Showing papers by "Collège de France published in 2017"

Hierarchically porous materials: synthesis strategies and structure design

Abstract: Owing to their immense potential in energy conversion and storage, catalysis, photocatalysis, adsorption, separation and life science applications, significant interest has been devoted to the design and synthesis of hierarchically porous materials. The hierarchy of materials on porosity, structural, morphological, and component levels is key for high performance in all kinds of applications. Synthesis and applications of hierarchically structured porous materials have become a rapidly evolving field of current interest. A large series of synthesis methods have been developed. This review addresses recent advances made in studies of this topic. After identifying the advantages and problems of natural hierarchically porous materials, synthetic hierarchically porous materials are presented. The synthesis strategies used to prepare hierarchically porous materials are first introduced and the features of synthesis and the resulting structures are presented using a series of examples. These involve templating methods (surfactant templating, nanocasting, macroporous polymer templating, colloidal crystal templating and bioinspired process, i.e. biotemplating), conventional techniques (supercritical fluids, emulsion, freeze-drying, breath figures, selective leaching, phase separation, zeolitization process, and replication) and basic methods (sol–gel controlling and post-treatment), as well as self-formation phenomenon of porous hierarchy. A series of detailed examples are given to show methods for the synthesis of hierarchically porous structures with various chemical compositions (dual porosities: micro–micropores, micro–mesopores, micro–macropores, meso–mesopores, meso–macropores, multiple porosities: micro–meso–macropores and meso–meso–macropores). We hope that this review will be helpful for those entering the field and also for those in the field who want quick access to helpful reference information about the synthesis of new hierarchically porous materials and methods to control their structure and morphology.

Thermoelectric transport in disordered metals without quasiparticles: The Sachdev-Ye-Kitaev models and holography

Abstract: We compute the thermodynamic properties of the Sachdev-Ye-Kitaev (SYK) models of fermions with a conserved fermion number Q. We extend a previously proposed Schwarzian effective action to include a phase field, and this describes the low-temperature energy and Q fluctuations. We obtain higher-dimensional generalizations of the SYK models which display disordered metallic states without quasiparticle excitations, and we deduce their thermoelectric transport coefficients. We also examine the corresponding properties of Einstein-Maxwell-axion theories on black brane geometries which interpolate from either AdS4 or AdS5 to an AdS2×R2 or AdS2×R3 near-horizon geometry. These provide holographic descriptions of nonquasiparticle metallic states without momentum conservation. We find a precise match between low-temperature transport and thermodynamics of the SYK and holographic models. In both models, the Seebeck transport coefficient is exactly equal to the Q derivative of the entropy. For the SYK models, quantum chaos, as characterized by the butterfly velocity and the Lyapunov rate, universally determines the thermal diffusivity, but not the charge diffusivity.

What is consciousness, and could machines have it?

Abstract: The controversial question of whether machines may ever be conscious must be based on a careful consideration of how consciousness arises in the only physical system that undoubtedly possesses it: the human brain. We suggest that the word “consciousness” conflates two different types of information-processing computations in the brain: the selection of information for global broadcasting, thus making it flexibly available for computation and report (C1, consciousness in the first sense), and the self-monitoring of those computations, leading to a subjective sense of certainty or error (C2, consciousness in the second sense). We argue that despite their recent successes, current machines are still mostly implementing computations that reflect unconscious processing (C0) in the human brain. We review the psychological and neural science of unconscious (C0) and conscious computations (C1 and C2) and outline how they may inspire novel machine architectures.

Activation of surface oxygen sites on an iridium-based model catalyst for the oxygen evolution reaction

Abstract: The oxygen evolution reaction (OER) is of prime importance in multiple energy storage devices; however, deeper mechanistic understanding is required to design enhanced electrocatalysts for the reaction. Current understanding of the OER mechanism based on oxygen adsorption on a metallic surface site fails to fully explain the activity of iridium and ruthenium oxide surfaces, and the drastic surface reconstruction observed for the most active OER catalysts. Here we demonstrate, using La2LiIrO6 as a model catalyst, that the exceptionally high activity found for Ir-based catalysts arises from the formation of active surface oxygen atoms that act as electrophilic centres for water to react. Moreover, with the help of transmission electron microscopy, we observe drastic surface reconstruction and iridium migration from the bulk to the surface. Therefore, we establish a correlation between surface activity and surface stability for OER catalysts that is rooted in the formation of surface reactive oxygen.

