TY - JOUR AB - In the high spin–orbit-coupled Sr2IrO4, the high sensitivity of the ground state to the details of the local lattice structure shows a large potential for the manipulation of the functional properties by inducing local lattice distortions. We use epitaxial strain to modify the Ir–O bond geometry in Sr2IrO4 and perform momentum-dependent resonant inelastic X-ray scattering (RIXS) at the metal and at the ligand sites to unveil the response of the low-energy elementary excitations. We observe that the pseudospin-wave dispersion for tensile-strained Sr2IrO4 films displays large softening along the [h,0] direction, while along the [h,h] direction it shows hardening. This evolution reveals a renormalization of the magnetic interactions caused by a strain-driven cross-over from anisotropic to isotropic interactions between the magnetic moments. Moreover, we detect dispersive electron–hole pair excitations which shift to lower (higher) energies upon compressive (tensile) strain, manifesting a reduction (increase) in the size of the charge gap. This behavior shows an intimate coupling between charge excitations and lattice distortions in Sr2IrO4, originating from the modified hopping elements between the t2g orbitals. Our work highlights the central role played by the lattice degrees of freedom in determining both the pseudospin and charge excitations of Sr2IrO4 and provides valuable information toward the control of the ground state of complex oxides in the presence of high spin–orbit coupling. AU - Paris, Eugenio AU - Tseng, Yi AU - Paerschke, Ekaterina AU - Zhang, Wenliang AU - Upton, Mary H AU - Efimenko, Anna AU - Rolfs, Katharina AU - McNally, Daniel E AU - Maurel, Laura AU - Naamneh, Muntaser AU - Caputo, Marco AU - Strocov, Vladimir N AU - Wang, Zhiming AU - Casa, Diego AU - Schneider, Christof W AU - Pomjakushina, Ekaterina AU - Wohlfeld, Krzysztof AU - Radovic, Milan AU - Schmitt, Thorsten ID - 8699 IS - 40 JF - Proceedings of the National Academy of Sciences of the United States of America SN - 00278424 TI - Strain engineering of the charge and spin-orbital interactions in Sr2IrO4 VL - 117 ER - TY - JOUR AB - Mitochondrial complex I couples NADH:ubiquinone oxidoreduction to proton pumping by an unknown mechanism. Here, we present cryo-electron microscopy structures of ovine complex I in five different conditions, including turnover, at resolutions up to 2.3 to 2.5 angstroms. Resolved water molecules allowed us to experimentally define the proton translocation pathways. Quinone binds at three positions along the quinone cavity, as does the inhibitor rotenone that also binds within subunit ND4. Dramatic conformational changes around the quinone cavity couple the redox reaction to proton translocation during open-to-closed state transitions of the enzyme. In the induced deactive state, the open conformation is arrested by the ND6 subunit. We propose a detailed molecular coupling mechanism of complex I, which is an unexpected combination of conformational changes and electrostatic interactions. AU - Kampjut, Domen AU - Sazanov, Leonid A ID - 8737 IS - 6516 JF - Science TI - The coupling mechanism of mammalian respiratory complex I VL - 370 ER - TY - CONF AB - Load imbalance pervasively exists in distributed deep learning training systems, either caused by the inherent imbalance in learned tasks or by the system itself. Traditional synchronous Stochastic Gradient Descent (SGD) achieves good accuracy for a wide variety of tasks, but relies on global synchronization to accumulate the gradients at every training step. In this paper, we propose eager-SGD, which relaxes the global synchronization for decentralized accumulation. To implement eager-SGD, we propose to use two partial collectives: solo and majority. With solo allreduce, the faster processes contribute their gradients eagerly without waiting for the slower processes, whereas with majority allreduce, at least half of the participants must contribute gradients before continuing, all without using a central parameter server. We theoretically prove the convergence of the algorithms and describe the partial collectives in detail. Experimental results on load-imbalanced environments (CIFAR-10, ImageNet, and UCF101 datasets) show that eager-SGD achieves 1.27x speedup over the state-of-the-art synchronous SGD, without losing accuracy. AU - Li, Shigang AU - Tal Ben-Nun, Tal Ben-Nun AU - Girolamo, Salvatore Di AU - Alistarh, Dan-Adrian AU - Hoefler, Torsten ID - 8722 T2 - Proceedings of the 25th ACM SIGPLAN Symposium on Principles and Practice of Parallel Programming TI - Taming unbalanced training workloads in deep learning with partial collective operations ER - TY - JOUR AB - Understanding the conformational sampling of translation-arrested ribosome nascent chain complexes is key to understand co-translational folding. Up to now, coupling of cysteine oxidation, disulfide bond formation and structure formation in nascent chains has remained elusive. Here, we investigate the eye-lens protein γB-crystallin in the ribosomal exit tunnel. Using mass spectrometry, theoretical simulations, dynamic nuclear polarization-enhanced solid-state nuclear magnetic resonance and cryo-electron microscopy, we show that thiol groups of cysteine residues undergo S-glutathionylation and S-nitrosylation and form non-native disulfide bonds. Thus, covalent modification chemistry occurs already prior to nascent chain release as the ribosome exit tunnel provides sufficient space even for disulfide bond formation which can guide protein folding. AU - Schulte, Linda AU - Mao, Jiafei AU - Reitz, Julian AU - Sreeramulu, Sridhar AU - Kudlinzki, Denis AU - Hodirnau, Victor-Valentin AU - Meier-Credo, Jakob AU - Saxena, Krishna AU - Buhr, Florian AU - Langer, Julian D. AU - Blackledge, Martin AU - Frangakis, Achilleas S. AU - Glaubitz, Clemens AU - Schwalbe, Harald ID - 8744 JF - Nature Communications KW - General Biochemistry KW - Genetics and Molecular Biology KW - General Physics and Astronomy KW - General Chemistry SN - 2041-1723 TI - Cysteine oxidation and disulfide formation in the ribosomal exit tunnel VL - 11 ER - TY - JOUR AB - Appropriately designed nanocomposites allow improving the thermoelectric performance by several mechanisms, including phonon scattering, modulation doping and energy filtering, while additionally promoting better mechanical properties than those of crystalline materials. Here, a strategy for producing Bi2Te3–Cu2xTe nanocomposites based on the consolidation of heterostructured nanoparticles is described and the thermoelectric properties of the obtained materials are investigated. We first detail a two-step solution-based process to produce Bi2Te3–Cu2xTe heteronanostructures, based on the growth of Cu2xTe nanocrystals on the surface of Bi2Te3 nanowires. We characterize the structural and chemical properties of the synthesized nanostructures and of the nanocomposites produced by hot-pressing the particles at moderate temperatures. Besides, the transport properties of the nanocomposites are investigated as a function of the amount of Cu introduced. Overall, the presence of Cu decreases the material thermal conductivity through promotion of phonon scattering, modulates the charge carrier concentration through electron spillover, and increases the Seebeck coefficient through filtering of charge carriers at energy barriers. These effects result in an improvement of over 50% of the thermoelectric figure of merit of Bi2Te3. AU - Zhang, Yu AU - Liu, Yu AU - Calcabrini, Mariano AU - Xing, Congcong AU - Han, Xu AU - Arbiol, Jordi AU - Cadavid, Doris AU - Ibáñez, Maria AU - Cabot, Andreu ID - 8747 IS - 40 JF - Journal of Materials Chemistry C TI - Bismuth telluride-copper telluride nanocomposites from heterostructured building blocks VL - 8 ER -