Second-order optimisation strategies for neural network quantum states

The Variational Monte Carlo method has recently seen important advances through the use of neural network quantum states. While more and more sophisticated ans\"atze have been designed to tackle a wide variety of quantum many-body problems, modest progress has been made on the associated optimisation algorithms. In this work, we revisit the Kronecker Factored Approximate Curvature, an optimiser that has been used extensively in a variety of simulations. We suggest improvements on the scaling and the direction of this optimiser, and find that they substantially increase its performance at a negligible additional cost. We also reformulate the Variational Monte Carlo approach in a game theory framework, to propose a novel optimiser based on decision geometry. We find that, on a practical test case for continuous systems, this new optimiser consistently outperforms any of the KFAC improvements in terms of stability, accuracy and speed of convergence. Beyond Variational Monte Carlo, the versatility of this approach suggests that decision geometry could provide a solid foundation for accelerating a broad class of machine learning algorithms.Comment: 32 pages, 9 figures, 4 tables. Submitted to PRS

Fluid Dynamic Modeling of Oxygen Permeation through Mixed Ionic-Electronic Conducting Membranes

[EN] The oxygen transport in a lab-scale experimental set-up for permeation testing of oxygen transport membranes has been modeled using computational fluid dynamics using Finite Element Analysis. The modeling considered gas hydrodynamics and oxygen diffusion in the gas phase and vacancy diffusion of oxygen in a perovskite disc-shaped membrane at 1273. K. In a first step, the model allowed obtaining the coefficient diffusion of oxygen. The parametric study showed that the set-up geometry and flow rate in the air compartment did not have major influence in the oxygen transport. However, very important polarization effects in the sweep-gas (argon) compartment were identified. The highest oxygen permeation flux and the lowest oxygen concentration on the membrane surface were obtained for the following conditions (in increasing order of importance): (1) a large gas inlet radius; (2) short gas inlet distance; and (3) a high gas flow rate. © 2011 Elsevier B.V.The Spanish Ministry for Science and Innovation (JAE-Pre 08-0058 grant and ENE2008-06302 project) and through FP7 NASA-OTM Project (NMP3-SL-2009-228701) is kindly acknowledged.Gozálvez-Zafrilla, JM.; Santafé Moros, MA.; Escolástico Rozalén, S.; Serra Alfaro, JM. (2011). Fluid Dynamic Modeling of Oxygen Permeation through Mixed Ionic-Electronic Conducting Membranes. Journal of Membrane Science. 378(1-2):290-300. https://doi.org/10.1016/j.memsci.2011.05.016S2903003781-

Highly conductive grain boundaries in cold-sintered barium zirconate-based proton conductors

Proton-conducting barium zirconate ceramics have shown large potential for efficient electrochemical conversion and separation processes at intermediate operation temperatures. The high energy efficiency, robustness, and intermediate-temperature operation (500-650 °C) make proton-conducting cells promising candidates for future energy conversion systems. However, the major disadvantages of these materials are the inevitable high-sintering temperatures (>1500 °C), leading to Ba-evaporation and formation of high-resistance grain boundaries, which dominate the electrochemical performance. Here, we introduce a novel processing route for proton-conducting barium zirconates, which, on the one hand, significantly lowers the maximum processing temperature and, on the other hand, overcomes the dominating influence of grain boundaries on total conductivity. The key step of this novel processing route is the cold sintering of the powder using pure water as a sintering aid to consolidate BaZrCeYO (BZCY) at 350 °C. We show that clean grain boundaries with a high acceptor-dopant concentration are preserved thanks to the recovery of the perovskite phase during thermal treatment at 1300 °C. This compensates the interfacial core charge, resulting in highly conductive grain boundaries, which do not limit the total conductivity. Consequently, dense BZCY electrolytes produced by our novel approach outperform the conductivity of conventionally sintered BZCY irrespective of the significantly lower maximum processing temperature and its nanocrystalline microstructure. Our presented approach opens up new possibilities for grain boundary engineering and might facilitate novel co-sintering pathways for barium zirconate-based components.The authors acknowledge Dr Doris Sebold for help with SEM investigations and Dr Yoo Jung Sohn for assistance with HT-XRD measurements. M. K. acknowledges financial support from the DFG under project number MA 1280/69-1. Additionally, D. J. and W. R. thank the DFG for funding within the Emmy Noether program (RH 146/1-1). A. V. expresses gratitude to Dr Ivan Povstugar for his insightful discussions on the quality of APT data and its reconstruction. The authors thank Hitachi High-Technologies for providing access to the HF5000 STEM located at ER-C

Neural crest-related NXPH1/α-NRXN signaling opposes neuroblastoma malignancy by inhibiting organotropic metastasis