Fundamental interplay between anionic/cationic redox governing the kinetics and thermodynamics of lithium-rich cathodes

Abstract: Reversible anionic redox has rejuvenated the search for high-capacity lithium-ion battery cathodes. Real-world success necessitates the holistic mastering of this electrochemistry's kinetics, thermodynamics, and stability. Here we prove oxygen redox reactivity in the archetypical lithium-and manganese-rich layered cathodes through bulk-sensitive synchrotron based spectroscopies, and elucidate their complete anionic/cationic charge-compensation mechanism. Furthermore, via various electroanalytical methods, we answer how the anionic/cationic interplay governs application-wise important issues—namely sluggish kinetics, large hysteresis, and voltage fade—that afflict these promising cathodes despite widespread industrial and academic efforts. We find that cationic redox is kinetically fast and without hysteresis unlike sluggish anions, which furthermore show different oxidation vs. reduction potentials. Additionally, more time spent with fully oxidized oxygen promotes voltage fade. These fundamental insights about anionic redox are indispensable for improving lithium-rich cathodes. Moreover, our methodology provides guidelines for assessing the merits of existing and future anionic redox-based high-energy cathodes, which are being discovered rapidly.

Heterogeneity of neuroblastoma cell identity defined by transcriptional circuitries

Abstract: Neuroblastoma is a tumor of the peripheral sympathetic nervous system(1), derived from multipotent neural crest cells (NCCs). To define core regulatory circuitries (CRCs) controlling the gene expression program of neuroblastoma, we established and analyzed the neuroblastoma super-enhancer landscape. We discovered three types of identity in neuroblastoma cell lines: a sympathetic noradrenergic identity, defined by a CRC module including the PHOX2B, HAND2 and GATA3 transcription factors (TFs); an NCC-like identity, driven by a CRC module containing AP-1 TFs; and a mixed type, further deconvoluted at the single-cell level. Treatment of the mixed type with chemotherapeutic agents resulted in enrichment of NCC-like cells. The noradrenergic module was validated by ChIP-seq. Functional studies demonstrated dependency of neuroblastoma with noradrenergic identity on PHOX2B, evocative of lineage addiction. Most neuroblastoma primary tumors express TFs from the noradrenergic and NCC-like modules. Our data demonstrate a previously unknown aspect of tumor heterogeneity relevant for neuroblastoma treatment strategies.

Upper Limits on the Stochastic Gravitational-Wave Background from Advanced LIGO's First Observing Run

Abstract: A wide variety of astrophysical and cosmological sources are expected to contribute to a stochastic gravitational-wave background. Following the observations of GW150914 and GW151226, the rate and mass of coalescing binary black holes appear to be greater than many previous expectations. As a result, the stochastic background from unresolved compact binary coalescences is expected to be particularly loud. We perform a search for the isotropic stochastic gravitational-wave background using data from Advanced Laser Interferometer Gravitational Wave Observatory’s (aLIGO) first observing run. The data display no evidence of a stochastic gravitational-wave signal. We constrain the dimensionless energy density of gravitational waves to be Ω 0 < 1.7 × 10 − 7 with 95% confidence, assuming a flat energy density spectrum in the most sensitive part of the LIGO band (20–86 Hz). This is a factor of ∼ 33 times more sensitive than previous measurements. We also constrain arbitrary power-law spectra. Finally, we investigate the implications of this search for the background of binary black holes using an astrophysical model for the background.

Evidence for anionic redox activity in a tridimensional-ordered Li-rich positive electrode β-Li2IrO3.

