@article{7126, abstract = {In the Minimum Description Length (MDL) principle, learning from the data is equivalent to an optimal coding problem. We show that the codes that achieve optimal compression in MDL are critical in a very precise sense. First, when they are taken as generative models of samples, they generate samples with broad empirical distributions and with a high value of the relevance, defined as the entropy of the empirical frequencies. These results are derived for different statistical models (Dirichlet model, independent and pairwise dependent spin models, and restricted Boltzmann machines). Second, MDL codes sit precisely at a second order phase transition point where the symmetry between the sampled outcomes is spontaneously broken. The order parameter controlling the phase transition is the coding cost of the samples. The phase transition is a manifestation of the optimality of MDL codes, and it arises because codes that achieve a higher compression do not exist. These results suggest a clear interpretation of the widespread occurrence of statistical criticality as a characterization of samples which are maximally informative on the underlying generative process.}, author = {Cubero, Ryan J and Marsili, Matteo and Roudi, Yasser}, issn = {1099-4300}, journal = {Entropy}, keywords = {Minimum Description Length, normalized maximum likelihood, statistical criticality, phase transitions, large deviations}, number = {10}, publisher = {MDPI}, title = {{Minimum description length codes are critical}}, doi = {10.3390/e20100755}, volume = {20}, year = {2018}, } @article{7277, abstract = {Solid alkali metal carbonates are universal passivation layer components of intercalation battery materials and common side products in metal‐O2 batteries, and are believed to form and decompose reversibly in metal‐O2/CO2 cells. In these cathodes, Li2CO3 decomposes to CO2 when exposed to potentials above 3.8 V vs. Li/Li+. However, O2 evolution, as would be expected according to the decomposition reaction 2 Li2CO3→4 Li++4 e−+2 CO2+O2, is not detected. O atoms are thus unaccounted for, which was previously ascribed to unidentified parasitic reactions. Here, we show that highly reactive singlet oxygen (1O2) forms upon oxidizing Li2CO3 in an aprotic electrolyte and therefore does not evolve as O2. These results have substantial implications for the long‐term cyclability of batteries: they underpin the importance of avoiding 1O2 in metal‐O2 batteries, question the possibility of a reversible metal‐O2/CO2 battery based on a carbonate discharge product, and help explain the interfacial reactivity of transition‐metal cathodes with residual Li2CO3.}, author = {Mahne, Nika and Renfrew, Sara E. and McCloskey, Bryan D. and Freunberger, Stefan Alexander}, issn = {1433-7851}, journal = {Angewandte Chemie International Edition}, number = {19}, pages = {5529--5533}, publisher = {Wiley}, title = {{Electrochemical oxidation of Lithium Carbonate generates singlet oxygen}}, doi = {10.1002/anie.201802277}, volume = {57}, year = {2018}, } @article{7271, abstract = {The recent demand of multifunctional materials and devices for advanced applications in energy conversion and data storage resulted into a revival of multiferroics, that is, materials characterized by the coexistence of ferromagnetism and ferroelectricity. Despite intense efforts made in the past decade, single-phase room temperature multiferroics are yet to be discovered/fabricated. Nanostructured ferroic materials could potentially exhibit multiferroism since a high fraction of their atoms/ions are superficial, thereby altering significantly the properties of the bulk phase. Alternately, a magnetic order can be induced into ferroelectric materials upon aliovalent doping with magnetic ions. Here, we report on the synthesis of aggregate-free single-phase transition-metal-doped BaTiO3 quasi-monodisperse cuboidal nanocrystals (NC) which exhibit multiferroic properties at room temperature and can be suitable for applications in data storage. The proposed synthetic route allows the inclusion of a high concentration of magnetic ions such as Mn+ (M = Cr, Mn, Fe, Co) up to a nominal concentration of 4% without the formation of any secondary phase. The size of the nanocrystals was controlled in a wide range from ∼15 up to ∼70 nm by varying the reaction time from 48 to 144 h. The presence of unpaired electrons and their magnetic ordering have been probed by electron paramagnetic resonance spectroscopy (EPR), and a vibrating sample magnetometer (VSM). Likewise, an acentric structure, associated with the existence of a dielectric polarization, was observed by lattice dynamics analysis and piezoresponse force microscopy (PFM). These results show that high-quality titanium-containing perovskite nanocrystals which display multiferroic properties at room temperature can be fabricated via soft solution-based synthetic routes, and the properties of these materials can be modulated by changing the size of the nanocrystals and the concentration of the dopant thereby opening the door to the design and study of single-phase multiferroic materials.