Neuroblastoma is a pediatric cancer that can present as low- or high-risk tumors (LR-NBs and HR-NBs), the latter group showing poor prognosis due to metastasis and strong resistance to current therapy. Whether LR-NBs and HR-NBs differ in the way they exploit the transcriptional program underlying their neural crest, sympatho-adrenal origin remains unclear. Here, we identified the transcriptional signature distinguishing LR-NBs from HR-NBs, which consists mainly of genes that belong to the core sympatho-adrenal developmental program and are associated with favorable patient prognosis and with diminished disease progression. Gain- and loss-of-function experiments revealed that the top candidate gene of this signature, Neurexophilin-1 (NXPH1), has a dual impact on NB cell behavior in vivo: whereas NXPH1 and its receptor α-NRXN1 promote NB tumor growth by stimulating cell proliferation, they conversely inhibit organotropic colonization and metastasis. As suggested by RNA-seq analyses, these effects might result from the ability of NXPH1/α-NRXN signalling to restrain the conversion of NB cells from an adrenergic state to a mesenchymal one. Our findings thus uncover a transcriptional module of the sympatho-adrenal program that opposes neuroblastoma malignancy by impeding metastasis, and pinpoint NXPH1/α-NRXN signaling as a promising target to treat HR-NBs.This work was supported by grants from the Ministerio de Ciencia e Innovacion, Gobierno de España (MCINN; BFU2016-81887-REDT and BFU2016-77498-P) and the Asociación Española Contra el Cancer (AECC CI_2016) to EM, from the Fondo de Investigación en Salud (FIS) - Instituto de salud Carlos III (PI14/00038) and the NEN association (Association of Families and Friends of Patients with Neuroblastoma) to CL, from the Instituto de Salud Carlos III-FSE (MS17/00037; PI18/00014; PI21/00020) to TC-T, from Instituto de Salud Carlos III (CP22/00127, co-funded by European Social Fund “Investing in your future”) to BMJ, from the Agence Nationale pour la Recherche (ANR-17-CE14-0023-01, ANR-17-CE14-0009-02) and the city of Paris (Emergence program) to ELG, from ISCIII-FEDER (CP13/00189 and CPII18/00009) to AMC. LF received a PhD fellowship from the Spanish Ministry of Science, Education and Universities (FPU AP2012-2222). LT-D was funded by a FPI Fellowship (PRE2019-088005). GLD was supported by the Asociación Española Contra el Cancer (AECC #AIO14142105LED)

Redox-stable composite electrodes for CH4 conversion reactors based on proton ceramic electrochemical cells

Electrochemical reactors based on proton-conducting ceramic electrolytes show a great potential in the conversion of hydrocarbons by enabling the intensification via the in-situ extraction of the H produced. However, non-oxidative operation conditions lead to the progressive coke formation on the catalyst and electrodes and thus, an oxidative regeneration cycle is required to restore the catalyst activity. Consequently, newly redox-stable electrodes are required to enable operation under both non-oxidative H-extraction and coke-oxidation conditions. Here, four composite materials were investigated as redox-stable electrode backbones for their integration in proton-conducting cells, composed by the proton conductor BaCeZrYO (BCZY27) and LaSrFeO (LSF8515), LaSrFeO (LSF55), LaSrCrMnO (LSCM) or LaSrMnO (LSM). Chemical compatibility with the electrolyte and electrochemical performance were characterized in the range 500–800 °C. LSCM/BCZY27 and LSM/BCZY27 showed the best performance. The electrode activity was boosted by catalytically activating with Pt and CeO nanoparticles while exhibiting outstanding stability upon redox cycling. LSM/BCZY27+Pt/CeO showed the lowest polarization resistance, i.e., achieving 0.7 Ω cm at 700 °C in 10% CH and 9% H and 0.14 Ω cm in air, revealing a high potential as redox-stable electrode for non-oxidative hydrocarbon conversion in electrochemical reactors.Part of the present research was developed in the frame of N. Bausá’s PhD thesis (Chapter 9) that has received funding from Spanish Government (RTI2018-102161 grant). This work has been also supported by the WINNER project. This project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking (now Clean Hydrogen Partnership) under Grant Agreement No 101007165. This Joint Undertaking receives support from the European Union's Horizon 2020 Research and Innovation program, Hydrogen Europe and Hydrogen Europe Research

Towards upscaling of La5.5WO11.25-d manufacture for Plasma Spraying-Thin Film coated hydrogen permeable membranes

Lanthanum tungstate (La6WO12) is a promising material for the development of hydrogen separation membranes, proton ceramic electrolyzer cells and protonic ceramic fuel cells due to its interesting transport properties and stability under different operation conditions. In order to improve the hydrogen transport through the La6WO12 membranes, thin membranes should be manufactured. This work is based on the industrial production of La5.5WO11.25-¿ (LWO) powder by spray drying and the manufacturing of thin membranes by low-pressure plasma spraying (LPPS-TF) technique. LPPS-TF allows the production of dense thin films of high quality in an industrial scale. The powders produced by spray drying were morphological and electrochemically characterized. Hydrogen permeation fluxes of a membrane manufactured with these powders were evaluated and fluxes are similar to those reported previously for LWO powder produced in the lab scale. Finally, the transport properties of LWO thin films deposited on Al2O3 indicate that LPPS-TF produces high-quality LWO films with potential for integration in different applications.This work was financially supported by the European Union (DEMOYS Project, FP7/2007-2013-Grant Agreement 241309) and the Spanish Government (RTI2018-102161, SEV-2016-0683 and IJCI-2016-28330 grants)