Abstract: Lithium-ion battery cathode materials have relied on cationic redox reactions until the recent discovery of anionic redox activity in Li-rich layered compounds which enables capacities as high as 300 mAh g-1. In the quest for new high-capacity electrodes with anionic redox, a still unanswered question was remaining regarding the importance of the structural dimensionality. The present manuscript provides an answer. We herein report on a β-Li2IrO3 phase which, in spite of having the Ir arranged in a tridimensional (3D) framework instead of the typical two-dimensional (2D) layers seen in other Li-rich oxides, can reversibly exchange 2.5 e- per Ir, the highest value ever reported for any insertion reaction involving d-metals. We show that such a large activity results from joint reversible cationic (Mn+) and anionic (O2)n- redox processes, the latter being visualized via complementary transmission electron microscopy and neutron diffraction experiments, and confirmed by density functional theory calculations. Moreover, β-Li2IrO3 presents a good cycling behaviour while showing neither cationic migration nor shearing of atomic layers as seen in 2D-layered Li-rich materials. Remarkably, the anionic redox process occurs jointly with the oxidation of Ir4+ at potentials as low as 3.4 V versus Li+/Li0, as equivalently observed in the layered α-Li2IrO3 polymorph. Theoretical calculations elucidate the electrochemical similarities and differences of the 3D versus 2D polymorphs in terms of structural, electronic and mechanical descriptors. Our findings free the structural dimensionality constraint and broaden the possibilities in designing high-energy-density electrodes for the next generation of Li-ion batteries.

PHIBSS: Unified Scaling Relations of Gas Depletion Time and Molecular Gas Fractions

Abstract: This paper provides an update of our previous scaling relations (Genzel et al.2015) between galaxy integrated molecular gas masses, stellar masses and star formation rates, in the framework of the star formation main-sequence (MS), with the main goal to test for possible systematic effects. For this purpose our new study combines three independent methods of determining molecular gas masses from CO line fluxes, far-infrared dust spectral energy distributions, and ~1mm dust photometry, in a large sample of 1444 star forming galaxies (SFGs) between z=0 and 4. The sample covers the stellar mass range log(M*/M_solar)=9.0-11.8, and star formation rates relative to that on the MS, delta_MS=SFR/SFR(MS), from 10^{-1.3} to 10^{2.2}. Our most important finding is that all data sets, despite the different techniques and analysis methods used, follow the same scaling trends, once method-to-method zero point offsets are minimized and uncertainties are properly taken into account. The molecular gas depletion time t_depl, defined as the ratio of molecular gas mass to star formation rate, scales as (1+z)^{-0.6}x(delta_MS)^{-0.44}, and is only weakly dependent on stellar mass. The ratio of molecular-to-stellar mass mu_gas depends on (1+z)^{2.5}x (delta_MS)^{0.52}x(M*)^{-0.36}, which tracks the evolution of the specific star formation rate. The redshift dependence of mu_gas requires a curvature term, as may the mass-dependences of t_depl and mu_gas. We find no or only weak correlations of t_depl and mu_gas with optical size R or surface density once one removes the above scalings, but we caution that optical sizes may not be appropriate for the high gas and dust columns at high-z.

Neurophysiological dynamics of phrase-structure building during sentence processing

Abstract: Although sentences unfold sequentially, one word at a time, most linguistic theories propose that their underlying syntactic structure involves a tree of nested phrases rather than a linear sequence of words. Whether and how the brain builds such structures, however, remains largely unknown. Here, we used human intracranial recordings and visual word-by-word presentation of sentences and word lists to investigate how left-hemispheric brain activity varies during the formation of phrase structures. In a broad set of language-related areas, comprising multiple superior temporal and inferior frontal sites, high-gamma power increased with each successive word in a sentence but decreased suddenly whenever words could be merged into a phrase. Regression analyses showed that each additional word or multiword phrase contributed a similar amount of additional brain activity, providing evidence for a merge operation that applies equally to linguistic objects of arbitrary complexity. More superficial models of language, based solely on sequential transition probability over lexical and syntactic categories, only captured activity in the posterior middle temporal gyrus. Formal model comparison indicated that the model of multiword phrase construction provided a better fit than probability-based models at most sites in superior temporal and inferior frontal cortices. Activity in those regions was consistent with a neural implementation of a bottom-up or left-corner parser of the incoming language stream. Our results provide initial intracranial evidence for the neurophysiological reality of the merge operation postulated by linguists and suggest that the brain compresses syntactically well-formed sequences of words into a hierarchy of nested phrases.