}, author = {Costanzo, Tommaso and McCracken, John and Rotaru, Aurelian and Caruntu, Gabriel}, issn = {2574-0970}, journal = {ACS Applied Nano Materials}, number = {9}, pages = {4863--4874}, publisher = {ACS}, title = {{Quasi-monodisperse transition-metal-doped BaTiO3 (M = Cr, Mn, Fe, Co) colloidal nanocrystals with multiferroic properties}}, doi = {10.1021/acsanm.8b01036}, volume = {1}, year = {2018}, } @article{7287, abstract = {Passivation layers on electrode materials are ubiquitous in nonaqueous battery chemistries and strongly govern performance and lifetime. They comprise breakdown products of the electrolyte including carbonate, alkyl carbonates, alkoxides, carboxylates, and polymers. Parasitic chemistry in metal–O2 batteries forms similar products and is tied to the deviation of the O2 balance from the ideal stoichiometry during formation/decomposition of alkaline peroxides or superoxides. Accurate and integral quantification of carbonaceous species and peroxides or superoxides in battery electrodes remains, however, elusive. We present a refined procedure to quantify them accurately and sensitively by pointing out and rectifying pitfalls of previous procedures. Carbonaceous compounds are differentiated into inorganic and organic ones. We combine mass and UV–vis spectrometry to quantify evolved O2 and complexed peroxide and CO2 evolved from carbonaceous compounds by acid treatment and Fenton’s reaction. The capabilities of the method are exemplified by means of Li–O2 and Na–O2 cathodes, graphite anodes, and LiNi0.8Co0.15Al0.05O2 cathodes.}, author = {Schafzahl, Bettina and Mourad, Eléonore and Schafzahl, Lukas and Petit, Yann K. and Raju, Anjana R. and Thotiyl, Musthafa Ottakam and Wilkening, Martin and Slugovc, Christian and Freunberger, Stefan Alexander}, issn = {2380-8195}, journal = {ACS Energy Letters}, number = {1}, pages = {170--176}, publisher = {ACS}, title = {{Quantifying total superoxide, peroxide, and carbonaceous compounds in metal–O2 batteries and the solid electrolyte interphase}}, doi = {10.1021/acsenergylett.7b01111}, volume = {3}, year = {2018}, } @article{7285, abstract = {Hydrogelation, the self-assembly of molecules into soft, water-loaded networks, is one way to bridge the structural gap between single molecules and functional materials. The potential of hydrogels, such as those based on perylene bisimides, lies in their chemical, physical, optical, and electronic properties, which are governed by the supramolecular structure of the gel. However, the structural motifs and their precise role for long-range conductivity are yet to be explored. Here, we present a comprehensive structural picture of a perylene bisimide hydrogel, suggesting that its long-range conductivity is limited by charge transfer between electronic backbones. We reveal nanocrystalline ribbon-like structures as the electronic and structural backbone units between which charge transfer is mediated by polar solvent bridges. We exemplify this effect with sensing, where exposure to polar vapor enhances conductivity by 5 orders of magnitude, emphasizing the crucial role of the interplay between structural motif and surrounding medium for the rational design of devices based on nanocrystalline hydrogels.}, author = {Burian, Max and Rigodanza, Francesco and Demitri, Nicola and D̵ord̵ević, Luka and Marchesan, Silvia and Steinhartova, Tereza and Letofsky-Papst, Ilse and Khalakhan, Ivan and Mourad, Eléonore and Freunberger, Stefan Alexander and Amenitsch, Heinz and Prato, Maurizio and Syrgiannis, Zois}, issn = {1936-0851}, journal = {ACS Nano}, number = {6}, pages = {5800--5806}, publisher = {ACS}, title = {{Inter-backbone charge transfer as prerequisite for long-range conductivity in perylene bisimide hydrogels}}, doi = {10.1021/acsnano.8b01689}, volume = {12}, year = {2018}, } @article{7286, abstract = {The solid electrolyte interphase (SEI) in Li and Na ion batteries forms when highly reducing or oxidizing electrode materials come into contact with a liquid organic electrolyte. Its ability to form a mechanically robust, ion-conducting, and electron-insulating layer critically determines performance, cycle life, and safety. Li or Na alkyl carbonates (LiAC and NaAC, respectively) are lead SEI components in state-of-the-art carbonate based electrolytes, and our fundamental understanding of their charge transport and mechanical properties may hold the key to designing electrolytes forming an improved SEI. We synthesized a homologous series of LiACs and NaACs from methyl to octyl analogues and characterized them with respect to structure, ionic conductivity, and stiffness. The compounds assume layered structures except for the lithium methyl carbonate. Room-temperature conductivities were found to be ∼10–9 S cm–1 for lithium methyl carbonate, <10–12 S cm–1 for the other LiACs, and <10–12 S cm–1 for the NaACs with ion transport mostly attributed to grain boundaries. While LiACs show stiffnesses of ∼1 GPa, NaACs become significantly softer with increasing chain lengths. These findings will help to more precisely interpret the complex results from charge transport and mechanical characterization of real SEIs and can give a rationale for influencing the SEI’s mechanical properties via the electrolyte.}, author = {Schafzahl, Lukas and Ehmann, Heike and Kriechbaum, Manfred and Sattelkow, Jürgen and Ganner, Thomas and Plank, Harald and Wilkening, Martin and Freunberger, Stefan Alexander}, issn = {1520-5002}, journal = {Chemistry of Materials}, number = {10}, pages = {3338--3345}, publisher = {ACS}, title = {{Long-chain Li and Na alkyl carbonates as solid electrolyte interphase components: Structure, ion transport, and mechanical properties}}, doi = {10.1021/acs.chemmater.8b00750}, volume = {30}, year = {2018}, } @inproceedings{7407, abstract = {Proofs of space (PoS) [Dziembowski et al., CRYPTO'15] are proof systems where a prover can convince a verifier that he "wastes" disk space. PoS were introduced as a more ecological and economical replacement for proofs of work which are currently used to secure blockchains like Bitcoin. In this work we investigate extensions of PoS which allow the prover to embed useful data into the dedicated space, which later can be recovered. Our first contribution is a security proof for the original PoS from CRYPTO'15 in the random oracle model (the original proof only applied to a restricted class of adversaries which can store a subset of the data an honest prover would store). When this PoS is instantiated with recent constructions of maximally depth robust graphs, our proof implies basically optimal security. As a second contribution we show three different extensions of this PoS where useful data can be embedded into the space required by the prover. Our security proof for the PoS extends (non-trivially) to these constructions. We discuss how some of these variants can be used as proofs of catalytic space (PoCS), a notion we put forward in this work, and which basically is a PoS where most of the space required by the prover can be used to backup useful data. Finally we discuss how one of the extensions is a candidate construction for a proof of replication (PoR), a proof system recently suggested in the Filecoin whitepaper. }, author = {Pietrzak, Krzysztof Z}, booktitle = {10th Innovations in Theoretical Computer Science Conference (ITCS 2019)}, isbn = {978-3-95977-095-8}, issn = {1868-8969}, location = {San Diego, CA, United States}, pages = {59:1--59:25}, publisher = {Schloss Dagstuhl - Leibniz-Zentrum für Informatik}, title = {{Proofs of catalytic space}}, doi = {10.4230/LIPICS.ITCS.2019.59}, volume = {124}, year = {2018}, } @article{7458, abstract = {The coupling between magnetic and electric subsystems in composites of ferromagnetic and ferroelectric phases is a product property that is facilitated by mechanical strain that arises due to magnetostriction and the piezoelectric effect in the constituent phases. Such multiferroic composites are of immense interests for studies on the physics of electromagnetic coupling and for use in a variety of applications. Here, we focus on magneto-electric (ME) coupling in nanocomposites. Particular emphasis is on core-shell particles and coaxial fibers, thin film heterostructures, and planar structures with a variety of mechanical connectivity. A brief review of models that predict strong ME effects in nanostructures is followed by synthesis and characterization. Core-shell particulate composites can be prepared by hydrothermal processes and chemical or deoxyribonucleic acid-assisted assembly. Electrospinning techniques have been utilized to prepare defect free core-shell nanofibers. Core-shell particles and fibers can be assembled into superstructures with the aid of magnetic and electric fields and characterized for possible use in advanced technologies. Chemical-vapor deposition techniques have been shown to be effective for the preparation of heterostructures of ferrites and ferroelectrics. Exotic planar multiferroic structures with potential for enhancing ME coupling strengths are also considered. Scanning probe microscopy techniques are ideal for probing the nature of direct- and converse-ME coupling in individual nanostructures. Magnetoelectric characterization of assemblies of nanocomposites can be done by ME voltage coefficient, magnetic field induced polarization, and magneto-dielectric effects. We conclude with a brief discussion on possible avenues for strengthening the product properties in the nanocomposites.