Evaluation of Er Doped CeO2-δ as Oxygen Transport Membrane

Ceria based materials are robust candidates for a range of applications involving redox reactions and high oxygen activity. The substitution of erbium in the ceria lattice introduces extrinsic oxygen vacancies. Further addition of Co introduces electronic carriers. We have studied the structural and redox behavior of CeErO (x = 0.1 and 0.2) and the influence of adding 2 mol% of Co in the electrochemical properties. A limitation in the solubility of Er cation is found. Diffusion and surface exchange coefficients have been obtained by electrical conductivity relaxation and the DC-conductivity and O permeation measurements show the importance of the electronic component in the transport properties, obtaining an oxygen permeation flux of 0.07 mL min cm at 1000 ºC, for a 769 μm thick membrane.This research was funded byMinisterio de Ciencia e Innovación, grant number IJCI-2017-34110

Interaction of bentonite with supercritically carbonated concrete

Bentonite and concrete are essential components in construction of a geological high level nuclear waste (HLNW) repository. Conventional Ordinary Portland Cement (OPC) used for concretes gives a pore water leachate with a pH as high as 13.5 in contact with ground water. This alkaline plume of leaching waters might perturb the engineered barrier system, which might include bentonite buffer, backfill material or the near-field host rock. The accepted solution to maintain the bentonite stability, which is controlled by the pH, is to develop cementitious materials with pore water pH around 11. Four lixiviation experiments representative of long-term interaction of solids and pore fluids at the concrete/bentonite interface were performed with two types of cement paste, Portland and calcium aluminate cement, before and after being carbonated under supercritical conditions, with granite water at 80 °C. The evolution of the pH indicates that the supercritical carbonation reduced the alkalinity of the cement pastes and calcite likely controls the equilibrium of Ca at the end of the experiments. The bentonite helps to buffer the alkalinity of concrete leachates through several reactions such as dissolution of montmorillonite and precipitation of secondary products as trioctahedral smectite, zeolites (gismondine), and presumably Mg hydroxides and amorphous gels. Carbonation may reduce propagation of the alkaline plume and enhance the barrier performance.Peer reviewe

HSP90 and checkpoint-dependent lengthening of the G2 phase observed in plant cells under hypoxia and cold

Proliferating cells of Allium cepa L. roots became adapted to hypoxia (5% oxygen) and cold (10°C) by acquiring new steady-state kinetics of growth. The cell cycle time increased from the 17.6 h in control meristems up to 29.7 and 69.0 h under hypoxia and cold conditions, respectively. Acclimation of the proliferating cells was stress specific. No acclimation took place after 24 h of heat treatment (40°C). Under cold treatment, all cycle phases enlarged uniformly. However, under hypoxia, while the G1 and S cycle phases roughly doubled in their timing, the expected checkpoint-dependent lengthening of G2 did not take place. This failure in lengthening G2 in response to hypoxia correlated with a failure in the overinduction of a single peptide with a molecular mass of about 134 kDa which is among those recognised by an HSP90 antibody. Moreover, the presence of this large peptide of the HSP90 family proved to be a marker for cell proliferation. It was always absent from the contiguous differentiated cells of the root. Lastly, the mitochondrial chaperonin recognized by an HSP60 antibody in these roots not involved in photosynthesis was always higher in the proliferating than in the nonproliferating cells

The Greatwall–Endosulfine Switch Accelerates Autophagic Flux during the Cell Divisions Leading to G1 Arrest and Entry into Quiescence in Fission Yeast

Entry into quiescence in the fission yeast Schizosaccharomyces pombe is induced by nitrogen starvation. In the absence of nitrogen, proliferating fission yeast cells divide twice without cell growth and undergo cell cycle arrest in G1 before becoming G0 quiescent cells. Under these conditions, autophagy is induced to produce enough nitrogen for the two successive cell divisions that take place before the G1 arrest. In parallel to the induction of autophagy, the Greatwall–Endosulfine switch is activated upon nitrogen starvation to down-regulate protein phosphatase PP2A/B55 activity, which is essential for cell cycle arrest in G1 and implementation of the quiescent program. Here we show that, although inactivation of PP2A/B55 by the Greatwall–Endosulfine switch is not required to promote autophagy initiation, it increases autophagic flux at least in part by upregulating the expression of a number of autophagy-related genes