Autoimmune and inflammatory manifestations occur frequently in patients with primary immunodeficiencies

Abstract: Background Primary immunodeficiencies (PIDs) are inherited diseases associated with a considerable increase in susceptibility to infections. It is known that PIDs can also predispose to cancer and immune diseases, including allergy, autoimmunity, and inflammation. Objective We aimed at determining the incidence of autoimmunity and inflammation in patients with PIDs. Methods We have retrospectively screened 2183 consecutive cases of PID in the Centre de Reference Deficits Immunitaires Hereditaires registry (CEREDIH; the French national PID registry) for the occurrence of autoimmunity and inflammation. Results One or more autoimmune and inflammatory complications were noted in 26.2% of patients, with a risk of onset throughout the patient's lifetime. The risk of autoimmune cytopenia was at least 120 times higher than in the general population, the risk of inflammatory bowel disease in children was 80 times higher, and the risk of other autoimmune manifestations was approximately 10 times higher. Remarkably, all types of PIDs were associated with a risk of autoimmune and inflammatory complications, although the greatest risk was associated with T-cell PIDs and common variable immunodeficiency. The occurrence of autoimmune disease is a negative prognostic factor for survival. Conclusions Our results provide the basis for a detailed prospective evaluation of autoimmunity and inflammation in the context of PIDs, with a view to accurately assessing these risks and describing the possible effect of medical intervention.

Intrinsic antiproliferative activity of the innate sensor STING in T lymphocytes.

Abstract: Activation of the cyclic dinucleotide sensor stimulator of interferon (IFN) genes (STING) is critical for IFN and inflammatory gene expression during innate immune responses. However, the role of STING in adaptive immunity is still unknown. In this study, we show that STING activation reduces the proliferation of T lymphocytes. This activity was independent of TBK1 and IRF3 recruitment and of type I IFN but required a distinct C-terminal domain of STING that activates NF-κB. Inhibition of cell proliferation by STING required its relocalization to the Golgi apparatus and caused mitotic errors. T lymphocytes from patients carrying constitutive active mutations in TMEM173 encoding STING showed impaired proliferation and reduced numbers of memory cells. Endogenous STING inhibited proliferation of mouse T lymphocytes. Therefore, STING, a critical innate sensor, also functions intrinsically in cells of the adaptive immune system to inhibit proliferation.

Maximizing the Photocatalytic Activity of Metal–Organic Frameworks with Aminated-Functionalized Linkers: Substoichiometric Effects in MIL-125-NH2

Abstract: Despite the promise of utilizing metal–organic frameworks (MOFs) as highly tunable photocatalytic materials, systematic studies that interrogate the relationship between their catalytic performances and the amount of functionalized linkers are lacking Aminated linkers are known to enhance the absorption of light and afford photocatalysis with MOFs under visible-light irradiation However, the manner in which the photocatalytic performances are impacted by the amount of such linkers is poorly understood Here, we assess the photocatalytic activity of MIL-125, a TiO2/1,4-benzenedicarboxylate (bdc) MOF for the oxidation of benzyl alcohol to benzaldehyde when increasing amounts of bdc-NH2 linkers (0%, 20%, 46%, 70%, and 100%) are incorporated in the framework Analytical TEM allowed assessing the homogeneous localization of bdc-NH2 in these mixed-linker MOFs Steady state reaction rates reveal two regimes of catalytic performances: a first linear regime up to ∼50% bdc-NH2 into the hybrid framework whereby in

High and Stable Ionic Conductivity in 2D Nanofluidic Ion Channels between Boron Nitride Layers.

Abstract: Achieving a high rate of ionic transport through porous membranes and ionic channels is important in numerous applications ranging from energy storage to water desalination, but it still remains a challenge. Herein we show that ions can quickly pass through interlayer spaces in hydrated boron nitride (BN) membranes. Measurements of surface-charge governed ionic currents between BN nanosheets in a variety of salt solutions (KCl, NaCl and CaCl2) at low salt concentrations (<10–4 M) showed several orders of magnitude higher ionic conductivity compared to that of the bulk solution. Moreover, due to the outstanding chemical and thermal stability of BN, the ionic conduits remain fully functional at temperatures up to 90 °C. The BN conduits can operate in acidic and basic environments and do not degrade after immersing in solutions with extreme pH (pH ∼ 0 or 14) for 1 week. Those excellent properties make the BN ionic conduits attractive for applications in nanofluidic devices and membrane separation.

