentally testable predictions on structural changes in protein domains that depend on the length of linkers.

Controlling Protein Surface Orientation by Strategic Placement of Oligo-Histidine Tags.

We report oriented immobilization of proteins using the standard hexahistidine (His6)-Ni2+:NTA (nitrilotriacetic acid) methodology, which we systematically tuned to give control of surface coverage. Fluorescence microscopy and surface plasmon resonance measurements of self-assembled monolayers (SAMs) of red fluorescent proteins (TagRFP) showed that binding strength increased by 1 order of magnitude for each additional His6-tag on the TagRFP proteins. All TagRFP variants with His6-tags located on only one side of the barrel-shaped protein yielded a 1.5 times higher surface coverage compared to variants with His6-tags on opposite sides of the so-called ß-barrel. Time-resolved fluorescence anisotropy measurements supported by polarized infrared spectroscopy verified that the orientation (and thus coverage and functionality) of proteins on surfaces can be controlled by strategic placement of a His6-tag on the protein. Molecular dynamics simulations show how the differently tagged proteins reside at the surface in "end-on" and "side-on" orientations with each His6-tag contributing to binding. Also, not every dihistidine subunit in a given His6-tag forms a full coordination bond with the Ni2+:NTA SAMs, which varied with the position of the His6-tag on the protein. At equal valency but different tag positions on the protein, differences in binding were caused by probing for Ni2+:NTA moieties and by additional electrostatic interactions between different fractions of the ß-barrel structure and charged NTA moieties. Potential of mean force calculations indicate there is no specific single-protein interaction mode that provides a clear preferential surface orientation, suggesting that the experimentally measured preference for the end-on orientation is a supra-protein, not a single-protein, effect.