}, author = {Viehland, Dwight and Li, Jie Fang and Yang, Yaodong and Costanzo, Tommaso and Yourdkhani, Amin and Caruntu, Gabriel and Zhou, Peng and Zhang, Tianjin and Li, Tianqian and Gupta, Arunava and Popov, Maksym and Srinivasan, Gopalan}, issn = {0021-8979}, journal = {Journal of Applied Physics}, number = {6}, publisher = {AIP}, title = {{Tutorial: Product properties in multiferroic nanocomposites}}, doi = {10.1063/1.5038726}, volume = {124}, year = {2018}, } @article{7717, abstract = {Background: DNA methylation levels change along with age, but few studies have examined the variation in the rate of such changes between individuals. Methods: We performed a longitudinal analysis to quantify the variation in the rate of change of DNA methylation between individuals using whole blood DNA methylation array profiles collected at 2–4 time points (N = 2894) in 954 individuals (67–90 years). Results: After stringent quality control, we identified 1507 DNA methylation CpG sites (rsCpGs) with statistically significant variation in the rate of change (random slope) of DNA methylation among individuals in a mixed linear model analysis. Genes in the vicinity of these rsCpGs were found to be enriched in Homeobox transcription factors and the Wnt signalling pathway, both of which are related to ageing processes. Furthermore, we investigated the SNP effect on the random slope. We found that 4 out of 1507 rsCpGs had one significant (P < 5 × 10−8/1507) SNP effect and 343 rsCpGs had at least one SNP effect (436 SNP-probe pairs) reaching genome-wide significance (P < 5 × 10−8). Ninety-five percent of the significant (P < 5 × 10−8) SNPs are on different chromosomes from their corresponding probes. Conclusions: We identified CpG sites that have variability in the rate of change of DNA methylation between individuals, and our results suggest a genetic basis of this variation. Genes around these CpG sites have been reported to be involved in the ageing process.}, author = {Zhang, Qian and Marioni, Riccardo E and Robinson, Matthew Richard and Higham, Jon and Sproul, Duncan and Wray, Naomi R and Deary, Ian J and McRae, Allan F and Visscher, Peter M}, issn = {1756-994X}, journal = {Genome Medicine}, number = {1}, publisher = {Springer Nature}, title = {{Genotype effects contribute to variation in longitudinal methylome patterns in older people}}, doi = {10.1186/s13073-018-0585-7}, volume = {10}, year = {2018}, } @article{7718, abstract = {Flores Island, Indonesia, was inhabited by the small-bodied hominin species Homo floresiensis, which has an unknown evolutionary relationship to modern humans. This island is also home to an extant human pygmy population. Here we describe genome-scale single-nucleotide polymorphism data and whole-genome sequences from a contemporary human pygmy population living on Flores near the cave where H. floresiensis was found. The genomes of Flores pygmies reveal a complex history of admixture with Denisovans and Neanderthals but no evidence for gene flow with other archaic hominins. Modern individuals bear the signatures of recent positive selection encompassing the FADS (fatty acid desaturase) gene cluster, likely related to diet, and polygenic selection acting on standing variation that contributed to their short-stature phenotype. Thus, multiple independent instances of hominin insular dwarfism occurred on Flores.}, author = {Tucci, Serena and Vohr, Samuel H. and McCoy, Rajiv C. and Vernot, Benjamin and Robinson, Matthew Richard and Barbieri, Chiara and Nelson, Brad J. and Fu, Wenqing and Purnomo, Gludhug A. and Sudoyo, Herawati and Eichler, Evan E. and Barbujani, Guido and Visscher, Peter M. and Akey, Joshua M. and Green, Richard E.}, issn = {0036-8075}, journal = {Science}, number = {6401}, pages = {511--516}, publisher = {American Association for the Advancement of Science}, title = {{Evolutionary history and adaptation of a human pygmy population of Flores Island, Indonesia}}, doi = {10.1126/science.aar8486}, volume = {361}, year = {2018}, }