Power-law statistics and universal scaling in the absence of criticality.

Abstract: Critical states are sometimes identified experimentally through power-law statistics or universal scaling functions. We show here that such features naturally emerge from networks in self-sustained irregular regimes away from criticality. In these regimes, statistical physics theory of large interacting systems predict a regime where the nodes have independent and identically distributed dynamics. We thus investigated the statistics of a system in which units are replaced by independent stochastic surrogates and found the same power-law statistics, indicating that these are not sufficient to establish criticality. We rather suggest that these are universal features of large-scale networks when considered macroscopically. These results put caution on the interpretation of scaling laws found in nature.

A ferroelectric quantum phase transition inside the superconducting dome of Sr1-xCaxTiO3-[delta]

Abstract: Slight changes in SrTiO’s nominal composition make it superconducting or ferroelectric. A compositional window for which the two phases exist is now reported; varying the fraction of Ca replacing Sr changes the superconducting critical temperature. SrTiO3, a quantum paraelectric1, becomes a metal with a superconducting instability after removal of an extremely small number of oxygen atoms2. It turns into a ferroelectric upon substitution of a tiny fraction of strontium atoms with calcium3. The two orders may be accidental neighbours or intimately connected, as in the picture of quantum critical ferroelectricity4. Here, we show that in Sr1−xCaxTiO3−δ (0.002 < x < 0.009, δ < 0.001) the ferroelectric order coexists with dilute metallicity and its superconducting instability in a finite window of doping. At a critical carrier density, which scales with the Ca content, a quantum phase transition destroys the ferroelectric order. We detect an upturn in the normal-state scattering and a significant modification of the superconducting dome in the vicinity of this quantum phase transition. The enhancement of the superconducting transition temperature with calcium substitution documents the role played by ferroelectric vicinity in the precocious emergence of superconductivity in this system, restricting possible theoretical scenarios for pairing.

Porous Boron Carbon Nitride Nanosheets as Efficient Metal-Free Catalysts for the Oxygen Reduction Reaction in Both Alkaline and Acidic Solutions

Abstract: Carbon materials have become a hot topic as potential substitutes for Pt/C catalysts for the oxygen reduction reaction (ORR). However, most of them exhibit their catalytic activities only in alkaline solutions, which severely limits their application in polyelectrolyte membrane fuel cells. To address this issue, here porous boron carbon nitride (BCN) nanosheets are fabricated by a facile and efficient polymer sol–gel method, which involves the annealing of polyvinylic akohol (PVA), boric acid, guanidine, and poly(ethylene oxide-co-propylene oxide) (P123) gel mixtures. The as-prepared porous BCN nanosheets possess a high surface area of 817 m2/g and display impressive ORR catalytic performance in both alkaline and acidic media, rivalling that of commercial Pt/C and other recently reported carbon materials. Importantly, the resulting metal-free catalysts exhibit much greater durability and higher methanol tolerance in both alkaline and acidic environments. This study provides a new insight into metal-free O...

Coupling between Myogenesis and Angiogenesis during Skeletal Muscle Regeneration Is Stimulated by Restorative Macrophages

Abstract: In skeletal muscle, new functions for vessels have recently emerged beyond oxygen and nutrient supply, through the interactions that vascular cells establish with muscle stem cells. Here, we demonstrate in human and mouse that endothelial cells (ECs) and myogenic progenitor cells (MPCs) interacted together to couple myogenesis and angiogenesis in vitro and in vivo during skeletal muscle regeneration. Kinetics of gene expression of ECs and MPCs sorted at different time points of regeneration identified three effectors secreted by both ECs and MPCs. Apelin, Oncostatin M, and Periostin were shown to control myogenesis/angiogenesis coupling in vitro and to be required for myogenesis and vessel formation during muscle regeneration in vivo. Furthermore, restorative macrophages, which have been previously shown to support myogenesis in vivo, were shown in a 3D triculture model to stimulate myogenesis/angiogenesis coupling, notably through Oncostatin M production. Our data demonstrate that restorative macrophages orchestrate muscle regeneration by controlling myogenesis/angiogenesis coupling.

Role of Electrolyte Anions in the Na–O2 Battery: Implications for NaO2 Solvation and the Stability of the Sodium Solid Electrolyte Interphase in Glyme Ethers

Abstract: Herein we investigate the influence of the sodium salt anion on the performance of Na–O2 batteries. To illustrate the solvent–solute interactions in various solvents, we use 23Na-NMR to probe the environment of Na+ in the presence of different anions (ClO4–, PF6–, OTf–, or TFSi–). Strong solvation of either the Na+ or the anion leads to solvent-separated ions where the anion has no measurable impact on the Na+ chemical shift. Contrarily, in weakly solvating solvents the increasing interaction of the anion (ClO4– < PF6– < OTf– < TFSi–) can indeed stabilize the Na+ due to formation of contact ion pairs. However, by employing these electrolytes in Na–O2 cells, we demonstrate that changing from weakly interacting anions (ClO4–) to TFSi does not result in elevated battery performance. Nevertheless, a strong dependence of the solid electrolyte interphase (SEI) stability on the choice of sodium salt was found. By correlation of the physical properties of the electrolyte with the chemical SEI composition, the cru...

Chemical Recognition of Active Oxygen Species on the Surface of Oxygen Evolution Reaction Electrocatalysts

Abstract: Owing to the transient nature of the intermediates formed during the oxygen evolution reaction (OER) on the surface of transition metal oxides, their nature remains largely elusive by the means of simple techniques. The use of chemical probes is proposed, which, owing to their specific affinities towards different oxygen species, unravel the role played by these species on the OER mechanism. For that, tetraalkylammonium (TAA) cations, previously known for their surfactant properties, are introduced, which interact with the active oxygen sites and modify the hydrogen bond network on the surface of OER catalysts. Combining chemical probes with isotopic and pH-dependent measurements, it is further demonstrated that the introduction of iron into amorphous Ni oxyhydroxide films used as model catalysts deeply modifies the proton exchange properties, and therefore the OER mechanism and activity.

Porous dendritic copper: an electrocatalyst for highly selective CO2 reduction to formate in water/ionic liquid electrolyte.

Abstract: Copper is currently extensively studied because it provides promising electrodes for carbon dioxide electroreduction. The original combination, reported here, of a nanostructured porous dendritic Cu-based material, characterized by electron microcopy (SEM, TEM) and X-ray diffraction methods, and a water/ionic liquid mixture as the solvent, contributing to CO2 solubilization and activation, results in a remarkably efficient (large current densities at low overpotentials), stable and selective (large faradic yields) electrocatalytic system for the conversion of CO2 into formic acid, a product with a variety of uses. These results provide new directions for the further improvement of Cu electrodes.

Vancomycin-Associated Cast Nephropathy.

Abstract: Vancomycin is a widely prescribed antibiotic, but the exact nature of vancomycin-associated nephrotoxicity is unclear, in particular when considering the frequent coadministration of aminoglycosides. We describe here the initial case of a 56-year-old woman with normal renal function developing unexplained ARF without hypovolemia after administration of vancomycin without coadministration of aminoglycosides. Studying the patient’s renal biopsy specimen, we ascertained that obstructive tubular casts composed of noncrystal nanospheric vancomycin aggregates entangled with uromodulin explained the vancomycin-associated ARF. We developed in parallel a new immunohistologic staining technique to detect vancomycin in renal tissue and confirmed retrospectively that deleterious vancomycin-associated casts existed in eight additional patients with acute tubular necrosis in the absence of hypovolemia. Concomitant high vancomycin trough plasma levels had been observed in each patient. We also reproduced experimentally the toxic and obstructive nature of vancomycin-associated cast nephropathy in mice, which we detected using different in vivo imaging techniques. In conclusion, the interaction of uromodulin with nanospheric vancomycin aggregates represents a new mode of tubular cast formation, revealing the hitherto unsuspected mechanism of vancomycin-associated renal injury.

Odor identity coding by distributed ensembles of neurons in the mouse olfactory cortex

Abstract: Olfactory perception and behaviors critically depend on the ability to identify an odor across a wide range of concentrations. Here, we use calcium imaging to determine how odor identity is encoded in olfactory cortex. We find that, despite considerable trial-to-trial variability, odor identity can accurately be decoded from ensembles of co-active neurons that are distributed across piriform cortex without any apparent spatial organization. However, piriform response patterns change substantially over a 100-fold change in odor concentration, apparently degrading the population representation of odor identity. We show that this problem can be resolved by decoding odor identity from a subpopulation of concentration-invariant piriform neurons. These concentration-invariant neurons are overrepresented in piriform cortex but not in olfactory bulb mitral and tufted cells. We therefore propose that distinct perceptual features of odors are encoded in independent subnetworks of neurons in the olfactory cortex.

Accurate construction of a hierarchical nickel–cobalt oxide multishell yolk–shell structure with large and ultrafast lithium storage capability

Abstract: Novel hierarchical nickel–cobalt oxide microspheres with a multishell yolk–shell structure have been accurately synthesized via a facile and scalable method. The multishell yolk–shell powder shows a significantly improved electrochemical performance in terms of high reversible capacity, good rate capability and excellent cycling performance.

Controlling Feynman diagrammatic expansions: Physical nature of the pseudogap in the two-dimensional Hubbard model

Abstract: We introduce a method for summing Feynman's perturbation series based on diagrammatic Monte Carlo that significantly improves its convergence properties. This allows us to investigate in a controllable manner the pseudogap regime of the Hubbard model and to study the nodal/antinodal dichotomy at low doping and intermediate coupling. Marked differences from the weak-coupling scenario are manifest, such as a higher degree of incoherence at the antinodes than at the ``hot spots''. Our results show that the pseudogap and reduction of quasiparticle coherence at the antinode is due to antiferromagnetic spin correlations centered around the commensurate $(\ensuremath{\pi},\ensuremath{\pi})$ wave vector. In contrast, the dominant source of scattering at the node is associated with incommensurate momentum transfer. Umklapp scattering is found to play a key role in the nodal/antinodal dichotomy.

Chemical vs Electrochemical Formation of Li2CO3 as a Discharge Product in Li–O2/CO2 Batteries by Controlling the Superoxide Intermediate

Abstract: The Li–O2/CO2 battery with high capacity has recently been proposed as a new protocol to convert CO2. However, the fundamental mechanism for the reaction still remains hazy. Here, we investigated the discharge processes of Li–O2/CO2 (70%/30%) batteries in two solvents, dimethyl sulfoxide (DMSO) and 1,2-dimethoxyethane (DME). During discharge, both solvents initially show the reduction of oxygen. However, afterward, the solvent affects the reaction pathways of superoxide species by solvating Li+ with different strength, depending on the so-called donor number. More precisely, the initial formation of CO4•– is favored in DMSO at the expense of lithium superoxide formation that we observed in DME. Despite the different intermediate processes, X-ray diffraction showed that Li2CO3 was the final discharge product in both solvents. Moreover, we observed that CO2 cannot be reduced within the electrochemical stability window of DMSO and DME.

A theory of working memory without consciousness or sustained activity

Abstract: Working memory and conscious perception are thought to share similar brain mechanisms, yet recent reports of non-conscious working memory challenge this view. Combining visual masking with magnetoencephalography, we investigate the reality of non-conscious working memory and dissect its neural mechanisms. In a spatial delayed-response task, participants reported the location of a subjectively unseen target above chance-level after several seconds. Conscious perception and conscious working memory were characterized by similar signatures: a sustained desynchronization in the alpha/beta band over frontal cortex, and a decodable representation of target location in posterior sensors. During non-conscious working memory, such activity vanished. Our findings contradict models that identify working memory with sustained neural firing, but are compatible with recent proposals of 'activity-silent' working memory. We present a theoretical framework and simulations showing how slowly decaying synaptic changes allow cell assemblies to go dormant during the delay, yet be retrieved above chance-level after several seconds.